# Pro amps for HT



## Ayreonaut (Apr 26, 2006)

Has anyone here had experience using pro amps for HT? I've seen it recommended in a couple of places. The watts/dollar and reported perfomance is very enticing. Right now I'm looking at a two channel amp to drive my mains.

The one concern I have is using unblalnced pre outs from my receiver to signal balanced inputs on a pro amp. Has anyone tried this? Would using a transformer isolator to eliminate hum comprimise the signal quality in any way?


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## brucek (Apr 11, 2006)

> The one concern I have is using unblalnced pre outs from my receiver to signal balanced inputs on a pro amp.


The only proper way around this is with an unbalanced to balanced converter. This of course adds a device in the chain (and noise).

The higher the cost, the better the specs usually on these devices. I've seen them in the $300US range.

here's one
here's another. The specs on this one aren't as good as the first one.

I would go with an amplifier that had the same interface as your receiver/processor has and not go through the conversion.

brucek


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## Ayreonaut (Apr 26, 2006)

Well, they can be had as cheap as $16.99 from Radio Shack. Behringer has a much nicer one for $99. But I suspected what you have voiced: A transformer in the signal path has got to affect the sound, maybe significantly.

I wonder what all the raves are about from enthusiasts who have had good luck with pro amps. They haven't mentioned this problem in their posts.


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## brucek (Apr 11, 2006)

> they can be had as cheap as $16.99 from Radio Shack


I hope you didn't want an opinion on that?



> Behringer has a much nicer one for $99


What's the model number?



> I wonder what all the raves are about from enthusiasts who have had good luck with pro amps


I suspect they have balanced outputs on their processors.

brucek


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## Ayreonaut (Apr 26, 2006)

brucek said:


> I hope you didn't want an opinion on that?


:laugh: Yeah, just kidding around.

But not kidding around, what are the chances of avoiding a ground loop if the amp and receiver are plugged into the same power strip? If that doesn't work, what about a cheater plug? Some people claim that there's really no problem with using one. 

Here's the Behringer:
*
ULTRA-DI PRO DI800*
Professional Mains/Phantom Powered 8-Channel DI-Box 









The *ULTRA-DI PRO DI800* is a professional mains/phantom powered 8-channel DI-box. It converts unbalanced line inputs into balanced outputs, featuring optional mains or phantom powered operation. Its servo balanced operation assures ultra-flat frequency response. Additionally, it allows direct connection to speaker outputs with up to 3,000 Watts. A ground lift switch as well as input attenuation/gain per channel round off this powerful device.


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## brucek (Apr 11, 2006)

> what are the chances of avoiding a ground loop if the amp and receiver are plugged into the same power strip? If that doesn't work, what about a cheater plug? Some people claim that there's really no problem with using one.


Do you have a ground loop that is causing a problem?

With regard to cheater plugs, I have a standard speech I make that is part of the BFD Guide and goes like this:
"The cheater plug effectively eliminates the third prong on the AC plug. The 'third prong' is the electrical safety ground and is there to protect you and anyone who uses your equipment from electrocution. This safety ground is a cold conductor designed to provide a path to ground for safety protection against internal shorts inside your equipment when equipped with the three prong plug. The third prong connects back to your service panel (where it is bonded to the neutral wire), and from there is connected either or both to your house plumbing or external ground rod. On equipment with a third prong, the metal case and external metal parts are all connected to this safety ground when you plug the electrical cord into the wall. If a component fails inside a piece of equipment and the 120 volts shorts to the equipments case, then that case is now live and can electrocute you. If the safety ground was attached, then a breaker would trip to indicate you had a fault." 

Use cheaters at your own risk..... 



> Here's the Behringer: ULTRA-DI PRO DI800


Yeah, that's a standard DI box (as they're called). The better quality ones don't add too much noise. You'd really have to test it out and see how it sounds to you first.

Why are you bent on a PRO amp? There are lots of regular amplifiers around that do a great job and don't cost too much. There's nothing special about a PRO amp other than it has balanced inputs and requires levels that a lot of regular receivers won't match...

brucek


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## Ayreonaut (Apr 26, 2006)

brucek said:


> Do you have a ground loop that is causing a problem?


 No. I was just wondering if this would be a deal breaker.



brucek said:


> Use cheaters at your own risk.....


 Yes, they scare me too. I don't know if it makes a difference, but a cheater on an 1800W amp scares me more than a cheater on a line level BFD.



brucek said:


> Why are you bent on a PRO amp?


 Oh, I'm not really. I'm just poking around and exploring my options. The watt/dollar value is pretty tempting on the pro amps and its hard to ignore.

Got any budget amps you'd like to recommend?


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## brucek (Apr 11, 2006)

> I don't know if it makes a difference, but a cheater on an 1800W amp scares me more than a cheater on a line level BFD.


No difference. It's the AC line voltage that is the culprit...



> Got any budget amps you'd like to recommend?


Not really, I do like Rotel and Outlaw. They're both conventional amplifiers with decent specs and good bang for the buck.

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

Ayreonaut said:


> Here's the Behringer:
> *
> ULTRA-DI PRO DI800*
> Professional Mains/Phantom Powered 8-Channel DI-Box
> ...


Daniel,

You have to keep in mind that a direct box is typically used, and designed for, *musical instruments,* not hi-fi listening. I don’t know if I would expect it to have audiophile-worthy specs. Also keep in mind that the instruments DI’s are intended for – guitars and electronic keyboards - have extremely low signal outputs. Feeding one a signal from a home theater pre-pro might overload it. Don’t assume that the speaker-level capability of this Behringer means it has miles of headroom. It probably has separate inputs for that, or a switch enabling that function (i.e., to pad down the signal).

