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Ring Mod Noise Problem [FIXED]
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Ring Mod Noise Problem [FIXED]
Flareless
I'm having a bit of an issue with my RM-4014. At first I thought it was ok but it seems to be acting a bit funky.

First off when I plug the X x Y port into my mixer for testing I get a lot of noise. The sound is like crackling, intermittent white noise. Some times it subsides but often it is loud enough to register on the VU meters. I've checked the connections on the 8 port connector to the 1/4" jacks and the seem ok. Wiggling them does not affect the noise. I've checked for loose components but can't seem to find any. Nor can I find any bridged solders. This, of course, isn't to say that there absolutely aren't any. Just none I can find.

More disturbing is the disappearance of sound from the X inputs. At first, despite the noise, I tested all 4 input jacks according to the documentation. The volume of each one was fine. At some point though, perhaps during the calibration, the X ports lost significant volume. I don't know if it was adjusting the trim pots that did it or if there is a deeper problem. I tried re-adjusting the trim pots after noticing the loss of volume but it's just ... gone.

Once again as a novice I'm not quite sure where to look for problems. Any help would be greatly appreciated. Thanks!
Synthbuilder
Both problems are perhaps the same problem. It sounds like a bad connection or connections somewhere. The usual suspects are the sockets themselves - even the mighty Switchcraft 112APCX can have faults out of the box - and then the solder joints on the wiring that connects them. It may be a good idea just to go over them again with a soldering iron making sure the molten solder wets all surfaces. Sometimes adding just a tad of fresh solder will help it flow better.

Tony
Flareless
Thanks for the reply Tony. I tried your suggestion but still got the noise. It's quite persistent and loud. To rule out bad jacks I alligator clipped pins 7 and 8 to the output jack.



To check if the problem was the output jack itself I wired a fresh out of the package 112APCX to the pins and the problem persisted.



Can you suggest a part of the circuit which may be causing the noise and the X ports to stop functioning?

I should also mention that I checked the interface cable to the mixer (I actually replaced it at one point). The problem also occurs when the 4014 is connected directly to the modular and a different mixer (not to mention power supply) so I'm pretty convinced I've done something to the board itself.
Synthbuilder
Flareless wrote:
Can you suggest a part of the circuit which may be causing the noise and the X ports to stop functioning?


Unfortunately, without it being on the bench here with me I won't be able to say for sure what could be wrong. The problem with ring modulators is that a fault in either X or Y input circuitry could cause a problem audible on the output.

However, intermittent noises are usually mechanical. So you should probably try pulling all the ICs from their sockets and replacing them. Making sure that the ICs fit snugly back into the sockets.

Check again that R6 and R16 are definitely 680R. You'll be able to measure their resistance with a meter with them still in circuit but with the module powered down.

Occasionally diode and transistors do go bad. It's extremely rare for them to do so early in their life but they can. Measure the voltage across C4 and then C17. Both should read a steady 1.2V or so. It should be steady and not bouncing around. If it is unstable, think about replacing D1, D2, D5 and D6.

Tony
Flareless
Thank you for the suggestions Tony. I understand how hard it is to diagnose a problem with a complex device from just a description. I'm a retired Computer Guy and I can't count the number of times I received support calls consisting of "My computer isn't working. What's wrong?" hihi

I've already re-seated the ICs but that didn't help. I then double-checked the solder joints by applying a bit more heat, softening the solder and adding a drop more where I felt I may have been a bit stingy. The crackling noise seems to have subsided but I am hearing a bit of background noise.

I'm still having a problem with the X input. I will check out the components you have suggested. If I still can't resolve the issue I will contact you privately via email and arrange to send the unit back for service.

Thank you again for your continued support.
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