Lectric FX Karaoke Chorus - how to get a slower chorus rate

[Locrian99]

Good morning (or whatever time of day you happen to read this),

I put together a karaoke chorus from lectric fx a while back.   I recently loan it to a friend and he asked if I could make him one but he was wanting to be able to get slower chorus rates.   I'm not sure how to make that mod was hoping someone could help me out with that. 

Thanks

https://lectric-fx.com/wp-content/uploads/2022/05/KARAOKE-CHORUS.pdf

[duck_arse]

I'd say increase the value of C6, maybe add a 4u7 in parallel, but that is a weird looking oscillator section.

[Locrian99]

I'd say increase the value of C6, maybe add a 4u7 in parallel, but that is a weird looking oscillator section.

Am I looking at this completely wrong I feel like that would effect the vibe rate.   

Easy enough to try though.  I think I have some 15u caps around actually as well.

[ElectricDruid]

I think C6 and C7 are filtering for the waveform when it's switched to Vibrato mode. There's clipping diodes to make a triangle more sine-ish, and then some smoothing filtering to try and make it even more sine-ish.

Instead, I'd try increasing C5/82n to 100n or more.

If you're using significantly slower rates, you might need to increase C6 and C7 as well to maintain the filtering effect even for the slower frequencies, but that will only affect the waveshape, not the rate (I think!).

[Locrian99]

Thank you for the responses guys.   I was leaning towards c5.   But I also feel I know just enough to make me think unknown what I'm doing and really screw it up .   I'm
Thinking I might just order up a second board and socket c5/6/7 to try some different values there rather than pull my current pedal apart and that thing just looks like a nightmare to breadboard. 

[ElectricDruid]

Yeah, if you're building a second one for a friend, start with a new PCB and make a few mods from the start. Definitely easier than trying to dig into one that's already done. Good luck!

[duck_arse]

a nightmare to breadboard

bah! there is no such thing. you would only need breader the oscillator section, mess about w/ the caps, see which is the timing cap. U5 and Q4 section, even comes with its own indicator of speed.