I'm no expert, so take this advice at your own risk.
I would start by gently wiggling wires near the rectifiers and power supply.
Does the hum change- go higher or lower?
Did you connect signal ground and power ground to the same point?
Try seperating them if you connected all grounds to the same point.
Maybe you inverted the ground pin and negative pin on a balanced input.
Check all your input wiring.
Try taking the Darwin input selector out of the chain to rule it out as the problem.
I would start by gently wiggling wires near the rectifiers and power supply.
Does the hum change- go higher or lower?
Did you connect signal ground and power ground to the same point?
Try seperating them if you connected all grounds to the same point.
Maybe you inverted the ground pin and negative pin on a balanced input.
Check all your input wiring.
Try taking the Darwin input selector out of the chain to rule it out as the problem.
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Both of them have massive hum when connected in Balanced mode to a balanced power amplifier.
When RCA is used there is no problem. I do not use the pots at the output.
I assume both cases above are the same amp? Or is this two different amps? I would like to rule out that it is not simply a ground loop issue with a certain amp?
I find my BZLS is very good at reducing noise to balanced amplifiers.
JJ
When RCA is used there is no problem. I do not use the pots at the output.
I assume both cases above are the same amp? Or is this two different amps? I would like to rule out that it is not simply a ground loop issue with a certain amp?
I find my BZLS is very good at reducing noise to balanced amplifiers.
JJ
Well I have tried all the things you mentions. I have not made anything wrong I think. It do not hum without the balanced cable on the input. Maybee I should try some other Resistors in series with the input. The Vishays are a bit like a wirewound . My Balanced cable is without screen. This hum is so loud that I do not have heard anything like it before. Maybe it is oscilation. Sunday I will measure it.
I have tried with 2 different poweramps. Both of them have a resistor in series with ground on the input.
I have tried with 2 different BZLS having the same problem.
Ups Bad Cabinet ! Tighting the screws all the way around almost solved the problem. The Cabinet have 6 parts. Now I am much nearer the goal.
But there is still much more hum in balanced mode than with RCA. More than anybody will acept. 😕🙁
It is much better but still there is a problem. In Denmark it is not normal with earth on the main. Maybee I will install an new Main installation with earth. I have 2 of this Nelson preamps this 25 kohm pot is for our clubpre. Now I use 50 kohm for single ended input. To avoid problems in balanced mode I will prefer 25 kohm.
Personally, I never couple my amplifier's circuit ground to earth ground. I ground the chassis and any metal to earth ground, but I keep the amplifier circuit ground separate. It floats. It's been my experience, if you connect your circuit ground to earth ground you can get hum. I remember studying some of Nelson's power supply schematics and he has some clever ideas to separate earth from circuit ground.
Have you posted a schematic of your complete amplifier/power supply layout?
I don't use balanced cable (ie xlr), but I am pretty sure you need to use the screen to connect (ie electrically) both preamp chassis and power amp chassis together.
When you use rca the chassis are connected via the screen. So I think this is the key to solving the problem.
You really need to show us a drawing on how you have wired everything up in both preamp and poweramp (if possible).
Have a look at this thread http://www.diyaudio.com/forums/chip-amps/115698-understanding-star-grounding.html
Hopefully it might help you solve your problem
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Hi Folks I just found the problem. I got tired of my own preamp. I had to change the potentiometer in the clubs version of this pre to a 4 deck Goldpoint. . I discovered a little difference in how I have mounted the 5 V for the Darwin Selector . I moved it from the Darwin print to the diodes and Heureka ! This is because there is another coupling of the 5 v to the boards trough the selector. So I had a loop in the 5 V supply for the relays. Does this sound reasonable ?
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