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#61

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

#62

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.

#63

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

#64

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.

#65

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!

#66

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

#67

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

Last post by lars - February 11, 2026, 02:30:37 AM

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

#68

Build Reports / Re: Polyphemus {One Knob Overd...

Last post by jessenator - February 10, 2026, 04:17:17 AM

#69

Open Discussion / Re: What are you playing? (gam...

Last post by jessenator - February 10, 2026, 03:22:55 AM

I still haven't installed BG3... or RDR2...

I did do a large run of Tale of Two Wastelands. I think I've exhausted any and all interest I ever had of FO3. Just vanilla FNV from now on, but after a break.

Finally installed Fallout London and have been very pleased with it. Though, having to install GOG Galaxy to get it installed properly was a faff, if the only one.

#70

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

Last post by phreek - February 09, 2026, 10:20:45 PM

I did a ton of reading in there... Felt slight panic... Ordered a PCB from aion.