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Recommend some class A amps...
Old 17th May 2006
Gear Head
🎧 10 years
Recommend some class A amps...

I need an decent amp to drive my PMC TB2s+ speakers (150W each) and XB1 subwoofer (200W). The sub has a built in crossover so I need one amp that delivers 250wpc minimum.

Obviously the Bryston 4B is a major contender, but what's the competition? I'm looking to buy one second hand, and spend up to $600. I don't want to rush in and buy a Bryston 4B when I don't know of any serious alternatives.

Any suggestions?


P.S. Why does this site crash every time I try to post a new thread?
Old 17th May 2006
Gear Head
🎧 10 years
somebody please...
Old 18th May 2006 | Show parent
Gear Guru
tINY's Avatar
1 Review written
🎧 15 years

If you want that much power and it has to be class A, you should probably post in the high end forum (or modify an arc welder).


Old 18th May 2006 | Show parent
Lives for gear
Steamy Williams's Avatar
🎧 15 years
Bryston power amps aren't Class A thoughout. I think most of them are a mixture of Class A and Class AB, I know the model I have is. Somebody correct me if I'm wrong, but not a lot of power amps these days are Class A - is not as practical as, say, with a microphone preamp because of the extra power consumption required.

I have Bryston PowerPac 60's with my PMC TB2SM+'s and they are a great match, although that particular model of Bryston wouldn't be suitable for you because of the Sub, but I highly recommend you consider the Bryston 4B (or the 3B if it's powerful enough for your setup) as PMC and Bryston are a match made in heaven.
Old 18th May 2006 | Show parent
Gear Guru
NathanEldred's Avatar
7 Reviews written
🎧 15 years
I think the position of Bryston in the marketplace is unique. They give you a very high quality product that isn't that much money, relatively speaking. The SST is an improvement even over the already great older ST line. Anything less expensive, and it's really not appropriate for critical listening IMO (i.e. better for project or live), and it's skies the limit with more expensive esoteric amps (and they get expensive real quick...often triple or more of what a Bryston costs watt for watt). Not that more expensive can't be worth it, especially in a mastering situation, but everything else should be equal in the studio if one is going to spend $10K+ on a stereo power amp (or pair of monoblocks).
Old 18th May 2006 | Show parent
Lives for gear
🎧 15 years
I saw a 100W mono class A power amp in a hifi shop once. It was basically a huge aluminium heatsink. I would like to try to shift it by myself. And I certainly wouldn't like to pay the power bills, let alone buy a pair of them ...
Old 18th May 2006
Lives for gear
🎧 15 years
Originally Posted by petermedland
I need an decent amp to drive my PMC TB2s+ speakers (150W each) and XB1 subwoofer (200W). The sub has a built in crossover so I need one amp that delivers 250wpc minimum.
I already recommended Bel Canto eVo 200.2 (120 wpc) in one of your other threads. That type of fast amp is very well suited to PMC in my experience. Nothing to do with Class A. I've had success with a variety of amplifier designs with many speakers -- the overall sound is what counts.

You said 120 wpc was not enough. Sorry if you already know all this, or perhaps I'm missing something about the setup, but let's look at it:

PMC specs the XB1-P sensitivity at 90 dB @ 1 w/m. If you are 2 m away, that SPL will drop to 84 dB according to the inverse square law. Of course these numbers are neglecting any room effects.

To double the apparent loudness you must increase the SPL by 10 dB. This requires you to increase the wattage ten times. So 10 watts gets 94 dB at 2 m. 100 watts = 104 dB.

Going to 120 watts will gain almost 1 dB, to 105 dB.

What do you get at 200 watts? Doubling the amplifier power will increase SPL by 3 dB. So 200 watts = 107 dB.

Adding 50 watts to get to 250 will add about 1 dB SPL, or 108 dB.

So, it's roughly 3 dB difference in loudness from 120 watts to 250 watts. As we know, that is about the minimum average increase to appear "slightly louder".

Now of course headroom is another issue, and I agree that power reserve can be nice for this. But that can get expensive, and not always as critical in studio use, with nice amps and speakers like you are using....

BTW, you do know that PMC recommends a power amp of 120 to 200 watts for the XB1, and 40-150 watts for the TB2?

I can see the convenience of using the sub's summing crossover in order to use a single stereo amp to power all three speakers, but I would personally not always want to limit the TB2 to 100 Hz. That speaker is capable of much lower extension, easily to 40-50 Hz.

Secondary to my main choice of Bel Canto, I'll offer some other cost-effective amplifier suggestions, but I have not personally tried these, only going off some research and conversations with the company: Odyssey Audio Khartago, $995 or Stratos for $1195. Maybe call Klaus and discuss them if you want, he offers a 30 day no-questions-asked trial period.

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