Tube Amps / Music Electronics
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|1/7/1999 10:11 PM|
||Muffin Fuzz Trans. Voltages|
Thanks again to everyone for their input, it gives me much to think about.
R.G. , here are those voltages you asked for-
the first 3 trans. are nearly identical-
Also R.G. , on your Parts and wiring diagram, the links between the 39K input resistor, and the 1uf input cap are wrong. What is the purpose of what looks like a 0.1 cap between b+ and ground.(center of the PCB,at bottom edge). you really ought to correct those 2 wiring schematics, Dorks like me spend hours argueing with ourselves, not wanting to believe that a Pro would print mistakes (input cap backwards, +,-, ).
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|1/8/1999 9:02 AM|
Voltages look OK, at least to a first approximation. The base-emitters of all the transistors are forward biased about 0.6V, and there's about 3 to 4 volts of swing available from the collectors. So much for the bias theory.
Another question comes to mind - are you working from a PCB or a toner package?
If the cap substitutions don't make it work right, you can send the unit to me for some gratis down-home tinkering. This comes with all GEO stuff, by the way.
Good catch. You are a careful cross checker. That trace is shown in the wrong place. The toner and PCB are correct. The parts placement is correct, and if you put the parts in the places shown, the PCB and toner-generated PCB work. Can you guess why that might be? By the way, you're the first person to notice one of these. I guess I should make some kind of award for the eagle eye.
It's a bit of additional bypassing on the B+ line. The original 47uF is all well and good, but it's not a good bypass at higher frequencies, so there is a place for an additional 0.1uF in case there is a problem with some specific set of transistors and parts at high frequencies.
I'm a nut about making sure that power supplies are clean.
Well, even pros make mistakes.
OK, had a minute to check the doco's on the Muffin. The capacitor orientation as determined by the actual circuit voltages are indeed shown correctly in all cases by the schematic symbol. The US convention for electros is that the bar side of the cap symbol --~p~(-- is positive, and the curved bar is negative.
However, there are what appear to be (-) signs on the positive end of two capacitors in the "original version" and a different one in the "improved, with true bypass" version for which the schematic symbol is correctly oriented. I've tracked this down to being an artifact of how my drawing program (Corel 5.0) deals with layers and my clumsy use of it. The original artwork has now been corrected. Thanks for pointing that out. Apparently none of the largish number of people who've built this thing ever put so much into cross checking the schematic with the board.
The schematic symbol is correct in all cases, and perhaps more importantly, the parts layout for the PCB shows the correct orientation not only for the ones shown as electros in the schematic, but also for the positions where electros are optional as coupling and clipping caps.
|1/8/1999 5:52 PM|
Believe me ,I did not mean to pick your "stuff" apart, I just don't remember the old "triangle" Muffs sounding like the one I built
So ,I was pouring over everything, (I used
your PCB) to find out what in the world was wrong. And its confession time, (R.G. ,I wish you would answer your own Email, so I would not have to tell the world.) Last night, I found that I accidently had damaged the trace,
coming from the tone pot, where it snakes
between double drilled 0.1 coupling cap holes,
on its way to the 39k-0.01 to ground. No
wonder the tone pot was not effective. I jumped the fragile section between the double
holes, and bingo- much better. Its still too
fuzzy on the big E,A and D. I think that its my substituting ALL caps to metal film ,thats
part of the problem- too much efficiency.
I'll keep at it.
You know what R.G. ,I know that those spots are double drilled to allow for parts subbing
BUT ,I think you should eliminate the inner most holes, and beef up those traces, after all, the cap leads can be bent to fit "one"
set of holes. Lastly, your earlier post about
advanced distortion, specificaly- "multiple
stages of very soft distortion" has my mind spining, R.G. ,would you be willing to answer a couple of questions about that?
Thanks, as always . Ed R.
|1/8/1999 6:43 PM|
On the contrary, I am very interested where I muff (?!) something up. Not a problem. I make no claim to being perfect.
That's the only way to improve, really. I just try to avoid thinking about the first twenty years of my mistakes
Yeah. This hits one of the places that I wind up having to compromise between the most flexibility and ease of populating on the circuit board, the simplest fabrication (because I make the toner transfer stuff the same as the commercial PCB's) and the best placement and efficiency on the board itself.
I made a board that was all compromise not all that long ago. I took a pass through my schematics file and found about fifteen distortions that use the basic Fuzz Face circuit and proceeded to lay out a PCB that could implement ANY of them depending on how you populated it. This thing nails every permutation of the FF known (to me at least) - FF, Meyer mod, Marshall Supa Fuzz, Vox Pro Mk 2, JEN, and many others. The problem is that I could never figure out how to write an instruction book to tell people how to put it together. Too many choices without a chapter per version. The Omni-Face remains a curiousity in my garage.
Sure. No mystery there. It's a concept that gets overlooked a lot, and one I DO spend a chapter on in the manuscript of the book I keep on writing on distortion effects.]
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