[creyc]

I've noticed something weird about my homebuilt cmoy amp. When I first turn it on with my KSC-75's/Sony V6 in I get a lot of nasty distortion in the music. Within around 10-20 seconds the sound is fine. ???

It's been this way since I built it. I've also noticed strange noise coming from the amp when I first turn it on after a while. Waiting a bit seems to correct it however, and then it sounds fine.

What's up with this? It's like something has to "charge" for the first few seconds of audio before it will work right. Once it's been running for a minute turning it off and back on is no problem and I wont get the distortion till I turn it off for an extended period of time.

Apple PowerBook>Griffin iMic>CMoy amp>Koss KSC75

 

[tangent]

This is definitely not normal. Go through the steps here.

 

[meat01]

Did you try it with a different battery?

 

[vixr]

My first CMoy had a problem like yours... It was built with rat shack parts and took about a minute to stop sounding thin and weak...like something had to "charge" I still have it and it still does it... I posted about it last year and got pretty much the same suggestions as you did... My solution was to get hooked and spend all my beer money on better parts and try again. My second amp was waaaay better.

 

[creyc]

All parts are from Digikey and are the recommended parts, plus a few of the optional parts. I'm using an OPA132 chip.

I'm acquiring another battery, I've also replaced the stereo cable, though I didn't think that would do anything.

 

[creyc]

oh god I'm building four huge, 300 watt power amps now! What the heck is wrong with me.

(I attribute the problem mentioned in this thread as a fluke, so as not to tarnish my building record

)

 

[MASantos]

Quote:

Originally Posted by creyc I'm using an OPA132 chip.

Do you mean OPA2132? Because the opa132 is a single channel opamp

 

[creyc]

Ah, right i knew there was an extra '2' in there someplace. My guess is I'm not using enough battery power. I'll add another 9v, adjust the gain and add R5 resistor for use with my ultra sensitive IEM's and call it a day.

 

[splaz]

Quote:

oh god I'm building four huge, 300 watt power amps now! What the heck is wrong with me.

lol. Thats what happened with me. Just built a dodgy little 1W thing to see if I enjoyed it and could do it.

Bout half the size of a matchbox.

Next week I'm doing a 2 channel 50W, LM3886 amp.

 

[bashot]

You shouldnt need 18V for a 2132 chip, but its worth a shot - 9V should be plenty. How accurately are your power rails split? Check if the virtual ground is stable during those first 10 seconds. Even if they are stable, I'd highly recommend a proper split with a tle2426 - just remove the R1s and drop it in there. Its a small modification. Otherwise try dropping the gain from 10 as you were and don't bother with R5 if the noise goes away; you're not trying to mask a problem but fix it.