# Very, Very Quiet Promethium Distortion/HM-2



## EmptyBuckets (Mar 7, 2022)

Hey guys, not sure what to make of this. I tossed together a Promethium Distortion and it's SUPER quiet. If I crank the volume pot all the way I'm at maybe 20% of line level. Everything appears to be working as expected, it's just too quiet!

Any ideas on possible culprit? Here's a couple gut shots. The ICs aren't socketed but I did them last and went quickly. The two diodes (D4-D5) are socketed Soviet Germanium D9Ks which I had read can be used instead of 1N34As. Could that have an effect on volume, though?


----------



## EGRENIER (Mar 7, 2022)

Only thing that strikes me is that C22 is in the output path and you used a polarized cap.  Have you check that it's installed the right way ?

I think that the positive lead should connect to R33 and the negative lead to R34.  So maybe a quick connectivity check could confirm this.


----------



## BuddytheReow (Mar 7, 2022)

I would make an audio probe and find out where the circuit “dies”. It sounds like a bad solder joint somewhere. I wrote about how to make one in my “troubleshooting 101” thread. Can we see the other side of the board?


----------



## Feral Feline (Mar 8, 2022)

Could be the wrong value resister, ie too big, like I recently had in my breadboard build 390k where a 390 Ohm goes).


----------



## jimilee (Mar 8, 2022)

Have you checked your voltages yet?


----------



## EmptyBuckets (Mar 14, 2022)

BuddytheReow said:


> I would make an audio probe and find out where the circuit “dies”. It sounds like a bad solder joint somewhere. I wrote about how to make one in my “troubleshooting 101” thread. Can we see the other side of the board?



Sorry for the delay - when I posted this I was hoping there was an obvious quick answer! I finally built an audio probe over the weekend and poked around a lot. Seems like it's something with the diodes. When the signal hits the "top" of D4 it's plenty loud and distorted but then the "bottom" of D4 is way more quiet. Things get quieter still at D5. I thought it was maybe a socket problem so I pulled the sockets and tried the diodes just directly on the board, no change in results. Going to swap out for another couple diodes and see if there's any change.


https://imgur.com/tJI2uC5




EGRENIER said:


> Only thing that strikes me is that C22 is in the output path and you used a polarized cap.  Have you check that it's installed the right way ?
> 
> I think that the positive lead should connect to R33 and the negative lead to R34.  So maybe a quick connectivity check could confirm this.


Ah, I definitely hadn't thought about that! I was so used to all the 1uF I needed previously being electrolytic that I didn't even realize the square pad... I've got a few 1uF WIMA caps in the mail so I'll swap that out and see if that has any effect.


Feral Feline said:


> Could be the wrong value resister, ie too big, like I recently had in my breadboard build 390k where a 390 Ohm goes).


Double checked and looks like all good there


jimilee said:


> Have you checked your voltages yet?


I have not yet, this is my next move after I try some diode swapping. What would be the important voltages to get here, the ICs?


----------



## Mcknib (Mar 14, 2022)

The double white stripe is the anode + side

I don't know a 100% If having the diodes in the wrong way around would affect it, I'm thinking as long as they're opposite  maybe not! Easy enough to flip them around to see, that part, D4 and 5 is apparently a coring circuit Mark Hammer explains a wee bit here






						back to back diode on signal path on BOSS HM-2 and AmpTweaker Tight Metal
					

back to back diode on signal path on BOSS HM-2 and AmpTweaker Tight Metal



					www.diystompboxes.com


----------



## EmptyBuckets (Mar 14, 2022)

Mcknib said:


> The double white stripe is the anode + side
> 
> I don't know a 100% If having the diodes in the wrong way around would affect it, I'm thinking as long as they're opposite  maybe not! Easy enough to flip them around to see, that part, D4 and 5 is apparently a coring circuit Mark Hammer explains a wee bit here
> 
> ...



Yeah, I double-checked +/- and even tried swapping, no difference. Seems like as long as they're opposite it works, it's just the volume was still low.

