someone upped this on "another" forum...worth a look!!!!!

[R.G.]

%^&*pit error on my end, R.G.,  I was hitting the front end too hard. When you turn up the drive, Q3 is the first transistor to go non linear, with the output of Q2 looking fine. Of course it is a unity gain follower so you're not running out of swing as on Q3.

No biggie. I've done some real big belly flops in my time. We all do. At least the ones who tell the truth do. 

What I don't have is any voltages on Q5, Q6, and Q21 other than Q21's collector voltage. The fuzz animation circuit obviously supplies the pulse necessary to turn on Q21.  But with the animation off, there must be a source to supply Q21's base to bias it on to some level, so the fuzz circuit will still pass signal.

Go here: http://geofex.com/Article_Folders/Ludwig_P2/Ludwig P2 Schemo.jpg
I had to go put the corrected one back up, as i had apparently taken the one from 2004 down. It's there now.

The answer to your implied question is that there is a voltage supplied to the base of Q21 through the fuzz mix pot and the fuzz footswitch. That section is in the upper left hand corner.

[Mr Bill]

I'm doing my "ten seconds out" pacing after having a post I spent 45 minutes on, dump when I went to post.... This happened last week, too...  Maybe I should compose it in Word, then cut and paste it in.

[Keppy]

Hi, Kep - Not trying to draw any controversy here (anything but), just making an observance. My boss noticed this immediately when taking a glance at the schematic, I mean the base-emitter is a shunt diode with the emitter tied directly to ground (clip).  It produces a haversine (old school) at the collector.  Unless you're swinging a tiny signal way below the peak-peak voltage of the diode junction voltage how would you expect to reproduce the whole waveform? If I can find a scope available this morning, with capability to capture the waveforms to file I will post the Q3 base/collector waveforms.
  My reason to post was that I was spinning my wheels trying to figure out how "my" clean signal wasn't clean.  It's not supposed to be at that point, it's by design..   

No worries. In my noobishness, I was looking only at the base despite the fact that you referenced the emitter grounding in the post. Essentially, I forgot about the fixed diode drop from base to emitter. You were entirely right about me being wrong. I'm still kinda sketchy on a lot of applications of transistors. So it makes sense that I would build the first working copy of a crazy effect with about 30 transistors. Umm, how'd that happen again?

[Mr Bill]

OK - guess I've "recovered" from losing my whole post.  Digi2t, I plan on fully documentating this unit on our Audio  Precision Analyzer as soon as I get full functionality..... Gain, FFT, Distortion, Noise Floor, etc....  No problem to look at the formant filters, with and without distortion.....

R.G., here's  what I don't know is in the design, or a quirk on my unit.  Q3 has a collector available rail ~10VDC.  Q3's quiescent collector voltage is at ~ 8.5VDC, (on my unit).  No leaky interstage caps to throw off bias.  It drives into the distortion through dc blocks to Q5/Q6.  I don't understand how my  "Q point" rail is close to the top rail instead of 1/2 rail,  unless intelligently designed in.

Anyhow, looking to tomorrow to intimidate the fuzz circuit....
   

[Mr Bill]

Kep -  Sorry to set you off, NEVER my intention...,you have been and, I hope will be a continued mentor to me... you guys have provided the golden keys to be able to resurrect these beasts and I've been waiting 37 years to resurrect the trek...

[R.G.]

R.G., here's  what I don't know is in the design, or a quirk on my unit.  Q3 has a collector available rail ~10VDC.  Q3's quiescent collector voltage is at ~ 8.5VDC, (on my unit).

With no info on the actual voltages, I just banged in a 12V supply for it, and it biased at 9V. Pretty similar.

No leaky interstage caps to throw off bias.  It drives into the distortion through dc blocks to Q5/Q6.  I don't understand how my  "Q point" rail is close to the top rail instead of 1/2 rail,  unless intelligently designed in.

Well, my time in the EE biz taught me that there are all degrees of "intelligently designed in".  

I guess, putting it the way Napoleon said it, never attribute to malice what can be explained by incompetence.  Or, by extension, ignorance or a boss demanding that it be on shelves yesterday coupled with a poor understanding of guitar signal levels. Overall, I'm not impressed with what little I can see of the design of this thing, with the exception that I don't understand how they got to the filters. I guess that the times and available parts, etc. were the pressures. Not all circuit designers are equally blessed with talent, just as not all painters (house or portrait) can do an equally good job.

For the purely techie side of it, the collector-base feedback circuit is poorly understood by even the minority of the small group of people who can design single transistor amplifiers instead of subbing parts. It's more complex to design than the four-resistor "stabilized bias" circuit, as the feedback resistor from collector to base is tied up in both DC bias conditions and AC gain at the same time, and in that it works best as a virtual-ground inverting amplifier with a series resistor in the front. Used like that, it makes the very best of the available power supply voltage. Or can, if you can get both the DC and AC conditions right. It loses none of the available power supply to an emitter resistor, but is still fully feedback stabilized and predictable in gain and other characteristics. DC stability is not as good as the stabilized-bias circuit or its stepbrother, the "noiseless bias" circuit, but it has its own beauties if you can get to them.

You can easily enough change that bias point. Increase that 10K from base to ground up to about 22K. This will increase the proportion of the collector voltage fed back to the base, allowing more base current and lowering the balance point to more like mid supply. In fact, in the simulation I did, a 22K put the collector at 5.1V with a 10V supply at the top of the 4.7K collector resistor. Clipping is really close to symmetrical.