I’ve had bad experiences using pro gear in my HT system in the past, so I’d be wary of anything you’d want to use. Don’t automatically expect that it will be clean or accurate until you give it a careful listening evaluation. I think I’d look first at pro amps that other audiophiles have used successfully. Also, see what kind of gear they have in the rest of their system to gauge how reliable their recommendation is. For instance, I wouldn’t be terribly impressed with a rave review of a pro amp if I saw they bought their speakers at Best Buy. 

Also note if they’re feeding it a balanced or unbalanced signal. It may not be an issue at all, as many pro amps carry 1/4” inputs labeled “Balanced or Unbalanced.” I’ll let brucek comment on the legitimacy of using these inputs as unbalanced.

Regards,
Wayne


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## Ayreonaut (Apr 26, 2006)

Thanks for your informative answers guys. Even if the pro gear did sound good, it may be more trouble than its worth, huh? I'm certainly not going to pass the signal through a transformer. I'd rather spend the money on the amp.


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## Ayreonaut (Apr 26, 2006)

Wayne A. Pflughaupt said:


> I’ve had bad experiences using pro gear in my HT system in the past, so I’d be wary of anything you’d want to use. Don’t automatically expect that it will be clean or accurate until you give it a careful listening evaluation. I think I’d look first at pro amps that other audiophiles have used successfully. Also, see what kind of gear they have in the rest of their system to gauge how reliable their recommendation is. For instance, I wouldn’t be terribly impressed with a rave review of a pro amp if I saw they bought their speakers at Best Buy.


Wayne,

I was searching around some forums for information on amps. I traced this pro amp idea back and it leads to you! :T Last July (on another forum) you recommended Carvin amps to Steve Callas for his subwoofer. He bought one and last November he pitted his Carvin HD1800 full range in a blind listening test against the PS Audio HCA-2. He and his friends could tell no significant difference between the two. And that got me turned on to trying a pro amp to drive my mains.

Small world, isn't it?

Daniel


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## JimPeitersen (Jul 15, 2006)

I use a pro amp for subwoofer duty, but I have tried them full range and to be honest didn't notice any difference from "home" stereo amps. The input sensitivity of some pro amps give people problems, and fan noise is an issue. If you were to pick a nice "studio" amp or one of the Crown K series I don't think you would have any problems - and the headroom from the extra power is always good:R 
JP


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## Ayreonaut (Apr 26, 2006)

I went ahead and ordered the Carvin HD1800 just to try it out.
This is the one that Steve Callas found very similar to a PS Audio amp.
It does accept unbalanced 1/4" tip-sleeve inputs.

Price - $319 + S&H
Power - 2 x 600W RMS into 4 ohms
Fan Noise - 53db at 1 inch away
Sensitivity - (4Ω, Vms) 1.0V
Damping Factor - >500
Slew Rate - 45v/us

I'll let you know how it works out!


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## Sonnie (Apr 11, 2006)

Interesting... will be looking forward to your thoughts. Sounds like a good price too.


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## Mark Seaton (Jun 22, 2006)

Hi Guys,

Better pro amps can function very well in the home with some attention to gain and noise issues. One of the biggest problems that I see so many blow off (pun intended) is fan noise. Dismissing the importance of the noise floor in a home audio system is a major oversight. Remember that "quiet" is the other half of your dynamic range. If you have your equipment in a sealed/enclosed rack or in an equipment room, pro amplifiers can be great options. While they have discontinued the line, QSC's SRA amplifiers were killer options for home theater. The DCA line and I think some of the new PLXII amps are similar, but with louder fans.

If you are looking for big power that you can't really find or can't find at a realistic price for home theater, some of the best sounding amplifiers in the pro market are from LAB GRUPPEN. Their fP series and newer 4 channel amps are ones I've been seriously looking at for use in theaters with equipment closets. They are in no way bargain amps, but the do have very good value to any other options that provides honest power at very low distortion as they do.


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## brucek (Apr 11, 2006)

> Remember that "quiet" is the other half of your dynamic range


Completely agree Mark. 

It's the one real problem I have always had with Pro-Amps, HTPC, Projectors, etc. Those pesky fans. 

That extra dollar you pay to have a high end audio system can be quickly eliminated when you introduce outside noise. 

In critical listening, the subtle sounds that separate high end from the rest of the pack is eliminated when your fridge in the kitchen turns on......  

brucek


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## Ayreonaut (Apr 26, 2006)

My DVR emits a very quiet hum, and my rather quiet fridge is in the next room with an open doorway. The HVAC system is by far the loudest when it's on. Such are the comprimises of domesticity for the average listener.

I'm a fire protection engineer, and my work includes designing systems for theaters and performing arts centers for universities. I work with acoustical engineers and architects and have observed the lengths they take to isolate the auditoriums from external noise. Beyond room treatment, those measures include structural isolation and low velocity air ductwork to name just two. It's absolutely critical to have virtual silence when you're listening to an unamplified actor in a large hall.

Such measures seem too extreme to even mention in the context of HT. But I can see myself taking mechanical systems into consideration in a future construction of a dedicated HT. At least I could minimise the noise coming from the HVAC ducts and put any equipment with fans in a dedicated closet.

_Back on topic,_ I chose one of the quietest budget amps I could find. Even so, one has the option of a fan modification if necessary. You can reduce the noise by replacing the fan with a quieter one or simply installing a resistor to reduce the fan speed.


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## Sonnie (Apr 11, 2006)

In our HT room... you can hear a pin drop on the carpet. Well... maybe I couldn't but Superman could. :R

Generally you can mod those fans with quieter ones with no adverse effects. I wanna say I've read something on the Behringer EP2500 I have, where you can rewire it to slow it down. Mabye it was at the CULT where I read it, but a lot of people have done it and again, absolutely no adverse effects that I've heard of anyway.


