Hi all,
I just put together an S-5 K12g for my first kit tube amp. I first put it together exactly as instructed (mounted on wood board, volume pot and inputs soldered directly on the board). I decided to build an enclosure and remove the ins and pot off the board and wire them.
Everything sounds great with the new build except for the volume pot. I replaced the old one with the same specs 100k dual gang audio taper. Now, at the lowest volume setting and at the highest volume setting I get a buzzing hum only on the left channel. It doesn't gradually increase with the volume setting, but crosses over a certain point near the low and high end of the volume range and sort of "clicks on" i.e., it's not a continuous problem throughout the volume range. I checked for cold solder joints and resoldered a bit but to no avail. I haven't ruled out a cold joint problem but would like to avoid going through and resoldering the 6 legs and the 6 points on the board.
Does anyone have any advice or a guess as to what this might be and how to fix it?
Thanks in advance for any help.
I just put together an S-5 K12g for my first kit tube amp. I first put it together exactly as instructed (mounted on wood board, volume pot and inputs soldered directly on the board). I decided to build an enclosure and remove the ins and pot off the board and wire them.
Everything sounds great with the new build except for the volume pot. I replaced the old one with the same specs 100k dual gang audio taper. Now, at the lowest volume setting and at the highest volume setting I get a buzzing hum only on the left channel. It doesn't gradually increase with the volume setting, but crosses over a certain point near the low and high end of the volume range and sort of "clicks on" i.e., it's not a continuous problem throughout the volume range. I checked for cold solder joints and resoldered a bit but to no avail. I haven't ruled out a cold joint problem but would like to avoid going through and resoldering the 6 legs and the 6 points on the board.
Does anyone have any advice or a guess as to what this might be and how to fix it?
Thanks in advance for any help.
Please post pictures of the build.
Cold solder joint
Poor ground connection problem.
Ground Loop Problem (ground the inputs at the input connectors and see if it still remains).
Cold solder joint
Poor ground connection problem.
Ground Loop Problem (ground the inputs at the input connectors and see if it still remains).
The pot. wipers could be losing contact with the resistive track, at the rotation extremes. Try connecting the I/P stage grids to ground via 1 MOhm resistors. That maintains the grid to ground connection, even if the pot. "drops out".
Isn't there an earth tag from the pot body to the pcb, is that connected ?
Link to schematic
http://diyaudioprojects.com/Gallery/displayimage.php?pid=368&fullsize=1
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I will try to post pictures tonight. So far, the issue remains even when no input (cd or turntable is connected). To ground the inputs would it be reasonable to ground the rca plug to one of the feet of the output transformers (those serve as the ground connections off the board in this kit)?
I've tried resoldering 3 of the feet so far that correspond to the left channel but no luck.
Thanks very much for your thoughts on this.
Yes. Sorry I said 6 joints but actually meant 7. The ground comes off of a collar around the post and that is connected.
I don't have the kit in front of me right now, but from the S-5 page they indicate the tubes are 10GV8. My signal source is either turntable or cd player. They plug into a Rolls source mixer:
Rolls MX42 Mini Stereo Mixer MX42 B&H Photo Video
and then into the amp.
Without any inputs hooked up, the hum is still there.
If I understand your first post correctly the amp functions fine between just above the lowest volume and just below the highest volume. I assume you have no balance issue.
Try putting the old one back, if it's still servicable. The new one may differ from the old in the way Eli has said in post 3.
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