I suspect the designer didn't think it mattered with a 100mV typical guitar signal at the high-Z input.

[Mr Bill]

THIS IS AN OFFICAL NOTICE TO RECOGNIZE THE REBIRTH OF MR BILL'S MODEL 9000, SERIAL #1480......

DIED IN 1974

REBORN ON AUGUST 17, 2011!!!!!!!!!

THINK I'LL CALL HIM LUDWIG...

http://www.youtube.com/watch?v=wP8q0kfnhn8

[R.G.]

Congratulations. Does the baby weigh the same as he used to?   

[Mr Bill]

Probably a few grams lighter with the cap replacements!  You're all-in-one schematic was the key.  I was able to whip through the circuit without having to flip between the interconnect, upper and lower schematics strewn all over the bench.  I had a bad connection on connection #30 on the upper deck.  That was the voltage I needed to bring it back to life,
  Now that all functionally and signal paths are restored, I've going to next change out the electrolytics on the top deck.  I'm debating on completely rewiring the entire unit with a molex connector that would allow me to unplug the upper/lower decks.
     
Then , the fine tuning of the trimmers, treadle travel, etc.  On the mechanical side, I have the long rubber strip that mounts to the bottom, but not the original feet, does anybody have the rough dimensions on these?  I can then pick something similar, that should be fairly easy.  The rubber pad on the foot pedal is gone, came off back in the 70's. It was always flapping in the breeze, as it was only being held by a small amount of rubber glue.  Why I didn't glue it back then is pure laziness on my part.
 
Lastly, on one of the stack-illuminated switches on the console I'm missing one of the color circles for one of the positions, (can't remember which).  Somebody posted the different colors/switch posistions either on this thread or on the clone thread.  Does anybody have this handy?  I was looking at three ring divider sheets which have different colored plastic where you insert a white piece of paper with what's contained in that section.  I was planning on cutting out a piece of the color strip with a paper hole puncher to make the little replacement color filter.   

[Mr Bill]

I want to give a heartfelt thank you  to R.G. , digi2t, Keppy and Jimi for your exceptional help on this resurrecting of this piece of metal!   

[Mr Bill]

My comatose child just opened it's eyes after 37 years and was fully competent, thank you, - Jimi!

[pinkjimiphoton]

dude, so glad it lives again!!!

hey, shot in the dark here, but you're not the same mr. bill that reverse engineered the harmonic percolator, are ya?



which switch did ya need the color for?

you're better off to just use standard gels, and cut it out...it should be like a round circle, with a slightly smaller square tab on one side to slide into the switch.

there were no rubber feet as i recall, just the hard rubber strip that everyone loses.

[pinkjimiphoton]

dude, it's all due to the hard work of the team here, not just me...dino, keppy, and especially r.g.!

[Keppy]

Congrats, Bill!

[Mr Bill]

Thanks, Kep! - And you other guys!  I LITERALLY  can't put into words how much you have helped.....I HATE to bring this 90's buzz word, to credibility, "Closure" but that us how I feel! 

[digi2t]

Really happy that we could be of help. Great, great bunch of people here. I may not have even a tenth of the technical expertise of a lot of people here, but I always figure that you get out what you put in.

Cut yer teeth, bust yer chops, and help a guy up. That's what it's all about, and when the time comes, they'll be a hand there for ya when you stumble.

Congrats on getting it up and running again. A please to meet a fellow "Lud-ite" 

P.S. Jimi had the same idea on the Molex connector. Personally, I'm planning on clipping all the board connectors, lengthening some strategic wires on the fall board, then drilling all the pads, and soldering all the wires to the boards. My #2 unit is especially bad. On many connectors, the wrap-around tabs have broken off. I know it will deduct from the "stockness" of these vintage pieces, but functionality dictates that I can't be doing 10 hours of maintenance, for ever hour of use. That's bull. Besides, the day I sell them, I want them to be as bullet-proof as possible. This effect IMHO was just way too far ahead of it's time, and still has plenty of relevence in todays music creation. I think it's only fair that some mods to improve the stability of the unit should be performed, without modifing the circuit, esthetics, or character of the effect. That's what the clone will be for  .

[Mr Bill]

digi2t - I'm not worrying about having the original wiring (so brittle), I've already changed all the lower board caps.. if somebodie's going to nitpick about the originality, well tough, I'm not selling, anyhow!  It's still the original chunk of metal!.
I still have the top board extended on  standoffs for troubleshooting purposes, , but need to get a picture or two online to celebrate...Then a video!  I've already forwarded this to a fellow buddy, Don Mancuso, who is Lou Gramm's current guitarist and just so happens to work with me. Lou lives a couple miles north of where I work, right on Lake Ontario. Don was on the road with Lou last week, but currently is on a family holiday this week. My guitar chops are about 10-15% of what I could do back in the 70's, but he can play FINE!

[Mr Bill]

The outside casing on the unit has a huge spray-painted tatoo, "PUTZ BROS"  My brother was in a band called the Putz Brothers in '72, actually predecessing the Schmenge's, with John Candy...  Somethin' like that...

[Mr Bill]

Yeah, Jimi - There were five little plastic feet, along with the rubber strip that I still have.  Just found out that we have a roll of adhesive-backed black rubber that will go on the pedal.  That was easy!  I think I'm missing two color gels. 

VOICE FUZZ = CLEAR
          FUZZ = RED

SLOW START = CLEAR
FAST START = GREEN

[pinkjimiphoton]

i think those ones only have the colours you have listed, bill..i'll try and check later, recovering from last nite...good gig, but man, am i tired.