Gravity Wave (Verified)

[madbean]

Well I don't know. But, it would reduce the gain of that output from the PT2399 which might help a lot. Or, not!

[Scruffie]

Actually, reducing them would change the cut off of the multiple feedback filter and increase gain.

Are we sure C9 is 330n? 33n makes more sense to me... also seems like there should be a cap to ground from R3.

So looking at the schematic, the input goes through an MPF in to the PT2399 and then the wet output goes straight to the output unfiltered and the feedback (or dimension) goes through another filter using the other PT2399 opamp before being fed back in to the PT2399 input.

Anyway, increasing R9 should limit the feedback, if you increase R10 you're adjusting other stuff too.

[bigzed]

I wondered about the C9 too! You are correct about R10 changing other stuff, that's why the mod using a 10k res and 1uf cap from pin 2 of the opamp to lug 3 of the dim was required and put the reverb back.

[madbean]

Actually, reducing them would change the cut off of the multiple feedback filter and increase gain.

Are we sure C9 is 330n? 33n makes more sense to me... also seems like there should be a cap to ground from R3.

So looking at the schematic, the input goes through an MPF in to the PT2399 and then the wet output goes straight to the output unfiltered and the feedback (or dimension) goes through another filter using the other PT2399 opamp before being fed back in to the PT2399 input.

Anyway, increasing R9 should limit the feedback, if you increase R10 you're adjusting other stuff too.

Reducing R7 increases the gain of the MFF, but reducing R8 decreases the output at pin 14. My thinking here was series resistance at R10 was not giving the right result so let's have less output at LPF-2 (although it does change the whole thing). But, you are probably right - just leave everything as is and make R9 bigger. I should really etch this board and build it.

I'll have to double check on that 330n cap.

[madbean]

Pretty sure 330n is right. It's on the trace schematic I have and if you look at gut shots of the SM, you'll see a huge Panasonic cap right around pin9 of the PT2399 which could only be that size.

[Scruffie]

Could that huge cap not be the 470n from the LFO?

[bigzed]

Ok..so i replaced all the changes I made 50k back to 5k pot, 120k to 8k2 R10 and removed the link 10k resistor and 1uf pot..

So back to square 1 and the whining is back as it was to begin with. I then changed the 1k R9 to a 10K and the whining stopped but the reverb was weak so I also changed  the 33K R7/8 resistors to 10k each and that seemed to increased the reverb. I think now it is exactly the same as the video demo. So with these changes I'd consider this Verified!

[Scruffie]

See, I think that whining is the MFF oscillating as the Q is too high, but if it was 33nF, it'd make much more sense... care to try if that works without having to change resistor values?

[bigzed]

I put it all back again and changed the cap from 330n to 33n but It still needs the 10K resistor for R9 to stop the whining! But changing the 330n cap to 33n really increases the reverb....a lot!!!

So to recap change R9 to 10k and the 330n cap to 33n leave everything else as is and it really works well. Well done Scruffie!

[bigzed]

Or to make it easier....remove the 0 from C9 and put it on R9!!!

[Scruffie]

Well, I can't say if that's how it's meant to be but if it works, great!

[selfdestroyer]

I wanted to add that C9 to 33n and R9 to 10K worked great for me.

Also, sorry I jumped the gun on verifying this build. I honestly thought the feedback was normal due to the slapback controls. Its all sorted now and I really love this effect.

Cody

[blearyeyes]

Cool thread.. Cool Pedal.

[djentleman843]

I've applied the fix listed here and while it kills the whine, it also makes that control so subtle its pretty useless. I would almost rather have the whine after 30% but still get that cool echo/verb.

Also- is there a way to slow it down... seems to be extremely fast even at slow settings.

[Scruffie]

I can't comment on how the mod sounds, so someone else will have to confirm if it makes it too subtle or if there's perhaps an error on your build.

Slowing down the LFO is easy though, just make C20 a 1uF NP.