twang-a-matic

[FUZZZZzzzz]

so, i found this schematic over at epanorama.. its from the seventies and decided to make a layout.
its unverified as I'm ashamed to say that i dont have some of the parts in stock at the moment.

im not expecting much from it, but will build this week and hope to verify it.

layout:


schematic:

[deadastronaut]

yay!..another 1 pot jobby....look forward to the soundclip?..

did you mess around with the kick drum thingy again?...

[FUZZZZzzzz]

yes i did.. lot of possibilities with the caps.. but got bored in the end   
had some fun though... with adding reverb and such ..

[deadastronaut]

yeah me too....great lil circuit to play with though!..cool metronome...

[LucifersTrip]

It's funny that they thought the in sound was twang in 1976 !

I love fuzz, but it's good to see a similar type of circuit used for something else...will most likely try it shortly

thanx for posting it

[Electron Tornado]

This was one of the first pedal circuits I ever built. It will distort all right, though it's very gated. If you're looking for a "banjo through a fuzz" sound, then this circuit is the one!

[FUZZZZzzzz]

This was one of the first pedal circuits I ever built. It will distort all right, though it's very gated. If you're looking for a "banjo through a fuzz" sound, then this circuit is the one!

sounds good enough for me thanks for your reply!

[FUZZZZzzzz]

hmm.. im doing something wrong here..  i tried 2n2222 and 2n3392 so far for this circuit but there must be an error in my layout.
can anyone spot it?.. im frustated as it is so simple

[ayayay!]

I don't see anything wrong with the layout meeself.  You didn't mention what the problem was though.  Is there no output? 

[amptramp]

With the way they do their bypassing, you cannot turn the pot down and get any signal bypassed.  The bypass switch should be connected with its arrow to the output jack and its other terminals to the input or the output.  And since the input impedance can never exceed 20K, tone sucking will be extreme.  This design needs true bypass or a JFET source follower at the input.

[FUZZZZzzzz]

I don't see anything wrong with the layout meeself.  You didn't mention what the problem was though.  Is there no output? 

sorry bout that. i connected everything according to the layout and hooked a 9 volt battery to + and grnd of the board
and a input and output jack to test it, but theres nothing at all coming through. ive socketed the transistors and try to audioprobe but no luck so far.

[FUZZZZzzzz]

With the way they do their bypassing, you cannot turn the pot down and get any signal bypassed.  The bypass switch should be connected with its arrow to the output jack and its other terminals to the input or the output.  And since the input impedance can never exceed 20K, tone sucking will be extreme.  This design needs true bypass or a JFET source follower at the input.

thanks for the info on that.. i have only tested the board with a 9 volt battery and two jacks connected..

[Vince_b]

Did you find the problem? I see at least one mistake in your layout. The output should be connected to the middle lug of the pot. I have breadborded the circuit and it works fine.

[Anthem]

Twang - A - Matic - Looks like some chaps can achieve miracles with breadboard, because the schematic could never, ever work !

Q1 and Q2 are both NPN transistors which are biased completely off to small signals in this circuit. Maybe a lightning bolt on the input will produce an output, but then you would be listening to angels playing banjos/mandolins if you were anywhere near the Stompbox.

In 1976 many of those 101 circuits never worked due to printing errors and faulty schematics which deviated from the working circuits, or if the magazine staff ever bothered to really see if they worked at all.

1000s of poor fellows making his circuit since 1976 and wondering why it does not work.

But I think I see what the solution may be:

Prior to 1976 many schematics used Germanium transistors and also used a positive ground, which I think was this circuit may have originated from. Then a mag staff may have converted to more modern NPN transistors from the PNP/positive ground original and reversing the polarity to suite.
Looks like this was an attempt to do that, but they got their wires crossed.

Solution A:
1. Swop the polarity of the 9V Battery clip.
2. Swop the NPNs c to e and e to c, base in the same place. (Maybe use a 2N3904, but yours are also OK, try them, should work)
3. Swing R7 pot from old -ve rail  to the new -ve rail.
4  Swing both earth shield (rings) to the negative rail.
5. I would put. say a 180K resistor in series with C1 so as not to load the guitar pickups much. Try a couple of highish values but not so much that you get too much attenuation, but not too low so that guitar tone gets dull.

