you can retwist and also lift the signal from the board, on my phono the 60hertz tube heater wires are lifter away from any board circuits.
120 hum is the rectifiers and some 240hz, make sure the wires input or output wires don't align with rectifiers (diodes)...
You could make a center ground from the inputs also, the best place to make a common 'star Groud' is at the capacitor bank.
Star ground works on the condition that all wires are same length so the signals cancel (each wire acts like an antenna and picks up a signal, but the signals but all the voltages are similar and cancel at the common point giving no room for potential buildup.
120 hum is the rectifiers and some 240hz, make sure the wires input or output wires don't align with rectifiers (diodes)...
You could make a center ground from the inputs also, the best place to make a common 'star Groud' is at the capacitor bank.
Star ground works on the condition that all wires are same length so the signals cancel (each wire acts like an antenna and picks up a signal, but the signals but all the voltages are similar and cancel at the common point giving no room for potential buildup.
Hard to say what it is. I would tighten it down. Toroids are sensitive to DC on your mains line so a DC blocker can help, but that may not be the actual issue at all. You have hum, and we need to know how much there is on the offending channel’s RCA output while shorting the respective input. Do you have an RMS voltmeter with a millivolt setting? If it won’t read mV, try volts instead (AC not DC).
Best,
Anand.
Going to find the leads for the Fluke. I know it can read that.
Hooked it up after the work, and it’s a bit better. Some of the secondary noise I’d gone, hum is cleaner sounding, but still there.
Hooked it up after the work, and it’s a bit better. Some of the secondary noise I’d gone, hum is cleaner sounding, but still there.
Thanks.
The black wire going to the pot, is the ground connector for the front panel, didn’t think it would matter if the ground went near the transformers?
Not sure what to do about the large caps by the transformers? Guess I could move them further away from the transformers and run longer twisted leads?
The black wire going to the pot, is the ground connector for the front panel, didn’t think it would matter if the ground went near the transformers?
Not sure what to do about the large caps by the transformers? Guess I could move them further away from the transformers and run longer twisted leads?
you could try, if the ground wire is not close to the metallic (steel) casing it could be acting like an antenna to catch a potential from the transformer.
Moved caps, twisted wires.
Moved ground wire away from transformer.
Switched the leads on 47uf caps +/- just to check foil wrap.
No difference.
Still hums.
Moved ground wire away from transformer.
Switched the leads on 47uf caps +/- just to check foil wrap.
No difference.
Still hums.
They are next on my list 🙂
I’m supposed to short the output when measuring the AC on the outputs?
I’m supposed to short the output when measuring the AC on the outputs?
No! Short the INPUTS not the outputs. Only the inputs. All of them if you can or if you can do just the one (the offending channel) that is selected through the selector switch that’s fine.
But I would short every single one personally, to isolate the problem and use your DMM (preferably RMS variety) set to AC with red lead connected to the RCA center pin and black lead connected to the RCA ground pin of each output channel. I would also have the volume control cranked all the way up so that the preamp is wide open during the test. You can do a similar test with a scope where you can visualize the signal as a wave instead of looking at numbers and also know what frequency it is. Is it 60Hz, 120Hz, XXHz, hard to know!
Good luck!
Best,
Anand.
But I would short every single one personally, to isolate the problem and use your DMM (preferably RMS variety) set to AC with red lead connected to the RCA center pin and black lead connected to the RCA ground pin of each output channel. I would also have the volume control cranked all the way up so that the preamp is wide open during the test. You can do a similar test with a scope where you can visualize the signal as a wave instead of looking at numbers and also know what frequency it is. Is it 60Hz, 120Hz, XXHz, hard to know!
Good luck!
Best,
Anand.
Last edited:
Thanks!
I unfortunately only have 4 of the RCA shorting plugs.
Going to have to figure out how to use the scope I have sooner than later I suppose…
Will pull the amp from the system shortly and measure the voltages.
Need more coffee…
I unfortunately only have 4 of the RCA shorting plugs.
Going to have to figure out how to use the scope I have sooner than later I suppose…
Will pull the amp from the system shortly and measure the voltages.
Need more coffee…
Then just short the inputs directly on the board. You won’t have to deal with the array of inputs you have on your back panel then.
You can remove these wires temporarily, tie them off and then just connect L+ in to ground and R+ in to ground. Now the PCB‘s analog inputs are completely isolated. You can even use clip leads if you don’t want to solder or just pinch a bare piece of copper and connect. Something easy!
I’m not sure why these kit designs have SO many inputs to be honest! Most audiophiles use vinyl or digital as their sources but I guess there are tapedecks, vcr’s, etc….Same question with the selector switch…most need just a toggle switch to select between two inputs.
Best,
Anand.
You can remove these wires temporarily, tie them off and then just connect L+ in to ground and R+ in to ground. Now the PCB‘s analog inputs are completely isolated. You can even use clip leads if you don’t want to solder or just pinch a bare piece of copper and connect. Something easy!
I’m not sure why these kit designs have SO many inputs to be honest! Most audiophiles use vinyl or digital as their sources but I guess there are tapedecks, vcr’s, etc….Same question with the selector switch…most need just a toggle switch to select between two inputs.
Best,
Anand.
Ha!
Yeah, I use no more than 3…
Phono, tuner, digital…
And great idea. That’s super easy to do!
Thanks
Yeah, I use no more than 3…
Phono, tuner, digital…
And great idea. That’s super easy to do!
Thanks
Left Channel
.5mv DC/1.6mv AC
Right Channel
1.1mv DC/1.5mv AC
Input shorted at the board.
Going to hook it up to the amp and see how the noise is with the inputs shorted, and no inputs connected at all.
I trust that is safe to do?
.5mv DC/1.6mv AC
Right Channel
1.1mv DC/1.5mv AC
Input shorted at the board.
Going to hook it up to the amp and see how the noise is with the inputs shorted, and no inputs connected at all.
I trust that is safe to do?
Yup. Use low efficiency speakers. Or have a way to turn any volume down from the digital side, i.e. dac or external volume control between dac and preamp or from your tuner directly which should have a volume control, etc…
Best,
Anand.
Best,
Anand.