Revv G4 clone issues.

[slashandburn]

I thought I was gonna solve this one on my own, indeed I managed to get it from not making any sounds at all to "hey it makes a noise and loosely resembles a distortion pedal" but it sounds terrible and the pots don't respond at all like you'd expect (noise, squeals).  A few of the IC voltages also look a bit weird:

TL074:
1. 6.7
2. 6.7
3. 6.7
4. 13.4
5. 6.4
6. 6.7
7. 6.7
8. 6.7
9. 6.7
10. 6.7
11. 0
12. 6.7
13. 6.4
14. 12.9. <<--  what's up with this?  I've ran a knife between all the traces around this section.

NE5532 (circuit calls for a 072)
1. 6.6
2. 6.6
3. 6.6
4. 0
5. 6.5
6. 6.6
7. 1.5 <<-- also strikes me a bit odd
8. 13.4

Here's the photos and the links to the Pcb and parts list.  Only subs I can recall of (besides a few series and parallel caps) are two 12n caps (in place of the 2x 10n down around the Mids pot) and a 2n4 and a 2n7 in place of the 2n2 (2n7 going to aggression sw 5) and 2n4 coming off treble pot lug 3, you see these guys fairly clearly on my photos, the only two green film caps).







Anyone able to spot something my eyes or brain are clearly missing?

Cheers
Iain

Edit: From what I gather the schematic used was this one here

https://www.pedalpcb.com/docs/PedalPCB-Sanguine.pdf

[mth5044]

Hello!

Bottom right and top left of center you have really big blobs of solder, make sure nothings shorting there.

Can you post a schematic?

Is your board shorting on the backs of the pots/switch when installed?

[slashandburn]

Thanks!  Schematic added. It shouldn't be shorting out on the pots, I have had this happen before so now I put a small square of card covered in insulating tape between the pots and the board. I'll check again over the areas you've mentioned (you're right, very sloppy soldering ), j just got tired going around the board with a knife and a magnifying glass so thought I'd throw this one to the forum!

[slashandburn]

So some. More poking about the weird looking 12v on pin 14 of the quad opamp.

I can't work out where it's coming from, but it's there on pin 14 but gone by the other side of the 22n cap. This is the output of IC 2.1 per the schematic from what I can tell.

I'll try measuring the empty sockets with the ICs removed in search of more clues, then try a different quad opamp if I still come up with nothing.

Edit: Dammit I'm stumped. Empty sockets everything looks fine. Supply V, Vref and 0v all where I'd expect it. Swapped in  some different opamps just for the hell of it. Same result, weird output noise (noisy crackly pots and a fizzy short decay, any thing played through it sort of sputters out sharply like it's being gated) and the same IC voltages.

[iainpunk]

hey

seing that there is a high dc current on the output pin of ic2.1 makes me believe there is a problem with DC continuity of that part, could you recheck the 150k resistor and the 4,7uF cap for resistance and continuity. and maybe do a resistance reading from pin 13 to ground without the IC in the circuit.

from one Iain to another Iain, i hope you succeed in this troubleshoot

cheers
iain

[slashandburn]

Good man! You even spell your name correctly. Cheers Iain! I've checked and double checked the 150k already (since it's it's two 300k in parallel) and it seems okay but I'll check over your other suggestions.

As an aside and probably unrelated, the only other place I'm finding DC where I wouldn't expect it (though for all I know it might belong there and in other places where it should be its missing) is across the Mids pot. I'm getting Vref across the lugs there which seems wrong to me.   

The only other change I've made since last update  is swap those 10n caps around this Mids pot (for which I'd thought I'd used 12n) for 8.2n since the 12n caps I reached for were actually marked n12 rather than 12n. Made no real difference though. Same voltages. Same weird sputtering gated thing going on.

[iainpunk]

As an aside and probably unrelated, the only other place I'm finding DC where I wouldn't expect it (though for all I know it might belong there and in other places where it should be its missing) is across the Mids pot. I'm getting Vref across the lugs there which seems wrong to me.   

no, that DC is supposed to be there. a bridged T filter (my favourite filter) has no dc current path to ground, making it excellent for pedals where you don't want to lose the bias in between stages or in the feedback loop of a non inverting op amp.

[slashandburn]

Good info. I've just done some light reading and realised I'd wrongly conflated baxandll and twin T tone circuits (not that I've even got a great understanding of either).

Back to the issue at hand, pin 13 to ground (empty socket) is 0v. The 300k seems good (though only measured in circuit) and I wasn't sure about the 4.7uf cap so I replaced it. Same result. Soon as the IC goes back in the socket, 12v appears on the output (pin 14) of that IC.

I had the audio probe out earlier trying to figure out where the weirdness got introduced but there's so much gain in this circuit all I could hear was "yup, signal!". If I'm still at a loss I'll likely do some more probing tomorrow.

[Slowpoke101]

I suspect that either the 074 is faulty or (and more likely ) it is oscillating supersonically. Swap out the 100pF capacitor and try a different value, say 220pF. See if it changes its behaviour.

[iainpunk]

Back to the issue at hand, pin 13 to ground (empty socket) is 0v.

i actually meant the resistance reading, not the voltage.

[anotherjim]

If I got this right, your pin14 corresponds to pin1 of IC1.1 in the Sanguine scheme.

The 82k feedback resistor between pins 13,14. Is it good and connected at both ends? The 47k between pins 9-13 also good?
Either...
No negative feedback and the op-amp has latched up.
Opamp -input source floating or connected negative of Vref.
Chip fried.
The -input of an op-amp is like the pivot of a seesaw (which stays put) and if one end of the seesaw is up, the other must be down.

