Revv G3 Pedal

[Strassercaster1]

[Frank_NH]

Hi guys,

Thanks a lot for trying to unravel this mystery.  Seeing what works and what doesn't helps me understand how these things work (or in this case, don't work ).

I went over the schematics for the both the G3 and G4.  They are essentially the same except that the G3 has an inverting gain stage with the double 1N4148 soft clipping before the LED hard clipping stage. So something about adding that stage is causing the issue.  You could confirm that on your bread board by bypassing that stage, putting a wire just after R18 to the input to the next stage (omitting the 4.7K resistor).   It should probably work as you now have the G4.

I thought it was interesting that battery power seemed to stop the squealing.  That would suggest some issue (noise) with the voltage being delivered to ICs 2.3 and 2.4.

I also thought that cross talk in the TL074 may have been the problem, and that rebuilding with TL072 would help, but given what we've learned I don't think that will help after all (I could be wrong...).

I did see something in the coupling between IC2.4 and IC2.3 on the G3 that perhaps you could try.  Put a 1uF capacitor just before R20 (the 4.7K resistor).  As it stands, the DC reference voltage between the two op amps IC2.3 and IC2.4 are directly coupled.  Maybe that's causing the feedback as any DC noise from IC2.4 is fed downstream to IC2.3.  Placing a 1uF cap there would break the DC coupling.  The G4 has a 4.7uF cap in that position, and you could use that value if you wanted.  Let me know if this works.  If not, then I guess we'll have to get the PCB version...

[Strassercaster1]

So pedal pcb sells these for this schematic /pcb build B5A798AD-B65A-4FE3-9501-61601D484281.png


Do you guys think thiese adapters  to 4 tl072 would make a difference ?

I ordered 2 if they work on one of my builds I’ll order more for the other one .

I went ahead and ordered a PCB I haven’t used a pcb in 5 years just my first couple of big builds  I made the Klon and univibe with madbean boards.
It will probably save an hour or so .
I really want this pedal ha ha . I watched tons of videos on it . The G4 is great and no way I’ll change it but it’s got a mid scoop to it .

[Frank_NH]

I actually like using PCBs, especially if you want something that will last.  My vero builds can be a bit fragile, though they've gotten better over the years.

Try my 1uF cap idea above before abandoning the vero...

[Strassercaster1]

So idk which 4k7 is it the one in row 22 21 or 18 ? If you souls pinpoint where to drop the 1uf/4uf I’d appreciate it . Did you see the layout I posted with the 100nf’s did this look like a good place to put them in ? Thanks man I spent 3 hours making the first one 4 making the second and about three one hour trouble shooting on the first one no problems found . I really went slow triple checked everything measured every part on the second build . 

On Mon, Mar 25, 2019 at 11:30 AM Frank_NH [via Guitar FX Layouts] <[hidden email]> wrote:

I actually like using PCBs, especially if you want something that will last.  My vero builds can be a bit fragile, though they've gotten better over the years.

Try my 1uF cap idea above before abandoning the vero...

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[daveycroc]

It's the one in column 21, from row T to row Y.

This links pin 14 to pin 9 on IC2.

I'll try it on my bread board tonight.

I've also reached out to someone who bought one of the pcb's to see if they are having any issues.

On Mon, 25 Mar 2019, 16:55 Strassercaster1 [via Guitar FX Layouts], <[hidden email]> wrote:

So idk which 4k7 is it the one in row 22 21 or 18 ? If you souls pinpoint where to drop the 1uf/4uf I’d appreciate it . Did you see the layout I posted with the 100nf’s did this look like a good place to put them in ? Thanks man I spent 3 hours making the first one 4 making the second and about three one hour trouble shooting on the first one no problems found . I really went slow triple checked everything measured every part on the second build . 

On Mon, Mar 25, 2019 at 11:30 AM Frank_NH [via Guitar FX Layouts] <[hidden email]> wrote:

I actually like using PCBs, especially if you want something that will last.  My vero builds can be a bit fragile, though they've gotten better over the years.

Try my 1uF cap idea above before abandoning the vero...

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[Strassercaster1]

Thanks to all . I checked the forum at pedalpcb but didn’t see anything . I’ll check again later today . 