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## Ayreonaut (Apr 26, 2006)

Well, gentlemen, I have taken possesion of my new amplifier.










I connected the pre-outs of my receiver (Denon AVR1905) to the inputs of the amplifier (Carvin HD1800) with RCA to 1/4" unbalanced cables. I plugged the amp into the same power strip as the reciever. There was no ground loop hum; I shouldn't have worried so much about that.

I read two ideas about how to set the level.
1. Set the reciever's pre-out to +0 and turn the amplifier gain down.
2. Set the amplifier gain to the max and adjust the receiver's pre-out down.

Option 1 is supposed to protect the speakers. If the reciever throws a spike, the amp output is attenuated and won't blow my speakers which are only rated to handle 150W. This amp is supposed to deliver 600W into 4 ohms, so being careful sounded like a good idea. I set it up this way, with the receiver at +0dB and the amplifier gain at -15dB.

I really wasn't that thrilled. I think the bass sounded a bit punchier and better damped. But my litmus test is the explosively dynamic orchestral soundtrack from Spirited Away. (In the store, I heard a Musical Fi amp and Revel Concerta speakers pass this dynamics test with flying colors. I just _have _to get there.) Just before I installed the new amp I listened the track "Dragon Boy" one last time from the receivers's speaker outputs for a comparison. With the new amp installed I listened to it again. Not really that much different. At the level I was listening to (-6dB) the horns glared and the cymbals sizzled. Just like they did before. I went to bed with doubts about keeping the new amp.

The next day I decided to try setting the level the other way. I turned the pre-out level all the way down to the minimum -12dB. I turned the amplifer gain up to -1dB to match reference level. I've heard not a hint of click, pop or thump when powering up the amp or receiver, so it seems safe enough to try it this way.

BINGO! I played "Dragon Boy" again at the same volume level and the difference was a revelation! I played it again at Reference Level, and still amazing. All of the hash, sizzle and blare is gone. At reference levels its incredibly easy to listen to.

My guess is that the reciever's pre-outs were clipping when asked to reproduce reference level. At -12dB there is no problem. Now I can listen to the amp unhindered.

While my wife was out I popped in a bunch of action movies and listened to them all at refence level very comfortably. It seemed so natural, I wondered why I had ever listened at levels below this. (Except LotR FotR. That movie is recorded HOT.) When my wife came home I played part of the DVD Spirited Away for the kids. Incredible. My wife walked into the room and began watching it with us, smiling. After a minute I remarked to her that we were listening to this at reference level. The volume is set to 0. She hardly believed it. "Really?" She knew that 0 was unlistenable, yet here we were listening to it and it was completely natural. I'm still astounded. We watched Star Wars III last night at reference level. Awesome, awesome, awesome. She never asked me to turn it down. :heartbeat:

OK, I know the experienced among you are rolling your eyes, :rolleyesno: since you've been enjoying this for years and have moved on to other considerations. But my system is just now reaching tonal neutrality and high levels without distortion. I'm thrilled to be at this point and excited about what lies ahead.

For $319, how can you beat that?


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## Wayne A. Pflughaupt (Apr 13, 2006)

Nice write-up, Daniel. Carvin claims their amps are very accurate, nice to see it passed the hi-fi test. By the way, what kind of speakers and receiver are you using?

Of course you probably know, Carvin is like the SVS of the pro audio world, in that they manufacture and ship direct. If that amp were another brand, it’d probably cost $500 or so.



> I read two ideas about how to set the level.
> 1. Set the reciever's pre-out to +0 and turn the amplifier gain down.
> 2. Set the amplifier gain to the max and adjust the receiver's pre-out down.
> Option 1 is supposed to protect the speakers. If the reciever throws a spike, the amp output is attenuated and won't blow my speakers


Who comes up with this stuff? :rolleyesno: You’re probably right, Scenario #1 probably max’d out the pre outputs.

Regards,
Wayne


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## Sonnie (Apr 11, 2006)

That's super good news Dan... :T That is definitely a bargain too.


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## Ayreonaut (Apr 26, 2006)

Wayne A. Pflughaupt said:


> By the way, what kind of speakers and receiver are you using?


My speakers are the DALI IKON 6. I'll deliver a promised review soon, now that I have a good amp.

My reciever is the Denon AVR1906. It has a nice DSP chip and DACs, but the amps are only 80W. With help from the Carvin for amplification duties, it sounds great.


Wayne A. Pflughaupt said:


> Who comes up with this stuff? :rolleyesno:


I think I got that impression from an Alesis amp manual.



Alesis said:


> The most common cause of noisy operation,
> especially in studio use, is that the amplifier's
> gain controls are left all the way up, while the
> mixer's output is turned down. This can lead
> ...


In my home theater application, there is no audible noise floor whatsoever, even with the amp gain set to maximum -1dB. 

But I did remember that bit of advice _out of context_ because the manual does goes on to say:


Alesis said:


> It is possible that the output signal from the source
> may be too high and, thus, distorted before it
> reaches the amplifier gain control, either because
> the source device is clipping or the amplifier input
> ...


Like you said.


Wayne A. Pflughaupt said:


> You’re probably right, Scenario #1 probably max’d out the pre outputs.


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## Mark Seaton (Jun 22, 2006)

Hi Ayreonaut,

Your experience is interesting, and I almost wonder how much of the difference was simply listening at higher levels. That is surprising that any pre-amp output would be clipping at such levels, but pro amps do typicaly require a higher drive voltage to reach their maximum output. Method #1 is often good practice to insure the lowest noise floor and ideally you would set up the system by determining where the pre-amp clips and then set the gain on the amplifier such that it reaches its maximum output just before the pre-amp clipping.

