1st post, reverse diode replacement question

[daizee]

Hello!

I've lurked for awhile, but recently bought and built my first pedal kits from Aion.
The first was a failure, but I've ordered replacement parts to make a second run at it.

The second, the Vulcan, was a success! Nice kit assembly, great instructions, and slightly more experienced builder. 

Here's my request for advice:
This pedal provides a ton of distortion. It's good. But it really only sounds good to me with the gain ("sustain") over 50% and the guitar volume on 10. The last 25% of the gain knob seems redundant. At lower guitar volumes the germanium diode clipping just sounds fizzy and lame. It's totally fine if this pedal is only a two-trick pony that adapts well to various guitars/signal chains (lots of widgets to twiddle). But....:

Can I replace those two symmetrical germanium 1N34A clipping diodes with a silicon pair with higher activation voltage? The theory is I can get a better rolled-back overdrive sound out of it if a bit more clean comes through. (LEDs would be too much here I'm here, I'm pretty sure).  If I had the parts on hand I'd be doing it instead of posting, but getting a good recommendation on diode selection before placing an order seems sensible.

Thanks for any advice y'all can provide!

-Daizee

[GGBB]

Welcome to the forum.

Doing that would be fine - experimentation is a good thing. Whether you end up liking it or not you will have learned something from the journey.

[andy-h-h]

The Foxx Tone Machine isn't really known for guitar volume pot cleanup.   There's also a fair bit of clipping happening before it reaches the hard clipping diodes.  There's even distortion introduced by passing through the diodes in the signal path that causes the octave effect.

Good to experiment, but you may find that there are several things happening here.   By changing to silicon diodes, you might also introduce additional distortion by hitting the last transistor with a lot of level. 

Enjoy the experiment.  Love a good Foxx.. 

[stallik]

Welcome

If you're going to try different diodes, you might consider using sockets such as these. Makes for rapid changes and can save making a mess of the pcb

[daizee]

Ah, good info, thanks! So far the octave is only usable for me lower on the neck. The upper areas are piercing. I have a mind to add/change a low-pass filter cap in the octave network too.

Tiny sockets!!! Thank you, I will look for those in a stash today, and order some if necessary.

[daizee]

Quick update!:

Did the diode mod tonight (bandmate was over for regular noisy time and extra hands helped). A pair of 1N914's replaced the original germanium diodes.

It did *exactly* what I wanted. Cleanup is now excellent and usable across the guitar volume range (I have a good subtle treble bleed in that guitar). Overall volume went up (less clipping). The fuzziest settings are a bit less thick and chaotic, but not much. And with the gain ("sustain") knob at noon, I can get light overdrive to the lower end of the fuzz range (you can hear the shelf where the transistor(s?) loses its mind).  There's even cleanup with the Octave setting now too, since there's more signal left. It doesn't just get quiet and fizzy - it gets a bit gated and fun-weird.  Jammed on it for a couple hours w/o the octave, and I'm DELIGHTED. Super versatile pedal now, what with the mids switch and all too.

[merlinb]

Alternatively you could have reduced the value of R11

[daizee]

What would that do, exactly?
Looks to my naive eye like it would reduce the overall input signal level to the entire circuit.

[antonis]

I think you're talking about complete different version of Vulcan..

OP deals with BJT circuit..
https://aionfx.com/app/files/docs/vulcan_kit_documentation.pdf

P.S.
Merlin deals with altering diode's characteristics by altering the current through it..

[daizee]

Ah yes indeed, that's a different circuit. I was only looking at the segment my browser showed me while rushing out in the morning. Just now opened it in another tab and saw the rest.

[andy-h-h]

Quick update!:

Did the diode mod tonight (bandmate was over for regular noisy time and extra hands helped). A pair of 1N914's replaced the original germanium diodes.

It did *exactly* what I wanted. Cleanup is now excellent and usable across the guitar volume range (I have a good subtle treble bleed in that guitar). Overall volume went up (less clipping). The fuzziest settings are a bit less thick and chaotic, but not much. And with the gain ("sustain") knob at noon, I can get light overdrive to the lower end of the fuzz range (you can hear the shelf where the transistor(s?) loses its mind).  There's even cleanup with the Octave setting now too, since there's more signal left. It doesn't just get quiet and fizzy - it gets a bit gated and fun-weird.  Jammed on it for a couple hours w/o the octave, and I'm DELIGHTED. Super versatile pedal now, what with the mids switch and all too.

Interesting - that's not what I expected at all.  I'll have to give that a try.

[daizee]

Something I wanted to mention (all with octave off):

It sounds to me like a regular hard-clipping distortion pedal with the Sustain knob at ~9-o'clock. Nice and tight. Guitar volume backs things down predictably without getting too quiet. It goes from nearly clean to distortion (w/ guitar vol).

With Sustain at Noon, it goes from light overdrive to the lower end of the "fuzz" range w/ guitar vol knob (sounds like transistors start to give it up).

With Sustain 3-o'clock, it goes from light overdrive deep into fuzz territory.

With the Octave network engaged, it now does a kind of gated thing when the guitar vol is rolled off, which is cool.  A bit more SuperFuzz in its sound, but I haven't messed with it much yet. Mostly I'm enjoying it as a normal fuzz.

Gonna give it a whirl with the Tele tonight and see how that goes.

[daizee]

The Tele pickups are a bit weak and bright for this pedal AND because it doesn't have a treble bleed, hard to compensate for. It goes dark as soon as the guitar vol is dialed back. One day this body will be replaced or the pickups/harness replaced to include a bit more output and another subtle bleed circuit like the humbucker semi-hollow.

The surprise is the hollowbody jazzbox w/ a neck P90.   
I've only got 3 guitars, might as well try them all. That one works remarkably well with this pedal/configuration. It has an aggressive factory treble bleed. Not that I'd pair it with a fuzz except for LOL's, but it IS usable until it starts feeding back.

This thing is very cool modifed this way, and I'm pleased. Thanks for the input.