Amp rating - power output - confusion

[bobs]

Since I want to switch to Processor/Power Amp configuration, I was on the lookout for affordable power amps. I considered Emotiva, but I'm afraid about handling defective gear should it come to that (I'm in Europe). Since the stuff is heavy, shipping costs are high.

I was looking for alternatives. The goal was to find a well designed, powerful fan less design - so no Europower for me (I know the fans can be changed, but I hate fiddling with stuff).

The Alesis or Behringer clone of the Alesis are too ugly for my eyes. So I found this amp:

http://www.apart-audio.com/products/productDetails.aspx?id=222

I ordered one to test it, simply use it for the fronts, connected via Cinch to my Onkyo 905. I have really blasted it (on my trusted PMC MB2i). So far I like the amp. Not once did the clipping light come up. I tried ear deafening levels. I tried hard to reproduce tracks (like the title track from "The Dark Knight OST" - it has some really deep bass). The amp never got warm even after hours of playback.

The bad thing is, I don't have any test gear. I don't know if the amp really is was well designed as it seems to be (e.g. frequency response). I don't hear any difference to my Onkyo, except in very high volumes, the bass is defined and does not "smear".

Apart also has a "strange" White Paper on the product page:
http://www.apart-audio.com/uploaded_files/productFiles/CHAMP-ONE/power_rating_Champ-One white_paper.pdf

It seems, the amp is designed to behave completely different than other amps, or with other parameters in mind. Just look at the way they test. It seems they put the focus on massive headroom. For a long term test, the amp can "only" deliver like 75 Watt - but without time constraint. On the other hand, it seems to able to handle speakers that dip as low as 1.7 Ohm, and it is also able to push put high peaks.

Since they also mention Meyer Sound (and I truly believe John Meyer knows what he talks about), here is a link to the White Paper from him:
http://www.meyersound.com/support/papers/amp_power.htm


What I was wondering about, how would for example an Emotiva XPA-1 or XPA-2 behave if you would test it like the Apart? With Brown Noise, the kick drum, etc etc.?

Anxiously awaiting your comments.

 

[XEagleDriver]

A very long way of saying "Class G amp"

. . . It seems, the amp is designed to behave completely different than other amps, or with other parameters in mind.
. . .

What I was wondering about, how would for example an Emotiva XPA-1 or XPA-2 behave if you would test it like the Apart? With Brown Noise, the kick drum, etc etc.?

Bob,

You are right, Apart sure muddied the water in their verbose explanation.

Bottomline: It is just a Class G (or H, which is the same thing) amp design. Class G is supposed to have efficiencies more akin to a Class D without the EMI frequency problems a Class D has to mitigate.

For more info on Class G read the following wikipedia article:

http://en.wikipedia.org/wiki/Electronic_amplifier#Class_G_and_H


And if you are curious how this differs from a Class D, read:

http://en.wikipedia.org/wiki/Electronic_amplifier#Class_D


As to the second part of your question, I have no idea!

XEagleDriver

 

[TLS Guy]

Bob,

You are right, Apart sure muddied the water in their verbose explanation.

Bottomline: It is just a Class G (or H, which is the same thing) amp design. Class G is supposed to have efficiencies more akin to a Class D without the EMI frequency problems a Class D has to mitigate.

For more info on Class G read the following wikipedia article:

http://en.wikipedia.org/wiki/Electronic_amplifier#Class_G_and_H


And if you are curious how this differs from a Class D, read:

http://en.wikipedia.org/wiki/Electronic_amplifier#Class_D


As to the second part of your question, I have no idea!

XEagleDriver

It is pretty simple. If you do standard test you amp will measure as a 75 watt per channel amp. The Emotiva and Behringer will develop their rated power.

Class G and H amps have switching power supplies, that can on a short term basis increase voltage to the output stage until time and current limited.

This technology does lead to a point of failure on occasions.

The benefit of class G & H is highly program dependent. A pipe organ for instance will run it out of gas fairly easily as an organ can put out high spl for an unlimited period as opposed to a piano for instance. I would imagine highly compressed pop music would also present a problem.

If you want a good power amp without fan in Europe, you need look no further than the Quad 909. This is an amp I recommend without reservation.

 

[KEW]

What I was wondering about, how would for example an Emotiva XPA-1 or XPA-2 behave if you would test it like the Apart? With Brown Noise, the kick drum, etc etc.?

I believe the common wisdom is that as long as you are not exceeding the power limits of the apart (and I assume you could not of the Emotivas), they would sound the same.

You may also want to look at the Yamaha P3500S (or other models in that series). While they do have fans, their fans have a reputation of being inaudible.
It is a shame that Behringer doesn't just spend $5 more on a quiet fan but I guess for most pro musicians, it'd be money wasted.

In the end, if you are buying a SS amp of adequate power, you are paying for looks and durability more than sound.

 

[bobs]

It is pretty simple. If you do standard test you amp will measure as a 75 watt per channel amp. The Emotiva and Behringer will develop their rated power.