[slashandburn]

I suspect that either the 074 is faulty

I've tried a few so can hopefully safely rule that out.

(and more likely ) it is oscillating supersonically. Swap out the 100pF capacitor and try a different value, say 220pF. See if it changes its behaviour.

Cool ill give that a go and report back

i actually meant the resistance reading, not the voltage.

Doh! Okay I'll check that out too.

If I got this right, your pin14 corresponds to pin1 of IC1.1 in the Sanguine scheme.

IC is the other way round, the values you mentioned are around pin 6 and 7. I double check those components all the same.

Cheers again!

[iainpunk]

If I got this right, your pin14 corresponds to pin1 of IC1.1 in the Sanguine scheme.

no it corresponds with IC2.1 pin 1

[dschwartz]

About the schematic..I think R27 is wrong
That's a twin-t boost, i suppose is to bring back the low end, but R27 being 1M defeats the purpose..i think it should be 1k or 10k at most.

[iainpunk]

About the schematic..I think R27 is wrong
That's a twin-t boost, i suppose is to bring back the low end, but R27 being 1M defeats the purpose..i think it should be 1k or 10k at most.

if there was a 1K resistor there instead of the 1M there would be around 30dB of boost at 487Hz, so its midrage.
with the 1M there, it's basically a booster with a 2dB gain at 487Hz

Iain, do you have an audio Probe? if not, i suggest you build one, if yes, on which pins of the ic's is the audio present and which pins not?

also, i suggest yo put in an actual 072 instead of the 5532 to try out of that helps

cheers,
Iain

[slashandburn]

Would you believe it, sorted.

So I checked for resistance between empty socket pin 13 and ground. Nada. Nothing. FWIW pin 12 to ground is reading about 3M which seems a bit high but what do I know.

I then took on slowpoke's (another Ian!) suggestion and swapped the 100pF for a 220pF and also replaced the 300k resistor while I was at it.  This seemed to fix the weird voltage problem on pin 14 and brought it down to Vref. The output was still weird though. Not even sure how to explain it, it just sounded wrong.

Last ditch attempt I swapped out the 5532 for a 4558 (couldn't find a 072, my desk is a total mess after this) and swapped in yet another quad while for sh*TS and giggles. As if by magic just came to life!

Massive thanks Iain. (and other Ian, and Another Jim) for taking the time out to look at this for me. I'm now off to get this boxed up, I'll post it up on the etched enclosures thread shortly.

Cheers again folks!

[iainpunk]

ill always try and help out another Iain. i'm so glad it works

cheers,
Iain

[dschwartz]

About the schematic..I think R27 is wrong
That's a twin-t boost, i suppose is to bring back the low end, but R27 being 1M defeats the purpose..i think it should be 1k or 10k at most.

if there was a 1K resistor there instead of the 1M there would be around 30dB of boost at 487Hz, so its midrage.
with the 1M there, it's basically a booster with a 2dB gain at 487Hz

Iain, do you have an audio Probe? if not, i suggest you build one, if yes, on which pins of the ic's is the audio present and which pins not?

also, i suggest yo put in an actual 072 instead of the 5532 to try out of that helps

cheers,
Iain

2db of mid boost. Still sounds weird to me..why bother having 2dB  of mid boost? I'm pretty sure there should be a 100hz 6 to 12dB bass boost for tight low end..
If not..i would modify it to do that...

[iainpunk]

hey Iain, is there any chance you could try out something for us? in the name of science?
we have a strong hunch that the encircled 1M should be 1K instead, this would give you more midrange punch and cut through the mix, i suggest holding a 1k in place parallel to the 1M (maybe using scotch tape) and comparing the result

About the schematic..I think R27 is wrong
That's a twin-t boost, i suppose is to bring back the low end, but R27 being 1M defeats the purpose..i think it should be 1k or 10k at most.

if there was a 1K resistor there instead of the 1M there would be around 30dB of boost at 487Hz, so its midrage.
with the 1M there, it's basically a booster with a 2dB gain at 487Hz

Iain, do you have an audio Probe? if not, i suggest you build one, if yes, on which pins of the ic's is the audio present and which pins not?

also, i suggest yo put in an actual 072 instead of the 5532 to try out of that helps

cheers,
Iain

2db of mid boost. Still sounds weird to me..why bother having 2dB  of mid boost? I'm pretty sure there should be a 100hz 6 to 12dB bass boost for tight low end..
If not..i would modify it to do that...

that's achieved easily by the baxandall tone stack.

[slashandburn]

hey Iain, is there any chance you could try out something for us? in the name of science?
we have a strong hunch that the encircled 1M should be 1K instead, this would give you more midrange punch and cut through the mix, i suggest holding a 1k in place parallel to the 1M (maybe using scotch tape) and comparing the result

Of course! Give me a few hours and I'll report back.

Edit: no shit. It's sounds really aenimic with that 1M compared to the 1k you suggested.   My phone doesn't pick it up too well but here's a very quick comparison. As you can tell, no effort was made to dial in a decent tone, and no knobs tweaked at all (the 1k resistor wasn't very secure in there, I couldn't find a way to flip the enclosure and be sure it was still in there properly) so no way to show to difference in overall response from the tone controls. All pots at roughly noon except gain at at about 3 o'clock and level at about 10 o'clock.   1k is first then back to 1M.  It's definitely punchier and sounds better to my own ear with the 1k, there's also a very noticeable (not so much on the video) drop in output when I take the 1k out and go back to 1M.

Excuse the mess, my cack-handed playing and the overall piss-poor audio quality of the video. The difference is more apparent using headphones. If I can find a mic somewhere I'll mic up the cab and try getting a better audio comparison.