Rust Bunny (Fuzzstainer MK?? clone) Demo added!

[midwayfair]

my own little bunny rabbit! I will name him george!

This is a cool little feedback fuzz, and an incredibly rare box indeed (at the time of that posting, there were only two 'real' units known to exist). It's vaguely similar to a fuzz face, in that it has two transistors, with negative feedback on the first transistor, but it also uses feedback on the second transistor. The bias trimmer has some "normal" sounds, but almost every setting has a little bit of gating. Despite the "stainer" name suggesting sustain, it's a very aggressive fuzz overall, with a sort of sticky attack that reminds me of a germanium MKII, and when it gates the attack is much more percussive than a lot of other vintage fuzzes.

The tone control is very effective, with a low pass counterclockwise and a highpass clockwise, and there's plenty of midrange. A small pF cap in the feedback loop between Q2's collector and Q1's emitter lops off some treble to keep things from sounding too fizzy. And as noted in Eddie's post, some of the gating sounds are unusually good (better than just "misbiased fuzz") and make the pedal more dynamic sounding. It cleans up linearly and isn't nearly as touch sensitive as a fuzz face, but it's better at that than, say, a big muff. I won't say it's my favorite fuzz or anything, but I also don't have anything else that sounds quite like it and I can certainly see using it on a recording.

Jerms traced the circuit for Eddie, and a lot of history is detailed in the post linked above. The original layout for the pedal was horrendous, with parts all over the place. I used Jerms's schematic for my layout, but added polarity protection and power filtering and made a few other adjustments:

1. The output section has been rejiggered for more available output. I doubled the volume pot and greatly reduced the 15K on the output

3. I used a 10KA for the bias and moved it external instead of the 22K internal trimmer. I found that once you got about about 7K, there wasn't much difference in settings, and at the top end of the trimpot it was kind of like flipping a coin if you'd actually get a note to come out, so I think 10KA gives you a better taper AND all the useable range, so it's less likely to get knocked out of the sweet spot.

3. I also added some minimum resistance to the trimmer. 2K is useable for most transistors. The minimum resistance is to prevent cutoff at the lowest bias settings, and then turning up the bias introduces more and more gating. This is because it would ground one end of the 1.5M on the base of Q1 and fail to provide any positive bias (which you get from the volt or so on the emitter of Q2), which = no sound from a BJT ... I wonder, though, if you could just stick a FET in there and it would work? Great now I have to try that ...

For the transistors, I just used some 2N5088. The original transistors don't have particularly good or consistent specs, so I wasn't about to track them down. 2N3904, BC108B, BC549B, etc. are also fine -- anything around 200-500 hfe works great and gives a good wide range on the bias trim sounds. You want to use two transistors with similar hfe, as they feed off each other. I tried different gain buckets in Q1 or Q2 and the further away from each other they were the less well-behaved the fuzz was. Also, I tried really high gain (MPSA13) and it got very dark, but it did have a fairly insane amount of sustain. Not really what this fuzz is meant to do. Low gain (<100hfe) was also undesireable and had a more narrow bias range to even work at all.

The layout and an etch mask are in my perfboard library if you're interested in making your own. I will probably also do a demo of this, since it's not like there are a bunch of them out there.

By the way, it's hard to read in the picture, but the controls are clockwise from the top left: thumpabuffer (tone), poof-loof (bias), bootlesnoot (fuzz), and fluffer buttle (volume), which are totally correct anatomical names of body parts on a bunny.

[rullywowr]

Wow Jon!  Excellent improvement on an existing rare layout.  All that is missing is some black epoxy and you could stand to make millions (jk) 

Cool idea, and nice mods.  Gotta check this one out, thanks for sharing!

[selfdestroyer]

Isn't  that enclosure a bit big for your standards? lol

Great build and of course your breakdown of the changes you made is VERY informative like always.

[midwayfair]

Isn't  that enclosure a bit big for your standards? lol

Yeaaaaahhh ... that enclosure shipped to me from Smallbear on 4/19/12. I figured I should just use it finally. I drilled it forever ago and just never decided what I wanted to put in it. Plus it let me use full-sized pots, which are cheaper, and I'm out of low-profile jacks for a while that aren't already spoken for, so no 1590As for me a bit.

[pickdropper]

That sounds like an interesting circuit.

I like the artwork, too.  Looks great.

[Bret608]

"...and I will hug him and squeeze him and pet him!" One of my all-time favorite Looney Tunes clips--thanks for reminding me!

Can't wait to hear a demo. I seem to remember Wright Pedals or someone making a very limited-run version of the circuit. I feel like I learned something from reading this too.

Not to derail, but have you tried pinkjimiphoton's Juergulator yet? I'd love to hear your thoughts on it. I've been playing around with the transistors in mine and am wondering what you think about transistor choice.

[midwayfair]

Not to derail, but have you tried pinkjimiphoton's Juergulator yet? I'd love to hear your thoughts on it. I've been playing around with the transistors in mine and am wondering what you think about transistor choice.

I breadboarded it, but I wasn't thrilled about it enough to make another one while I was busy (I still like the Albini specs perc I made a while ago). I just use the button 3565s that Smallbear sells and a really low gain PNP (just whatever I have around that's 40-60 hfe), and that's it. The better thing to worry about imo is the Fv on the diodes. It sounds better to me when you raise the Fv a little. I also think it helps to lower the gain of the whole thing a little. To me, the real issue with the perc continues to be the noise level, not the functionality (which is great even stock, and jimi's perc control is awesome), and so far as I know no one has found a good solution ... mostly because PNP transistors are always noisier in NPN circuits, and germanium is noisier, too.

[Bret608]

Thanks Jon, I'll play around with the diodes and see what that gets me. I've got a 2n1305 (50-ish hfe) and a 2n3565 at the moment. The perc control is really cool. I had some luck flipping the transistors around as well. This is the third perc version I've built, and is the only one where I've had much noise. The other two were Albini and "stock", both done to Bean's schematic. I think the 1n5/1n cap to ground must play a big role in the circuit, judging by how different the Juergulator (which doesn't use a cap there) sounds.

{ends derail}

Now, off to read up on the links you included! 

[catfud]

I'm wondering what it sounds like - is there any chance of a demo, Jon? [Edit: sorry, ignore that, i just re-read your post where you said you might well make one]

[midwayfair]

I'm wondering what it sounds like - is there any chance of a demo, Jon? [Edit: sorry, ignore that, i just re-read your post where you said you might well make one]

As I said near the end of the report, I will try to get one done. Not sure how soon, though. I have another demo in line ahead of this one.

[lincolnic]

This looks awesome, and I can't wait to hear the demo, but I have to ask: how exactly are those controls labeled?

[midwayfair]

This looks awesome, and I can't wait to hear the demo, but I have to ask: how exactly are those controls labeled?

Are you asking about material? It's handpainted. Otherwise, the controls labels are listed in the last paragraph.

[Urs]

Isn't that enclosure a bit big for your standards? I also agree. I am always overwhelmed by your builds

[lincolnic]

Are you asking about material? It's handpainted. Otherwise, the controls labels are listed in the last paragraph.

I meant the latter. It's hard to read them from the photo! Though if I hadn't missed the very end of your post they would've been a lot easier to see...

[midwayfair]

And here's the demo! I like this fuzz more and more the more I play with it.