SOLVED Rat (Muroidea) breadboard has low output volume

[nasawhy]

Hi, first time posting, I'll do my best to start with some good info, please let me know what I can do better to make it easier for others to help troubleshoot!

I'm breadboarding the Rat (Muroidea) schematic that is shown in this post:
https://forum.pedalpcb.com/threads/muroidea-proco-rat.12237

The schematic I'm using is attached. A photo of my breadboard also attached. The large yellow capacitor near the top left is just for my audio probe. Normally I bypass that when testing with the volume knob, but in this photo I forgot to remove it. That makes no discernible difference in volume whether it's included or not. Let me know if we need more photos or voltage readouts!

Note that I've got a separate little perf circuit I made that provides VREF and that vref is coming into my board on the right at G1. I actually used a different power circuit there from a Wampler lesson. I've tried it with the voltage separator in the schematic, and it made no difference in volume level. It actually produced a weaker VREF around 4.2v (maybe just variance in the parts I used) so I went back to my external VREF module for convenience.

The issue is that it while it sounds right as far as I know, the volume is very low when the Vol knob is maxxed out. It's at about unity when cranked.

I built a vero board rat (I assume a similar/same circuit) and it's in an enclosure. The one in the enclosure is at Unity when the knob is at about 7:30. Turning up that vero build vol knob will get the signal really loud above unity.

I used an audio probe and noticed that on the diode side of R6 my signal is pretty quiet (same volume as when going through the vol pot when dimed) so I'm not sure if the diodes are dropping voltage too much or if there's another problem elsewhere. I've tried swapping diodes for other 1N4148s and the transistor. Currently I have a 2N5457 in there (so does the vero build) and I put a J201 in there and it's the same volume level. The opamp is a OP07.

Some voltage readings on my breadboard:
V+ 9.73v
VREF: 4.84v
IC 1: 9.68v
IC 2: 4.86v
IC 3: 4.37v
IC 4: -.2mv
IC 5: 1.7mv
IC 6: 4.83mv
IC 7: 9.75v
IC 8: 9.68v
R6: 4.82v (between R6 and C7)
FILTER pin1: .682v
Q1 D: 9.74v
Q1 S: 1.225v
Q1 G: 3.7mv

Components I've tried replacing in case they are damaged/defective:
D1
D2
C7
C10
Q1

From what I can gather on other posts, my source voltage should be about right as long as it's above 1v, so I'm just not sure what's up.

 

[nasawhy]

Another photo from a slightly different angle. I've rechecked my component values and layout like three times now, but I'm new at this so I could still very well be doing a few things wrong yet!

Oh I don't have a 1.5k (R7) resistor or a 560 (R3) so that's what the two jumbles of resistors are about. I've checked the resistance across those in series and they are correct.

 

[Nostradoomus]

You want your source voltage on the fet the be at least 3V, try some other ones...if you socketed the one in your vero build give that a try.

 

[Locrian99]

use your audio probe and see where you get the volume drop. Is the volume good at pin 6 of the ic? If yes then move to the next area.

 

[nasawhy]

I just checked resistance between the IN and OUT wires and when the switch engaged and not engaged, both readings were about ~1.7M

 

[nasawhy]

Sorry I wasn't clear in my original post, the Diode side of R6 is where the volume drop is. The only other 2N5457 I have is soldered into the vero build.

I have this substitution device from Coppersound, and when I tried J201 (or any other J) there the volume didn't change, but I can try later tonight and check voltages on source. I'm going to be away from my computer for a few hours, but will report back. Thank you!

 

[Nostradoomus]

Just for a quick check, you can skip Q1/C9/R10 altogether and tie vol 3 to the junction of C9/R8. It doesnt need a buffer if the next thing after it is your amp so it won't hurt anything. See if you have good volume, then we know it's probably the fet.

 

[nasawhy]

Just for a quick check, you can skip Q1/C9/R10 altogether and tie vol 3 to the junction of C9/R8.

I just put a jumper from VOL 3 to C9/R8 and it's actually a little quieter? I didn't unhook anything else.

 

[Nostradoomus]

ya gotta disconnect the buffer section

 

[nasawhy]

I disconnected the output buffer from the Q1 gate to VOL 3 and jumpered from C9/R8 to VOL 3 and no additional volume.

With my audio probe, anywhere between IC 6 and C7/R6 is noticably loud, like probably too loud.

 

[nasawhy]

Just checked voltage in the vero/enclosure build at the transistor S pin and got 1.195v and that pedal can get a really loud output.

 

[nasawhy]

Do I need to bias this JFET? Or does VREF or some other part of this circuit do that already? If I do need to bias it and adjust a resistor, maybe I just got lucky with the vero build.

 

[Nostradoomus]

I missed it earlier but are you really only getting readings in the millivolts on pin 6? it should be around 4.5v

 

[nasawhy]

I swapped for a new OP07 and got a reading in volts (can't remember, 3 or so volts maybe). Then switched it on (or turned off bypass), played guitar and now pin 6 is in mV again. Something in my circuit might be frying ICs? I've only got two more OP07s so I'm afriad to try anymore right now.

 

[nasawhy]

Edit: nevermind, I used a different lead for ground on the multimeter, and I get 4.84v on pin 6. I'm going to get new readings and make sure previous readings weren't inaccurate due to using a bad ground point or something.

 

[BuddytheReow]

If you've got significantly lower volume on a breadboard, there's a good chance a component is not making a solid connection with the breadboard tracks. You'll have to poke and prod with your finger on each component to find the "bad" one. This happens more often than you think. Unless of course you paid for a higher end breadboard...

 

[nasawhy]

Hmm... updated voltages:

IC 6: 4.83v (yeah I think I just put mv accidentally at first)

Q1 D: 9.74v
Q1 S: 5.6v (weird this is so high now)
Q1 G: 3.3mv

 

[Nostradoomus]

source voltage between 3 and 6 is fine

 

[nasawhy]

Is 1.4M resistance between in/out ok?

Other than that, I feel like there must be a mistake in my circuit that's draining voltage or maybe a bad component, but if voltage looks ok at Q1 that doesn't leave much, right?

 

[Nostradoomus]

I'd go over all your connections with a fine tooth comb, breadboarding leaves a lot of room for error if you aren't careful