Standard tests means a 1 KHz sine wave? How long does a measurement like this play the sine wave? I bet other amps will heat up as well. Can a XPA-2 for example output 400 Watt/4 Ohm for an hour or will it too heat up and sht down?

The benefit of class G & H is highly program dependent. A pipe organ for instance will run it out of gas fairly easily as an organ can put out high spl for an unlimited period as opposed to a piano for instance. I would imagine highly compressed pop music would also present a problem.

They print a table at the end of the white paper with measurements using different signals (Page 5).
Looks especially for peak voltage it is able to put out (70.13 Volt - this seems to be crazy high).

I already tried all kinds of different music, even pop music stuff like Lady Gaga, at deafening levels. Clipping never occurred, it also seems the built in protection circuit never got active (-6 dB should be easy to hear).

I'm kind of happy with the thing, it's just very confusing. Since I always read on this forum I know the mantra "There is no such thing as RMS power" - yet Emotiva exactly advertises their amps like this.

 

[highfigh]

Standard tests means a 1 KHz sine wave? How long does a measurement like this play the sine wave? I bet other amps will heat up as well. Can a XPA-2 for example output 400 Watt/4 Ohm for an hour or will it too heat up and sht down?

They print a table at the end of the white paper with measurements using different signals (Page 5).
Looks especially for peak voltage it is able to put out (70.13 Volt - this seems to be crazy high).

I already tried all kinds of different music, even pop music stuff like Lady Gaga, at deafening levels. Clipping never occurred, it also seems the built in protection circuit never got active (-6 dB should be easy to hear).

I'm kind of happy with the thing, it's just very confusing. Since I always read on this forum I know the mantra "There is no such thing as RMS power" - yet Emotiva exactly advertises their amps like this.

70.13VAC peak comes out to about 615W into an 8 Ohm load.

Sending a 1KHz sine wave to an amp is great if that's what it's being used for, or the manufacturer wants to show the highest power output, but it's always better to test at wide bandwidth, stating how much deviation from flat frequency response it caused.

Also, if you're playing music at deafening levels, it's almost impossible to hear what you posted that you didn't. The amp may not have indicated clipping but it could have been- it's just not possible to hear it unless it reaches high enough %. Hearing dynamics at those levels is hard because the hearing threshold shifts under stress.

 

[bobs]

The amp may not have indicated clipping but it could have been- it's just not possible to hear it unless it reaches high enough %. Hearing dynamics at those levels is hard because the hearing threshold shifts under stress.

Since it's a pro amp it has a clipping indicator in the front. These are usually very accurate. Another interesting note on amp power is power output depending on frequency. Over at AVS one guy measured various pro amps and occasionally there was an amp with a low output at low frequencies.
http://www.avsforum.com/avs-vb/showthread.php?t=855865

The more I read, the more I'm convinced that the normal measurement methods are not able to show the true "face" of an amp. For example, my Onkyo 905 was measured by various publications. It comes out to over 200 Watts on 4 Ohm.
http://www.audio.de/Produktdaten/Onkyo-TX-NR-905-Details_645020.html
Should be more than enough to provide clear sound to almost any speaker. Now, if my new Apart is only a 75 Watt amp, how is it sounding better at high volumes? Well, the Apart has a classic power supply (toroidal) and 46 MF of secondary buffer.

Would be nice if Gene would chime in. Maybe I will get AP data soon from Apart, I asked a couple of times.

 

[highfigh]

Since it's a pro amp it has a clipping indicator in the front. These are usually very accurate. Another interesting note on amp power is power output depending on frequency. Over at AVS one guy measured various pro amps and occasionally there was an amp with a low output at low frequencies.
http://www.avsforum.com/avs-vb/showthread.php?t=855865

The more I read, the more I'm convinced that the normal measurement methods are not able to show the true "face" of an amp. For example, my Onkyo 905 was measured by various publications. It comes out to over 200 Watts on 4 Ohm.
http://www.audio.de/Produktdaten/Onkyo-TX-NR-905-Details_645020.html
Should be more than enough to provide clear sound to almost any speaker. Now, if my new Apart is only a 75 Watt amp, how is it sounding better at high volumes? Well, the Apart has a classic power supply (toroidal) and 46 MF of secondary buffer.

Would be nice if Gene would chime in. Maybe I will get AP data soon from Apart, I asked a couple of times.

The spec that was used in the past for consumer amps stated W/ch, both channels driven, 20Hz-20KHz +/- x.xdB (or wider),with no more than .xxx%THD. This didn't necessarily maximum power, it's the power output at the distortion stated. This easily allows for an amp's frequency response not being flat but many are.

I'm not sure why you call a toroidal transformer a 'classic' power supply. 46MF- you really mean Mega Farad? You mean 46,000 uF, right?

This amp may sound better at high SPL because it has more headroom and the fact that it's only an amplifier instead of trying to do everything, with a power supply that was limited by available chassis space, is a likely factor.