My Zero Zone Preamplifier has a strange hum problem. I swapped tubes, dropped the AC ground, using a test probe tried to rearrange ground connection. Only does it on Right channel. Is not volume control dependent. Does not increase as volume is raised. Same hum whether source connected or not. As you can see in video, hum increases only on this channel as pencil is introduced. Any ideas?
YouTube video:
YouTube video:
Is the volume pot properly grounded? I chased my tail for months on two preamps until I grounded my Khozmo attenuators at the body. Despite the fact I had the audio ground hooked up to the terminal marked GND, I still had weird variable hum until I ran a separate wire to ground! Seemed like the mounting hardware would have sufficed but no.
How is the noise if the cover is securely bolted on the chassis, with shorting plugs in all inputs?
Has the preamp ever been without the hum, and if so when did it start?
Have you checked all the solder joints for problems? Have you tried tightening all the set screw connections?
Try connecting only the right output to the power amplifier. Is the hum still there?
Have you checked all the solder joints for problems? Have you tried tightening all the set screw connections?
Try connecting only the right output to the power amplifier. Is the hum still there?
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I bought it used from an older fellow who I don't think could hear it. It has been humming ever since I've owned it.
I did see a couple solder joints that concerned me. I resoldered them with no effect.
If I disconnect the left, yes, the hum is still there on the right.
I well tighten all connections...Not sure how I let that slip by!
I did see a couple solder joints that concerned me. I resoldered them with no effect.
If I disconnect the left, yes, the hum is still there on the right.
I well tighten all connections...Not sure how I let that slip by!
Keep posting, this should be fixable. But it's quite possible that this is a design defect that has
been there since it was built. First you will need a schematic, reverse engineered if necessary.
been there since it was built. First you will need a schematic, reverse engineered if necessary.
You've already got lots of excellent troubleshooting tips, but one more: it would be interesting to unscrew the input signal wiring from the board and to test both without and with shorting jumper wires in place of signal. Might help to divide and conquer.
All good fortune,
Chris
All good fortune,
Chris
I tightened everything down. A few connections were loose....But no joy...Hum is still there....🙁
Tomorrow I'll pull the board and look for a cold solder joint on the back side....
Tomorrow I'll pull the board and look for a cold solder joint on the back side....
I pulled the PCB and resolder a few suspect connection...Still hum.
Can a capacitor become "microphonic"?...When I touch that capacitor in the video with a screw driver it is just like touching a microphone. The other channel dos not do this.
If I decide to replace this cap, is it a simple electrolytic capacitor?
Can a capacitor become "microphonic"?...When I touch that capacitor in the video with a screw driver it is just like touching a microphone. The other channel dos not do this.
If I decide to replace this cap, is it a simple electrolytic capacitor?
That appears to be a film type capacitor, and is unlikely to be bad. But if you want to check for sure,
I'd suggest that you exchange the corresponding capacitors between the channels. That way if the noise
remains in the same channel, you don't need to do anything more with the capacitor, since it is fine.
I'd suggest that you exchange the corresponding capacitors between the channels. That way if the noise
remains in the same channel, you don't need to do anything more with the capacitor, since it is fine.
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I assume you are experienced at soldering and desoldering. The pcb could easily be damaged otherwise.
Keep the orientation of each capacitor the same as the other one was in that place before.
Notice that the left and right capacitors at the top edge of the board are reversed relative to each other.
Keep the orientation of each capacitor the same as the other one was in that place before.
Notice that the left and right capacitors at the top edge of the board are reversed relative to each other.
Also try to flip the capacitor pins. Some large film capacitors have a terminal that is more sensitive to hum pickup than the other (search for the keywords "outer foil capacitor").
Added clarification: I would: desolder the hum-sensitive non-polarized film capacitor and connect it the other way around. If this does not fix the issue, then I would swap the capacitor between the two channels.
Added clarification: I would: desolder the hum-sensitive non-polarized film capacitor and connect it the other way around. If this does not fix the issue, then I would swap the capacitor between the two channels.
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Not until AFTER the two capacitors are swapped while preserving the proper orientation as supplied.
You only change one variable at a time. First we are testing for whether one capacitor is "bad".
That is not likely, but this possibility should be eliminated first, before considering changing the orientation
of an individual capacitor. However, the absolute orientation is also unlikely to cause such a problem.
You only change one variable at a time. First we are testing for whether one capacitor is "bad".
That is not likely, but this possibility should be eliminated first, before considering changing the orientation
of an individual capacitor. However, the absolute orientation is also unlikely to cause such a problem.
Changing one variable at time is the correct way to solve the issue, for sure (I also added a clarification to my previous post). Based on my experience, the likely cause of this hum issue is a capacitor fitted backwards. So I would first reverse the sensitive capacitor. Swapping capacitors is a bit trickier because it is imperative to check the connection on the PCB, as you already stated on post #15, and turn the capacitors accordingly if needed. If the swap is done incorrectly, the hum may migrate to the other channel and the capacitor may be deemed bad, while it is only fitted backwards.