i "found" an effect! reverse engineered it

[birt]

i found a really old pcb made by my grandpa.
its so old it has mustard caps on it, and rusted trannies :p

now here's what happened:
i figured it must've been some kind of amplifier circuit and it said 9v so i plugged my ipod into it and put a little speaker on the output.
the sound was harsh and a bit distorted with lots of overtones.

then i decided to just give it a shot and put it in front of my guitaramp and plugged my guitar into it

MASSIVE high gain distortion! nice palm mute sound.. i mean... Great with a capital G :p
but there's a lot of hiss (really old caps and carbon comp resistors, old transistors, no shielding...)

so now i'm trying to draw the lay-out of the pcb with the components on it... this shouldn't be a problem except for the fact that there is a tiny transformer on it wich i haven't seen before...

i'll keep you guy's informed

(did i already mention my grandpa was cool? :p)

[stm]

If you post pictures of the board and its components we might help you.

[j0shua]

YOU CAN PUT THE PCB ON FOTOCOPIER AND GET THE BACK SIDE FOR EASY WORK

[birt]

YOU CAN PUT THE PCB ON FOTOCOPIER AND GET THE BACK SIDE FOR EASY WORK

since it's a really old one with the traces ticking out above the board itself i did the paper and pencil trick (like you can draw a coin when you put it under a paper :lol: )

[birt]

got it!


Q1-3 are OC71, Q4-5 are OC74
where it says 2x2nf those caps are parallel.
the trimpot was hard to measure (it's all rusty and the contact isn't good anymore) it a little less than 5K.

here's the board: http://users.pandora.be/vandijckheffen/bert/distboard.jpg

[Paul Perry (Frostwave)]

I think that was intended to be a small audio amp, I remember when the OC71 and OC74 came out & were used in these. (early 1960s).
The trimpot (guess) might be balancing the OC74 output pair, if the trimpot is buggered, that would be a good source of distortion :wink:

[birt]

I think that was intended to be a small audio amp, I remember when the OC71 and OC74 came out & were used in these. (early 1960s).

wel it sounde too distorted for audio, but in front of my amp it's high gain hair metal in a box. i think if i can make it a good stompbox i'll cal it "instant spandex"  :lol:

but i might want to use transistors that are more common and i really want to know what the transformer does

edit: in fact all those old components can create distortion.. a bad pot, old caps and carbon resistors, old transistors...
it would be a shame if i make it with new components and the beautifull distortion is gone :shock:

[toneman]

I'd call it the "GrampaFuzz"

[Dragonfly]

I'd call it the "GrampaFuzz"

dude....thats kinda gross !   :shock:

[Paul Marossy]

How are you powering this spandex metal pedal?

[toneman]

Oh Kay--

How bout.....

"The Distorted Gampa"

This could B re-re-released as a oldie, moldie
MOJO-line Fuzz.....just like your Grandpa used 2 play!!

Hey, how old is the TubeScreamer & the FuzzFace anywho??

most definitely!
stayfuzzed
tone

[Dragonfly]

Oh Kay--

How bout.....

"The Distorted Gampa"

This could B re-re-released as a oldie, moldie
MOJO-line Fuzz.....just like your Grandpa used 2 play!!

Hey, how old is the TubeScreamer & the FuzzFace anywho??

most definitely!
stayfuzzed
tone

[sir_modulus]

nice nice...I found an old fuzz face once....well...actually it was a board that had the caps leak all over it till it looked kinda like a fuzzface board...if you looked at it all odd  :lol:

that serves as a good warning though...take off any electrolytic caps...they'll leak!

Cheers,

Nish

[niftydog]

it's got to be "The Moldy Oldy" doesn't it?!

Grampa Grunge?

no, no, no, Dragonfly has tainted that whole theme...  :shock:

[Dragonfly]

no, no, no, Dragonfly has tainted that whole theme...  :shock:

HEY....DON'T BE TALKIN' ABOUT MY TAINT !!!! [/color][/size]






 Just kiddin' !!!!

[birt]

How are you powering this spandex metal pedal?

connected a 9V battery where it said 9V :lol:

but can't someone tell me a little something about the schematic?? like why there is no volume control, what does the transformer do in there, substitutes for the old transistors, will the gain be gone if i make this with new components....

[geertjacobs]

It looks a like a push-pull poweramp using the transformer as a phase-splitter. Would make sense since the pcb was probably made shortly after the tube amp era an in tube amps they sometimes used  transformers as phase splitters.
An 18V top-to-top sine would make quite some fuzz indeed

:shock:

G.

[birt]

*bump*

cmon guys what would you do with this (except for throwing it away because you've already got a nice distortion pedal  :lol: )

[Joep]

What about the +9V and -9V? Is it the + and - of a 9V batery? So actually -9V is GND right?

[birt]

What about the +9V and -9V? Is it the + and - of a 9V batery? So actually -9V is GND right?

i figured the same thing so that's the way i connected the battery clip...