A little Madbean Poindexter help

[mordechai]

I just wired up a Poindexter from Madbean.  I switched in a 100KB pot for the volume instead of the 50KB pot, and it's not performing terribly well...virtually no sound until the last 40% of the pot rotation.  I suspect that switching it to the 50KB pot will fix that.  BUT -- I am getting very little distortion/fuzz from the unit.  Even with the gain pot turned all the way up, it's only giving some mild drive...not much fuzz at all.

Any idea what might be causing this?

[Mark Hammer]

Well it's definitely not the layout.  I made one a while back and that thing is a monster.  It is essentially a modded Superfuzz.

As for what could be the problem, from what you've described, it is impossible at this point to predict what it might be from theory.

[digi2t]

I just wired up a Poindexter from Madbean.  I switched in a 100KB pot for the volume instead of the 50KB pot, and it's not performing terribly well...virtually no sound until the last 40% of the pot rotation.  I suspect that switching it to the 50KB pot will fix that.  BUT -- I am getting very little distortion/fuzz from the unit.  Even with the gain pot turned all the way up, it's only giving some mild drive...not much fuzz at all.

Any idea what might be causing this?

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[mordechai]

Thanks digi2t, that was helpful.

Having read that guideline post...the only change I made was that I changed C5 and C6 -- the two 10uF caps coming off of Q2 immediately before the octave-producing Q3/Q4 pair -- to two 1uF caps...I ran out of 10uF's, and I had seen a schematic out here where someone substituted 1uF's throughout most of the circuit and said that it worked fine.

Other than that, no changes.

[digi2t]

Time for transistor voltages then.

[mordechai]

Okay...I'll measure, collect the info and post tomorrow.  Stay tuned, and a proleptic thank you for the help.

[mordechai]

Umm...nevermind.  Problem solved.

(Pin-out miscalculation.  I'm an idiot.)

Mark is right, this thing is a total beast.

[Mark Hammer]

Umm...nevermind.  Problem solved.

(Pin-out miscalculation.  I'm an idiot.)
Nope.  You're just following in the footsteps of many before you. 

Mark is right, this thing is a total beast.

The build document lists the volume pot as 50Kb, but I think it should be'50Ka' instead.  I find that for even modest amounts of volume boost in effect mode, you can't go past the 7:00 position.  That tells me there is a taper issue.

Given the high similarity of their tone-control/shaping structure, I suggest you look at this thread: http://www.diystompboxes.com/smfforum/index.php?topic=102818.0  and what I did with an FY-2 and a 3-position toggle.  I think you'd quite enjoy the mod; especially if you already have the Poindexter's variable scoop installed.

BTW mazeltov!

[mordechai]

Baruch Ti-hiyeh, mark.  it is a delight to play this thing.  It is also surprisingly quiet.  I used metal film resistors and BC550 transistors throughout, which I think may be helping here.  I'd be curious to see what happens if I switched out the octave-generating pair to other resistors of lower gain, though...from a number of forum posts, it seems like the octave pair works better with lower gain resistors, though I don't know why. 

I also posted something recently in another thread...I tried using a "starve" pot (5KB) and it works...when it's fully clockwise (5:00 on the rotation) the sound is full, and as I back off on it slightly, it effectively starves the circuit.  But anything past about 2:00 in the rotation cuts out the signal.  Do I need a lower value pot here to make it more effective?  5KB seems to be standard on lots of fuzzes with starve mods but maybe the FY-6 demands something else...

[Mark Hammer]

The "starve" is current limiting, and the amount of current-limiting needed to produce the range of useable changes will depend on the amount of current the circuit draws to do what it does.  It a circuit draws a half a milliamp, I would imagine that a larger "starve" resistance would be needed to produce audible change since many lower resistances will still permit the required current to flow to the circuit.

I have yet to play with it myself, but I have been intrigued by the approach taken to current limiting adopted here in this older post-humous article fro Charles Fischer: http://www.generalguitargadgets.com/tech-pages/46-articles/36-em-fuzz

[mordechai]

That's a very cool article.  He seemed like a very idiosyncratic guy in terms of circuit design, but in a great way.  Ill read it again more carefully when I have a bit more time.

I agree re: the taper.  At the 9:00 position, I am we'll beyond unity gain.  It doesn't bother me but some folks might prefer a more controllable volume sweep.

On a related note, I ran out of 50kb pots, so I used a 100kb pot for the volume.  I actually quite like it.  The tone is a little "fuller", a touch darker, but still familiar in terms of the superfuzz sound.  I suspect this is because the increased pot value changes the frequency corner going to the output, correct?

I also installed a socket for different input caps.  I currently have the standard 10uF in there, but I have tried a 4.7uF with pleasant results.  I've seen schematics where people even use a 1uF but that seems a bit too much of a reduction for me.

Finally...I increased the value of the 470R coming off of q3 and going into Q5 to 1.2k.  I read somewhere that this resisto value needs to be bigger than 470R for tho rave to stand out more.  I wonder if increasing it even a bit more, to 1.5k, might increase the effect even more, though I am sure there are drawbacks here too...

[mordechai]

Correction...that's the resistor coming off Q2, going into Q4...I forgot that the poindexter initial stage is different than the superfuzz initial stage.  But I'm sure you knew what I was trying to say.