[firedog]

Someone is trying to interest me in a stereo power amp he built. I don't have much technical knowledge. Here are the specs he gave me regarding power:

85 WPC (conservative) @ 8 ohms, 170 @ 4 ohms; 250W peak/transient power
Transformer: 500VA toroid

4 industrial-grade,
high-current rectifiers (Dual-Mono configuration).   
 
Total capacitance of 88,000mF total for two channels, 4 x top of the line  Mundorf
caps  – each channel has its own reservoir.     

 8 dual-stage voltage
regulators, powering each internal component individually (input stage and
drive-stage are fully-regulated and powered separately from the output-stage).   


I'm trying to understand how much current this amp actually can produce and how powerful it actually is.  It has much less "WPC" than my current amp, but I understand that that doesn't really mean much. The 88000 mF sounds like a very large amount for an amp with that kind of power output, especially as I'm more interested in it's ability to play peaks and transients loudly and cleanly than in the overall power rating.

But aren't I missing some needed info here?

Of course I plan to listen to the amp. I just want to make sure it meets some minimum requirements before I invest time and effort in auditioning it.

Any help would be appreciated.
 

[Ericus Rex]

Those specs don't mean it will sound good...or bad.  I remember years ago when all the SS amp manufacturers were trying to get the absolute lowest distortion ratings possible.  And great sounding tube amps, which are the benchmark for most ss manufacturers, don't even list that spec (usually around 1%, I think).  Just listen and let your ears make the call.

[firedog]

thanks for your interest. But I'm trying to interpret the power specs of the amp. I need a high current amp with my setup and listening habits. No point in going to the trouble of auditioning it otherwise.

[srb]

It's hard to say from the specs you were given.  WPC without bandwith and distortion don't mean so much.  As a rule of thumb, one would like to see at least 60% more power at 4 ohms than 8 ohms.  The ideal amplifier would double power at 4 ohms and double again at 2 ohms.  But not a lot of amplifiers can do this.
 
Power output vs distortion graphs could tell a better story, but are rarely provided, and even then may be hard to interpret.  I like to see specs that rate WPC both at clipping as well as at a lower distortion rating, say .01% or .1% THD at any frequency between 20Hz and 20KHz.
 
On paper, this amp looks like it doubles power at 4 ohms (85W/170W).  But what if the power at clipping is actually 120W at 8 ohms and 170W at 4 ohms?  Not a doubling of power, but if the 8 ohm rating is downrated "conservatively" to 85W it looks like it does.
 
Some manufacturers will spec continuous as well as maximum current output per channel.  As far as the 500VA transformer and 88K uF capacitance, they should be enough to be able to feed a high current amplification circuit in this power range.
 
I would be more interested in what kind of circuits they are.  Are they factory amp modules added to a power supply or are they built from the ground up?  What does the layout and wiring look like?  What area of heat sinking is provided?  Lots of variables beyond WPC, transformer VA and capacitance.
 
What is the asking price of the amplifier?  Maybe there are some factory-built power amps that actually have known current output specifications that could compete in price.  What is your current amplifier?
 
Steve

[sts9fan]

What kind of amp is it? Push pull or single ended? Single stage?

[*Scotty*]

I would assume that the amp has the rated power claimed for it. If the 500 watt transformer has 4% load regulation then the peak power will be virtually the same as the RMS power. It would be nice if that 250 watt peak power claim had an impedance associated with it.
 Your Devores have a sensitivity of about 90dB,if the amp does 100watts into 8ohms, you have a theoretical peak SPL of about 110dB before clipping.
 The whole discussion of what the amplifier will do with your speakers in your room is loaded with speculation and is more than a little bit fuzzy. Which begs the question, can you borrow the amp and listen to it in your system. What it will actually do and how it sounds is much more important than any specification claimed for the amp.
Scotty

[*Scotty*]

sts9fan, unless I am mistaken we are speculating about a SS amp which is more than likely a Class AB amp.
Scotty

[firedog]

Hi-
Thanks for your help. Yes, it is solid state A/B. I am going to audition it, it is just that it is somewhat involved for me to do so.

So I wanted to make sure it wasn't a waste of time before I went to the trouble.

The amp modules themselves are factory made (Danish) - I don't know the manufacturer. All the rest is bought and put together by the seller,
who is a professional in the audio field. He repairs, upgrades, and builds equipment.

When I get a hold of the amp, I will send photos of the inside (probably next week).

Thanks

[*Scotty*]

Who is the manufacturer of the kit?
Scotty

[firedog]

Hi-
Got this amp in for audition today. More info: the amp module can be found here: http://www.groundsound.com/diyproducts.php#pa , model PA1CC.

It's built with Mundorf capacitors and Teddy Pardo style (same design/build, but not built by Teddy) regulators.

Just started listening to it a few hours ago, first impression is good.

My present amp is a ClassDAudio SDS-470.

This amp has a more open, live sound. That's how I can describe it - music sounds more "lively", less like something coming through a stereo.

This is definitely a high current amp. The SDS-470 is rated at 300WPC into 8 ohms; this at 85 WPC (spec for board allows for up to 150 max WPC, this was built for lower continuous output, as the board can run very hot. This amp doesn't get too hot); but it runs my speakers at a seemingly louder level than the ClassD amp. Transients like drum thwacks also sound better - more thwack behind them. I guess this is an example of the idea that high current reserves and peak current availability is more important than Wattage rating.  Haven't tested it yet with any orchestral pieces with lots of dynamics, that will also be an interesting test.

I have it on a 2 week audition, so I can really give it a good workout and see if I start to hear things I don't like after a while.

[motorcitym3]

Sounds interesting

[firedog]

Update: after listening, decided the amp and my DAC weren't a good match in terms of gain - my DAC was too "hot" for the amp. Sent both to the amp builder, with a few comments on the sound.

Am seeing if the amp can be adjusted to match my DAC