As your experience suggests though, we can't take for granted solid performance at high drive level from pre-amp outputs, especially from receivers. Who would have thought that a 0dB setting of channel level and main volume would have chanced clipping with a digital input!?!


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## Ayreonaut (Apr 26, 2006)

Mark Seaton said:


> Your experience is interesting, and I almost wonder how much of the difference was simply listening at higher levels.


I know that neither my old speakers or the receiver could handle the higher levels. The new speakers and amp both take it in stride. For sure the biggest improvement that I'm hearing is in higher listening levels without distortion. I can't say that this amp is better than some other, but it is completely capable. My speakers driven by this amp sound natural and effortless.


Mark Seaton said:


> As your experience suggests though, we can't take for granted solid performance at high drive level from pre-amp outputs, especially from receivers. Who would have thought that a 0dB setting of channel level and main volume would have chanced clipping with a digital input!?!


I never imagined it either. In fact, the output of this reciever may be limited more by the internal preamp section than the 80W amplifiers.


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## Darren (Apr 20, 2006)

I saw noisy fans as an issue for Pro amps. It only takes about $8 and 10 minutes to fix that problem. Buy a Panaflow quite fan. I replaced my Behringer fan and it is completely silent now. Of course that is a well known fix but I was surprised to see it listed as an issue.


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## Chrisbee (Apr 20, 2006)

Darren said:


> I saw noisy fans as an issue for Pro amps. It only takes about $8 and 10 minutes to fix that problem. Buy a Panaflow quite fan. I replaced my Behringer fan and it is completely silent now. Of course that is a well known fix but I was surprised to see it listed as an issue.


I have my EP2500 out in my IB enclosure.

It can be heard through the AE IB15 speaker cones as quite a loud rushing noise.

It can be heard vibrating in the bathroom immediately below the IB enclosure.

Shouldn't someone speak to Behringer about this racket so we don't have to negate our guarantees with this "well known fix"?!!? :scratch:


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## Darren (Apr 20, 2006)

Actually you can replace the fan without any snipping... the mini-molex connectors can be bought and used so you don't have to snip the original leads to the fan it comes with. When it comes time for a warranty claim, just replace fan and add some hot glue to the plug and it's back to factory spec... I know, a little shady but not a big deal.

I think they see the slower speed fan as a warranty issue since they are designed for heavy use and operate at much higher temps in situations where they are powering band equipment etc... We don't need the high CFM for home theater use.

I have instructions on how to do it using a common mini-molex from an old computer power supply here:

http://www.ibsubwoofers.proboards51.com/index.cgi?board=amps&action=display&thread=1145627913

I see you have already seen that thread though...


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## kingkip (Apr 20, 2006)

I have a crown xls 402 powering my IB and just for kicks I tried it on my mains to see the difference from my parasound 1500. The crown just wasn't there especialy as far as the mid range was concerened. I thought that the parasound killed the crown in every test. Though I am pretty sure you could kick the crown down a flight of stairs and it would be just fine. Built like a tank. 

Could be my setup but at least this config didn't work well with pro amps.


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## Darren (Apr 20, 2006)

kingkip said:


> I have a crown xls 402 powering my IB and just for kicks I tried it on my mains to see the difference from my parasound 1500. The crown just wasn't there especialy as far as the mid range was concerened. I thought that the parasound killed the crown in every test. Though I am pretty sure you could kick the crown down a flight of stairs and it would be just fine. Built like a tank.
> 
> Could be my setup but at least this config didn't work well with pro amps.


There are some people using Behringers for their mains...I'm not one of them, mine does sub duty only.


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## Ayreonaut (Apr 26, 2006)

The fans on my amp are pretty quiet. I only really hear them when I mute the volume, or am listening late at night at -50 dB. But I figured for $8 and ten minutes, why not silence the amp altogether.
:scratchchin:
 
First I removed the top cover just to get a look at the fan and determine what size it was. There were two fans and they were 80mm x 25mm. Only one fan runs unless the amp gets too hot and then the other would run too. Since there were two, I decided to try the recommendation to wire them in series. This is supposed to halve the voltage across each fan and slow them down so that they are inaudible. I tried that, but the fans didn't turn at all, they just buzzed. No go. Since I wanted to replace the fans I didn't bother to restore the wiring. I called around town and found the Mad Dog WhisperFans for sale at Cricuit City and Comp USA. The box claimed 23 dB at 25 cfm. I picked up two for $6.99 each.
:spend:

Removing the old fans was not easy or safe. The two fans are arranged in series between the back of the case and the two large heat sinks. The rear fan is screwed to the case, the front fan is screwed to both heat sinks, and the fans are bolted to each other. The rear fan is wedged in under the lip of the back of the case, so all of the screws and bolts must be removed before the front fan can be lifted out. When the screwdriver touched the screw that hold the front fan to the top heat sink, it arced and popped as a huge amount of stored electricity discharged through the screwdriver to the case. It burned a pit in the side of my screwdriver. I wasn't hurt, but I was badly shaken. Can someone please explain to me why the heatsinks were charged? I could have been badly hurt. Not knowing what else to do, I used the screwdriver to discharge the other heatsinks to the case with the accomapnying pops and sparks. Very scary. I do not recommend this at all.
:scared:

I wrestled the old fans out and the new fans in. I trimmed the yellow leads off of the new fan connectors leaving red and black and plugged them in. I got everything screwed back together. All of this took about two hours, and the scare probably took two years off my life. And the fruit of my efforts? The rear fan was the one running and it was obviously defective. It made a clicking sound. So I opened the case back up and switched the fan leads to try the other one. This one wasn't defective, but the hiss and purr was actually louder than the old fan. So much for the so-called "WhisperFan." I spent another hour or so restoring everything to original condition. (Again the scary sparks and pops as I discharged the heat sinks.) I had cut the original an leads to run them in series, so I soldered those back together. I finished around midnight. What a waste of time.
:rant:

I suppose I could buy other fans online and try them to see if they are better than the "WhisperFans." But at this point I am loathe to even open the case again. I might try installing a pot in the fan lead to see if I can trim the voltage just enough to slow the fan without stopping it. Maybe. My courage has waned significantly.
:surrender:

Here's another lesson I learned. After I had set everything back up, I noticed a hum coming from the speakers. I tried some different things and noticed that turning the TV on was causing the hum. The amp was sitting right over my CRT and the signal cables were hanging down behind. Moving the cables around changed the magnitude of the hum, but I couldn't eliminate it, nor did I want the hum to return if the cables got shifted around. It seems that my CRT is throwing a lot of RF energy around and my unbalanced signal cables pick it up. Combined with the high gain from the amplifier, it results in a pretty audible hum. I finally moved the amp and the signal cables away from the TV and cleared this up.

So I spent my weekend getting things back to the way that they were. :blink:


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## brucek (Apr 11, 2006)

> Can someone please explain to me why the heatsinks were charged? I could have been badly hurt. Not knowing what else to do, I used the screwdriver to discharge the other heatsinks to the case with the accomapnying pops and sparks. Very scary. I do not recommend this at all.


Power transistors have metal cases which are connected to the transistors collector lead internally, so it is necessary to insulate the metal heat sink from the transistors metal case when mounted. The insulator generally used is a thin sheet of mica that unfortunately doesn't conduct heat as well as you might like even though thermal paste is used on both sides. Plastic sleeves are also used on the transistor bolts to isolate them also from the heatsink.

To get around this heat transfer problem when designing an amplifier you can skip the insulator, and bolt the power transistor directly to the heatsink, and then simply isolate the heatsink itself from the chassis ground. This trick allows for a smaller heatsink to be used (I personally just don't like the design myself). 

It also means the heatsink, which is connected to the power transistor collector leads is also connected to +VCC and indirectly to your very large filter capacitors. They store energy when the power is off.

Discharging your power transistors collectors to ground is a sure recipe to weaken or blow those transistors.

[scolding on]

The fact that you aren't aware of this is the reason people in the electronics field warn anyone that isn't qualified from opening up their equipment.

I would stop the practice of discharging your heatsinks with a screwdriver.

[/scolding off] :nono: 

brucek


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## Darren (Apr 20, 2006)

A good way to discharge the capacitors is to use a standard lightbulb with wires soldered to the positive and negative poles. Put the lightbulb across the caps and it will light up discharging the caps.


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## Ayreonaut (Apr 26, 2006)

brucek said:


> The fact that you aren't aware of this is the reason people in the electronics field warn anyone that isn't qualified from opening up their equipment.


I deserve that, and a scolding is much more welcome than a bad shock. I want everyone who reads this to be aware of this danger. I worked up the courage to attempt my first ever modification, and this is how it turned out. I knew that energy was stored in the capacitors, and I was very careful not to poke around anywhere except to unscrew the fans. I figured that the diconnected fans and the heat sinks to which they were screwed were both safe, since other people have done this fan mod and recommended it. I was wrong.


Darren said:


> A good way to discharge the capacitors is to use a standard lightbulb with wires soldered to the positive and negative poles. Put the lightbulb across the caps and it will light up discharging the caps.


Thanks for the help. (Now you tell me. :joke

Should I try this again the right way, or live with the tiny fan hum? First I open up the case and then I use my lightbulb with attached leads to discharge the caps, right? Should I touch the leads to the heat sinks and case, or to some other two points? Should I try some other fans or should I install a potentiometer in the existing fan leads? (The fans in there are quieter than the "WhisperFan," but still a bit audible.) Any other bright ideas?


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## Ayreonaut (Apr 26, 2006)

Another question: The amplifier is still working properly. Can I conclude that I did no real damage to the transistors, or what else might I have damaged?


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## SteveCallas (Apr 29, 2006)

Ayreonaut said:


> The idea to use a resistor to decrease the voltage is another hair-brained suggestion that I read in an online forum. I'm starting to think that nothing I've read is true. Except you guys of course. You seem to know what you're talking about.


Ayreonaut, I believe you mentioned you are using a Carvin HD1800 - a simple resistor mod worked extremely well for me. I went from 53db at 1" from the faceplate to unregisterable at 1", and from barely audible at the seat to silent at the seat. ThomasW from htguide.com sent me a few of these connectors










so I could keep the mod discrete, as I didn't want to do anything permanent. The plastic connectors he gave me were a bit large compared to the ones Carvin uses, so I cut them open and found the plastic isn't needed at all, inside the two wires have small, hollow, metal connector attached to their ends - perfect. I experimented with a few different resistors - I started too high and the fan wouldn't turn on.....after going lower and lower I settled on a 39ohm resistor, as the fan turns on and still sucks up a good amount of air, but the noise is reduced considerably. The resistor goes on the red lead of the LEFT fan plug, as that is the fan (the back one) that will turn on at startup. The Carvin only starts up with one fan, and I guess if it detects hot temperatures, the second one is initiated as well - mine has never gotten warm to the touch, always cool, even with hours of use, both before and after the mod. 

The resistor should look like this - I'll double check the colors on the one I used and make sure it is 39ohm when I get home tonight.










