Hi all, it thought I had hum problem in my turntable, however after some time I discovered the hum was still present unchanged when I unplugged everything from my phono stage of my preamp.
My phono preamp is an Altronics phono kit as per the design in the silicon chip magazine. This was mounted in a plastic kit case as part of a passive preamp, which consists of a input rotary switch and a volume knob.
Hum is only present when the phono stage is selected, I have also switched to a better metal box since the photo was taken (using the same layout) changed to a metal box for better ground shielding but with no appreciable improvement.
The kit offers a suggested upgrade to a grounded power supply, but suggests this is normally unnecessary.
Any thoughts (especially from those who have built this kit) as to why I'm having this problem?
Note bank of resistors is for quick input load change
My phono preamp is an Altronics phono kit as per the design in the silicon chip magazine. This was mounted in a plastic kit case as part of a passive preamp, which consists of a input rotary switch and a volume knob.
Hum is only present when the phono stage is selected, I have also switched to a better metal box since the photo was taken (using the same layout) changed to a metal box for better ground shielding but with no appreciable improvement.
The kit offers a suggested upgrade to a grounded power supply, but suggests this is normally unnecessary.
Any thoughts (especially from those who have built this kit) as to why I'm having this problem?
Note bank of resistors is for quick input load change
Thanks for the quick reply Nigel. Power amp is a Quad 303, which is plugged directly into the wall using an earthed lead, however I haven't checked if the amp uses the earth pin. The turntable did not have an earthed lead, however it made no difference when I added one. Turntable is grounded to the preamp, but as I said it hums with or without the turntable connected if the phono stage is selected.
The hum is not earth shattering, in fact not noticeable at normal listening volume unless using headphones, but rapidly becomes loud beyond that point. I know it reduces sound quality so I want to to reduce it further.
Meanwhile, I am Very happy with the sound quality improvement over my old Quad 33, which despite revision, remained Woolley!
Transformer is external, incoming power cables run near the power circuit next to a shield. Case is shielded and I have tried wrapping grounded foil around the cable connected to the case that is grounded to a specified part of the circuit board. Also checked no other power cords in vicinity, besides it get no hum when switched to other inputs so out put is not picking anything up.
Obviously the board is not grounded well enough somewhere
No it still hums, but I accidentally connected the outside of the rca socket to the case and it halved. Then I connected it to the centre of the phono stages own output volume control spindle (mounted off the pcb as a posed to my master volume on the front of the case) ???
The component hums when it doesn't know the words to the music
I must have a very musical system!
On related matter, I replaced the internal wire with shielded type, which made a massive difference and added an earthed power supply that also helped.
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