Revv G3 Pedal

[Strassercaster1]

HoZy messages me he has made a G3 and G4 I wasn’t sure he made both . I’ll rebuild it Sunday am and use that to figure out what’s wrong with my first build hopefully

[Hozy31]

IC voltages of my build for reference.

Voltage in - 9.11v

IC1
1 4.33
2 4.33
3 4.33
4 8.68
5 4.33
6 4.33
7 4.57
8 4.33
9 4.33
10 4.1
11 0
12 4.33
13 4.33
14 4.33

IC2
1 4.33
2 4.33
3 4.33
4 8.68
5 4.1
6 4.33
7 4.33
8 4.27
9 4.33
10 4.33
11 0
12 4.33
13 4.33
14 4.33

[Frank_NH]

The voltages look reasonable.  Did your build squeal, Hozy31?  Did you use TL074s?

[Hozy31]

No, no squealing in my build and yes used TL074s.

[daveycroc]

Interesting. My voltages are fairly except pin 8 of IC2 which is over 5 volts.

Hozy, could you please post a photo of your build?

Also, what version TL074 are you using? I currently have TL074CN.
I know that there are potential difference but I don't know enough to even work out what matters.

[Hozy31]

I'll post photos etc when i get back from work later.

[Hozy31]

Photo of verified Revv G3. Excuse the picture quality, taken on mobile, and my shaky hands. As you can see its also still unboxed.

[daveycroc]

Thanks hozy.

Looks exactly like mines. Only difference is the 100pF caps. Mines are the
orange ceramic ones.

Were these parts all from tayda?

[Hozy31]

The only parts not from Tayda are the electrolytic caps which i buy from China and the white 4n7 which i'm not sure where i got, but was in spec.

[Hozy31]

Also i just ran out of ceramic 100pfs so used MLCCs instead.

[daveycroc]

So pretty the same parts as me. It's a bit is a stumper

[Hozy31]

Ok, since i was running this pedal in a chain with other pedals i decided to isolate it and guess what, some really horrible squealing. I presume its the buffering that's preventing the squeal when its in the chain. At least its now obvious that there is definitely an issue with this layout.

[Hozy31]

Possibly a grounding issue?

[daveycroc]

Oh that's interesting!
Though I don't think it's this layout, as I used the schematic to breadboard and still got the squealing.

[Frank_NH]

That behavior is precisely what happened with my OCD build (squealing was prevented by placing a buffered BOSS pedal in bypass mode in front of the OCD).  Again, the remedy was replacing the TL072 with a TL082.  I still have that around - I may unearth it to do some experiments on noise suppression.  Anyone try the 100nF cap near the power pins of the TL074s?  Or maybe it needs to be redone with TL072s.  That's the only reason I can see that the G4 works and the G3 doesn't as they have similar circuit topologies...

T-I does make a TL084 quad op amp chip...

[Strassercaster1]

Man I’m bummed out on this one . I was holding off to do some recording on a song that this pedal would have been perfect for .Vino Alan came in 3rd on Xfactor show . Was in a band with him around 2002. He is in town for a couple shows .  So we were gonna do an old original that never got done . 

The g4 is identical the first 1/4 of the circuit on both schematics .isnt it ? If your getting squeal that early that’s weird . I need to get a breadboard set up . I like vero.i got the old radio shack desoldering iron and swapping parts is quick easy and the vero tracks are a lot tougher than most pcb tracks. Perfect for botweaking ha ha .

 If I use a pcb I don’t  feel as proud . Although I am terrible at layouts . I haven’t done a layout bigger than a fuzz face ha ha . I do usually look at the schematic and follow the layout . I get brain freeze trying to do big layouts . 

HoZy did confirm he made a g3 and a G4 no problems with Anders layout . So on Sunday I’m going to reflow everything change the diode and electrolytics . If that doesn’t work .  I will rebuild it again . I just did a $100 order from Tayda Monday . I ran out of tl074 a50k and Dpdt on off on . So I’ll be reclaiming a couple parts . 

At this point I spent 2:45 making it and 2 hours messing with it . My time is so stretched these days . 

On Fri, Mar 22, 2019 at 2:07 PM daveycroc [via Guitar FX Layouts] <[hidden email]> wrote:

Oh that's interesting!
Though I don't think it's this layout, as I used the schematic to breadboard and still got the squealing.

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[daveycroc]

I'm part way through rebuilding it in bread board. Going to try out your suggestions once built.

On Fri, 22 Mar 2019, 21:55 Frank_NH [via Guitar FX Layouts], <[hidden email]> wrote:

That behavior is precisely what happened with my OCD build (squealing was prevented by placing a BOSS pedal in front).  Again, the remedy was replacing the TL072 with a TL082.  I still have that around - I may unearth it to do some experiments on noise suppression.  Anyone try the 100nF cap near the power pins of the TL074s?  Or may it needs to be redone with TL072s.  That's the only reason I can see that the G4 works and the G3 doesn't as they have similar circuit topologies...

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[Strassercaster1]

Thank you so much

[daveycroc]

Finished building this on breadboard using TL074's

Had horrible squealing initially, tried the 100nF caps from the power pins to ground. Eventually tried a battery and managed to get the squealing to stop. I'm sure I tried the vero build with a battery so maybe a dodgy component there or a problem with the layout.
I think I have a problem with the power in my house too, as I was causing ground hum by touching my heating radiators!

After that I tried to see what the 100nF caps changed, and couldn't hear anything, that's not too say they didn't.

I also converted the gain section to the G4 and reconnected my mains power and that had no squealing even with tl074.
It seems like he additional op amp stage of the G3 really causes it to squeal if the power isn't clean.

I wonder if this circuit might need boxed up also to avoid picking up excess noise.

To sum up. I've honestly no idea if this layout works or was just power issues before.

[Strassercaster1]

Well I finished second build. Squeals as well. Put in 2 100nf about  were the schematic shows. There are 2 100nf left off this build looking at the schematic power section and parts list. Hozy  does your pedalboard  use a good power supply like a voodoo lab pedal power or something high quality??


 That could be it as well. i looked at the schematic last night and What Frank was saying and sure enough there are 2 100 nf in the power section going to ground right about where  Frank is saying. I was suprised adding them didnt help/ Maybe I addded them in the wrong spot. I will post pictures late tonight .I made a tunderbird that squealed on high settings before i boxed it but decided to box it and unless everything was dimed no squeal. i kept the in and out wires seperated .

. I am just using a crappy  wall wart on my bench. I am gonna try using a battery for power .Now i have 2 that squeall ha ha. i will get some ceramic 100nf on tuesday if my local store has them. I tried tl084 and it squealed even more. i used a 125b  i could make a buffer for it and give up the battery.