I swapped in a new pair of diodes and the result is identical. I probed around some more and one thing I noticed is that IC1 pins 6 & 7 have loud distorted audio but IC2 and IC3 are silent on those pins. I'm not sure if this is relevant (I haven't yet learned my way around schematics) but it seemed worth noting. Could this be a sign that those two ICs are fried? Like I mentioned before I didn't socket them but I was quick and did them last but...


----------



## Mcknib (Mar 14, 2022)

If you loose signal at D4, 5 everything after it would be the same

The top joint of R20 looks like it needs a reflow

Probing, as you know, leads you to the problem area rather than what's faulty

Rather than change components the first thing I do if I find a problem probing is inspect and reflow solder joints even if they look good

From what you've said I'm assuming signal is good at both sides of C10 and R19 and you get lower volume at D4 anode and nothing both sides of R20?


----------



## EmptyBuckets (Mar 15, 2022)

Mcknib said:


> If you loose signal at D4, 5 everything after it would be the same
> 
> The top joint of R20 looks like it needs a reflow
> 
> ...



Yep, all of this except the bottom of R20 does have a faint signal. Going to try reflowing and see where that gets me.

Edit: I reflowed that whole row with R20 and still no change. I noticed that also the top of C20 is quiet and the bottom is loud. 

Here's a picture of the bottom of the board:


----------



## BuddytheReow (Mar 15, 2022)

I would give that board a good scrubbing with some 90% IPA. Just be careful not to get any inside the pots.


----------



## EmptyBuckets (Mar 15, 2022)

BuddytheReow said:


> I would give that board a good scrubbing with some 90% IPA. Just be careful not to get any inside the pots.



As soon as I posted it I thought "I really need to start wiping down my boards!" hah


----------



## fig (Mar 15, 2022)

jspencer said:


> I definitely hadn't thought about that! I was so used to all the 1uF I needed previously being electrolytic that I didn't even realize the square pad... I've got a few 1uF WIMA caps in the mail so I'll swap that out and see if that has any effect.



C10, C11,C22,C12 should also have polarity confirmed.


----------



## EmptyBuckets (Mar 15, 2022)

fig said:


> C10, C11,C22,C12 should also have polarity confirmed.



What's the best way to go about determining that? I'm trying to find info on this but obviously it's not an ideal swap and most discussions seem to be about using film in place of electrolytic, not vice-versa. 

Would it be the case that the component that follows the cap (left to right) on the schematic is where the positive lead should be "pointing" (i.e. C10 should have the positive leg going toward R19, C11 toward C12, C12 toward R24, and C22 toward R34)?


----------



## BuddytheReow (Mar 15, 2022)

You'll need to look at the board itself or the build doc. The positive end of the cap is clearly marked with a "+" on the board. The positive lead is longer on the cap itself. The negative lead is shorter and marked with a "-" and has a grey stripe on it.

Edit: It looks like your good for the "stock" electrolytics in terms of orientation.


----------



## fig (Mar 15, 2022)

jspencer said:


> What's the best way to go about determining that? I'm trying to find info on this but obviously it's not an ideal swap and most discussions seem to be about using film in place of electrolytic, not vice-versa.
> 
> Would it be the case that the component that follows the cap (left to right) on the schematic is where the positive lead should be "pointing" (i.e. C10 should have the positive leg going toward R19, C11 toward C12, C12 toward R24, and C22 toward R34)?


Someone would need to confirm this, but I would think they are oriented in the direction of electron flow.

As @EGRENIER pointed out, the electron flow is FROM Q4. OUT and pin 1 of R34 is more negative than pin 2 of R33 so the orientation for C22 would seem to be pin 2 negative (which may even be a standard designation?).





Edit: Or just ask someone smarter than me. You can't hardly take a step without bumping into someone with those credentials.