On Mon, Mar 25, 2019 at 12:02 PM daveycroc [via Guitar FX Layouts] <[hidden email]> wrote:

It's the one in column 21, from row T to row Y.

This links pin 14 to pin 9 on IC2.

I'll try it on my bread board tonight.

I've also reached out to someone who bought one of the pcb's to see if they are having any issues.

On Mon, 25 Mar 2019, 16:55 Strassercaster1 [via Guitar FX Layouts], <[hidden email]> wrote:

So idk which 4k7 is it the one in row 22 21 or 18 ? If you souls pinpoint where to drop the 1uf/4uf I’d appreciate it . Did you see the layout I posted with the 100nf’s did this look like a good place to put them in ? Thanks man I spent 3 hours making the first one 4 making the second and about three one hour trouble shooting on the first one no problems found . I really went slow triple checked everything measured every part on the second build . 

On Mon, Mar 25, 2019 at 11:30 AM Frank_NH [via Guitar FX Layouts] <[hidden email]> wrote:

I actually like using PCBs, especially if you want something that will last.  My vero builds can be a bit fragile, though they've gotten better over the years.

Try my 1uF cap idea above before abandoning the vero...

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[Strassercaster1]

So out a 1uf  in row Y 14 and 18 should it be electrolytic ? If so put  the negative  side in hole 18 ? 

On Mon, Mar 25, 2019 at 1:13 PM Strassercaster1 [via Guitar FX Layouts] <[hidden email]> wrote:

Thanks to all . I checked the forum at pedalpcb but didn’t see anything . I’ll check again later today . 

On Mon, Mar 25, 2019 at 12:02 PM daveycroc [via Guitar FX Layouts] <[hidden email]> wrote:

It's the one in column 21, from row T to row Y.

This links pin 14 to pin 9 on IC2.

I'll try it on my bread board tonight.

I've also reached out to someone who bought one of the pcb's to see if they are having any issues.

On Mon, 25 Mar 2019, 16:55 Strassercaster1 [via Guitar FX Layouts], <[hidden email]> wrote:

So idk which 4k7 is it the one in row 22 21 or 18 ? If you souls pinpoint where to drop the 1uf/4uf I’d appreciate it . Did you see the layout I posted with the 100nf’s did this look like a good place to put them in ? Thanks man I spent 3 hours making the first one 4 making the second and about three one hour trouble shooting on the first one no problems found . I really went slow triple checked everything measured every part on the second build . 

On Mon, Mar 25, 2019 at 11:30 AM Frank_NH [via Guitar FX Layouts] <[hidden email]> wrote:

I actually like using PCBs, especially if you want something that will last.  My vero builds can be a bit fragile, though they've gotten better over the years.

Try my 1uF cap idea above before abandoning the vero...

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[daveycroc]

Yes electro would work.

To do this on the vero layout you would need to disconnect the 4k7 from 21,20
The positive connection of the cap goes to 21, 20 then the negative end of the cap goes to the end of the 4k7 just disconnected from 21,20

[Frank_NH]

Here's how to hot-rod the current vero.  Remove the existing 4.7k (white rectangle) then daisychain the 4.7k resistor and 1uF cap as shown.  Let me know if it works.

[Strassercaster1]

I am off at 6 today home about 7 I’ll be playing by 8 . It would be awesome if this works !

On Mon, Mar 25, 2019 at 2:23 PM Frank_NH [via Guitar FX Layouts] <[hidden email]> wrote:

Here's how to hot-rod the current vero.  Remove the existing 4.7k (white rectangle) then daisychain the 4K resistor and 1uF cap as shown.  Let me know if it works.

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[Strassercaster1]

i tried the 1uf it didnt work .After that  i also added the 2 100n that were missing on my new  build. i guess i could still try the 4.7uf and will in a little while .

[daveycroc]

I also tried adding the 1uf Electro cap and it didn't make much difference. I did also experiment with other types and found that a 1uf Polyfilm seemed to work better (though I don't recall if I'd changed anything else)

I've had feedback that the G3 PCB from PedalPCB is very noisy too and unusable after gain at 9 o'clock.

I have my Gigrig generator home with me so can try that out to hopefully eliminate any issues cause by bad power.

