Suggest me a low-power Class A amp

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Joku

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Joined 2009
Hi,

My MOSFET amp which is 100W to 8 ohms is a bit too powerful for my Fostex FE207e speakers, so I'm considering to build a low-power class A amp.

I'd prefer it to be relatively simple and cheap-ish, but still hifi, so no preferrably not Zen amps. Also, I have 180VA and 100VA +-12V transformers lying around, and it would be nice if I could use them. If I didn't screw up my math, +-12V would result in something like 15 watts which should be plenty for my speakers.

So, any suggestions are appreciated. :)
 
dragonweed

dragonweed

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Joined 2010
Hiraga Le Monstre (push-pull), or in SE, the Amp Camp Amp by Nelson Pass. Both are very simple, sound extremely good, both run on your specified voltage range (Le Monstre is +/-12 Volts, the ACA on a single +19-22 V supply). But in class A with those voltages do not expect more than 6-8 Watts on 8 ohm...
 
dragonweed

dragonweed

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Joined 2010
The possible "weaknesses" of the Zen family amplifiers might be their relatively highish output impedance (which should not be a big problem for a wide range driver in a TL, or QW box anyway), also that they are capacitor coupled on both ends. But on the other hand this can be an advantage in some cases......
 
a.wayne

a.wayne

Member
Joined 2008
Joku said:
Hi,

My MOSFET amp which is 100W to 8 ohms is a bit too powerful for my Fostex FE207e speakers, so I'm considering to build a low-power class A amp.

I'd prefer it to be relatively simple and cheap-ish, but still hifi, so no preferrably not Zen amps. Also, I have 180VA and 100VA +-12V transformers lying around, and it would be nice if I could use them. If I didn't screw up my math, +-12V would result in something like 15 watts which should be plenty for my speakers.

So, any suggestions are appreciated. :)
Click to expand...

Could you explain this more, what is meant by too powerful, if playing too loud, i heard turning down the volume helps .. :) Sounds like clipping is whats up next if using only 10watts ...



:sax:
 
J

Joku

Member
Joined 2009
a.wayne said:
Could you explain this more, what is meant by too powerful, if playing too loud, i heard turning down the volume helps .. :) Sounds like clipping is whats up next if using only 10watts ...



:sax:
Click to expand...

With too powerful I mean that if I accidentally turn the potentiometer too much, my Fostex elements could get wrecked. :p

dragonweed said:
Hiraga Le Monstre (push-pull), or in SE, the Amp Camp Amp by Nelson Pass. Both are very simple, sound extremely good, both run on your specified voltage range (Le Monstre is +/-12 Volts, the ACA on a single +19-22 V supply). But in class A with those voltages do not expect more than 6-8 Watts on 8 ohm...
Click to expand...


Note that the transformers are +-12V AC. When rectified, this should result in about +-16V supply voltage.
 
J

Joku

Member
Joined 2009
dragonweed said:
Hiraga Le Monstre (push-pull), or in SE, the Amp Camp Amp by Nelson Pass. Both are very simple, sound extremely good, both run on your specified voltage range (Le Monstre is +/-12 Volts, the ACA on a single +19-22 V supply). But in class A with those voltages do not expect more than 6-8 Watts on 8 ohm...
Click to expand...

A push-pull design is more what I had on my mind than a SE design. Where can I find schematics for Le Monstre, and can it be used for a bit higher supply voltages (those trafos would produce maybe ~+-16V DC when rectified under load?)? :)
 
tvrgeek

tvrgeek

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Joined 2009
What I have to ask is of what use is a low power class A amp? I had one. 10W. Useless. As a can amp, well yes, that is another story and I intend to build one someday myself, but to drive speakers? Anything less than about 50W just can't handle a reasonable quality speaker at more than background levels where it does not matter anyway.

Have you looked at the ideas in the first or second issue on Linear Audio from Jan? Class A, but more efficient.
 
J

Joku

Member
Joined 2009
tvrgeek said:
What I have to ask is of what use is a low power class A amp? I had one. 10W. Useless. As a can amp, well yes, that is another story and I intend to build one someday myself, but to drive speakers? Anything less than about 50W just can't handle a reasonable quality speaker at more than background levels where it does not matter anyway.

Have you looked at the ideas in the first or second issue on Linear Audio from Jan? Class A, but more efficient.
Click to expand...

Depends on what kind of speakers you have. For example, my Fostex speakers have sensitivity of about 95dB/W at 1 metres, so they should be just fine with 10-20W of power.
 
tvrgeek

tvrgeek

Member
Joined 2009
Fostex. That's what I was afraid of. I respect that a small community gets great pleasure out of them. I flat can't understand it and actually can't stand to hear them.

If one were looking at using some of the ultra efficient PA mids, active crossover, to a ultra efficient compression horn, (kind of like the good Dr. Earl has done but without wasting power in a passive crossover) maybe a pair of 10Watt'ers could do OK in an apartment. I can almost see the tube guys here because of the softer clipping, but then you are hearing all the distortion from the tube amp too. Kind of the opposite goal of a class A amp. This route may do better in what Paul Klipsch used to mean when he cried out what the world needs is a good 10W amp. Maybe, but we need the speakers that can use it first. In the mean time, I am very glad we can make very, very good class B amps. Someday we will have good Class D amps I hope.
 
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