Pauper pooper

[Mike McLane]

Building my second Pauper. First one went fine. Just completed the second one and volume, gain, tone and toggle all seem be doing what they're supposed to do RELATIVELY speaking, however, the unit only puts out about half the gain and volume of my real Prince of Tone. The first Pauper basically stood toe-to-toe with the real deal. I double checked the component values and all seem to be correct (I checked them all with a meter before installation). I included a gut shot in case anything look suspicious. Any advice would be helpful.

 

[Chas Grant]

Keep us updated! The hardest issues to find are intermittent and/or when something is just slightly off!

 

[Mike McLane]

Intermittent??. . . slightly off?? Sounds like me !!

I found a pdf on audio probe and they suggested mapping the most direct "line" thru the circuit to the output. The "detours" off of the "line" are somewhat secondary unless problems are encountered with "line" components that are directly linked to them. Generally disregard the paths to ground or Vref. I've mapped it out on the schematic. If you have other thoughts please let me know.

 

[Chas Grant]

Thats the route I would take, some of the signals on IC1.2 can get weird in the secondary loop, thats the feedback loop that gets distortion to op amp. When checking those try to have the pedal at unity and the switch in the clean boost mode at first, this should remove the diodes from the circuit.

 

[HamishR]

It could be that you did actually damage the PCB while removing pots. It's happened to me! Have you checked continuity between the pots legs and where they are supposed to go in the circuit? You can always add a wire from the pot leg to where it's supposed to go if the PCB tracks have been disturbed.

And i'm sure you've already fixed it but pin 1 of the gain pot's soldering looks a bit dodgy.

 

[Mike McLane]

Yep. . . corrected the ugly solder joints on the pots. Attached is my sleuthing with my new found friend, the audio probe. These are subjective notations of volume with 5 being the reference of the incoming signal on the upstream side of C1. Volume & Gain pots were max'd.

First, I didn't realize that there would be that much signal drop across a cap, but C1, C2 & C5 all showed a significant drop. I was using a C4 (middle C on a synth, not explosives although the thought did occur) as a test tone and I would guess a higher pitched test tone would experience more drop out than a lower one because of the filtering effect of the cap. Make sense? Just a curiosity for future reference.

Second, R16 (or something related to it) seems to be the choke point. Does this suggest re-soldering or replacing R16? I may have mis-noted my reading, but I don't know why I would get 5 at T3 on the drive pot, but get a 1- btw R16 & R6. Finally, at one point I think I may have detected a VERY faint signal on the downstream side of C5.

Third. How on God's green earth did a full signal get back into IC7???? Does it come through the IC internally from the other side? Don't get that one AT ALL.

 

[Chas Grant]

You answered the question of where's the problem. With the drive pot maxed (Fully CW) You should have the 5 on pin 3 of drive pot, and R16 (1-) and R6(1-). It would seem that the connection somewhere between Drive pot pin3 and R16/R6 isn't what it should be. Try soldering wire between drive pin 3 and R16/R6 connection. I would take it down the side and connect to R6. Green line below. And put it on the backside so it doesn't show

 

[Mike McLane]

The traces are obscure in the PCB image above, but it appears I want to run the jumper down the left side of R6 & R16. Will do and report back. I wish PPCB would publish clear layouts of the trace routings just for this type of exercise.

 

[Chas Grant]

The traces are obscure in the PCB image above, but it appears I want to run the jumper down the left side of R6 & R16. Will do and report back. I wish PPCB would publish clear layouts of the trace routings just for this type of exercise.

The green line is where to run the wire. You can see the trace from R16 to R6 on the image above

 

[Mike McLane]

Well, I've got good news and bad news. Good news, the jumper did the trick. The thing actually came alive. As I tried to close it back up it went back to its old tricks and I noticed that it flashed in and out as I pushed and pulled on the Drive pot. No grounding issues so I figured the pot was bad (I had suspected that before). It was probably the problem all along. I dropped in a new B100K and this time the solder terminals in the PCB punked out. Now I have a dead Pauper . That said, this has been an absolutely eye opening process for me and well worth the cost of wasted parts. You helped me successfully diagnose and fix a real sneaky problem and I am very grateful. This one ought to go into the PPCB folder of Troubleshooting Case Studies. You can turn your Tenderfoot badge over now that you've completed your good deed.

 

[Mike McLane]

DON'T SAY IT!!!! I'm way ahead of you. I went ahead and jumpered all three terminals of the Drive pot to the appropriate point in the PCB and, voila, . . . .



Only problem now is that its very ice picky shrill. Turning the Tone total CCW gets a slightly dark tone, but I would expect darker. On the CW end it will break glass and permanently mame dogs. Any mod suggetions. . . C7 maybe?

 

[Chas Grant]

Did you check the dip switch the bottom one should affect tone

 

[Chas Grant]

C6 and C7 will affect the tone. The nice thing is you can tack a second capacitor onto existing cap to raise value. It won’t take a big change to lower the freq on the tone, try a second 10n same with treble

 

[Mike McLane]

Will do. Thx for all your help.

 

[Chas Grant]

No problem, I enjoy troubleshooting and I learn a lot from helping out, so its all good!

 

[Mike McLane]

Well, I spoke too soon. You say play with C6 & C7 to alter the tonality. I would think both affect treble roll off like a guitar tone knob. Full CW = no roll off = 100% intrinsic tone of the circuit design. CCW rotation passes increasing amounts of this signal to the cap, the cutoff frequency of which is based on the value of the cap. But the "intrinsic signal" is complete ice pick. I would think we'd look elsewhere in the circuit to tame the inherent nature of the beast. How about C3 &/or C4?

 

[Chas Grant]

Check R4 real quick. It’s hard to tell from pics but it looks like it’s 3.3k, should be 33K. It’s part of a low pass filter and 3.3k will raise the cut frequency, letting higher frequencies into the op amp

 

[Mike McLane]

It's 33K.

 

[Chas Grant]

Darn, 3.3 would explain the ice pick

 

[Chas Grant]

Try C3 and C4, I went trough the circuit and it shouldn’t be shrilled, it should cut more high frequencies than other pedals based on the Guv’nor


You could use the audio probe to try and find where the shrill is introduced in circuit, then check resistors and caps in that are for a bad solder connection. You may have a cap not soldered well, so no filter. Once you find area of shrill, google high pass and low pass filter, then check the filters in that area

 

[Mike McLane]

Will do. Yeah, I was thinking that R4 has to work with C3 to form the low pass. . . correct? If so, C3 would still be a "person of interest" in our investigation. . . right? I'll check values and solder joints again.