# Underpowered Amplifier Need Guidance



## bobcat16 (Jul 31, 2015)

So I'm new to these forums and I'm not sure if this is a stupid question or not. So I have two floor PA speakers, (WELTON AUDIO PS412-1 TOWER SPEAKER). They have a rating of 150 W NOM (I'm assuming RMS) and 400 W max. I currently have them running them through aa Adcom GFA-535 II preamp which is rated at 60 W RMS. I wanted to upgrade to a more powerful amp so I purchased the musysic sys-2000 amp which is rated at 250 W RMS at 8 Ohms (which I'm assuming is the resistance of the PA speakers. According to these numbers I was under the impression that the new preamp would blow the Adcom out of the water. However after comparing the two preamps, the adcom is by far louder and cleaner than the musysic amp. What am I missing here? And if I did want to power my speakers effectively would preamp would you recommend? I can't post any links to the items i own since I'm a new member hope you guys can help out.


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

Welcome to the Forum bobcat!

First, The Adcom and Musysic are amplifiers, not preamplifiers.

Second, I assume you had the gain knobs on the Musysic amp all the way up?

Nevertheless, it stretches the imagination that a $100 amplifier can really put out a true and clean 250 watts RMS per channel. That Adcom amp cost $300 twenty-five years ago. What is that, over $500 today? A good clue is that Musysic's web site does not qualify what the distortion level (THD) is at 250 watts, nor at what frequency or frequency range, as you find with most good home audio amplifiers.

For example, compare the power specs of this amplifier from Yamaha:
Rated Output Power (20Hz – 20 kHz, 2 channels driven): 150 W (8 ohms @ .06% THD)
Rated Output Power (1 kHz, 1 channel driven): 190 W (8 ohms @.09 THD)

You can see from this that the way the amplifier is rated makes a difference. With only one channel driven, and at a single frequency (1 kHz), the amp puts out “more” power. A broadband signal (20 Hz – 20 kHz) generated with both channels driven is a much more demanding (and I might add, real-world) situation. Subsequently the power output is less, but more realistic as no one listens to 1 kHz sine waves.

Now look at the power specs of the Musysic amp:
250 W @ 8 ohms

As you can see, this spec has absolutely no relevance: Was it generated at a single frequency or broadband? Single or both channels driven? What is the THD at 250 watts? After all, clean power is all that matters. Any amp is capable of delivering tremendous peak wattage if you can live with distortion that makes your ears bleed.

Note that the Musycic amp does have a _separate_ THD rating of 0.1%, which is a respectable figure, but there is no indication at what power output that it exhibits that rating. For all we know the amp could be generating 20% distortion at 250 watts.

Bottom line, at the end of the day it’s very likely that your two amps are not that different in power outputs, as Adcom adheres to the same specification standards shown in the Yamaha example above, and indeed had a reputation for _underrating_ their amplifier power.	

Nevertheless, power ratings don't matter so much as whether or not you're able to play the system as loud as you want to. If the Adcom can do that, then there was no reason to buy the Musysic amp to begin with.

Regards, 
Wayne


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## Insearchof (Oct 21, 2014)

^^^Agree. The specs for the Musysic amp aren't very clear and lead me to suspect they aren't as they appear.
For a little bit more money, the lesser Crown and some QSC amps are a lot of bang for the buck.

The Crown XLS and XLi series seem to be good performers and have decent specs.


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## bobcat16 (Jul 31, 2015)

Thank you for your help! I should've assumed the musysic amp wouldn't have done the job properly and wasn't sure how to interpret some of the specs it gave. 

With that being said I would like my system to get louder before my speakers start to clip. Right now I'm looking at the crown XLS-1000 which I know is a reliable brand. 

Thanks again guys I really appreciate it!


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## NBPk402 (Feb 21, 2012)

Check out the Yamaha Pro amps too... excellent build quality, sound great, and usually zero fan noise.


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## tcarcio (Jun 27, 2007)

I agree with the above post for sure but here is another option. B+H photo is selling Crowns for a great price and the XLS-2000 would be all the amp you need for a great price. Check it out ...http://www.google.com/aclk?sa=l&ai=...&Q=&sku=674285&is=REG&BI=225&kw=CRXLS2000&m=Y


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## bobcat16 (Jul 31, 2015)

Yes I was considering the XLS 2000 as well. I found a great local deal on a new XLS 1000 for 150 though so I don't think I can pass that up.


