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Total Recall Calibration Issues

Started by hossymandias, February 09, 2021, 06:38:10 PM

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hossymandias

Hi, I have successfully built a pretty great sounding Total Recall.

Everything works great except there is clock noise (high pitched whining) in the delays past about 3 o' clock on the delay time pot. This isn't a huge issue, except that I have spent so much time on this build, I want it to be ironed out.

I originally followed the calibration-by-ear instructions in the build document but when the clock noise issue surfaced, I attempted an oscilloscope calibration.

Not all of the readings measured the same as in this guide:
https://sites.google.com/a/davidmorrin.com/www/home/trouble/troubleeffects/electro-harmonix-memory-man/eh-7850/eh-7850-calibration

Specifically I ran into problems when trying to reach unity gain between pins 14/15 and 7 on the NE570. With the trimmers in their max positions, I can still only get about half the gain on 14/15 as I get on 7.

I don't know if this issue is related to the clock noise issue, but I'd love to get input on these issues.

Things I've tried:

reduced C40 to 220pf (this didn't seem to change much)
replaced the compander (tried SA571, NE571, and NE570 with little to no difference)

Thanks in advance for your input!


LaceSensor

#1
play with the clock capacitor.

also check the value of the ?B100k delay time pot.

Which BBD are you using?