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Glad you got it working!

Bump for thoughts?

Are you perhaps talking about the Guitar PCB mini klone? :/

The best part of this thread is the hilarious names Bean keeps giving to the projects.

/quote]

You are beating me by a long shot then ...

Sharpie on the pot shaft - so simple it's genius.

Came here to say that. I like the little piece of cheese.

I think I said this last time, but that layout is really slick.

-Did you use C7, R10, and R11, and what are their values? C7, when you roll down the volume, forms a low-pass filter that varies with how much you turn down the volume; if it's too large, you will cut lots of highs.

-What are your voltages?

-Does the same thing happen when you change the guitar volume?

The switch is just named differently. Check the schematic. The up/down switch is the range switch. The "range" switch in the schematic changes the reference voltage for the LEDs after the signal is rectified, thus changing whether the LEDs turn "on" when the envelope voltage signal is driven through them or whether they turn "off" when the rectified signal reduces potential at their cathodes. Read this article if you want to learn more: http://www.geofex.com/article_folders/ecftech/ecftech.htm

The switches are/were poorly named ... I think part of the reason is that "Sweeping downward while idling at the upper end of the sweep/sweeping upward while idling at the lower end of the sweep" is hard to fit on your typical label.

The input op amp on the Rub A Dub has 2x gain. If you use higher output pickups or using a boost in front of the Rub a Dub, you can exceed the 2.5V peak-to-peak that the Belton Brick can handle.

You can reduce R3 to 180K or increase R2 to 360K, with either change making the input stage 2x gain. You then have to double R5 to 24K (or 27K for a very slight boost) to get the output to unity. Basically, you're flipping whether the boost happens before or after the brick.

This change does add a tiny bit of noise at the output; in general it's a little better to cut the signal after the digital module, but the brick is fairly quiet regardless.

If you're actually overdriving the op amp, then you'll have to make other changes.

Hmmm, I've been meaning to probe the pins on the brick like I did on the PT2399 to find out if the LED limiter will work ...

Low hfe transistors are really going the way of the dodo ... 2222s are above 100hfe now, BC10_"A" are getting tough to find, and all the really low-gain stuff like smallbear carries are either dead or significantly higher gain in their modern form. (I like these in particular, but then I have an irrational fondness of low-gain transistors.)

In my experience with fuzz faces, it's not so much the gains that are important as the ratio between Q1 and Q2. You want Q1 to be perhaps 66-75% of the gain of Q2, though it can be half or even less and still work right. For some reason the closer you get to the same hfe, the worse it is at things like cleaning up with the volume pot. I built a fuzz face once with two germanium transistors with hfe of only 60 each and it was just a wall of mush, even with the guitar volume at half way and an input trimpot! It's almost like it starts seeing the guitar as a voltage source. I swapped out the first for hfe 40 and it sounded really excellent. I've also gotten excellent behavior from a silicon with BC107A in Q1 and BC109B in Q2. The gain ratio was maybe half. It did have the 10pF bypass cap as designated in the Hipster -- silicon transistors aren't "lossy" like germanium ones, so you just have to simulate the leakage in some way. Forrest's Si tonebender (Grindy's "Bendover") uses those caps, too.

I was getting some squeal in a lowrider I just built originating at 6&7 of IC5B. It appeared on the pins, but if I touched the junction of R33/R32 it went away. I started poking around a bit and experimenting and I found I could make it go away with about 33pF of capacitance across IC33, or by shunting the same amount to ground, or adding some capacitance to C21 (but that took more). It still squeals a tiny bit on power up for about 2-3 seconds (obviously only if the second octave down pot is turned up at all). I went and grabbed my old lowrider and noticed that it had a little "peep" on power up, but it didn't last as long, maybe a quarter of a second.

Increasing the capacitance strapped across R33 decreased the amount of time the squeal was audible, but it also cut the volume of the second octave down. I ended up using 150pF, which resulted in perhaps a 1 second squeal with minimal volume loss (which I didn't care about too much ... I boosted R52 on this one anyway so that the whole effect has more output now).

Nothing is wrong with the effect -- it works just fine, tracking is just as good as ever, no magic smoke, etc.

Could anyone venture a guess as to what is (a) causing the squeal (I've swapped the 074 with no change - so it's not a bad op amp) and (b) if perhaps a part went bad that I didn't think of?

Post all voltages at all pins of both transistors, and pictures.

I assume this is why this particular diode is called a 'detector diode'.

Not quite ... detector as in radio detector.

http://en.wikipedia.org/wiki/Diode_detector

*WARNING this link poses a Wikisurfing danger*

In radios, lower Fv makes for a better detector. Before Schottky diodes were available or in widespread use, Germanium diodes were the way to get a low Fv. The ones with lower Fv were better ... this is part of why 1N270s are more expensive than 1N34As.

The Russians stuck with germanium in their semiconductors longer than western Europe and the U.S., so they tend to have a lot of Ge parts that are particularly good. Their detector didoes (the "D" series, followed by a number [usually 9 or 2] and a letter [A, B, V, G, D, E, J [actually the sound is a y-glide], K]) all have very good Fv, with almost all below .35, and a huge cluster around .27V. I have a pile of them below .2V, but the package is larger so they're a bit awkward to use in stompboxes.

I specified 24V because you have to think in terms of peak-to-peak when discussing the audio signal (the circuit runs on DC, but your audio is still AC! it's just not swinging across 0V but some "fake" 0V, like 4.5V in an op amp ). In a 9V circuit, your power rails are 9V and 0V, with your signal swinging between them; rarely are you going to see more than 6V on one side of the swing. I suppose 18V is enough to have a 12V+/6V- split with asymmetrical biasing, minus some loss on either side, so 24V might have been an exaggeration.

Well, this is incredibly useful for my current adventures ... thank you!

EDIT: Apparently I already bookmarked the parent site ... 

uglyface! (not you, Jon)

I've been called worse by close friends!