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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.

Since then everything seems to be working but I've noticed a strange modulation or tremolo effect that is just barely noticeable when notes ring out.

Sounds like pumping (basically, voltage building up and discharging in the envelope section at an unsteady rate), and you might have just not noticed it before. Double check the 100K and 4.7uF cap after the diode to ensure they're the right value; you could try increasing the decay (increase the resistor to, say, 120K or 150K) to help cure it, or possibly replace the cap to make sure it wasn't bad. But you should first adjust the bias carefully and see if that does anything to help.

Congrats!

The boards look great, and having breadboarded yours and Forrest's designs over the weekend, they sound great, too. I have big plans for the SMD pcb.

Nurse Quacky. Doesn't really get any simpler.

Also, the BYOC envelope filter was my first working pedal.

Brian has a PCB for a Seamoon envelope filter clone on his upcoming releases list, but I don't know when that will happen. That's an incredibly simple project, too, simpler than the Nurse Quacky.

Getting the right pot is always preferable, but to start: a linear pot with a resistor bootstrapped over it will never remain linear.

I agree Paul however, I would be pretty confident saying that it will get you where you want to be 

It would be close enough to a linear taper that it would work. If you want perfection.... then get the 250KB pot. If you want it to work NOW, use the 500KB pot with a 500K (or 510K) resistor strapped between Lugs 1 and 3.

A small sacrifice for having it completed now. 

Yeah, you can certainly do this to see everything works, but when the pot is used as a variable resistor, like the gain control in the Egodriver, this won't work......... Sorry for being an ass, I really only try to help. 

Paul

Why do you say that? Connect lugs 2 and 3 and it's two resistors of 500K = 250K.

Diode color codes are just like resistor color codes when they're used. It's 1Nxxx (or OAxxx). The T could be for Telefunken.

More gain?  Go Thor!

+1, that thing's insane. Not scooped, though. Maybe the Umble instead? I remember that having so much gain it didn't make it off the breadboard.

Yes, germanium transistors sound different from off-the-shelf silicon transistors. And I say this as a lover of germanium. But the reason is that they just happen to have some properties (mainly leakage) inherent in their construction. You can fake leakage. You can match the lower gain characteristics (it's tough getting low-gain silicon, but nothing says that you have to max out the gain on any particular transistor ...). There is really only one property of germanium that can't be faked with a couple extra passives, and that's temperature drift -- a characteristic that we usually take measures to minimize or eliminate!

The one thing I don't think you can "fake" is the much lower Base-Emitter forward voltage.

Do they? Last time I measured germanium transistors they had a .6v Fv just like silicon. But it's been a while and maybe I dun it rong.

You should be able to fake that, though: Strap a diode across the base to emitter. (Arranged like the 9.1v zener in Mosfets.) Fv divides in parallel (er ... sorta, but I don't know what the formula is).

about 10 minutes.

FTFY, based on this video and the similar parts count:

Except, build that, because it's a Bazz Fuss and will sound awesome.

I'll go through your suggestions one at a time and then suggest a few things.

1. I would not change Q1. You will increase the gain with a J201 in that position, but you will also lose some benefits of the 2N5457 in input stages, which could result in some bad behavior with larger signals or loss of treble.

2. 33K/220pF is fine for that resistor and more in line with present FETzer valve design. However, recognize that decreasing that will increase the cutoff frequency of the input treble cut. The frequency cutoff is pretty far up there already (over 7K). With a 33k, you'd increase it to ~22K Hz. There's nothing coming out of a guitar's strings up that high. Heck, you can't even hear that high. There's some extra capacitance hidden in FETs that will add to that, but it's still going to be way up there. It's mostly to avoid noise. But that input cap combination is part of the sound of the amplifier.

3. Don't rebias the FETs. At least, not without realizing what you're doing. Read this: http://runoffgroove.com/fetzervalve.html. The FET biasing introduces harmonics at the proper ratio to make it sound more like tubes. Just underbiasing the transistors -- and a certain booteek company went this route -- might produce more gain, but it won't sound the same either. If you REALLY want to increase the gain, put 22uF-47uF caps from the source to ground on Q1 and Q2. This will max out the gain for all frequencies on the guitar without upsetting the bias. Again, part of the modern FETzer valve design. However, recognize too that you can send the FETs into cutoff, which could result in bad behavior. The circuit already has what I think is a lot of gain; it's enough to "sag" the FETs, which indicates that they are already quite saturated.

4. That's a low-pass filter in conjuction with the 100K before it. What are you trying to achieve by increasing the capacitor?