Due to the mod being discrete, I can remove it whenever I want and simply plug the fan connector right back to where it would be stock, nothing is altered. It really works extremely well, and it's very easy. All you need is a soldering pen to connect bare wire to the resistor ends. If I had a digital camera, I'd take some pictures for you - I have one on order from CC, when it eventually comes in, I'll post some in this thread. I modded both my HD1800s this way - no problems and definitely no shocks - sorry to hear about that one :yikes: The fans Carvin uses are already very quiet to begin with, I'm sorry I didn't catch this thread earlier to save you some time and money.

Hope that helps.


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## SteveCallas (Apr 29, 2006)

Also, as to the issue of amplifier attentuation/gain and processor output levels, there have been many discussions about it on other forums. I suggest the method you found to work best - turn the processor level down, and the amp up. Some say you are more prone to picking up noise this way, but I just don't see it that way. I see it as you adding distortion into the mix when boosting the processor level, as who knows what level of quality that attenuation/gain device is in the processor? The preout signal probably won't be clipped or distorted with low to moderate listening levels, but at louder levels, and especially with dynamic peaks, it basically comes down to whether you trust the internals in the amp more than the attenuation/gain device in your processor, which is probably only a few cent part. My money is on the amp  Glad to hear you are enjoying it :T 

The only thing I might be concerned with is that -12 on your receiver may cap some of your potential output a little early. But if the reference levels and beyond you have enjoyed the past few days are loud enough, and you don't see yourself going significantly louder than that, don't worry about it. 



Mark Seaton said:


> That is surprising that any pre-amp output would be clipping at such levels, but pro amps do typicaly require a higher drive voltage to reach their maximum output


Agreed, but the Carvin is an odd ball - it has a sensitivity of 1V.


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## brucek (Apr 11, 2006)

> a simple resistor mod worked extremely well for me


Ayreonaut, today Steve and I are going to disagree.  No disrespect of course, but I'll just give my opposing opinion and you will then be armed with information.

Yeah, you can use a series resistor to drop the voltage across your fan to slow it down, but it's considered a bad idea with a DC fan. They really like their designed terminal voltage present, so depending on the load they will be able to draw the appropriate current, specifically on start up where the load is the greatest. 
The drawback of introducing a fixed series resistance is that if the load on the motor increases (bearing or sleeve wear or start up requirement), then as the motors current increases, so does the voltage dropped across the fixed resistor, thus supplying even less voltage for the motor and so on until the motor stalls or can't start in the first place.

The only correct way to control speed on a DC motor is to supply the required specified voltage with a varying pulse width through a speed controller.

There are kits avaliable at very cheap prices to affect a speed change in a DC fan. You could hide and connect it externally with connectors, so as not to modify the amp for warranty or sale concerns.

Everyone used to sell these kits, but now you see them sold as pre-made PC fan speed controllers that mount in a 5.25" drive bay. I see Radio Shack sells one from Thermaltake for $26 (kinda expensive). It controls up to four fans with different colored lites...... funny stuff. Most PC stores sell them. You'd need the correct molex connector though.

Anyway, just some thoughts on it.

brucek


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## SteveCallas (Apr 29, 2006)

brucek said:


> Ayreonaut, today Steve and I are going to disagree. No disrespect of course, but I'll just give my opposing opinion and you will then be armed with information


:T No worries, my education in electronics is very limited, and what you say makes sense. Weighing the potential benefits vs drawbacks though, with this being the main drawback,



> until the motor stalls or can't start in the first place.


I'm not overly concerned, as the mod I made is discrete. Were that to happen, which is what happened when I used too high a value resistor, I could just take it out and use a smaller value resistor or stop using one all together. 

Surprisingly, with the resistor in place, the fan really doesn't suck up much less air at all than it did before. I've never been successful in getting the amp warm to the touch. Oh, and something else I have done to decrease fan noise even more is to put some small plastic caps beneath the rubber feet to raise the top amp higher above the bottom one, and to raise the bottom one higher off my shelf. With too close a boundary, I was finding what I will assume to be air flow turbulence creating more noise.


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## Ayreonaut (Apr 26, 2006)

Thanks for your input Steve and Bruce. 

I agree that the stock fan noise isn't very loud. The only time I can hear it is when I'm listening late at night very quietly, and the central air and ceiling fan are both off. Still, I thought if it was easy to eliminate, that I would give it a try. It's too late for _me _to avoid doing anything permanent as I have already clipped the fan leads and soldered them back together, so I may try soldering the resistor in-line. I will stay _very far away_ from the caps and heat sinks, and I'll touch only the fan leads.

Bruce, if I introduce a resistor and the fan starts up and turns normally could it become a problem after that?


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## SteveCallas (Apr 29, 2006)

Well do you still have the plastic connector piece on the end of the fan lead, the one that connects to the (what I guess you would call) circuit board of the amp? If you do, you can still make a discrete mod. However those wires are connected on the fan side doesn't really matter.


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## Ayreonaut (Apr 26, 2006)

The fan leads were cut, but now they are soldered back to the way that they were. Wouldn't I need an extra connector to build a "resistor insert?"


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## brucek (Apr 11, 2006)

> Bruce, if I introduce a resistor and the fan starts up and turns normally could it become a problem after that?


Yes, it could. 

Here's the scenario. You install a resistor in series and find that the fan starts up nicely and is now completely silent. You're happy.

Unknown to you is the fact that you chose a resistor that is right on the edge of allowing startup, but because the fan is new everything is fine.

A year goes by and because fans are quite cheap (two for $6.99), the bearings or sleeves have dried up somewhat and so the load on the fan has increased. Under normal unmodified conditions this would be fine, but because you've put a fixed resistor in series the fan now will not start since it can't draw sufficient current.

