Amek Angela SLS Bleed

[pinebox]

Hello, I have been modifying an Amek for a studio. For the first time in the owners history, we have hooked up the SLS but there is bleed from the stereo bus even when the pot is all the way down. There even is some bleed when a different source is selected feeding the SLS.
-I have tried all sorts of grounding stuff, but no luck.
-I have soldered a wire directly from the motherboard to avoid the patchbay and still there is bleed.
-I have patched from the monitor outputs into the SLS amp and it works from the monitor pot as it should.
-I have replaced the SLS pot.
-I have strengthened ground connections from the pot to the ground plane, and still not an improvement.
-I have swapped out the op amps in the signal path out of desperation and I am just not having a good time.

I am curious if anyone has any ideas or has encountered a stubborn issue like this in the past? Everything I know is saying it obviously isnt getting a good ground connection but idk how that can be because the monitor pot shares the same input signal and ground plane and does not have the same issue.

 

[user 130681]

Most likely there is either a grounding issue or a switch/relay issue.
Insert a clean signal at an input. Trace the signal back from the output and see where the leak is introduced.
You will need a good quality oscilloscope and signal generator.

 

[Matt Syson]

Is the 'bleed' the SAME level and frequency range on both left and right of the SLS outputs?
What is the SLS selector 'selected to, and are THOSE inputs TERMINATED? What actual lEVEL of bleed are you getting? Many monitor amplifiers are too sensitive, meaning 0dBU for 'clipping' is quite common. Without proper measuring gear it could take a long time to find a resolution.

 

[pinebox]

Jon, thanks for the advice, I own scopes and generators, but lack of extender cards makes poking around with a scope not so simple. I have been searching for an Amek extender for a year now, I check ebay, reverb, all the usual sources pretty much every other day. If it comes to it I will solder leads in in certain places and have them hanging out between modules for testing. It may come to that soon.

Matt, the bleed seems to be a bit more on one side. The monitor pot and the SLS pot switches are fed by the same traces, yet bleed is only on the SLS side. We have replaced those switches and no luck. I also considered that it may be a ground or sensitivity in the SLS amp like you say, but in that case patching the monitor output into them would cause bleed in the same manner, which it does not.

 

[JohnRoberts]

Hello, I have been modifying an Amek for a studio. For the first time in the owners history, we have hooked up the SLS but there is bleed from the stereo bus even when the pot is all the way down. There even is some bleed when a different source is selected feeding the SLS.
-I have tried all sorts of grounding stuff, but no luck.
-I have soldered a wire directly from the motherboard to avoid the patchbay and still there is bleed.
-I have patched from the monitor outputs into the SLS amp and it works from the monitor pot as it should.
-I have replaced the SLS pot.
-I have strengthened ground connections from the pot to the ground plane, and still not an improvement.
-I have swapped out the op amps in the signal path out of desperation and I am just not having a good time.

I am curious if anyone has any ideas or has encountered a stubborn issue like this in the past? Everything I know is saying it obviously isnt getting a good ground connection but idk how that can be because the monitor pot shares the same input signal and ground plane and does not have the same issue.

Its hard to read the schematic without stopping to count how many times they misspelled "bus".

How is the fader kill for the other similar fader circuits (CR send etc)?

I do not see any differential ground reference around the fader support circuits but more of a brute force "pull wiper to ground trace". Any impedance in that ground trace can result in a voltage build up from the sundry signal currents flowing into that single ground trace.

I do not suggest redesigning the fader glue circuitry to make it a proper differential. Presumably it worked adequately enough once.

Perhaps check solder connections or fader wires. With brute force ground strategy impedance matters. Besides elevated ground trace impedance alternately an inadvertent short could be dumping signal current into that clean ground trace. In that case some other circuitry in the area would be misbehaving.

JR