# Is 1 volt too low to feed a pro amp?



## Jerm357 (May 23, 2006)

How much signal is my Pro amp missing out on if my receiver Pre out is only sending out a 1v unbalanced signal. Is 1 volt low enuff to justify the purchase of an art cleanbox? I am using an Onkyo receiver (TX-SR600) and an ep1500 pro amp. I just think the amp is not getting all the signal it needs even if its not lacking a huge amount. Has anyone else with an Onkyo felt need for a stronger signal to feed a pro amp?


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## brucek (Apr 11, 2006)

> I just think the amp is not getting all the signal it needs


Pro equipment usually uses about +4 dBu (1.24 volts rms) as a nominal level. Generally equipment engineers design their products to have a reasonable amount of headroom above this average level. You'll usually see a spec for nominal and maximum to make up for this crest factor.

For example the BFD has a nominal input spec of +4dBu (1.24vRMS) and a maximum input level of +16dBU (4.89vRMS). This allows peaks to pass without clipping the amplifier.

I looked at the EP1500 spec manual and only see input sensitivity at 3.4dBu (1.15vRMS). I suggest this would be the nominal spec. Seems reasonable.

I would assume your 1 volt that you specify would be consumer level maximum. Generally consumer levels would be nominal about -10dBV (315mvRMS) and maximums around 2dBV (1.26vRMS). - (note we are now using dBV and not dBu). 

So your 1 volt maximum which calculates to 0dBV or 2.2dBU is certainly not enough to properly drive an amplifier expecting 3.4dBu nominal.


brucek


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## Jerm357 (May 23, 2006)

Wow, thanks for the detailed answer. Looks like Im gonna get a cleanbox


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## Danny (May 3, 2006)

or you could use a mixer. In Australia you can pick one up for $129. But it is important to give the pro amps the signal that they are expecting otherwise you may blow the input stage.


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## Chrisbee (Apr 20, 2006)

An alternative way of matching domestic pre-output levels with pro gear is to boost the input and output signals on an active crossover. (like the Behringer CX2310) 

It depends on your system whether you want to use a crossover. 

If you are using a pro-amp in a straight stereo system then an active crossover makes more sense than in a typical surround system. 

The superb flexibility offered by an active crossover is incredibly useful in a stereo system.


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## Otto (May 18, 2006)

Danny said:


> But it is important to give the pro amps the signal that they are expecting otherwise you may blow the input stage.


Hi Dan,

What do you mean by "blow the input stage"?

Should the OP be concerned about this, specifically as he's concerned about "under-signalling" the input of his Behringer pro amp?

Thanks!


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## Danny (May 3, 2006)

This was told to me by a mate of mine so i'm not exactly sure of the details, i'll ask him next time we chat. However i'm thinking that a continued overvoltage eg above 10Dbu would do it. Blow the input stage as in the amp doesn't work. His is lacking so I don't really see a problem with that, it's what happens in most pro sound installs when they aren't running the desk at full.


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## jagman (Jul 8, 2006)

The analog subwoofer output on my Nakmichi IA-1z is rated at 1.65 V/1 kohm. I have no idea whether that is RMS or maximum. I have ordered the BFD but it hasn't arrived. A already have a Samson S700 prosound amp driving my dual 18" IB. I looked through the S700 manual and I don't see the input sensivity listed anywhere. Based on this info, it seems like I might not need an Art cleanbox as my max appears greater than the likely minimum necessary... but I'm not sure. What are your recommendations?


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## brucek (Apr 11, 2006)

> What are your recommendations?


Well, your Nakamichi outputs a maximum of 1.65vRMS. That's fairly standard consumer level. It will be a fine match for the BFD that requires 1.26vRMS maximum input level with the level switch in the -10dBV position.. You'll adjust your subwoofer output trim to match that BFD level.

Then you can use the balanced outputs of the BFD to feed the Samson S700.

If you read your Samson S700 manual real close you'll see two references to input sensitivity (shown in the jpgs below).

It would seem the S700 has an attenuator control on its input that allows levels as low as 0dBu to derive maximum power. 
0dBu is 0.775vRMS, so the 1.26vRMS (~4dBu) will be quite adequate to drive the S700.....



















brucek


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## jagman (Jul 8, 2006)

Bruce... thank you for the thorough response. You really went above and beyond. This is a great fourm. 

I'm just waiting to ge the cables now. I've e-mailed MonoPrice, BlueJeans and RAM for quotes. They are all closed over the weekend, so hopefully I'll get answers on Monday. Oh the wait! 

BTW, I was really annoyed when the BFD arrived. The outside box was in poor shape with minimal tape holding it together. The box was also rather big considering the size of the BFD's box. It was surrounded by plastic air pocket protectors, so that was good. But, the BFD box was heavily taped shut. Moreover, the rack mount on the right side was significantly bent. I think Music123 sent me a refurb, and a bad one at that. Judging by how bent the metal is, it looks like it's been dropped or poorly taken care of :explode:? I called Music123 and they said it was shipped directly from Behringer and that a new model is backordered 2 months. Not only that, but they said I have to return this now in order for them to order the new one for me. So, it looks like I'll have return the BFD and then buy it elsewhere. There's no way I'm waiting for two months!


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## jmprader (Apr 19, 2006)

Many local music stores carry BFD's and BFQ's and the prices are only a bit more than the best net deals. I paid $12 (and CA sales tax) more than the then-best-price net dealer I could find...and I live in the hinterlands. Check out the locals, I'll bet they won't be far off.


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