Mutant Clap DIY Advice - Reverb Section is all Noise

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bpcmusic
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Mutant Clap DIY Advice - Reverb Section is all Noise

Post by bpcmusic » Fri Feb 26, 2016 6:42 pm

Looking for some advice on where to look for a problem with my just-completed Mutant Clap build.

PROBLEM: Turning Reverb ON (to I or E) routes noise to the module's OUT. Otherwise, unit works as expected (and is awesome).

[video][/video]

Above video shows clap with reverb off and set to the two modes; it also shows an external audio input with reverb in the two modes.

Attempting to calibrate, my voltmeter measures just under 12 Volts at the test point (!). Trims do nothing to affect this or the sound. The only thing that changes the volts a bit is turning the pot for REV DEC (11.07 - 11.4).

I've put electrical tape on the tall caps to keep them from touching the board above them.

My prime assumption is that I'm bridging the noise out to the reverb circuitry somewhere - though I don't see any obvious bridges. Any other ideas as to the potential culprit? Any place for me to look extra closely and probe?

THANKS!

b

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frankaponte
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Post by frankaponte » Wed Mar 02, 2016 7:25 pm

Looks like the "Null Offset" trimmer is connected to the differential input pins of the LM13700 (IC4). Maybe something is wrong with that IC?

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bpcmusic
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Post by bpcmusic » Thu Mar 03, 2016 8:25 pm

frankaponte wrote:Looks like the "Null Offset" trimmer is connected to the differential input pins of the LM13700 (IC4). Maybe something is wrong with that IC?
Thx - I'll check there. Perhaps a couple of pins on the socket solder-bridged under the socket where they are hard to see...

Really appreciate the reply!!

b

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bpcmusic
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Post by bpcmusic » Sat Mar 05, 2016 12:40 pm

From a cross-promote that created some cross-post potential (my bad):
billieblaze wrote:Having the same problem here! Did you figure it out yet? Going to dig up the schematic tonite as have a look I suppose.
--
TimoRozendal wrote:this is a common problem with this build, 2 things to check:
- are any tops of elco's touching the board on top if it?
- can the problem be reduced by carefully doing the calibration again?, this seems to be really sensitive

see also here

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bpcmusic
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Post by bpcmusic » Sat Mar 05, 2016 12:44 pm

@TimoRozendal - I've had put electrical tape on the tops of the super-tall caps; the noise sounds more like the module's noise source is being unleashed in the reverb portion without any attenuation.

@frankaponte - I've done some additional visual inspections of my build and don't see anything; perhaps one of my chips is bad? I plan to reflow the board, closely inspect the path around that trimmer and potentially even replace the LM13700 (IC4). I'll post any progress.

Thanks for all the assistance!!

b

vinylvandal
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Post by vinylvandal » Mon Jun 06, 2016 7:13 pm

i just built one of these and turned it on to get the same problem. i havent done any calibrating though so i will try all that tomorrow

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bpcmusic
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Post by bpcmusic » Tue Jun 07, 2016 6:57 am

vinylvandal wrote:i just built one of these and turned it on to get the same problem. i havent done any calibrating though so i will try all that tomorrow
Let me know; my build is still sitting in my DIY ER box. ;)

I've paused the debugging.

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vinylvandal
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Post by vinylvandal » Sat Jun 11, 2016 11:30 am

I calibrated it today and that seems to have fixed it. I am in general getting quite a bit of hiss out of the unit though

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batch
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Post by batch » Tue Jul 05, 2016 11:13 pm

Same issue. Have tried calibrating and no cigar. Otherwise works great, especially with something random through the external in.

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