REVV G4 clone not working properly

[Jarmake]

Hi everybody!

I've been building my own Revv G4 clone for a while. I did my own pcb by milling it with dremel on a board. I transfered the pcb image on the board from http://effectslayouts.blogspot.com/2019/11/revv-g4.html and it should be a verified schematic/layout.

For offboard wiring I used the same site, http://effectslayouts.blogspot.com/p/general-layout-notes.html

I use an old wall wart (~10V) as a psu that I have hardwired to the board temporarily. I have replaced some resistors to the nearest values that I had in my box, but the value differences are negligible. I also replaced the 1n5817 diode with a 1n5822, which I think is different on voltage/amp rating only? Correct me if I'm wrong! All the caps are the correct value, IC's are the TL074&TL072, potentiometers are the correct value and everything should be working as planned... but no! It's not working very well at all.

When the pedal is off I can't get any sound at all. So that leads me to believe there is something wrong with the switch maybe? I've wired it according to the picture on the site I've linked above. When I push the pedal on the led lights up as it should and I do get some sound (soundclip link somewhere below!), but it sounds like farting with an octaver on. Which isn't quite what I was looking for when I started building this pedal.

I have gone through all the traces for bad solderjoints and solder bridges, but couldn't find anything at all. The voltages across the IC's are as follows:

TL074:
1: 7,3V
2: 7,3V
3: 7,3V
4: 14,7V
5: 7V
6: 7,3V
7: 7,3V
8: 7,3V
9: 7,3V
10: 7,3V
11: 0V
12: 7,3V
13: 7,15V
14: 13,7V

TL072:
1: 7,3V
2: 7,3V
3: 7V
4: 0V
5: 7,25V
6: 7,3V
7: 7,15V
8: 14,5V

I have no idea if these voltages are even near the ones that should be...

Here's a low quality video/soundclip of the pedal. Sorry for the messy table and the wiring is a temporary one. I'm going to tidy it up once I have my enclosure ready to go. As you can see on the video the volume works, the eq pots work fine, but when I turn the gain pot the gain does ramp up, but so does the interference and there's very little sound from the guitar. Also there's this octaver pedal style sound in there... When playing it's like adding a lower octave in the mix!

https://www.youtube.com/watch?v=0TdfCah3fcc

[iainpunk]

posting the schematic, layout and pictures of you board (both the solder and components sides) will help, but a pointer:

12: 7,3V
13: 7,15V
14: 13,7V

these values should be super close to each other.
i suspect there is something wrong with the feedback loop of that opamp.
check the components that go from its output to the (-) input

cheers, Iain

[duck_arse]

I use an old wall wart (~10V) as a psu that I have hardwired to the board temporarily.

more information links pictures circuits, as Iain sez, pleeze, and info on this adaptor. it's not AC output, is it?

[temol]

I use an old wall wart (~10V)

L074:
4: 14,7V
14: 13,7V

14V with 10V supply?

[Jarmake]

posting the schematic, layout and pictures of you board (both the solder and components sides) will help, but a pointer:

12: 7,3V
13: 7,15V
14: 13,7V

these values should be super close to each other.
i suspect there is something wrong with the feedback loop of that opamp.
check the components that go from its output to the (-) input

cheers, Iain

Hi!

Thanks for that pointer, I'll check the feedback loop as soon as I get to my workstation again!

-Jari

[Jarmake]

I use an old wall wart (~10V) as a psu that I have hardwired to the board temporarily.

more information links pictures circuits, as Iain sez, pleeze, and info on this adaptor. it's not AC output, is it?

I'll take some pictures when I get to my workstation again. Nope, it's a DC output wall wart. 9,6VDC and 250mA output.

Thanks.

-Jari

[Jarmake]

I use an old wall wart (~10V)

L074:
4: 14,7V
14: 13,7V

14V with 10V supply?

'

Yeah, that's correct. When I measure straight from the power input to the ground it's 9,85V and when measuring between ground and pin 4 and 14 it's ~14,5V and ~13,5V.

Here's a couple of pics and a bit of a video, where you can see the input voltage and 4&14 pin voltages.

[anotherjim]

14v from a 10v supply can be explained if the PSU only contains a bridge rectifier and has no smoothing capacitor.
Once connected to the board which does have capacitors, the voltage rises to the peak voltage of the transformer output. It will be about x1.4 greater than the transformer AC. 10 x 1.4 =14! If there is a series protection diode going into the boards +power, it will stop the meter seeing the rise to 14v if measured before that diode.

We do need a schematic (aka circuit diagram) but +1 to there being a fault on the TL074 section in pins 12,13 & 14.

 

[Jarmake]

Thanks, anotherjim!

This place seems to be a great place for learning about electronics.

Unfortunately I haven't been able to find a schematic for this circuit, only the pictures I've posted in the first message. I am going to check out the components around 12, 13 & 14 for faults and shorts tonight. Fingers crossed I find the culprit there!

Thanks again, you've all been very helpful and patient with my noobness!

[temol]

You'll find a schematic here.

anotherjim - thanks for the explanation. Seems obvious now.

[iainpunk]

I am going to check out the components around 12, 13 & 14 for faults and shorts tonight

i suspect its a bad connection of some sorts, probably not a short, 95% sure, but you never know...

cheers, Iain

[anotherjim]

Unfortunately, the pedalPCB scheme uses multiple TL072 so its pinouts don't follow for the TL074. A little bit of circuit tracing is needed to find the culprit and compare to that schematic. Connections to pots/switches etc can be a useful guide to which opamp is which.

[Jarmake]

Unfortunately, the pedalPCB scheme uses multiple TL072 so its pinouts don't follow for the TL074. A little bit of circuit tracing is needed to find the culprit and compare to that schematic. Connections to pots/switches etc can be a useful guide to which opamp is which.

Yeah, at first I was thinking that the sanguine distortion is some other thing, but then I realised the 074 is just two 072's in one package. I'll have to take a careful look around the ic some day. But now I kinda feel burned out with this thing and it's like I'm blind looking at the pcb. So a bit of a rest comes in handy right now... I've been doing this pedal for quite a few days now.

[temol]

Quick look at the layout and schematic.

schematic - layout

IC1.1 - TL074 5,6,7
IC1.2 - TL074 8,9,10
IC2.1 - TL074 12,13,14
IC3.1 - TL072 1,2,3
IC3.2 - TL072 5,6,7
IC2.2 - TL074 1,2,3

[Jarmake]

Quick look at the layout and schematic.

schematic - layout

IC1.1 - TL074 5,6,7
IC1.2 - TL074 8,9,10
IC2.1 - TL074 12,13,14
IC3.1 - TL072 1,2,3
IC3.2 - TL072 5,6,7
IC2.2 - TL074 1,2,3

Hey, thanks a bunch! You saved me some time, since I am not that good at reading schematics anymore. It's been a long while since I last did pedals and had to look for schematics and stuff.

My kids are old enough so they don't require constant watching eye anymore, so I thought I'd pick up this hobby when I still understand something about electronics and remember some basic stuff I was taught at school. Maybe I'll have to dust off all those old books and remind myself how it's done