ProCo Rat veroboard squeal. Is it the layout?

[Elijah-Baley]

Hi guys.
After I built two Rat on veroboard using the Sabrotone layout, the one with three clipping options, I wanted to build the original stock version.

This is the famous schematic:


I used this layout http://tagboardeffects.blogspot.com/2013/12/proco-rat-2.html, just because the board was smaller than the ProCo Rat layout, but I followed the values of the original. So I replaced the 33pF cap with a 30pF, the two 2.2M resistor with two 1M, I swapped the 2.2uF and the 4.7uF (because it was inverted), I added a missing 1nF between pin 3 and 4, I replaced the 10uF output cap with a 1uF and left out the 10k resistor from the output and the ground. I used a LM308 and a 2N5458.
The only thing I didn't change, maybe I could, is the 100R in the 9V. It should be 47R, but I guess it should be ok.
I tried with a power supply and the battery. I tried even a 2N5457. And I tried without the addeed 1nF.

I never had a problem with the Sabrotone modded version, but with this circuit, still out of the box, I got a common problem. It sounds, but squeals at high settings of the distortion. Especially with humbucker at bridge position. Turn the Distortion pot or the guitar volume the pitch of the squeal change, a bit like the Fuzz Factory.

Is the problem the layout?

[rankot]

I had a similar problem with one of my Rat builds and never found a cause. I'd be grateful to anyone who can explain how to troubleshoot this kind of a problem. 

[pokus]

You could try adding another cap at pin 3 to 4, or replace C4 by a larger value one. 3n3 did the job for me.

[antonis]

Try to enlarge C5 (100pF) value..
Start with 10 times bigger (1nF) and size it accordingly to your gain/squeal taste..

[Elijah-Baley]

I'll try to swap increase C4 and/or C5. Unfortunately I have just some ceramic cap like 560pF or 820pf at max. None 1nF. And I wanted to finish it soon.
I perfectly built this twice: https://www.sabrotone.com/?attachment_id=2127
But this is very disappointing. I wanted to build the original schematic.

Rankot, what board/layout and schematic you followed?

[rankot]

I've built two Rats: both on my PCB layouts. Schematics is the standard one, actually I added Lube pot and Mud switch (not shown on good working PCB, but actually present in the pedal, cause those are actually only one pot and one switch in series with R6 and R7).



On "screaming" one I wanted to try to implement optofet switching (the first one had some popping), but maybe that was the problem - in and out traces are very close??? Turbo switch is just for LED/1N4148 clipping choice.

[Elijah-Baley]

Ok, thanks.
The left one was the faulty Rat and the right on was the good Rat? Did you use a "normal package" LM308 IC?

With the both Sabrotone I built I added the Lube Pot, too. That was ok with and without it. The first time the LM308 was from Musikding, the second one (and this time) from an italian shop I trust.
I really didn't want to use the bigger layout from Sabrotone, and to desolder all the parts (no extra parts in my stock).

[rankot]

The left one is faulty.

I used LM308 for it (bought from Aliexpress), but also tried different single opamps (TL071, OP07, UA776, CA3130) bought from reliable sources and the circuit behaved the same.

[Elijah-Baley]

Could someone say that the Rat is really sensible to the layout?
I really can't find any clue why sometime the Rat has the squeal.

(The Sabrotone layout I used and worked twice has something bizarre, but probably not much important. It has the 47R in line with the 9v, but just on the IC track, the 9v goes straightly in the Drain of the jfet. I guess should be really easy move the 47R a bit near the edge of the board just after the 9v wire.)

[Elijah-Baley]

I desoldered the componets from the fautly veroboard (i have just those available) and I built the Sabrotone layout, but I omitted the extra clipping parts. It sounds perfectly! Actually, I used new resistors and two new 1N914s, I didn't want desolder them now because I had new ones, but I am pretty quite with that parts, I don't think it was bad or I make something wrong with them.

I'm really sorry about the simple layout, because I liked the idea to have the smallest layout for the stock version, but unfortunately... it didn't work to me.
I read that we can fix the oscillation issue changing some caps like somebody here have suggested, but it is a bit a bad thing. We could even adding a buffer in front to stop the oscillation. But even this is not the thing I wanted to do in the Rat.

[pinkjimiphoton]

usually in my experience, high pitched squealing on a high gain distortion device means one of the following
bad solder
pots need to have their cases grounded, especially OUT of an enclosure
solder bridge somewhere
bad ground connection

check all your grounds, and reflow any suspect joints with fresh solder.
also make sure ya didn't smoke or bridge any coupling caps in the neighborhood of the offending pot on the vero you made.

i see ya got a new one made, cool, but still... for future ref

[Elijah-Baley]

Thanks for the adivce, pinkjimiphoton! Very useful in case of high gain pedal. I am usually very lucky with this stuff about noise or oscillation. I built Rat, BSIAB II, Triple Wreck (twice) and I have even a Tight Metal (a ton of gain), and each circuit worked fine and pretty noiseless out of the box.
I'll never know if that layout works fine into the box, maybe someone built a working Rat because was directly wired into the box. I use to test the circuit before work to the box and to the offboard wiring.

