Recent posts

#41

Open Discussion / Re: Happy New Year 2026, Pork ...

Last post by museums - February 16, 2026, 06:29:20 PM

I only just saw this thread. I'm not sure how a CE-2 would sound with a purely sine wave modulation. I think it might ened up sounding a little lop sided because the peaks and valleys would be much more drawn out.

Shortening the delay time helps with a sine LFO quite a bit in my experience. You get that super smooth sweep without spending a ton of time at the long end of the clock sweep.

#42

General Questions / Re: Repair help

Last post by jessenator - February 16, 2026, 06:05:21 PM

I didn't know I needed pedal name ideas, but now I've got 'em.

Your next one needs to be called "Thanks, Geoff"

#43

General Questions / Re: Repair help

Last post by derevaun - February 16, 2026, 05:03:03 AM

I didn't know I needed pedal name ideas, but now I've got 'em.

#44

VFE Projects / Re: Mini Mu Help

Last post by wizestwizard - February 16, 2026, 03:38:27 AM

One breakthrough, though the mystery continues...

I didn't think I had any other single op-amps on hand but then I realized that I had a CA3130EZ. I popped it in and that solved the voltage readings on pins 1 and 5 of the IC! Pin 6 was still off (more on that later) but I figured I'd plug in and give it a shot.

The pedal basically works now. I built a Naughty Fish a few years ago so I'm familiar with what to expect from all the knobs and switches. I noticed a bit of extraneous interference-type noise which was probably just due to the open enclosure. However, there's a lot of scratchy/static noise when I turn the level knob. Maybe this is related to the fact that I'm seeing DC voltage (~4v depending on level knob setting) on pin 6 (output).

So two questions remain:
1. What's the likely source of the DC voltage on pin 6, and is there any chance this is related to the CA3130EZ substitution?
2. How in the world did I end up getting two OPA134s from Mouser that didn't work correctly? I've ordered parts from them for years without encountering this kind of problem. I can't imagine that these are fakes (see pictures).

Thanks again, everyone!

Ok I missed this... that solved my voltage issue but not the overall problem I'm having.

#45

VFE Projects / Mobius Strip and Mini Mu just ...

Last post by wizestwizard - February 16, 2026, 03:26:03 AM

I'm working through a pile of boards that I finally got around to, I'm having some weird results with both the Mobius Strip and Mini Mu. Both are just passing clean signal, bypassed or not, and no controls appear to do anything on either. The switching board works and LED lights up etc. On the Mobius Strip, all voltages match up to those posted in the build doc, on the Mini Mu (I've built this pedal before, so extra frustrating here lol), everything is right EXCEPT pins 1 and 5 of the OPA134 should both be ~ -8.5 V and are +8.2 V and 0 V respectively *EDIT - this is from a bad OPA134, switching it out fixed the voltages but not this issue*. Pictures of both builds attached here. I've built probably 10-15 VFe pedals and have never had this issue before. Any input is appreciated!

Derek

#46

VFE Projects / Re: Mini Mu Help

Last post by wizestwizard - February 16, 2026, 02:54:24 AM

Thanks, all! I inspected the board and couldn't find any solder bridges. However, I did see that I missed one of the socket pins for the TLE2074, so I soldered that (and reflowed anything that looked like it could use it). I'm now getting sound when the pedal is engaged, though the envelope effect is barely noticeable and the up/down switch doesn't seem to make a difference. Here are my new voltages with ICs installed. In summary the TLE2074 seems fine, the LM358 seems fine except for pin 2, and the OPA134 has a few anomalies (pins 1 and 5, in particular). Any ideas?

IC1 OPA134
1   8 (should be -8.4)
2   0 (should be 0)
3   0 (should be 0)
4   -8 (should be -8.4)
5   0 (should be -8.4)
6   0 (should be 0)
7   8.3 (should be 8.
8   8 (ignore)

IC2 LM358
1   7.1 (should be 7.57)
2   0.03 (should be 2.24)
3   4.1 (should be 4.35)
4   -7.9 (should be -8.44)
5   0.02 (should be 0.027)
6   0.03 (should be 0.03)
7   0.5 (should be 0.36)
8   8.3 (should be 8.

IC3 TLE2074
1   0 (should be 0)
2   0 (should be 0)
3   0 (should be 0)
4   8.3 (should be 8.77)
5   0 (should be 0)
6   0 (should be 0)
7   0 (should be 0)
8   0 (should be 0)
9   0 (should be 0)
10  0 (should be 0)
11  -7.9 (should be -8.4)
12  0 (should be 0)
13  0 (should be 0)
14  0 (should be 0)

Were you ever able to find your issue? I've built this pedal a few times before with no issues but I am getting the same voltage problems you are on the OPA134, all other voltages check out. Pedal just passes clean signal even when it's on, no controls affect anything. Interestingly from the schematic... those pins (1 and 5) aren't attached to anything that I can see, though the VFe schematics are often a bit of a nightmare to deconvolute lol.

#47

General Questions / Re: Rate/Mod Rate LED for Poly...

Last post by wizestwizard - February 13, 2026, 11:25:00 AM

Thanks Brian! I'll test em out and see how it goes, I'll report back

#48

General Questions / Re: Rate/Mod Rate LED for Poly...

Last post by madbean - February 13, 2026, 03:32:09 AM

Hey guys, recently had a request from someone to add a rate LED to a Polytrog I build for them. I assume it will follow the "rate" pot if I put it in parallel with the LDR LEDs? If I do this, should I put it after all of the vactrol LEDs and then lower R42 to ~250R? This is a complex circuit compared to what I normally mod, so want to make sure I cover my butt before I start poking around in it!

If I wanted it to pulse with the "mod rate" pot, where would be the best place to tap into that voltage? Thanks!

For the Rate pot you would put the LED in series with VC1-3_L, nt in parallel. Lowering R42 might compensate or prove unnecessary. For the Mod_Rate I'd try a 10k CLR and LED connected to pin7 of IC9_B first. Do it on a breadboard where you can easily disconnect the LED and see if it impacts performance.

These are just educated guesses.

#49

General Questions / Rate/Mod Rate LED for Polytrog

Last post by wizestwizard - February 12, 2026, 11:50:33 PM

Hey guys, recently had a request from someone to add a rate LED to a Polytrog I build for them. I assume it will follow the "rate" pot if I put it in parallel with the LDR LEDs? If I do this, should I put it after all of the vactrol LEDs and then lower R42 to ~250R? This is a complex circuit compared to what I normally mod, so want to make sure I cover my butt before I start poking around in it!

If I wanted it to pulse with the "mod rate" pot, where would be the best place to tap into that voltage? Thanks!

#50

Open Discussion / Re: Got bored, building a bass...

Last post by phreek - February 12, 2026, 06:41:38 PM

My favorite heavy bass distortion ever was actually the drive circuit built into the Gallien Krueger Backline 250 head. It was kind of a Big Muff sound, but heavier and less scooped. GK tried to build that circuit into their Diesel Dawg pedal, but managed to mess it up, so it never sounded like the amp head. By comparing the schematics of the two you can find the changes, and I actually modded a Diesel Dawg to sound much closer to the 250 head. The key resistors and caps that need to be changed (6th post) are outlined in this posting I made years ago:
https://www.madbeanpedals.com/forum/index.php?topic=27915.0

that sounds like ima have to give this a good look, thanks for the heads up