Solution B:
1. Remove NPN transistors altogether and replace with PNP (2N3906 - OK), but the emitter must be where the old NPN collector was and the collector must be where the old NPN emitter was for both Q1,Q2. Base kept in the same place.
2. Leave the rest of he circuit unchanged.
3. again, I would put. say a 180K resistor in series with C1 so as not to load the guitar pickups much. Try a couple of highish values but not so much that you get too much attenuation, but not too low so that guitar tone gets dull.

Let me know how it sounds. Should work in theory. You will get a signal from input - through the circuit - to output like this, without the need for flashes of light in the sky !

[Vince_b]

Looks like some chaps can achieve miracles with breadboard, because the schematic could never, ever work !

I have to admit that I used different transistors when I breadboarded it because I didn't have the right ones on hand. I can't remember what I used but I definitely HAD an output without any divine intervention. The level was low but I thought it was only because I didn't used the transistors specified in the schematic.
When I will have the time, I will try the solutions that you have proposed. Thanks for sharing your knowledge.

[Anthem]

Another Idea -

Geranium transistors can have their c-e pins swopped around and they will still work OK except to lose current gain. Could be that they unwittingly did this and got the circuit working like that.
The transistors I have suggested are highish gain types, but to simulate this possibility is to use low gain types instead.

Solder tulip sockets for the transistors so you can swop them easily and see the difference.

BUT if a silicon will survive this then it could also work. Modern silicon transistors have a reverse base emitter breakdown capability of about 5 to 7V. The old Geraniums did about 30V with base emitter reversal on the base collector being the same. Some circuits may work better this way as the trannies abilities are reigned in.

This is the black art of distortion after all ! Try it if you're willing to sacrifice some trannies, should it fail. Heard that a 2N3906 reversed c-e worked OK elsewhere.

[Anthem]

Looks like some chaps can achieve miracles with breadboard, because the schematic could never, ever work !

I have to admit that I used different transistors when I breadboarded it because I didn't have the right ones on hand. I can't remember what I used but I definitely HAD an output without any divine intervention. The level was low but I thought it was only because I didn't used the transistors specified in the schematic.
When I will have the time, I will try the solutions that you have proposed. Thanks for sharing your knowledge.

Hi Vince

Could admittedly maybe work with a reversed polarity batt clip. See my last comment. Maybe works even better this way, for all the wrong reasons. This is distortion after all !
But would definitely swing the R7 over before trying this. Some amps may not block + DC biased input signal.

Sorry, not meaning to denigrate anyone ! Regards.

[Mark Hammer]

The Twang-a-matic circuit was a staple in the various "99 Solid-State Circuits" and "101 IC projects" compendiums that Gernsback would publish "back in the day".  I know I have it in one of those collections in my stackof those delightful newsprint mags, and probably more than one.

Unfortunately, although they were published by the same folks spitting out Popular Electonics and Radio Electronics, they were one-offs, and not simply "special issues" like the Elektor Summer Circuits issues I used to live for.  So, where Elektor, ETI, et al, had the luxury of issuing a correction an issue or two later, to correct an editting oversight in the circuit collection issue, there was no dependable means for reaching purchasers of these project collections to let them know there was an "oops" in project #43.

[slacker]

If you make R3 about 220k, that should bias the first stage properly, making it into a treble booster. You should then get some sort of gated fuzz as the second stage will only pass large signals and will cut off as the signal decays.

No idea if that's how it's supposed to work though.

[Electron Tornado]

The Twang-a-matic circuit was a staple in the various "99 Solid-State Circuits" and "101 IC projects" compendiums that Gernsback would publish "back in the day".  I know I have it in one of those collections in my stackof those delightful newsprint mags, and probably more than one.

Unfortunately, although they were published by the same folks spitting out Popular Electonics and Radio Electronics, they were one-offs, and not simply "special issues" like the Elektor Summer Circuits issues I used to live for.  So, where Elektor, ETI, et al, had the luxury of issuing a correction an issue or two later, to correct an editting oversight in the circuit collection issue, there was no dependable means for reaching purchasers of these project collections to let them know there was an "oops" in project #43.

That was "99 IC Projects" from 1980, and I still have it as well. It had 99 IC projects and 30 or so transistor projects. It worked as I said, like a banjo thru a fuzz box. Not what I had hoped and I always wondered if it was partly me.  That same magazine has a circuit called the "Wide Range Funk Box" which I guess presumed to be some sort of wah circuit. I tried it not long ago with less than stellar results. I had much better results with a couple of circuits from British electronics hobby mags.