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Hum from a Doepfer 124 Wasp filter
MUFF WIGGLER Forum Index -> Eurorack Modules  
Author Hum from a Doepfer 124 Wasp filter
fireclown
anyone else experienced hum from the outputs of a Doepfer 124?
Stuffed what I could into an older ASol plastic case for a cross country run, and found myself very disappointed by a steady low level hum coming out of the Wasp filter. Especially disappointed because I really didnt pack any VCA's into the case. Thought I would ask around if this was a normal problem, or if anyone has an idea what the issue is?
thanks!
b-art
I bought one, it stopped working within a couple of days, returned it for RMA.

They replaced some chips and send it back to me, 1 week later it stopped working again...

Did some research on it and found that some units just seem to have a lot of problems... burned chips, hum, sudden weird behavior, etc.

If you google for it you will find threads on multiple forums about that. Shame tho because it's a wicked filter but it totally ruined the Doepfer experience for me. hmmm.....
skyshaver
I bought one used and have never had an issue. Sorry, that sucks, I guess that's why they're so cheap.
fireclown
well, i cant be sure whether this is a new issue or not. seems like I may have noticed it before and forgotten about it, OR it could be I touched a magnetized screwdriver against a chip while farting around juggling modules.
its a pretty squirrely power cable/supply arrangement in this case, so once I get home I will see if those are at fault.
thanks for the help.
I have had this one for years, and so very few problems with Doepfer modules I would never complain about them.
may be I never noticed because normally it would feed a vca. here Im cheating without, and thats not much fun!
sounds cool for now though.
paperCUT
The Wasp filter abuses some logic chips to do it's magic, I've had experience with doing that and some batches of chips just don't like the abuse. If they are in chip sockets you could try a few replacements and see if they work better, cost per chip is about 20 cents depending where you get them, quantity etc.
yghartsyrt
b-art wrote:
I bought one, it stopped working within a couple of days, returned it for RMA.

They replaced some chips and send it back to me, 1 week later it stopped working again...

Did some research on it and found that some units just seem to have a lot of problems... burned chips, hum, sudden weird behavior, etc.

If you google for it you will find threads on multiple forums about that. Shame tho because it's a wicked filter but it totally ruined the Doepfer experience for me. hmmm.....


This has nothing to do with Doepfer, but with the way this filter works. Just get some spare chips - and you should be fine. The problem, if I remember correctly seems more that a certain batch / production run of the IC seem to be more prone to fail than others. I changed my IC three years ago, after it first went kaputt and never had an issue since.
fireclown
just want to follow up- when I got the 124 back in a decent case minus all the out of control ribbon whoring it was attached to, no hum discernible. cranked up the mixer ins with no vca and nothing. seems to work fine.
just so nobody thinks those filters are sketchy, this one has survived a lot!
mmagin
Ah, this seems like a good example of a module that's very susceptible to power supply noise and ripple -- a victim in the terms of the LIBB white paper.

Got mine recently and put it in my oldest Doepfer A-100G6. I'd bought this one used, it had the original PSU1, and though I had a PSU2 on the shelf, I'd been too lazy to replace it, instead just putting low current per HP modules in there generally. Well, this is the first time I can say I've had power supply problems in eurorack, it had a consistent background noise (not exactly a hum). Moved it to another case and all was well. Latter replaced that PSU1, the capacitors on it seemed possibly bad, they wobble on the component leads.

Here's what I think is at work - if Doepfer's design is anything like Haible's adaptation of the Wasp filter, http://www.schmitzbits.de/wasp.html -- compared to op-amps, this abuse of CMOS inverters as amplifers is sure to result in an amplifier with rather poor PSRR (power supply rejection ratio), thus ripple and noise will carry over into the audio easily.
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