.. and still there seems to be a problem now that I had time to test it properly: I don't know what the real English name for it is, but the bass seems to "cracle" really badly. Mids and highs seem to be as should..
If you have not done it yet, I would suggest a complete re-capping of the electrolytic capacitors. Failure of one cap usually signifies the demise of the other electrolytics too, especially for a long unused amp or one that is "antique" as the caps can dry-out.
Actually the amp is only about 3 years old so there shouldn't be bad caps. I measured every cap thats under 20uF (my voltage meter's upper limit) and everything seems to be within +-10%.
The "cracling" background sound when playing bass increases when I increase the volume.
Could this just due to a bad solder joint somewhere, or could there be some problems that can't be measured in the chokes?
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Sounds like it's power related, possibly the amp draining the power supply, causing the voltage to sag, which results in bad clipping...which would point towards the electrolytics once again; perhaps one of the bigger ones is bad? A bad soldering joint could be a possibility, but it should be fairly easy to reproduce by tapping components/PCB/connections while the amp is running (be careful for electrocution and whatnot). A choke problem...nah, don't think so.
Hi,
Is the crackling in both channels? If it is then as mastodon says it is probably power related. Power caps should not go "Bad" after 3 years are you running to high a voltage on them?
Check the PSU resistors if one is faulty it will produce the noise you talk about when bass is drawing higher current!
The 100K on the 125V rail would be my first check after the diode issue! Half watt on a power rail, what is the working voltage of it?
Are the diodes all holding up OK now?
The only other thing with the caps are they getting hot from a position near to something? Heat will dry them out!
Regards
M. Gregg
Is the crackling in both channels? If it is then as mastodon says it is probably power related. Power caps should not go "Bad" after 3 years are you running to high a voltage on them?
Check the PSU resistors if one is faulty it will produce the noise you talk about when bass is drawing higher current!
The 100K on the 125V rail would be my first check after the diode issue! Half watt on a power rail, what is the working voltage of it?
Are the diodes all holding up OK now?
The only other thing with the caps are they getting hot from a position near to something? Heat will dry them out!
Regards
M. Gregg
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Omg, it might interest you that the 125V rail measures only 68V on both channels.
The 300V point as 293V, 220V and 260V points measure about as they should.
So, there's something wrong with my 5uF caps? (Though they measure 4,85uF both.) Or my zeners still do something wrong? 😱
There's no heat source near them.
If your other voltages are OK try changing the resistor in front of the 5uF it looks like 100K half watt. Put in the correct value and increase the wattage to 2W then re-check the voltage. It could be the cap however try replacing the resistor first! (It may have gone high in value)
If you do have to change the cap try and fit a higher voltage 5uF. Just for interest if your schematic is correct when the diodes were damaged you may have put 300V on the 5uF cap which has a working voltage of 250V!
Regards
M. Gregg
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