Author Topic: Is it possible for an LFO to stall?  (Read 291 times)

Is it possible for an LFO to stall?
« on: June 17, 2022, 09:41:39 AM »
Iíve built a phase 45 and everything sounds great except for one thing. Itís like the ďmanualĒ setting on an EHX Bad Stone has been switched on, the LFO seems like itís stationary instead of actually oscillating. The phase can be shifted using the bias trim pot, but I kind of need both my hands to play.  Has anyone experienced something similar? Or can somebody point out where on the schematic the LFO is generated? Iím not experienced enough with electronics yet to visually identify the section.
The schematic for reference:

http://www.generalguitargadgets.com/pdf/ggg_p45_sc.pdf
Thanks a ton!

antonis

Re: Is it possible for an LFO to stall?
« Reply #1 on: June 17, 2022, 09:51:47 AM »
can somebody point out where on the schematic the LFO is generated?

IC2b and relevant circuitry..
(R20 to R24 and C9)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Re: Is it possible for an LFO to stall?
« Reply #2 on: June 17, 2022, 11:00:09 AM »
Thanks, I appreciate the info!

antonis

Re: Is it possible for an LFO to stall?
« Reply #3 on: June 17, 2022, 04:44:11 PM »
More strictly speaking, basic LFO consists of R20, C9, IC2b, R21 and R22..

Your issue might be due to op-amp out saturated on either supply rail or discontinuity between R24/R27/R25/C10/GND/R23/R25..

Could you take a measurement on pin7/R22/R24 joint..??
In case of getting a fluctuating signal, check continuity path as below:






"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Re: Is it possible for an LFO to stall?
« Reply #4 on: June 24, 2022, 08:26:50 AM »
That was it! There was a tiny break in the trace between R24 & R27. I spend so much time looking for solder bridges and unintentional trace links I donít know how I missed the break. Been staring at the damned thing too long and went blind I guess lol. Thank you for narrowing the problem area down, thatís been bothering me for weeks!