I've also bought a small oscilloscope in the hope that can help to debug this too.

[daveycroc]

Another interesting thing is that Thomann allows you to try out streaming though a real G3, amongst other pedals.

https://www.thomann.de/gb/stompenberg_revv_g3_distortion.html

It doesn't seem to have the same problems (as you'd expect)


The function on Thomann to try the pedals out is very interesting, they seem to have replaced all the pots with digital pots.

[Frank_NH]

Thanks guys.  

The only other thing I can think of to try is to reduce the gain of one of the two inverting stages, or change the capacitors in the feedback loops to 1nF from 100p to filter out more high frequencies, bit then you're changing the fundamental character of the pedal's tone.

What confuses me is the fact that it appears to work OK with battery power.  The power filtering on the G3 seems more than adequate, but who knows.  Maybe using a 470uF versus 100uF will help, or perhaps making other mods to the power filtering and bias voltage parts of the circuit.

One final thing - I searched the internet for a picture of the original G3 PCB, and found one here:

https://pedalauthority.com/2018/11/25/revv-g3-distortion/

Interestingly, it appears to show SMD dual op amps and not quad!  So as a final experiment, you can try modifying the circuit to use 4 dual TL072s rather than the TL074s.  Maybe that's the trick after all?

[BuGG]

The Tyrian PCB is designed using TL074's to save space, and doesn't have any oscillation issues using the components shown in the schematic.

With that said, there is also an optional Dual -> Quad opamp adapter if you choose to use TL072 opamps instead.

It has been built using both methods with none of the issues that are being battled here.   I haven't looked over the vero layout to confirm, but assuming it does match the schematic (you guys usually nail it) maybe the problem is caused physical proximity of components/offboard wiring?


Here's a clip of the Tyrian with the gain control dimed (Treble/Mid/Bass at noon, Voice switch in the middle).
https://soundcloud.com/pedalpcb/tyrian
   
I would say the noise level is perfectly acceptable for this amount of gain.   This one was built using TL074's.  Guitar > Pedal > Direct into audio interface, no buffered pedals, powered from a cheap 1-Spot wall wart.

BTW, I have these if someone wants to try the vero layout with TL072 instead of TL074, without having to completely rework the layout...  You can have a pair for free (just cover shipping)


Coupon code: TAGBOARDFX (grants two free)

[Strassercaster1]

I ordered a Tyrian and two of these on Monday they came first thing today . PedalPcB rocks that was super fast and shipping was under 3 bucks ! Very impressed ! PedalPcb also does like Tayda they have 15% off coupon codes a few days a month. Tayda is selling predrilled Boxes for Pedal Pcb Boards as well ! I work 8-10 today if I have  the energy I’ll try them on the Vero layout tonight . My builds both squealed with a battery . It’s got to be proximity . I am also gonna out my boss tuner into my test box and see if the buffer helps . If that’s the case I’ll make a couple Cornish buffers . They sound good and little to no switch pop as a bonus .

I highly doubt the schematic has any errors . It’s probably right . I’ll try to check the schematic as I build the Tyrian . I’m glad I socketed the TL074’s. I will try to do it tonight and post before midnight . I got 10 hours in two of these counting over 4 hours trouble shooting . I sure would like to make these two builds work . I already have a couple people asking if I can make them one.

Thanks to all once again . It has to be proximity or cross talk like Frank and Bugg are saying . Although HoZy said it did it on breadboard ?

[Strassercaster1]

Are you the Owner of Pedal PCB ? Thanks for all the help ! I ordered two of these
Monday and already got them ! I will need 4 more one set  for the real Tyrian and one set for my second build . I think I am gonna buy a face melter as well that layout isn’t right either yet . I got my boxes drilled decaled and clearcoated  for a face melter and a revvG3  . I’ll have to repurpose them for the pcb builds .buwill.

[BuGG]

Probably goes without saying, but make sure you install the pins into the adapters before you install the TL072's.  

[Strassercaster1]

Thanks ya I got it . I went and bought some dual sided 40 pin headers today .
Man I am beat watching the clock . Left for work at 8 and get off at 9 won’t get home till 945/10 . I didn’t know fonoll mess woth it tonight I been yawning the last hour ha ha .. I am gonna order more of it works .