PCM-42 Won't Modulate

T

Toneseeker504

New member
Hello + I hope this finds you well! Thought to ask about a bit of a riddle with a PCM-42. Have combed through it with the service manual and schematics, the unit works perfectly – except – it will not modulate. Can’t think of anything else to check. It's been recapped, pots are good, and all healthy otherwise. Sounds perfect, other than not being able to modulate. Wondered if anyone had ever seen this anomaly before, or had any ideas what part(s) to check on the board or which part is controls the modulation. Thank you in advance for any leads!
 
Thank you @panhead ! I've heard the Eventide units can be tricky to restore. It has been really tough to find anyone that has seen this anomaly on the PCM-42. The delay sounds awesome, and works great – I just want to restore to factory spec and get the modulation section happening. These older units are so cool, worth the stretch to make them sing!
 
PCM42 "modulation" is a different one! Back in those days most DDLs didn't modulate the delay time. The VCO would sweep the sampling frequency which in turn would shift the pitch of the input signal. Because of this technique the chorusing can be used with moderation as it gets wild as soon as you raise the knobs. Back then there was no digital workflow... so you could mess with sampling as much as you liked.... same happens in some H3000 algorithms....
If I remember correctly there is an LFO which is sweeping the VCO connected to the control logic processor. That's the area your tech should look into.
Two 42s in parallel and you get spectacular chorusing or amazing swept delays!
Good luck!
 
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Anyone able to reccomend someone in the bay area? I just need to remove the dry signal from my Yamaha D1500 delays.
 
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