60hz hum in component system

wimpy · 27th May 2011, 06:13 PM

tt/cd/tuner to modded dyna pas3 to diy kt88pp mono block amps all stacked on glass shelving - power amps hum even if cables are disconnected (same level on open or shorted amp input). they are dead quiet on work bench w/wo pas3 connected. if cd player is connected directly they are MUCH quieter. changing cables or adding ground interconnects didn't help. All components work well when placed in my other system = ??

nightanole · 27th May 2011, 06:51 PM

Are your heaters lifted above ground? Is your chassis earth grounded? Is your audio ground connected directly to chassis, or does it go through a ground loop breaker?

wimpy · 28th May 2011, 01:58 PM

nightanole - thank you very much for suggestions - units are the peter milett diy universal pp kt88 - heater ct to ground, chassis is earth grounded, audio to chassis - checking to see if I have open to ground - wouldn't be the first oversight I've committed - wmp

nightanole · 28th May 2011, 02:40 PM

heater ct to ground is your problem. Im surprised it didnt arc with that much voltage between heater and plate.

lift the ct of the heaters above ground using the boards built in r23 and r24. You should be good then.

wimpy · 29th May 2011, 05:23 PM

uniamp green original board doesn't have the 10k r24 of the uniamp2 red board - how/where can I add the 10k lift resistor? Also, while I am asking - I see the version 2 deletes c11 for choke input. I added dropping resistors on b+ to get hv down to reasonable. should I delete c11 on version 1 as well?

27th May 2011, 06:13 PM	#1
wimpy diyAudio Member Join Date: Sep 2008	60hz hum in component system tt/cd/tuner to modded dyna pas3 to diy kt88pp mono block amps all stacked on glass shelving - power amps hum even if cables are disconnected (same level on open or shorted amp input). they are dead quiet on work bench w/wo pas3 connected. if cd player is connected directly they are MUCH quieter. changing cables or adding ground interconnects didn't help. All components work well when placed in my other system = ??

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27th May 2011, 06:51 PM	#2
nightanole diyAudio Member Join Date: Feb 2009	Are your heaters lifted above ground? Is your chassis earth grounded? Is your audio ground connected directly to chassis, or does it go through a ground loop breaker?

28th May 2011, 01:58 PM	#3
wimpy diyAudio Member Join Date: Sep 2008	nightanole - thank you very much for suggestions - units are the peter milett diy universal pp kt88 - heater ct to ground, chassis is earth grounded, audio to chassis - checking to see if I have open to ground - wouldn't be the first oversight I've committed - wmp

28th May 2011, 02:40 PM	#4
nightanole diyAudio Member Join Date: Feb 2009	heater ct to ground is your problem. Im surprised it didnt arc with that much voltage between heater and plate. lift the ct of the heaters above ground using the boards built in r23 and r24. You should be good then.

29th May 2011, 05:23 PM	#5
wimpy diyAudio Member Join Date: Sep 2008	uniamp green original board doesn't have the 10k r24 of the uniamp2 red board - how/where can I add the 10k lift resistor? Also, while I am asking - I see the version 2 deletes c11 for choke input. I added dropping resistors on b+ to get hv down to reasonable. should I delete c11 on version 1 as well?

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