I just built a Underminer sub-octave and almost no volume

[kingbarnes]

I built the underminer sub-octave synth. When not active, sound passes through no issue. Activate the pedal, and even with Volume maxed, there's very little sound. I have inspected it and can't see any issues. This is not my first pedal but it is my first failure; worst part is it's a bday gift for my bro. Of course. Only things different about this pedal during the build is I had to use an MPSA13 instead of the called for MPSA14, which wasn't available anywhere that I could find. I also had one 47uF 25V 105C Radial Electrolytic Capacitor instead of the usual 16V version I normally would use. Every other part is exactly to spec. I'm not an electrical engineer, just a hobyist, so I can't do "debugging" and getting all the readings I've seen other post. Basically, any guesses, anybody have this thing happen and find the cause? I mean, i'll blow my amp if i keep the volume cranked up and switch the pedal to bypass! Any help is appreciated but not expected since I can't give more info, save to say that all other parts in this pedal, save for the IC, I have used before with no issues. I am building a second one, which was to be one for me, with hopes that it will work and I can then gift that one. Thanks!

 

[Nic]

For one, a picture would be helpful. My second build was the underminer, I've had one chip acting very inconsistant. How are your knobs dialed? Do switches change anything? Guess you checked your wiring.

 

[music6000]

I built the underminer sub-octave synth. When not active, sound passes through no issue. Activate the pedal, and even with Volume maxed, there's very little sound. I have inspected it and can't see any issues. This is not my first pedal but it is my first failure; worst part is it's a bday gift for my bro. Of course. Only things different about this pedal during the build is I had to use an MPSA13 instead of the called for MPSA14, which wasn't available anywhere that I could find. I also had one 47uF 25V 105C Radial Electrolytic Capacitor instead of the usual 16V version I normally would use. Every other part is exactly to spec. I'm not an electrical engineer, just a hobyist, so I can't do "debugging" and getting all the readings I've seen other post. Basically, any guesses, anybody have this thing happen and find the cause? I mean, i'll blow my amp if i keep the volume cranked up and switch the pedal to bypass! Any help is appreciated but not expected since I can't give more info, save to say that all other parts in this pedal, save for the IC, I have used before with no issues. I am building a second one, which was to be one for me, with hopes that it will work and I can then gift that one. Thanks!

Please supply Pictures of PCB & ALL connections ( Footswitch, Input & Output Jacks, Power Jack ) to it along with a clear explanation of the Issue.

 

[kingbarnes]

I will upload pix tomorrow, as I just saw this request and don't have time right now. Know that this isn't a regular job. All pots and toggles were wired, not put on the pcb, and I have wires and elec tape, like a lot, making it very hard for pix to help. All connections have been triple checked, all pots and toggles work, its just the sound output is VERY low, like 1/20th of what it should be, if that, and a terrible "hiss" and "crackling" kind of sound instead of a clean silence when nothing is being played. My bro wanted a 1590BB case with controls spread out, hence not doing this "standard" way for a 125B enclosure. Thank you for the replies!

 

[Laundryroom David]

if all your solder joints are good and all your switches, pots and non-ic components are good, then why not pop a fresh PLL in there and see what happens? Maybe you got a dodgy ic. Even reputable sources can have a hard time stocking consistent ic’s.

Beyond that idea I got nada without pics. Good luck.

 

[music6000]

This looks Great but not so much in a pedal :

 

[Nic]

I've wired pots to move them without problems, but 1 stray wire and everything go wrong. Check your volume pot wires, they may touch somewhere. If you have a second PLL I would try that first.

 

[kingbarnes]

 

[kingbarnes]

So after some research, I'm leaning towards the use of the MPSA13 instead of the MPSA14 being the cause of the issue. Since it does sort of work (all pots and toggles do affect the sound), and I'm reading now that the 13 is NOT the same as the 14 and is not a suitable substitute, despite what I read when I initially was ordering parts, this is most likely the issue. I found a parts site that does have the MPSA14 so I ordered a few and will replace the transistor with that when I get it. I'll report back here once I make that change. Should be Th/Fr timeframe.

 

[Nic]

It's worth it to try the MPSA13 MPSA14, I found those from a local store, but had to pay like 10$ of shipping for those and some diodes.

It may also be a good idea to clean the pcb, I see a lot of solder splatter and some leads looks dangerously close (IC 11 and 12, but some other too). Maybe it's just the angle of the pics.

 

[kingbarnes]

All solder points are good, no cross-over at all. I have MPSA14 transistors on the way, supposed to be delivered today but FedEx has screwed up again and the parts are in Mississippi still and have been for 2 days. Pathetic. If I ever get those, I'll swap out the MPSA13 for the correct 14 one, see if that gets it going.

 

[kingbarnes]

Built a second one with all new parts. SAME BULLSHIT, no sound at all. MUST be a bad batch of IC chips from Tayda, can't be anything else. Going to make a 3rd attempt IF I can find this chip elsewhere.

 

[Nic]

How are your pots set ? Have you tried audio probing.

 

[Laundryroom David]

i just noticed something. You might want to socket the ic instead of soldering directly to the board. Both because it makes troubleshooting easier and because one can roast an IC more easily than one might expect. Worth a shot.

 

[Nic]

And .... next build, socket your ICs.

I would start by probing. IF the IC is really bad, you could cut the legs and carefully desolder each one from the board.