The veroboard here was quite small, and I can't see any mistake like bridges, or missing wires, etc... I can say that there's a lot of comment in Tagboard Guitar FX ProCo Rat 2 page (and even in the ProCo Rat page) where some guys had this issue. Someone was lucky, or maybe the guitar was less prone to the oscillation. There's really something wrong with that board?
I played some secs wiht my Stratocaster and I got the oscillation just with bridge pickup, in my case an humbucker. I wonder what would have happened if there was just single coil pickups. (My second guitar has two humbucker.)

When the wires of the pot, in veroboard layout, are near I use to twisted. My faulty Rat had it, the Sabrotone layout not, it was impossibile. I question myself about anything now, but it could be counterproductive in this case to twist the two gain pot wires?

[bluebunny]

Also consider using screened cable for your inputs and outputs (grounded at one end only), and keep your input wires away from your output wires.

[Elijah-Baley]

Thanks, bluebunny. I have a piece of thin shielded cable, I needed that for a patch bay where the box was ungrounded. But I never used shielded cable because as I told I never had noise problem.

Just a bit of ticking noise in a Zombie Chorus, once, only with very high settings. But then I read that the Tagboard Guitar FX sometime has that issue though the anti-ticking mod. Next time I'll build the Sabrotone layout, that should be perfect.

In case I'll use the shieleded cable.

[antonis]

high pitched squealing on a high gain distortion device means one of the following
bad solder
pots need to have their cases grounded, especially OUT of an enclosure
solder bridge somewhere
bad ground connection

Small (or open) cap inside NFB loop.. 


Sorry Jim, but I can't get the reason for many people omiting that "obvious" issue.. 

[pinkjimiphoton]

antonis, you know wayyyyy more than me, great call, bud!!!!

also check resistors for voltages. in the past i've run into many resistors that look fine, appear to be soldered well, but are OPEN inside!!
sometimes i guess due to manufacturing mistakes, the inside of the resistor will actually break off from the lead poking out of it. i call it "internally decapitated".
it seems to happen when the space is kinda tight and the resistor leads are drawn thru their holes too tightly.

ya wanna unsolder one side, and hit it with the meter.

but i gotta feeling antonis may have nailed your issue!

lol i remember the first "sagitarian charger" i built wayyyyyy back when baja first released the project.

could NOT get it to work. finally figured out one of the diodes was backwards... as it was in the project. flipped it around, and all fixed.

i learned about grounding pot cases when i built gus smalleys' ousb

that thing squealed like a pig until it was cased.

[Elijah-Baley]

The only thing I didn't tried with my faulty veroboard was to put the circuit into the box.
I always measure the resistors before to solder them on the board and when all the resistors are on the board. It's a bit excessive, but I can be sure at 99% that the resistors are ok. Except in case or mistake or measurement, or reading, etc... I remember I missed, resoundingly, just two resistors value in one of my first circuit. I confused two 100R with two 100k. Sometime, maybe, I wrongly swapped two resistors, but then I noticed during the building.
My multimeter can't measure the caps, but I can verify the continuity between the stripe and the lead before cut it. The same with the diodes, when  I can't verify the forward voltage. I verify the continuity of the socket pin and the socket IC with some spot in the board. even of the wires. I measure the resistance of the pots between some spot on the board.

In case of doubt about orientation or other thing about the schematic I compare the layout with one or more version of schematic. Sooner or later the mistake have to come out.

Currently, I have two boards (veroboard) that doesn't work fine. I suspect one of them of some mistake, though it's verified.

Anyway. I still have the old veroboard with all the resistors, the socket IC and the diodes soldered. I could save it for another attempt.

[italianguy63]

The only thing I didn't tried with my faulty veroboard was to put the circuit into the box.
I always measure the resistors before to solder them on the board and when all the resistors are on the board. It's a bit excessive, but I can be sure at 99% that the resistors are ok. Except in case or mistake or measurement, or reading, etc... I remember I missed, resoundingly, just two resistors value in one of my first circuit. I confused two 100R with two 100k. Sometime, maybe, I wrongly swapped two resistors, but then I noticed during the building.
My multimeter can't measure the caps, but I can verify the continuity between the stripe and the lead before cut it. The same with the diodes, when  I can't verify the forward voltage. I verify the continuity of the socket pin and the socket IC with some spot in the board. even of the wires. I measure the resistance of the pots between some spot on the board.

In case of doubt about orientation or other thing about the schematic I compare the layout with one or more version of schematic. Sooner or later the mistake have to come out.

Currently, I have two boards (veroboard) that doesn't work fine. I suspect one of them of some mistake, though it's verified.

Anyway. I still have the old veroboard with all the resistors, the socket IC and the diodes soldered. I could save it for another attempt.

That's why I don't do vero!!!

Just bustin' on ya!  Keep after it!

MC

[Elijah-Baley]

I can build board just with stripboard. In rare case with protoboard.

I guess these mistake can occur even with PCB.