Since the fan is so quiet after doing the mod, you have no idea that this problem has occured and so your nice amp overheats and dies without you ever knowing. :surrender: 

brucek


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## SteveCallas (Apr 29, 2006)

Ayreonaut said:


> Wouldn't I need an extra connector to build a "resistor insert?"


Yeah, you would need one so you can connect the front end of the mod into the circuit board. To connect the back end of the mod to the plastic piece at the end of the fan leads, just use a more rigid, single core piece of wire.

To get that extra connector, I'd shoot Thmoas an email - if he doesn't have any left, see if you have any old cordless telephone battery packs. If you don't, you should be able to find the little plastic connector at Radio Shack or somewhere like that.


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## brucek (Apr 11, 2006)

> To connect the back end of the mod to the plastic piece at the end of the fan leads, just use a more rigid, single core piece of wire.


OK, a picture is worth a thousand words.

Come-on Steve, get a camera for gosh sakes... 

brucek


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## SteveCallas (Apr 29, 2006)

brucek said:


> Since the fan is so quiet after doing the mod, you have no idea that this problem has occured and so your nice amp overheats and dies without you ever knowing.


Woah, woah woah, wait a second  I don't mean to argue Bruce, but I think there are a few failsafes that won't allow him to get to that level.

First, these amps can't be turned on remotely as far as I know, so you have to go up to it to turn it on. You will be able to tell whether or not the fan is running when you are right up next to it, just put your hand by the outlet, look through the outlet, or listen to determine whether the fan is on. The fans won't register on a RS spl meter (50db low limit) at 1" away from the front faceplate, but they aren't silent at 1" from the faceplate - they are silent at the seat. 

In addition, if the first fan doesn't kick on at startup, but it is still plugged in to the first fan outlet of the circuit board, you should definitely be able to hear a slight hummm or buzzzz.

Second, if the first fan doesn't kick on, when the internal temperature of the amp gets to whatever predefined level, the second fan should kick on automatically.

If you have any concern at all with these issues Ayreonaut, then I definitely would second Bruce's opinion and say to just leave the top shut - the fan noise ain't bad to begin with, and it's probably not worth it. That said, I think you would have to be somewhat negligent to miss if the fan wasn't on at startup.


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## SteveCallas (Apr 29, 2006)

brucek said:


> OK, a picture is worth a thousand words.
> 
> Come-on Steve, get a camera for gosh sakes...


I know I know  My wording is probably very confusing in that explanation. I ordered a camera about three weeks ago....they are waiting for the local CC warehouse to get it back in stock.


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## Ayreonaut (Apr 26, 2006)

I'll let you two figure it out. My courage level is still pretty low.

Steve, while we've you're here, would you care to post a bit about your listening impressions of the Carvin HD1800? Maybe a _short_ comment on your double blind test and a comparison to any other amps you've heard.

Obviously there are audible differences between some amps. I just don't have anything high-end to compare with right now.



kingkip said:


> I have a crown xls 402 powering my IB and just for kicks I tried it on my mains to see the difference from my parasound 1500. The crown just wasn't there especialy as far as the mid range was concerened. I thought that the parasound killed the crown in every test.


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## SteveCallas (Apr 29, 2006)

My belief is that there are audible differences between two similarly powered, quality solid state amps that are both run within their operating range and both have a flat FR _when you can see which is being used when_. Make that a blind, level matched test that takes place in one sitdown using the same music clip that the listeners are already familiar with over and over, and well...things become a LOT more difficult :scratchchin: 

If you were to measure the signals being output from two comparable amps that meet the criteria I stated above, using the same input, and chart it on a computer, you may find some minute differences that would fall well below the threshold of audibility. I'm definitely not ashamed to admit I could not pick up on any differences between the Carvin and the PS Audio, and neither is the owner of the PS Audio, and I pride myself on my hearing based on the semi annual hearing evaluations I have to take for work. Some will say we didn't know what to listen for - to them I say get off your high horse and join us next time  It's amazing how many excuses they come up with not to.

Now am I saying there are no audible differences between any and all amps? No, just when the criteria I mentioned in the first sentence is met. With my mains and center having an in room sensitivity of ~93db, being 8ohm loads, and the Carvin having 350 watts on tap, I have much, much more than I need. Everything leads me to believe that Carvin puts out a quality solid state amp, so truth be told, I don't fret about my amplification at all. I use a receiver to power my surrounds, and while that amplification could probably be a bit better, I'm just not concerned, as I'm not left wanting anything more in the sound quality of surround effects in movies :rofl: More money could be much better spent in other areas.


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## bobgpsr (Apr 20, 2006)

brucek said:


> ...Yeah, you can use a series resistor to drop the voltage across your fan to slow it down, but it's considered a bad idea with a DC fan. They really like their designed terminal voltage present, so depending on the load they will be able to draw the appropriate current, specifically on start up where the load is the greatest...


I used to think so to --- until I started seeing a lot of PC cooling fans with multiple position speed switches just use a couple of series resistors. A lot of techy (but cheap) audiophiles have been modifying pro amp fan circuits with series resistors for use in their systems. 100 ohm 10 watt for Crown XLS amps, etc. 

http://www.avsforum.com/avs-vb/showthread.php?t=418666

I experimented and ended up with 130 ohms for my Mackie M1400 pro amp that drives my DIY sub -- but added a switch on the front faceplate to allow bypassing the series resistor if I'm about to really give the amp a workout. :devil: Like Steve says, you know when you turn on the amp if the fan does not start up (for those of us who still do it manually at the front of the amp).

Bob


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## SteveCallas (Apr 29, 2006)

130 ohms? Wow. The Carvin must be putting out a really low signal.


