SEWA - Seven Watt Amplifier

[Mad_K]

All good suggestions djk

[demogorgon]

you know steenoe, those small perky single ended class a amps are just too simple not to give a try, made myself a headphone amp with those smtp mosfets you gave me btw, it hums like mad, but the music it makes is nothing to sneeze at. (if you can ignore the HHUUUMMM)

i have to at least try some different paths to audio nirvana.

-Marius

[planet10]

Originally posted by demogorgon
those small perky single ended class a amps are just too simple not to give a try

They too have fasinated me for a long time...

dave

[steenoe]

(if you can ignore the HHUUUMMM)

How is your grounding done? Did you make a starground?
Hum is absolutely not funny, especially into headphones.

Dave, with your interest in fullrange speakers, some kind of Zen amp ought to be just the thing

Steen

[planet10]

Originally posted by steenoe
with your interest in fullrange speakers, some kind of Zen amp ought to be just the thing

Got one of those coming together. Boards swapped for postage. Power supply surlus from a DEW line installation (ie military grade CLC 48V 10A) $5, Board populated to collect a debt i wouldn't otherwize have collected. Heat sinks for helping a guy move. Just need a bit of chassis, and some assembly.

dave

[demogorgon]

Originally posted by steenoe
How is your grounding done? Did you make a starground?
Hum is absolutely not funny, especially into headphones.

Steen

huumm(phun), i made a starground yes, even used a big phat choke on the power rail. oh well i have not the time to be playing to much with it now anyways, i'm building the critical q subwoofer, two of them to be precise.

oh, i'm looking forward to hearing them sing.
making my own amps though, offcource.

[Asen]

The attached file includes the djk sugestions and why not "let there be light"... as maybe Mr. Pass would say. At least one can save heatsinks.

Nice project, BTW. Looks more linear than Follower99, published years ago in an Italian site.

Regards
Asen

[Mad_K]

I was kind of hoping someone would suggest some illumination

No need for a 10uF input cap with 470K input R 0,47-1uF will be plenty. It is also important to add a similar cap in paralelll with the 10000uF outputcap.

After listening to the amp for some weeks, I am stunned over the performance. Especially the pitch black silence (it is absolutely quiet) followed by firm and controlled bass attacks!

edit: There is also no turn on thump, because the bias network starts the amp up slowly. It takes a little minute to fire it up, and another hour to warm up.


I didn't specifiy a powersupply, but I use a 600VA toroid (~32VAC secondaries would be nice) rectified by ISL9R3060G2 30A 600V Stealth diodes and a pi filter with 22000uF-0,22 Ohm-22000uF Evox-Rifa PEH200 caps. One secondary/rectifier/filter per channel.

[janneman]

Hi Mads,

Nice circuit! Just some suggestion: if you make the no-signal output voltage closer to 20V (half supply), you can have less current through the FET with less dissipation and still have a bit more output power (probably closer to 12 W or so) in full class A. Seems like a win-win change

Jan Didden

[Mad_K]

If you replace the resistor with a active current source you can do this, but not in this circuit. If you set the dc level at 20V it will clip very early on the negative side