Soundcraft delta 200 input strips J williams mods

[tonycamp]

Hi fella's, anyone know this noise??? these samples are 2 identical soundcraft delta 200 input strips, JW mods, one is making a strange crackling sound, the volumes on the samples are extreme, and never to be seen in the real world, they are cranked all the way up to expose the problem. The first part of the clip is a properly functioning strip, all my other strips sound like this one. The second part of the clip is the weird one. It passes audio, but something clearly is not right..so...any ideas?

edit; i have reflowed the solder joints, switched opamps  and transistors from the bad module with a good one, no change
thanx for any help
T

https://soundcloud.com/tonycamp/help-me

 

[AudioHammer]

Can you post some pictures of the mods and a schematic to get an idea of the circuit changes?

 

[tonycamp]

Sorry, can't do that, this is Jims mod, it's pretty advanced, he can give away his secrets if he wants to, it's not my place. I'm just trying to see if anyone recognizes that frying bacon sound, so i don't need to bug him with this, and i may be able to pick up some knowledge myself along the way.

thanx for any help
T

 

[timshel!]

Sounds a little like bad silicone somewhere in there... If you've replaced all the transistors and opamps, look for a diode or something that might be used as a voltage reference in the audio path somewhere.

We can hear it clear enough, so if you're able to stick a scope on the thing and narrow down where in the circuit the noise is coming from that would make life easier from a troubleshooting perspective.

 

[AudioHammer]

I am not asking for you to give away the mod itself.  How about a signal flow diagram of the circuit with some of the details omitted such as part numbers. etc.  I do not know what the original delta 200 circuit looks like.

The Frying sound does sound like a bad silicon junction to me.

 

[tonycamp]

i'll try to get a schematic of the original module, the biggest changes are opamps and ridding of electrolytics due to better opamps blocking dc?, lots of film caps everywhere, seems like a lot of engineering has gone into stabilizing the opamps, it's really way over my head. It sounds incredibly better than the stock modules though, even with the frying bacon way down there, the eq is really solid and focused sounding, the noise floor is amazingly lower, and the bottom is stout, overall very impressive, i'm excited as heck about this console!

im going to double check all transistors/opamps.
one other total newb question, what other components may qualify as silicone?

thanx guys
T

 

[AudioHammer]

Silicon devices could be diodes, opamps, transistors, voltage regulators, voltage references to name a few.

How many modules have this issue?

If Jim modified these modules am I am certain he would stand behind his work and support you in finding a solution.

 

[tonycamp]

Thanx audiohammer, Jim does indeed stand behind his work, this is me trying to advance my rather limited knowledge of electronics, and understanding of how my new console's put together. I've done quite a few diy mods and projects, but it seems when ever i run into a problem, if i get to the bottom of it on my own,(even with some help), i learn a lot more. and that is kind of where i'm at.

thanx again for the help, i won't be able to dig in till next week, work n all, but i'll report back what i find or don't find

T