AMB Laboratories DIY Audio

[bazier]

After I've recently finished making CK2III and follow initial setup. Checking the voltage at the +15V and -15V test pad are OK. Measuring the both DC offset voltage are under 1mV (around -0.3mV) But the problem occurs on the right channel only. When R43 trimpot was turned to the minimum position, I measure the voltage across R47 is around 30mV after I turn on for a little while. In the other hands, the voltage across R23 can be changed properly while R19 is adjusting. I've tried to replace R43 trimpot with the new one but still same problem. Could anybody pls suggest me how can I fix it?

[amb]

Check the values of R41 and R42 to make sure you didn't put the wrong ones in. Also, verify that R47 (and R48) are still 0.47 ohms (DMM may not be too accurate at such low resistances, but should be within +/- 1 ohm if it's any good).

[bazier]

Thanks for your fast suggestion. As picture show, I use R41=1.8k, R42=2.4k and R47-48=0.47 for both channel. I've tried to replace a quad of JFET by another one I bought from AMB shop but it's still same problem. I'm newbie and need help. Thank you again

[amb]

Measure R41/R42 and compare to R17/R18 just to make sure.
Does adjusting R19 have any effect at all (on the voltage across R47)?
Did you use the correct transistor for Q22? Try replacing it with another one.

[MisterX]

Nice "DIY heatsinks" for the output transistors.

[bazier]

Measure R41/R42 and compare to R17/R18 just to make sure.
Does adjusting R19 have any effect at all (on the voltage across R47)?
Did you use the correct transistor for Q22? Try replacing it with another one.

It's OK right now after replacing Q22 by new one. Many thanks for your help. One more question about Ground loop breaker, can I whether use 4.7ohm resistor in parallel with a 0.1µF capacitor instead of 10Ω 5W or not? Thanks AMB

[bazier]

Nice "DIY heatsinks" for the output transistors.

Thanks for your recommendation, That's why I ask for helping. coz I worry it should be melted if it had around 30mA of quiescent current through the output stage.

[amb]

[One more question about Ground loop breaker, can I whether use 4.7ohm resistor in parallel with a 0.1µF capacitor instead of 10Ω 5W or not? Thanks AMB

4.7Ω would be less effective as a ground loop breaker. If you don't have a 10Ω, I would rather you use something a little higher in resistance, 15Ω is fine, or 22Ω is ok too.