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## Andre (Feb 15, 2010)

I own the Crown XLC2500, I preferred the XLC over the XLS because the XLC is a class AB amp and the XLS is a Class D. The XLC also has the ability to change the input sensitivity


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## chashint (Jan 12, 2011)

tcarcio said:


> I agree with the above post for sure but here is another option. B+H photo is selling Crowns for a great price and the XLS-2000 would be all the amp you need for a great price. Check it out ...http://www.google.com/aclk?sa=l&ai=CP3t36p27VZb8OcWjfKmciYAHkrWcwgbC6ofGnQL615WsvQIIBhABKAhgyfaliqSkxBGgAZ3kyPcDyAEHqgQnT9AikmrsJvfnj-t7R8G5X3boPeANJO7Zf1Gi6fKS8gs4XBWP5vDdwAUFoAYmgAek_oUJkAcBqAeiwhuoB6a-G9gHAeAS5qXGxLro_eRK&sig=AOD64_2YcQkED5XU0OI2Asltgr51CbRt8g&ctype=5&clui=18&rct=j&q=&ved=0CKUBEPQOahUKEwjD_ITz4IXHAhWLnYAKHQhGAHo&adurl=http://www.bhphotovideo.com/bnh/controller/home%3FO%3D%26A%3Ddetails%26Q%3D%26sku%3D674285%26is%3DREG%26BI%3D225%26kw%3DCRXLS2000%26m%3DY


Thanks for the link, that is a good price.
As far as pro amps go this one is about as home audio friendly as they get with the inclusion of RCA jacks and speaker terminals. 
Do you have any additional information on the >.5% THD spec ?
It's kinda open ended being greater than vs less than.


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## tonyvdb (Sep 5, 2007)

Also look at the Samson servo http://www.bhphotovideo.com/c/product/396457-REG/Samson_SA300_SERVO_300_Power.html at B&H I have one of theses and two of the servo 600 amps. They also have rca inputs.


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

chashint said:


> Do you have any additional information on the >.5% THD spec ?
> It's kinda open ended being greater than vs less than.


Not sure where you’re seeing that; every place I look it says <.5%.

Regards, 
Wayne


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## chashint (Jan 12, 2011)

Wayne A. Pflughaupt said:


> Not sure where you&#146;re seeing that; every place I look it says <.5%. Regards, Wayne


 I got it from the Crown website. http://www.crownaudio.com/en-US/products/xls-2000

Sensitivity	1.4Vrms (for full rated power at 4 ohms)
Frequency Response (at 1W, 20 Hz - 20 kHz)	+ 0 dB, -1 dB
Signal To Noise Ratio (A-weighted)	>103 dB (rated as dBr to full rated 8 ohm power output)
Intermodulation Distortion	(60 Hz and 7 kHz at 4:1, from full rated output to -30 dB) <0.3%
Damping Factor	(8 ohms, 10 Hz to 400 Hz) >200
Crosstalk (below rated power) 20 Hz to 1 kHz	>85 dB, >55 dB
Input Impedance (nominal)	20k ohms balanced, 10k ohms unbalanced
Load Impedance	2 to 8 ohms per channel in Stereo, 4 to 8 ohms in Bridge Mono
AC Line Voltage and Frequency Configurations Available	(+/- 10%) 120VAC 60 Hz, 100 VAC 50/60 Hz, 220 and 240VAC 50 Hz
Dimensions	19" x 3.5" x 10.7" (48.3cm x 8.9cm x 27.2cm)
Weight	10.8 lbs (4.9 kg)
Shipping Weight	15.8 lbs (7.1 kg)
IEC Power Connector	15A
THD	> 0.5%


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

I’m sure it’s a misprint. No one gives specs like that. The Data Sheet and Manual both say <.5%.

Regards, 
Wayne


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## Eric180db (Nov 7, 2015)

Pro audio amp can need up to 1.4v to go to full power. Home audio will be around .3v so the gain is drastically different. This could be a12db+ difference. Are you able to bring the musysic amp to clipping on the indicators? If not then it's not the amp. You will probably need a preamp to get pro audio voltage levels.


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

The input sensitivity for the Musysic amp is only 0.77v. Any consumer pre amp can drive it, as most have voltage outputs well over 1 volt (some as high at 10).

Regards, 
Wayne


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## proverbs (Apr 7, 2013)

I stepped up from a crown Xls2000 to crown xls2500 in my home theater running a JL12w7 in a ported box tuned to 21hz about 5 cu.ft volume . I noticed a little difference . 

Then I moved the jumper to 1.8 vrm high sensitivity in my balanced Minidsp and my crown xls2500 was running at full 2400 watts @4 ohms and that JL12w7 rated at 750 RMS and 1000 max was living all that clean Power . It's has never sounded better . The bass was amazing . I had to turn the gain down on my receiver It was way to much bass, Shaking , walks . Keep in mind I did setup the anti-clip feature on the crown amplifier and monitor red and green meter lights in front of the amplifier To find the best gain setting . It's was like night and day when u moved that jumper over . 

You should look at the new crown xls2002 or 2502 that have a similar vrm setting you can adjust via the buttons on the front of the amplifier . They designed this way so you could run a home audio device with a pro audio amplifier like the crown amplifiers .
You could also pick up a balanced mini DSP


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