I bought an old Sonab turntable the other day with a Shure cartridge, that I intend to use for copying all my old LP’s to cd.
I cannot for the life of me track down a bad hum that it produces.
I have run right through the diagnostic steps set out on this page. Everything that should have continuity does, everything that should not, does not.
I have shorted the inputs at the pre-amp and at the turntable (just before the cartridge) and that gets rid of the hum, so as I understand it, that isolates it down to the cartridge.
I can’t find anything wrong with the cartridge itself.
The turntable is grounded to the amp, just in case you were wondering.
The troubleshooting info I have read suggests that one possibility is that the cartridge is picking up hum from some mains source such as another component, or the turntable motor and that you can check for this by moving the cartridge or turntable around and seeing if the hum changes. I have tried this. It does not.
Did you test that the actual tonearm is grounded, as opposed to just the “tonearm earth lead spade” ? An alligator clip between the cartridge head and your ground wire will kill the hum if that’s the problem.
Actually no. Using my home built pre-amp is my ultimate intention, but at this stage I am just trying out the turntable with my quite new, so far entirely reliable, main Yamaha amp (I thought that trying out two new pieces of equipment at once was asking for trouble :)).
My main amp is a Yamaha with built in pre-amp and phono stage, so it only has one case and one ground terminal.
Are you recording to a computer with a CD burner, or a component CD recorder?
I’ve run into problems with the former arrangement, even with the turntable grounded to the amplifier, and all components plugged into a common source. Somehow, even with grounded power supplies, there was a floating ground between the amplifer and computer. I was able to eliminate the hum by attaching a one end of a wire to the ground terminal on the back of the amp, and the other end to one of the computer’s case screws.
Try it using your homebuilt pre-amp going to aux input. It’s barely possible that the Yamaha phono amp is causing the hum. It shouldn’t be, but if it’s the first time you’ve used it…
It has been a couple of years since I have had it set up, but I had a similar problem with my stereo. IIRC, the solution lay in connecting/disconnecting and tying/untying grounds.
p.s. Do you realize that half the people on this board have no idea what this thread is about?
p.p.s. I want to do something similar. Can anyone recommend softare to eliminate pops and clicks (and, in an ideal world, flutter and wow)?
Just in case anyone is interested: I now realise that part of my above OP was misleading. The turntable has a small (100 ohm) resistor between the earth lead and the rest of the earth circuit (tonearm, turntable etc). So there was full continuity between the earth lead and the turntable, but with 100 ohms resistance.
I knew that when I posted my OP, but I assumed that that must be OK because I have the original circuit diagram for the turntable and it shows that the 100 ohm resistor is as per factory spec, so I didn’t mention it.
Needless to say, when I shorted across the 100 ohm resistor, the hum went, so I’ve soldered a bridge across it, and it all works OK now.
I have no idea why the turntable was built with that resistor, it must have served some purpose, perhaps it suited an original cartridge or something.
Emolson, I do know of such software, a friend has recommended some to me. I don’t have the name to hand. I’ll post it in the next couple of days. Watch this space.
Yep, felt like a complete ass when I realised. When I first found the resistor I thought “what the hell?” but then when I checked the circuit and found it was factory spec, I thought: “Well that must be meant to be there, so it can’t be the problem” and put it out of my mind.
You know what Benny Hill said about “assuming” don’t you? :smack:
