SSL clone hum
« on: July 12, 2004, 07:02:39 PM »

Still suffering from the hum problem I posted about a while ago. I think it is a grounding issue but can't make any sense of it. The hum almost dies out when I connect two ground-points on the board with a wire. The result is the best when choosing two points closest to, when looking at the bottom of the board with the controls-connector facing you, bottom-left and top-right. Little hum in the right channel, bit more in the left.

I have connected all input and output grounds at one point at the left input and threw in the mains-earth as well. No ground-connection between the outputs and the board..

Any suggestions? Moving the transformer doesn't have any effect.


SSL clone hum
« Reply #1 on: July 12, 2004, 07:12:12 PM »
Just a guess... as I´m no expert. Maybe you could try 10ohms resistors betwee audio grounds and star point.


SSL clone hum
« Reply #2 on: July 12, 2004, 07:37:18 PM »
I'm a bit confused on your grounding scheme. I hope I'm not going over things you've already gone through before.

I might be misunderstading you, but:
I don't understand why you have your input and output gnds connected together and why you don't have a ground connection between the outputs and the board.

Please take a look at this picture and I'll try to explain as best I can.
But then again, this might not solve your problem.

For the outputs (group of black wires): Connect the gnd of the ouput connection points on the main PCB to pin 1 on either left or right output then jump to the other pin 1.

For the inputs (group of red wires): Same thing, connect the gnd of the input connection points on the main PCB to pin 1 on either left or right input then jump to other pin 1. In addition , connect the input pin that was "jumped to" to the chassis. Then connect the GND of the IEC connect to the chassis at this point.

Please refer to that picture. It should be clear. From my understanding, this is the best to make sure no ground loops form.  The output gnd reference should not be coming from the IEC, it should be coming from the board.

I hope this helps.
Greg Stein
New Orleans, LA


SSL clone hum
« Reply #3 on: July 13, 2004, 03:12:54 AM »

I've tried this but it didn't help. I think something's wrong on the board, maybe a component. I can't understand why making an extra connection between two already connected groundpoints seems to solve a lot of the problem.  :?


SSL clone hum
« Reply #4 on: July 13, 2004, 04:54:34 AM »
If you have hum on the compressor, you probably have some sort of powersupply error. Check the 12 and 15V voltages for hum.
..note to self: don't let Harman run your company..

Steve Jones

SSL clone hum
« Reply #5 on: July 13, 2004, 06:42:20 AM »
Dry joint on a filter cap?
Synthesizer technician
Sydney Australia.


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