Last check before ordering (Opus) (Gamma 2 now)

[backefel]

Finally, the exams are over and I've manage to put the ck2iii amp together *yey*

 but it isn't working, well not the way I want.
The led glows and the right channel seems ok (+- 0.2mV) but the left channel seems to oscillate slowly. I might be wrong but it seems like it's something wrong with the negative feedback.
It fluctuates ~1.1 mV from 7.2 to 8.3 every 10 sec and it seems to have a negative temp coeff? I know it should be positive but it keeps sinking.
 
I don't have the heatsinks yet but the components doesn't seem to hot. Another thing that might be irrelevant is that the left channels -15V is more like -14.7 (compared to 15.02 on the right).
It shouldn't matter if you ask me but the right channel seems considerably hotter.
 
(I've checked all transistors and they seem to be in the right place, and the gain on both channels seems to be around 4)

 

[amb]

Quote:

Finally, the exams are over and I've manage to put the ck2iii amp together *yey*

 but it isn't working, well not the way I want.
The led glows and the right channel seems ok (+- 0.2mV) but the left channel seems to oscillate slowly. I might be wrong but it seems like it's something wrong with the negative feedback.
It fluctuates ~1.1 mV from 7.2 to 8.3 every 10 sec and it seems to have a negative temp coeff? I know it should be positive but it keeps sinking.

This amp has no global negative feedback.  It has a DC servo, if that's what you're referring to.
What voltages are these that you're reporting?  DC offset?  If so, the temperature coefficient of the transistors should not affect it over time.
 
Quote:

I don't have the heatsinks yet but the components doesn't seem to hot. Another thing that might be irrelevant is that the left channels -15V is more like -14.7 (compared to 15.02 on the right).
It shouldn't matter if you ask me but the right channel seems considerably hotter.

Since both channels share the same power supply rails, it's not possible for one to be higher in voltage than the other.
The output transistors' temperature depends on how high you adjusted the quiescent current.
 
Quote:

(I've checked all transistors and they seem to be in the right place, and the gain on both channels seems to be around 4)

"Seem to be in the right place" doesn't sound very definite.  Double check to be sure.  Also, check all your solder joints to make sure you don't have any cold joints.  Reflow all joints to be sure.  If you have a spare DC servo opamp, maybe swap it in to see if the situation changes.

 

[backefel]

Quote:

Quote:

Finally, the exams are over and I've manage to put the ck2iii amp together *yey*

 but it isn't working, well not the way I want.
The led glows and the right channel seems ok (+- 0.2mV) but the left channel seems to oscillate slowly. I might be wrong but it seems like it's something wrong with the negative feedback.
It fluctuates ~1.1 mV from 7.2 to 8.3 every 10 sec and it seems to have a negative temp coeff? I know it should be positive but it keeps sinking.

This amp has no global negative feedback.  It has a DC servo, if that's what you're referring to.
What voltages are these that you're reporting?  DC offset?  If so, the temperature coefficient of the transistors should not affect it over time.
 
Quote:

I don't have the heatsinks yet but the components doesn't seem to hot. Another thing that might be irrelevant is that the left channels -15V is more like -14.7 (compared to 15.02 on the right).
It shouldn't matter if you ask me but the right channel seems considerably hotter.

Since both channels share the same power supply rails, it's not possible for one to be higher in voltage than the other.
The output transistors' temperature depends on how high you adjusted the quiescent current.
 
Quote:

(I've checked all transistors and they seem to be in the right place, and the gain on both channels seems to be around 4)

"Seem to be in the right place" doesn't sound very definite.  Double check to be sure.  Also, check all your solder joints to make sure you don't have any cold joints.  Reflow all joints to be sure.  If you have a spare DC servo opamp, maybe swap it in to see if the situation changes.

 
 
Well even though it took a bit longer than I wanted, am at it again, trying to finish the amp.
I've bought the heat sinks and the amp seems more temperature stable than before but the left channel still seems to have some problems. I also checked the transistors again and they're all in the right place.
 
The right channel is pending between 0.1mv and 0.8mv which seems fine (dc offset). If I turn on the amp, the offset is around 50mv and decreasing rapidly (5-6s) to 0.5.

The left channel however is pending between 0.8 and 1.3 mv (but is this really a problem?). One thing I did notice was that the servo seems to be much slower on the left channel. 10-12s before reaching ~0.8mv.  Is this something I should be concerned about?
 
I also hooked up a signal generator and an oscillioscope and there weren't any oscillations or noise on the output.
As a final test i tried to hook up a small speaker (with the signal generator on the input) and it...well it sounded like a sinus wave so no suprise there. There were some pops but it might just have been microphonics since i didn't solder.
 
One more thing when I adjusted the quiescent current both channels were pending 14+-0.8 mv, the left channel seemed more responsive but I guess thats the dc-servo again?

 

 

[amb]

Sounds to me like your amp is working fine.

 

[backefel]

Wonderful! Thanks again for all the help and for putting up with my dumb questions.