Mystery component...

[Pedal love]

Like I said, I don't really know, can't tell from the photo.

Well put.
I agree about diodes there not allowing an output, but it sounds like some of you guys are saying no circuit can work with a diode like this in any way- thats wrong.

[Skruffyhound]

Sorry Analogguru, I wasn't having a dig at you, I just read the post as if it was the manufacturer's schem not a reverse.

[Pedal love]

When you talk about a circuit that has a part that is undefined there are many variables that simply exist. Need more info guys.

[PRR]

Coil may be unusual, but not pointless.

If you just bias-up a grounded-emitter transistor, and hang wire (AKA guitar cord) off the base, it will pickup every strong radio station in town. A naked junction will rectify anything over about 20mV. Local broadcast radio in a few yards of antenna tends to be 2mV to 200mV. AM radio demodulates with simple rectification.

An awful lot of simple naked-transistor stomps have quite large resistors between base and external antenna. That against base impedance will cut both radio and guitar, a bit more radio-cut than guitar cut due to base capacitance.

If the posted plan is slightly right, this designer uses a fairly small series base resistor. And maybe got the local MoR AM radio, or garble from truck CB (if anybody still has CB?). Even, very likely, hash when the cellphone does its things. (I don't leave my cellfone next to my clock/radio any more, it makes nasty static in the middle of the night.)

"I say", ignoring Dirty Tricks, it looks like a thousand uH coil.

HERE is a picture of a high-current choke of similar construction. Use a smaller core, one layer of much smaller red wire, it's about the same.

To "do something" it must act larger than Q1 junction, which I estimate near 600 ohms. 1000uH at 1MHz is 1,000 ohms. If this eyeball estimate is correct, it does nothing below 500KHz. You may breadboard for audio with a short. If RF is a problem, try 1,000uH coil.

[John Lyons]

This is the circuit in question.



All of the parts are accounted for except the inductor (or whatever it is).
I have traced the board top and bottom from pics.

Thanks for the reasoning Paul.
The coil may be omitable I take it. Seems likely as an interferance band aid
against radio... Much simpler to work that out with an input ferrite bead of cap/resistor
if need be.

[R.G.]

The coil may be omitable I take it. Seems likely as an interferance band aid
against radio... Much simpler to work that out with an input ferrite bead of cap/resistor
if need be.

With only eight resistors, four caps, two transistors, the simple thing to do is to build it
and try it, whether real or in a simulator. Sub in diodes, caps, shorts, and inductors
for the mystery part and see what makes it look like it's working.

[John Lyons]

I've built it on the breadboard. It sounded like crap (in an bad way .
I need to try some other transistor gains etc.

[joegagan]

one of the guitar sounds that made me so excited to be a guitar player when i was 14 was the flanged out fuzzed out solo on grand funk's radio hit remake of 'locomotion'.  
john if you can get this circuit to sound like this, you are my new hero.

solo starts at 1:17 - fasten your harness!

http://www.youtube.com/watch?v=jxyU4W8iyeI

[John Lyons]

Ha! Yeah, that sounds like your kind of tone/solo/feeling Joe!
Cool stuff. I guess I need to put on my breadboard hat for a bit.

[PRR]

> It sounded like crap (in an bad way)

Not a shock. The biasing doesn't "force" transistors to any specific operating point. Changing simulated transistors (even for types I would call "interchangable" in most circuits) gives quite different op-point. Battery drop changes bias violently; good thing it pulls nearly no current, and a dry cell will give shelf-life. Temperature effects are strong, though I guess the player will faint before the biasing does. (Would not be my first choice for New Year or July 4th shows.)

Have you IDed the transistor material and hFE-zone?

As a sanity-check: collectors should sit significantly below 1.5V (I got plausable waveforms with 1.3V and 1.1V), yet probably more than a few tenths volt above ground. Really-crappy suggests the darn thing is jammed-up, or just miswired.

There's some interesting interactions. Q2 input resistance is 10K-30K, a very heavy load on Q1's 22K for up-swing. Q1 can pull-down far better, but in sustained overdrive of course charge must equalize so C3's voltage will shift. That cap may be sized for the speed/dynamic of guitar and inventor's taste, and a very different cap may give a very different sound.

C2 is either a treble roll-off or an RF cap. A plan like this probably wants some fizz rounding, so that may need to be in a certain zone.

[PRR]

Did you copy the layout very-very well?

This thing has a lot of gain and (unlike simpler stomps) is non-inverting. If output gets to input, it will oscillate. If you don't hear that, it squals above the audio band. That may be why the emitter choke, and why that choke is laid-out quite oddly down the length of the board instead of like the other emitter resistor.

[John Lyons]

I'll try it again and report back.
From the first attempt it was dull and anemic
not much fuzz at all. With this new insight I'll
see what I get and maybe I has something
miswired in the breadboard.

Again Paul, thanks for the ideas.

[pygmygoatllama]

O.K. everyone,  If you want to see this very circuit board in action it's on youtube now:  http://www.youtube.com/watch?v=m5EJUFVptHo  or just type in   MESSENGER FUZZ   it's posted by spacetonemusic    For this video the guitar is being used with just a solid state Peavy practice amp but you get the idea.  And YES this is the guitar that has the very exact circuit being post by John Lyons   

[John Lyons]

Sounds good. That sounds like the sound we want.
Not mind blowing but it sounds like the grand funk sound.
thanks for that clip!

John

[pygmygoatllama]

Also on that youtube video it's just the tiny microphone on a digital camera.  In person with any good tube amp the fuzz is mind blowing.  It gets all the Grand Funk Railroad sounds and it can do a whole lot more.

[John Lyons]

Yeah, I agree, it sounds good. Especially considering the mic and amp...
thanks for posting that. Can you give us some info on the guitar?
It seems like a repro messenger.  Is is old?

[pygmygoatllama]

No way a reissue.  Original 1960s Messenger Magna with no sound holes.  How many Magnas has anyone seen before? The Magna was only listed in one of their 2 catalogs.    Previously owned by the guitar player for Helloween in Germany and he is a Mark Farner fan.  Don't know if he did the changes: bridge, tuners, and re fret with jumbo frets.  Some experts say finish is original and some say overspray but absolutely original color.  There is metallic green paint under the serial number label on the inside.   

[John Lyons]

That's why I asked...the guitar looks in great shape!
I remember Helloween 

[pygmygoatllama]

There is some natural weather checking that doesn't show on the video.   Also though some Messengers did have a Bigsby tailpiece, this one was most likely added.........

[pygmygoatllama]

I'm getting emails about the Magna saying there's no such Messenger and posts on another saying the same thing.  Here's one in their catalog.

http://home.g09.itscom.net/gfr1212/otakara/images/Eric_Collection02.jpg