Hi all, id love some help with this, any suggestions would be great.
On my k-12G over the last month or so any volume setting below 25% creates audible hum. Past this point it goes away, coming back at only 100% which i never use when playing music. This is only something that has happened recently, past two years amp has worked fine.
It sounds like a ground issue, but i cant find it. its been driving me crazy, ive checked easy things like the following:
1. Grounding of RCA inputs (two, via dpdt)
2. New tubes 10gv8
3. Volume pot ground goes to the board, tried re-routing to chassis, or other parts of board, even no ground volume pot. no change. vol pot is 100k
4. Hum is same through both channels
5. Hum remains if no input connected.
ive read two other threads on it, this one didnt really help, i swapped old pot back in and hum still there
http://www.diyaudio.com/forums/tubes-valves/236665-volume-pot-hum-low-high-volume.html
this one didnt seem to have a final output on what the OP did to fix in the end.
http://www.diyaudio.com/forums/tube...int-max-no-hum-if-volume-knob-max-zero-2.html
ill get some pics over shortly
Thanks
On my k-12G over the last month or so any volume setting below 25% creates audible hum. Past this point it goes away, coming back at only 100% which i never use when playing music. This is only something that has happened recently, past two years amp has worked fine.
It sounds like a ground issue, but i cant find it. its been driving me crazy, ive checked easy things like the following:
1. Grounding of RCA inputs (two, via dpdt)
2. New tubes 10gv8
3. Volume pot ground goes to the board, tried re-routing to chassis, or other parts of board, even no ground volume pot. no change. vol pot is 100k
4. Hum is same through both channels
5. Hum remains if no input connected.
ive read two other threads on it, this one didnt really help, i swapped old pot back in and hum still there
http://www.diyaudio.com/forums/tubes-valves/236665-volume-pot-hum-low-high-volume.html
this one didnt seem to have a final output on what the OP did to fix in the end.
http://www.diyaudio.com/forums/tube...int-max-no-hum-if-volume-knob-max-zero-2.html
ill get some pics over shortly
Thanks
Problems that appear in both channels simultaneously tend to be power supply related. You might start by measuring AC and DC voltages at both ends of R14 and R18. Is there any reference for normal operating voltages?
Have you observed this note from the S5 website?:
"Since the transformers and volume control are mounted on a wooden board, there can be some coupling of power line noise or high frequencies into the volume control.
"To stop the possibility of high frequency oscillations, due to the coupling from the output to the input the volume control body and the output transformers frames should be grounded. The most convenient circuit ground is the – side (black post) of the output terminals. A hook-up wire from ground to one of each of the output transformer's mounting screws and to the volume control bushing will achieve maximum noise reduction. These must be good / clean electrical connections."
Have you observed this note from the S5 website?:
"Since the transformers and volume control are mounted on a wooden board, there can be some coupling of power line noise or high frequencies into the volume control.
"To stop the possibility of high frequency oscillations, due to the coupling from the output to the input the volume control body and the output transformers frames should be grounded. The most convenient circuit ground is the – side (black post) of the output terminals. A hook-up wire from ground to one of each of the output transformer's mounting screws and to the volume control bushing will achieve maximum noise reduction. These must be good / clean electrical connections."
Totally missed that, thanks heaps! i shall get onto it later (its aussie rules grand final day today!)
also will try shielded input cables from RCAs to Board and see if that helps.
Shall measure those volts and keep anyone informed if they are keen.
Also found an old 470ohm choke i want to try in PS.
thanks
also will try shielded input cables from RCAs to Board and see if that helps.
Shall measure those volts and keep anyone informed if they are keen.
Also found an old 470ohm choke i want to try in PS.
thanks
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