----------



## EmptyBuckets (Mar 15, 2022)

fig said:


> Someone would need to confirm this, but I would think they are oriented in the direction of electron flow.
> 
> As @EGRENIER pointed out, the electron flow is FROM Q4. OUT and pin 1 of R34 is more negative than pin 2 of R33 so the orientation for C22 would seem to be pin 2 negative (which may even be a standard designation?).
> 
> ...


Welp, you lost me there. I think I need to just replace these with some film caps until I better understand schematics! 😵‍💫


----------



## EmptyBuckets (Apr 4, 2022)

Alright y'all, I'm back. I waited a while for some 1uF film caps to arrive (the slow Tayda shipping option has gotten _really _slow) and I swapped them all in for the electrolytic caps I had mistakenly used. Unfortunately, the problem remains the same as before.



jimilee said:


> Have you checked your voltages yet?




*Pin 1**Pin 2**Pin 3**Pin 4**Pin 5**Pin 6**Pin 7**Pin 8**IC1*4.24.24.20.03.33.33.38.6*IC2*4.24.24.10.04.14.24.28.6*IC3*4.24.24.10.04.14.24.28.6


*Anode**Cathode**D1*3.33.4*D2*3.33.2*D3*3.33.3*D4 (Russian GE)*0.6*D5 (Russian GE)*-0-0*D6*00*D7*00*D8*8.88.6


*D**S**G**Q1 (on daughterboard)*8.65.13.8

It's gotta be those Russian Germanium's right? I don't know much about reading these voltages but given the results of the audio probe and the significant difference in readings from those two compared to the other diodes, it makes me (guess) it's those?


----------



## benny_profane (Apr 4, 2022)

D4/D5 should be at 0V potential—they are isolated from DC voltage via C10 and C12. Is the D4 cathode reading correct? It should be the same as D5 anode since they're connected. Try either jumping D4/D5 or replacing them with Schottky diodes (e.g., BAT46) to rule this area out as the problem.


----------



## EmptyBuckets (Apr 8, 2022)

I don't have any Schottkys on hand but I swapped out the Russian GEs for some proper new 1N34As and the problem is exactly the same as before.


----------



## EmptyBuckets (Mar 7, 2022)

Hey guys, not sure what to make of this. I tossed together a Promethium Distortion and it's SUPER quiet. If I crank the volume pot all the way I'm at maybe 20% of line level. Everything appears to be working as expected, it's just too quiet!

Any ideas on possible culprit? Here's a couple gut shots. The ICs aren't socketed but I did them last and went quickly. The two diodes (D4-D5) are socketed Soviet Germanium D9Ks which I had read can be used instead of 1N34As. Could that have an effect on volume, though?


----------



## zgrav (Apr 8, 2022)

I suspect the issue has more to do with a bad solder connection somewhere than a bad part.


----------



## EmptyBuckets (Apr 9, 2022)

zgrav said:


> I suspect the issue has more to do with a bad solder connection somewhere than a bad part.



But if it's just a soldering issue wouldn't that mean it has to be D4 since that's where things die when testing with the audio probe? If that's the case I'm not sure that my soldering would be the problem - I've now soldered the diodes 4 times now (first sockets, then straight to the board, then swapped in the opposite direction, and finally now with the new 1N34As, not to mention reflowing things a few times at various points throughout. 

I'm a bit stumped as to what my next move should be outside of just re-soldering everything. I did give it a good scrub with some iso so I'll try to get a new photo up of my soldering work to see if anything sticks out to someone but I think it's looking pretty decent!


----------



## zgrav (Apr 9, 2022)

do you get sound on both sides of D4?    How about D5?   So you hear any difference in each of the diodes with the audio probe?

If you check the schematic, the only things that D4 should connect to are D5, R19, and R20.  Confirm those connections with your meter and then make sure that D4 is not accidentally contacting C7 or any other nearby part of the PCB. Also check to see if either side of D4 has connection to ground.   You can also temporarily jump each side of D4 together to see if it is really the diode that is blocking the sound.  Does any of that make a difference in what you hear through the pedal?


