Yes. Both clockwise until they click. Turning them the opposite way the voltage increases.
When I get back home I’m going to pull the diodes and take a close look to see if I can read what they are. Might have grabbed some that weren’t in the right bin.
When I get back home I’m going to pull the diodes and take a close look to see if I can read what they are. Might have grabbed some that weren’t in the right bin.
Normally you would lower the effective R9 value only if you cannot increase bias to the desired level.
If your bias starts up high even if P1 is set to its maximum value then try removing the parallel 10K at R9.
If your bias starts up high even if P1 is set to its maximum value then try removing the parallel 10K at R9.
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Dear Diyaudio community.
I need your help again.
I have now finished my second balanced monoblock and one of the circuit boards is behaving strangely.
After a cold start I can set both the quiescent current and the offset without any problems - everything is fine.
However, the offset then starts to rise as it heats up. After about 20 minutes it is then around 300mV, for example, and continues to rise.
After setting the offset to 0mV again it continues to rise, etc. - regardless of whether I connect the input to ground or not.
The quiescent current behaves completely normally and symmetrically as far as N and P are concerned.
After my inspection, all solder connections seems to be OK, all components are in the right place with the correct values.
Does anyone have any idea how I can get to the bottom of the problem and fix it?
Attached are pictures of the faulty circuit board.
Further up in the thread you can find pictures of the entire setup.
https://www.diyaudio.com/community/...ing-the-pass-f4-amplifier.234355/post-7728704
I need your help again.
I have now finished my second balanced monoblock and one of the circuit boards is behaving strangely.
After a cold start I can set both the quiescent current and the offset without any problems - everything is fine.
However, the offset then starts to rise as it heats up. After about 20 minutes it is then around 300mV, for example, and continues to rise.
After setting the offset to 0mV again it continues to rise, etc. - regardless of whether I connect the input to ground or not.
The quiescent current behaves completely normally and symmetrically as far as N and P are concerned.
After my inspection, all solder connections seems to be OK, all components are in the right place with the correct values.
Does anyone have any idea how I can get to the bottom of the problem and fix it?
Attached are pictures of the faulty circuit board.
Further up in the thread you can find pictures of the entire setup.
https://www.diyaudio.com/community/...ing-the-pass-f4-amplifier.234355/post-7728704
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Are you talking about the offset or the bias?
I just dealt with this exact same issue but the bias kept rising (not offset) and forgot to post that I corrected the problem.
Put R9 back to 10k ohms and don’t parallel another 10k unless you absolutely need it.
The F4 I just finished had one channel where I had to add a 10k resistor and the other channel I did not.
However, you mentioned you can’t get the offset to settle where my issue was the bias.
I just dealt with this exact same issue but the bias kept rising (not offset) and forgot to post that I corrected the problem.
Put R9 back to 10k ohms and don’t parallel another 10k unless you absolutely need it.
The F4 I just finished had one channel where I had to add a 10k resistor and the other channel I did not.
However, you mentioned you can’t get the offset to settle where my issue was the bias.
JFETs were confirmed to be well matched? (at least within 1 mA idss) MOSFETs were confirmed to be well matched? Flux residue can cause instability if in a critical area... between MOSFET solder joints / pins, between JFET solder joints / pins, between TL solder joints / pins... etc. A stiff brush, alcohol, and compressed air are your friend. Flux is fantastic for assembly process, terrible for operating process.... Speaking of the TL... that guy can be troublesome. Certain variations won't work properly in this circuit, or could be on the "hairy edge" of working. I used the "it absolutely works" NCP431ACLPRAG in my boards. Check the datasheet for your part, it should have a minimum current requirement of less than 300 uA (0.3mA). Some MOSFETs don't like "too low" of a gate stopper resistor, a little undesired high freq. oscillation can definitely make things go stupid. Maybe something like a 220 ohm resistor there will make those behave, if that is happening.... just some ideas..
JFets are having nothing with DC offset in F4 ......... as long they're real deal, even misssssssmatched ones will have nuttin' with offset
Heureka!
It's working! Offset is rock stable now.
Zen Mod! You are my hero!
Changing the TL431 (AP431SAZTR with100uA minimal current) and the zeners solved the Problem with the increasing offset!
Everything is fine now!
Next step is to finish the wiring and then having fun with listening!
Thanks to everyone who reached out to help
Great community!
It's working! Offset is rock stable now.
Zen Mod! You are my hero!
Changing the TL431 (AP431SAZTR with100uA minimal current) and the zeners solved the Problem with the increasing offset!
Everything is fine now!
Next step is to finish the wiring and then having fun with listening!
Thanks to everyone who reached out to help
Great community!
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