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## brucek (Apr 11, 2006)

> 130 ohms? Wow. The Carvin must be putting out a really low signal.


Not really. The steady state and start up current is varied among different models of DC fans. The resistor value is chosen depending on the current, such that the voltage across itself results in a slower fan speed. A fan that draws a lot of current will require a different value resistor than one that draws a small amount of current.

I read bobgpsr's AVS thread he referenced above in his post and got a kick out of the guy who adds a completely different fan, then adds in a resistor value that someone mentions in another thread and then finds that his fans draw a lot of current until they're up to speed (as I warned in my threads above). So much so that he activates his power supplies current limiting protection crowbar.

He says: _"When I first did this modification, I still had the Nexus fans in the amplifier. Here is where I found another flaw in the Nexus fans. When the switch turned on and the fans started, the amplification to the speakers would completely cut off for about 1 or 2 seconds while the fans ramped up to speed. When I removed the Nexus fans and put the stock fans back in, the problem went away completely."_

Oh well.....  

brucek


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## Ayreonaut (Apr 26, 2006)

Steve, did you get a chance to double check that resistor value?


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## SteveCallas (Apr 29, 2006)

I'm sorry, I didn't check, I was under the impression you decided not to go forward with the idea. I will check tonight.


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## Ayreonaut (Apr 26, 2006)

I'm still mulling it over. When you get your camera, a picture would be very helpful. Thanks Steve.


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## SteveCallas (Apr 29, 2006)

Man, CC had a great sale on a HP 5 megapixel camera for $99 about a month ago - I realize it's probably not very high quality, but since I'm by no means a big photography guy, it will be more than what I need for my typical applications, so I jumped on it. All stores in my region were sold out at the time of the sale, but they still took my purchase and are waiting for the warehouse to get them back in stock. Here I am about a month later, and still no success. I'm starting to think it was inventory clearance for a discontinued SKU addle:


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## SteveCallas (Apr 29, 2006)

Ok, opened up one of the amps - the color bands are orange, white, black, gold, in that order. Assuming my electronics 101 is up to snuff, that would appear to be 39 ohms, yes? :scratch: 

EDIT -  well this makes it official http://www.dannyg.com/examples/res2/resistor.htm

Also looked at my CC receipt, it was actually only $79 for that 5 megapixel camera, and I ordered it on July 10.


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## SteveCallas (Apr 29, 2006)

Well, any updates Ayreonaut?


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## Ayreonaut (Apr 26, 2006)

No, I've been trying to finish a summer research paper before I go on vacation next week, and so my evenings have been packed. The amp will have to wait until the week of the 24th.

One other delevopment is that I noticed that the speakers were reproducing a very high frequency pitch that my CRT television emits faintly. There was also a bit of broadband static, but these were both at low levels (you have to put your ear close to the speaker to hear exactly what's going on.) The high frequecny pitch was irritating me though, so I tracked it down. It's the noise floor of the Denon reciever which must be picking up junk from the TV either through the AC lines or RF. The reciever's noise floor is independant of the pre-out level. I had the pre-outs set at -12 dB and an extra 12 dB of gain on the amp to compensate, so the noise floor was 12 db higher than it used to be. So the short term solution was to put the pre-outs back to 0 and dial back on the amplifier gain. The noise floor is now inaudible.

For reference level movie playback, the pre-out clipping is really not an issue. It only comes into play if I listen to music at incredibly loud levels. I put the speakers through their paces and found that they have their limits too, and if I'm not pushing the speakers too hard, then I won't be clipping the pre-outs either.

(The _no comprimise_ long term solution would be to get a better receiver or processor, and speakers that can dish out more clean volume than I can take.)


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## SteveCallas (Apr 29, 2006)

I've tried a HK 635, a Pioneer 1015, and have now settled on a Yamaha 5890 to replace my old RCA receiver. Out of the four, even with my rat's nest of intermingled cables, the HK was the only one that had a dead quiet noise floor - too bad it suffered from other problems. The Pioneer 1015 was extremely noisy/dirty, worse than my old RCA, and the power supply even caused magnetic interference on my tv. The Yamaha 5890 is very quiet, not dead quiet like the HK, but enough that I have to put my ears within a couple inches of the tweeter to hear anything - at 1' away I can't hear it. I'm more than willing to accept that considering everything else works perfectly. I was starting to fear I would never find a mid level receiver that didn't suffer from big problems.


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## eddthompson (Aug 19, 2006)

Just to jump in, i love my pro amps, POOWWEERR is goooood :laugh: 

if your interested heres my setup on another forum, http://www.avforums.com/forums/showthread.php?t=378214

I added the bfd today and will update wheni remember.

edd


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## Sonnie (Apr 11, 2006)

Solid rack of amps there edd... also a mighty fine collection of DVDs. I've the EP2500 for my IB subs when I get the time.

You can upload those picks to the Home Theater Photos area here if you want. Nice system!


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## Nick77 (Oct 19, 2006)

Been mulling over trying my ep2500 to power my mains. After reading such positive results I am thinking my HK635 could use sum more power! :T


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## SteveCallas (Apr 29, 2006)

Yeah, go for it. Not only will your mains have more capability for music, but you'll lighten the load on your HK, potentially helping your center and surrounds.


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## rosco968 (Oct 19, 2006)

I use a Sampson 1000 with my 2- SVS subs and the fan noise is a problem during quiet passages. The amp works great with the subs, but I would not use it with my mains. I have often thought of yanking the fan out and replacing it ,but did not know what to use. I will try the Panaflow idea. That would make things much better. The amp does not get hot even with lots of bass.


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## SteveCallas (Apr 29, 2006)

If the fans are modular, you may just want to try putting a resistor in line first.


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