----------



## EmptyBuckets (Apr 10, 2022)

zgrav said:


> do you get sound on both sides of D4?    How about D5?   So you hear any difference in each of the diodes with the audio probe?
> 
> If you check the schematic, the only things that D4 should connect to are D5, R19, and R20.  Confirm those connections with your meter and then make sure that D4 is not accidentally contacting C7 or any other nearby part of the PCB. Also check to see if either side of D4 has connection to ground.   You can also temporarily jump each side of D4 together to see if it is really the diode that is blocking the sound.  Does any of that make a difference in what you hear through the pedal?



Nice loud, nicely distorted audio on top/K of D4 but the bottom/A has barely perceptible audio when at all the way at max volume. D5 is even more quiet / essentially silent. Same results as when I first probed back when I was still using the Soviet diodes. I reflowed _everything_ adding a little more solder here and there. A few of these look a bit flat because a I had snipped a few leads too short after I first soldered them in.

Checked continuity and D4 is indeed only connected to D5, R19, and R20. No connection anywhere else around. Not shorting to ground either.

How exactly would I go about jumping D4 together? That's not something I've done before.

Here's some newer photos, post-iso scrub but re-dirtied a little by the reflowing. (the diodes are left long & tall because ideally once I get things figured out here I'll pull them and put back in the Soviet diodes)


----------



## zgrav (Apr 11, 2022)

by "jumping D4" you would temporarily touch a wire to each side of it  so the signal bypasses the diode. then see if you hear a difference.  either the diodes block the sound or there is something on the other side of the diode that is draining the signal (short) or blocking it (bad connection). Look at the schematic in the build document and note the each side of D4 and D5 should connect to each other -- use you meter and confirm that is OK.  Then use your meter to make sure one side of D4 and D5 connect to R19 and the other sides connect to R20.  Also double check to make sure you have the right values for R19 and R20 (10K each).


----------



## EGRENIER (Apr 11, 2022)

EmptyBuckets said:


> Nice loud, nicely distorted audio on top/K of D4 but the bottom/A has barely perceptible audio when at all the way at max volume. D5 is even more quiet / essentially silent. Same results as when I first probed back when I was still using the Soviet diodes. I reflowed _everything_ adding a little more solder here and there. A few of these look a bit flat because a I had snipped a few leads too short after I first soldered them in.
> 
> Checked continuity and D4 is indeed only connected to D5, R19, and R20. No connection anywhere else around. Not shorting to ground either.
> 
> ...


From this last picture it looks like you have a 1u at C11 instead of a 1n.... So that can't help...

I just went through a long troubleshooting session with a Frost Bite and after 2 weeks of searching for issues, turns out I had a 33n instead of a 33p in my drive stage.  Looks like that can suck a lot of signal out 

I would also double check your C19 and C20 as you had mentioned volume lost in that part of the circuit also...


----------



## Coda (Apr 11, 2022)

A quiet probe around D4 and 5 doesn’t surprise me…there is still a lot of opamp to go through in the circuit. C12 also definitely appears to be wrong. You have an electrolytic in that spot. According to Coda’s Rough Guide to Capacitors, nF = box, uF = electrolytic. That cap is pulling way more out of the signal than it should be…


----------



## EmptyBuckets (Apr 12, 2022)

EGRENIER said:


> From this last picture it looks like you have a 1u at C11 instead of a 1n.... So that can't help...
> 
> I just went through a long troubleshooting session with a Frost Bite and after 2 weeks of searching for issues, turns out I had a 33n instead of a 33p in my drive stage.  Looks like that can suck a lot of signal out
> 
> I would also double check your C19 and C20 as you had mentioned volume lost in that part of the circuit also...



 Oh wow, can't believe I missed that! When I went and swapped all 1u electrolytics for 1u film caps I just went on ahead and swapped that for a 1u, too. Going to swap that as soon as I have time to get to the bench again. Thanks for spotting! I would love for this to solve the problem hah!