5. See above. You could add presence, or increase the total gain. You can't do both. This is a bright circuit already, and I would have to cut the treble on my amp if I had the tone control all the way up. What specifically about the sound are you trying to change about the pedal in making this change? The better place to make this change would be Q3; if you add presence early in the circuit, you'll increase the treble and introduce more intermodulation (by boosting the harmonics, which would sum poorly), but most of the increase will be lost by the multiple low-pass filters in the circuit and by the FETs themselves (which do not perfectly reproduce high treble frequencies).

6. The 68nF cap is the output capacitor. It forms a high-pass filter with the volume control. The cutoff frequency is ... 23.4 Hz. That's at the basement of human hearing and certainly passes all frequencies on a guitar; the lowest frequency experiencing any attenuation is ~80Hz, with the low E (72Hz) experiencing perhaps one or two decibels of attenuation. Changing this cap will do little, if anything. In fact, it's probably a fuller response curve than your amplifier unless you run your bass control at max.

You mentioned that you wanted to scoop the mids. That's a tough one. Almost anything you do for that will cut the output or the gain. However, you could steal the last 6 components in the Azabache to introduce a 400Hz notch. You could also split the Q3 biasing resistor (the trimpot) into two resistors as a divider. One goes to the +9V, one goes to the Q3 drain, and the output is taken from their junction. You only need about 3.3K total. For an example, look at the Fuzz Face. I don't have a good explanation, but this produces a midrange notch and it's one reason a lot of vintage fuzzes have scooped tones.

Of course, adding a big muff tone stack is the other way to go about it. This loses a lot of output and would especially lose a lot of treble, so I'd suggest sticking a buffer on the end of the circuit, then putting in the tone stack and tweaking, THEN buffering the output after the tone stack once more to prevent whatever follows from being loaded down by the tone control.

Also, recognize that it will get a lot more distorted simply by including the "Bottom" switch. I left it out in mine because it was more gainy than I needed.

I want to say too that you might consider making another pedal based on a different amp if you want a different sound. ROG tailored this circuit to sound like the Supro 16T, and it's as close to dead on as you can get. There are other designs on ROG based around different amps that might be more in line with the sound you want. But few FET designs sound particularly good for high gain. If you want that, I suggest just building a fuzz or distortion and using it with the overdrive.

Happy 1000! It's a start ....

[Resistors]

Oh man.

I'd like any audience members with sensitive dispositions to leave the building now. I don't think it'll be an unpopular opinion, but you never know ...


...


I'll just go through individual parts ...

Resistors

RG Keen did an excellent article on Carbon Comp resistors, which is fortunate because I don't have the equipment to test this. They are capable of introducing resistor distortion at VERY high voltages. This property CANNOT occur in stompboxes. I'm not saying "is likely inaudible" or "maybe a little once in a while." It is literally impossible to produce this property in a stompbox running on 9, 12, 15, 18, 24, or even 30 volts, which I imagine is every guitar pedal and almost every rack unit ever created.

I did matched resistor replacements one at a time and could not hear a difference except a little added noise. That was good enough for me.

Notice no one claims that carbon film resistors have mojo? Maybe it's because they just weren't used during a period of time where people think everything had mojo.

Now you want some REAL mojo, get spendy and find glass resistors. Those things look frigging awesome and are super rare and expensive. I never was able to get enough together for a treble booster, but I really wanted them for an all-glass-and-metal booster.

Capacitors

There's another RG Keen article where he examined capacitor types and scoped them. This is another thing that only appears when you have enough voltage and bandwidth to produce changes.

Most of the capacitor mojo ends up being applied to guitars, where it is utterly and completely absurd. A lot of multimeters (including mine at home) don't measure capacitance, and capacitors have horrible tolerances, so it gets particularly laughable when people swap them out in a guitar or something and say, "look, this one sounds so much WARMER" (and man what a stupid word that is). Add to that the fact that the human brain is incapable of remembering a sound for more than 2 seconds (which is surely longer than it took you to switch that cap in your guitar) and it's <shakes head> time. In particular, because it's an RC filter, differences between caps become even less noticeable the second the guitar's tone pot is adjusted.

However, caps really do sound different in the right circumstances. Some electrolytics have less internal resistance, so they actually work better, which can be important for filtering out noise. Ceramics really do introduce distortion when working with enough voltage (not the couple hundred microamps your pickups). Film caps have reliably good performance. Some paper in oil caps really do have the lowest distortion of any other types of caps.

