Phase Shifter Troubleshooting

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johnstilton
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Phase Shifter Troubleshooting

Post by johnstilton » Tue Jul 06, 2021 11:35 am

This weekend I wired up a MFOS phase shifter to my panel and it does not work correctly. It acts more like a strange amplifier wavefolder with a lot of parasitic oscillations than a tame phaser.

I populated two of these PCBs, which are the revised versions BTW, a couple of years ago but only got around to wiring them up now.

Interestingly the second one behaves the same way.

I probably have made the same mistake on both but scrutinizing the values against the documents no incorrect resistor or capacitor values jumped out to my attention.

Notably, I also found that the gain of 4 of U1 was way too hot so I replaced R65 with a jumper wire to restore OUT 1 to unity gain. That made the levels bettter but the operation is still haywire and definitely, "not a phaser"

I do see that Ray included a pic on his site for this build in which an LF442 instead of the 082 is being used in the LFO section.

Anyone else have any success in this build?

My latest thought is to separate the LFO from the CV summer, to see if the former is inducing the unwanted behavior onto the latter and then to the Expo V/A converter.

Ill update this thread as I troubleshoot.

http://musicfromouterspace.com/index.ph ... 90&VPH=602

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johnstilton
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Re: Phase Shifter Troubleshooting

Post by johnstilton » Wed Jul 07, 2021 8:02 am

Update:

Pulled out the depth pot from the CV summer. Fine looking waveshape from the LFO.

Input a DC voltage from a joystick into a CV input and got the same unwanted behavior.

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johnstilton
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Re: Phase Shifter Troubleshooting

Post by johnstilton » Thu Aug 12, 2021 10:04 am

Update:

I never did get either one working properly.

I decided to shelve them.

in the empty panel space I used two ECHOFXXX modules which work nicely from the first power up

Maybe when Synthcube has pre-populated shase shifter SMT euro boards again, I might buy one and try again with that.

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wackelpeter
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Re: Phase Shifter Troubleshooting

Post by wackelpeter » Fri Sep 03, 2021 10:57 am

Maybe post your problem again in the DIY section, as the usual folks that lurk in that sub possbily never or too rarely look into this side of the forum.

I'm pretty sure you'll get some answers there, when you post that again, an link to the schematic and some pictures of the boards and possibly wiring.

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