Coda said:


> A quiet probe around D4 and 5 doesn’t surprise me…there is still a lot of opamp to go through in the circuit. C12 also definitely appears to be wrong. You have an electrolytic in that spot. According to Coda’s Rough Guide to Capacitors, nF = box, uF = electrolytic. That cap is pulling way more out of the signal than it should be…



Thank you but I think you must be looking at a photo on page 1 of the thread. I had originally populated with 1u electrolytics but I've since swapped C12 and the others for proper 1u film caps.


----------



## EmptyBuckets (Apr 12, 2022)

EGRENIER said:


> From this last picture it looks like you have a 1u at C11 instead of a 1n.... So that can't help...
> 
> I just went through a long troubleshooting session with a Frost Bite and after 2 weeks of searching for issues, turns out I had a 33n instead of a 33p in my drive stage.  Looks like that can suck a lot of signal out
> 
> I would also double check your C19 and C20 as you had mentioned volume lost in that part of the circuit also...



Just swapped the 1n in and no noticeable change... Argh!!

Going to try @zgrav 's jump suggestion, hopefully this evening, and will report back


----------



## EGRENIER (Apr 12, 2022)

EmptyBuckets said:


> Just swapped the 1n in and no noticeable change... Argh!!
> 
> Going to try @zgrav 's jump suggestion, hopefully this evening, and will report back


Did you double check on C19 and C20 ?


----------



## Chuck D. Bones (Apr 13, 2022)

All of your voltages look good except D4 cathode.  You can re-check that one because it should be exactly the same as D5 anode.  What model DMM are you using?

Audio Probe IC2 pin 1 & IC1 pin 1.  Set all knobs to 11 when probing.

Until you have a better idea where the problem is, swapping parts is a bad idea.


----------



## EmptyBuckets (Apr 16, 2022)

EGRENIER said:


> Did you double check on C19 and C20 ?



Double checked C19 and C20 and R19 and R20 but they're all as they should be.



Chuck D. Bones said:


> All of your voltages look good except D4 cathode.  You can re-check that one because it should be exactly the same as D5 anode.  What model DMM are you using?
> 
> Audio Probe IC2 pin 1 & IC1 pin 1.  Set all knobs to 11 when probing.
> 
> Until you have a better idea where the problem is, swapping parts is a bad idea.



Re-checked D4 & D5 and I'm still getting the same results as before: .3-.6 on D4 cathode, zeros across the other three. I'm using an AstroAI AM33D multimeter.

Pin 1 on IC1 & IC2 were both totally silent when probed.



zgrav said:


> by "jumping D4" you would temporarily touch a wire to each side of it  so the signal bypasses the diode. then see if you hear a difference.  either the diodes block the sound or there is something on the other side of the diode that is draining the signal (short) or blocking it (bad connection). Look at the schematic in the build document and note the each side of D4 and D5 should connect to each other -- use you meter and confirm that is OK.  Then use your meter to make sure one side of D4 and D5 connect to R19 and the other sides connect to R20.  Also double check to make sure you have the right values for R19 and R20 (10K each).



Jumping gave me very similar results to when I probe the anode of D4, distorted but very, very quiet.


----------



## zgrav (Apr 16, 2022)

EmptyBuckets said:


> Double checked C19 and C20 and R19 and R20 but they're all as they should be.
> 
> 
> 
> ...


so something is draining most of your audio signal past that point.  an extra short to another part, a bad connection, or wrong part value.  what is your measured resistance to ground on each side of the diode where the sound level drops?


----------



## Chuck D. Bones (Apr 16, 2022)

EmptyBuckets said:


> Re-checked D4 & D5 and I'm still getting the same results as before: .3-.6 on D4 cathode, zeros across the other three. I'm using an AstroAI AM33D multimeter.


What do you mean "across?"  Make measurements from each circuit point to gnd unless otherwise specified.



EmptyBuckets said:


> Pin 1 on IC1 & IC2 were both totally silent when probed.


Since you hear signal at IC2-7 and nothing at IC2-1, the problem is between those two points.  My guess is that in all of this parts swapping, you broke a pad or trace.


----------