But like resistors, most people building mojo-riffic products, and dare I say it most people building their own stompboxes with mojo parts, get it into their head that some type of capacitor sounds better, so when they go to test it OF COURSE it sounds better, and you will never be able to convince them otherwise, even if you run it through a scope with matched capacitance. Suddenly it'll become the Emperor's New Ears, or "the scope isn't sensitive enough" (!), or something like that.

Transistors
Yes, germanium transistors sound different from off-the-shelf silicon transistors. And I say this as a lover of germanium. But the reason is that they just happen to have some properties (mainly leakage) inherent in their construction. You can fake leakage. You can match the lower gain characteristics (it's tough getting low-gain silicon, but nothing says that you have to max out the gain on any particular transistor ...). There is really only one property of germanium that can't be faked with a couple extra passives, and that's temperature drift -- a characteristic that we usually take measures to minimize or eliminate!

Germanium transistors ARE useful in that different types might have more of a particular property that you need without needing the extra parts (usually a treble bypass and an adjustment of the positive bias resistor). Use them for that reason. Don't use them because you think germanium is some magic spice. It isn't.

Diodes

Let's all have a nice laugh at Am for tracking down some super rare silicon diode and buying all of them up because they think that forward voltage can't be matched with other diodes.

Germanium diodes also have leakage, which results in a softer knee. If you want to fake this with schottky diodes, you can use some small amount of resistance in series with the diodes.

Temperature drift is, again, not generally considered a desirable characteristic by anyone.

...

For the most part, mojo is almost entirely about the idea that older components somehow sound better. You can always introduce flaws intentionally. Even a lot of cheap modern parts are made better than older parts, but the high-quality components now are worlds better and more reliable. Every time I see someone posting that the carbon comp resistors are what makes their pedal sound so good I want to ask them if they're typing their build report on an Apple 2 or a Commodore 64.

This stuff, but I'd really like to find something better:



It's more durable than what I used to use, but still not quite there for wrap-around art. The good news is that it doesn't make 95% of acrylics run even with a slightly thicker coat.

Don't worry about part numbers. Just sort them by composition and Fv and them try them in your favorite distortion circuit. But here's a quick list of some representative Fv from my measurements for diodes that appear in circuits:

Germanium
1N100/1N60: .23-.28V
1N695: .25-.3VV
1N19x: .25-.3V (I think Smallbear's generics are this series)
1N270: .28-.33V (however, some might be lower)
1N34A: .32-.38V

This is the simplified "how jon understands stuff" explanation. There's probably a better one out there.

[R5 + speed], C1, and C2 are mostly responsible for setting the minimum and maximum speeds.

Let's break it down. We have a gain loop between the non-inverting input and output, which puts out a signal with one phase (let's call that "up"). But we also have a gain loop from the inverting input THROUGH the speed pot and R5, which is then connected back to the output (let's call that "down") with a 10nF capacitor also between those pins. We're feeding non-inverted signal back through to in inverting signal, which under the right circumstances will create enough gain to freak out the chip and trigger oscillation.

This is actually the same type of oscillation that is heard as things like whine from power supplies, or squealing in high-gain effects. What we need to do is make it a really, really low frequency. The lower the frequency, the slower the speed between pulses. There are a few ways to do that.

One way is to filter out the high frequencies. Those 100uF and 100nF caps in the power section of every effect (e.g. C6 here)? They are the equivalent of C2 in our oscillator. Increasing the size of C2 will lower the frequency of the oscillation in the gain loop.

For the other way, let's go back to what I said about oscillation and squealing in high-gain effects. You might recall that a lot of effects have really small bypass capacitors for cutting treble, either between the base and collector in a transistor or (looks familiar ...) between the pins in an op amp. These capacitors prevent certain frequencies from being amplified by the device. In this case, we have C1, which is much, much larger than we're used to seeing. It turns out that making it smaller will vastly increase the maximum frequency, even put it into the audio range -- some people mod this sort of oscillator to become a ring modulator just by changing that cap (though it doesn't work particularly well with a light dependent resistor, which is not really fast enough for true ring modulation ... though an H11F1 might be ...). Increasing the size of it will also slow down the oscillation by filtering out frequencies.

What's the speed pot + R5 doing? They're setting a low-pass filter along with C2. (This is where it becomes really helpful to remember that filters of any sort are altering time constants.) As you decrease the resistance, the frequency increases and the speed of the oscillation goes up.

R5 is simply a minumum resistance.

The takeaway from this is that you can use a pot with a really great taper and change other components to get around the limitations of the pot's resistances.