Mosrite Thrown together but

[8mileshigh]

Hey Analog Dude,

I fired up my Ge Fuzzrite clone (built from Andy's layout) when I got home today and found that one side of the blend rips and the other sound terribly lame.  Anyway, the good side maxed is a pretty cool sounding fuzz.   Here are my readings:  Hopefully this will guide you to getting yours working better, I consider my unit to be a small tweak away from being killer. 
Transistors are  Raytheon T59247
Q1
C=2.77v
B=0.1v

Q2
C=0.2v
B=0.08v

I can only assume the Q2 is horribly misbiased and might try to rebias it when I get a chance.  Thuth is, that I know nothing about electronics so I just fumble my way through these builds and pray that they finally work in end after hours of trouble shooting.  I work in stained glass and was looking for another place to stick my iron 

[analog kid]

thanks man , I think I'm also gonna perf up this little circuit too to be able to 'play around' with HOW it biases . I hadn't thought of even doing that before even though I have the schematic ( and the original)  BECAUSE I figured I have the real thing , what need do I have to rebuild it? Well , that's the need! To mess with the circuit w/o hacking up my vintage piece.
Anyway I like seeing those C/B vltgs on Q2.( as well as on Pete's Silicon unit)  being very low biased collector.  I do however have to believe that when that C/B drop gets much smaller ( yours is like 120mv right?)  then that's when it's gonna start to get a bit gated. (??) Mine sitting at less than 20mv between Collector adn Base is surely got to be a problem.
   another thing that would help me IF you don't mind is to put your meter across that 100k resistor (r4) in circuit,  that's tied between the collector resistors. I'd like to see what resistance yours reads. If you get the full 100k value then I may have a wildly out of spec resistor.
thanks if you could do that as well

I work in stained glass and was looking for another place to stick my iron 

Cool! I haven't heard that one before that's for sure.  Whatever it took to get you into effects/electronics... I hope you get much use and enjoyment from it. Don't feel bad or discouraged that you fumble through the simplest of projects, The fact that it forces you to learn to troubleshoot  properly and before you know it you WON'T be making the mistakes in the first place!! even on larger circuits.  Have you worked ONLY with Veroboard btw?, perf?  You've not done any pcb fabrication I assume?   stripboard is definitely a unique medium, especially for learning to do your own layouts!
  Thanks again man

[Gus]

from reading 8mileshigh last post about a new build it might be how the circuit was designed.

8mileshigh try a 470K and then a 2.2meg to start for the 2nd transistors base to collector resistor.   Then try other values measure the 2nd collector voltage.  For each R3 value write down the collector voltage, when you get the 2nd C about 2v I would give it a try.

[analog kid]

thanks gus, this suggestion is intended for me as well I guess?
I see you obviously think that the B/C Resistor for Q2 is more important in this case for biasing the Coll.?  and that you are suggesting trying both 470k (a much lower than stock) and a 2.2M ( a much higher than stock) Subbed for the 1M to see which way we need to go to 'bias' it , Right?
Matter of fact if a lower value would end up doing the trick here for bringing up the Collector  then I could easily try a 470k or so in there w/o mucking about with the board!!   this is something i can't do for the 100k (which is reading 47k)(  R4 though since(as far as i know ) there's not a way to bet a higher value parallelling a 47k resistor.  which....
   Did anyone have an answer for me on why maybe that 47k thats seriesed between a 22k and 47k R's and between the Collectors  MIGHT READ BELOW it's value of 100k?!
i hate to pull that resistor out only to find that it does indeed measure 100k after all!

[Gus]

analog kid  Yes and no about "this suggestion is intended for me as well I guess?"  8mileshigh sounds like it is a new build and has no vintage value.

I agree with you about not doing anything to the effect until you are certain: However try jumpering (With jumpers) in a 1meg in parallel across the B to C resistor for 500K.

The value were about 1/2, 470K and X 2, 2.2meg

[analog kid]

thanks gus, yeah I am going to parallel it with a 470k tonight, but no I'm not doing much til I know for SURE how things bias on it. Which I may have to learn from putting one together not even putting jacks on it to play though most likely(although I'm sure it'll be way too tempting! I've never put a circuit together w/o listening to it)  Someone suggested that I drill a couple small holes aside the collector resistor(s) and CUT AWAY the existing resistor and solder in a trimpot to have the most precise control of biasing.  I Say NO WAY to that!! I pretty much HAD TO try lifting the base Cap.
Mine actually still has most , a good bit , of the lettering on the enclosure although pretty weathered and pitted. that's sort of rare on these. the lettering comes off with the scratch of a fingernail.   The way I heard it , in the beginning the Mosrite guy was pretty much producing these boxes " on his kitchen table" literally!! and i believe it
   Don't mean to beat a dead horse but, No opinion on whether or not that R4 100k resistor SHOULD or SHOULDN"T actually measure it's full ohms value?!!  I know often resistors will read different values depending on what they're connected to and need to be lifted on one end to get actual value.  But in this ones case (seriesed) It doesn't seem to me any reason I shouldn't get 100k across it! (?)  I only get 47k

[8mileshigh]

Analog,

I thought you'd have to physically remove the resistor to get a proper reading of it.  I did, however, get a 5.23v reading from touching both ends of the R4 with the volt meter if that's any help to you.

Gus,

Thanks for the suggestions, you may be right that it was designed like this but it just doesn't sound quite as good as I think it can. I was chatting with the guy on Ebay that makes those homemade looking Spooktone pedals & he says he knows a guy that built some of the old Mosrites in the day and said they were built with those low collector values on purpose.  Maybe they came to the conclusion that  the Ge didn't sound great & abandoned the circuit and went to the silicon version.  I'll try rebiasing when I get a bit of free time, maybe in the next couple of days.  My next challenge will be to try and record some soundclips.

Chris

[petemoore]

  Kind of like a dam for guitar signal...
  Ie, a small window of bias on the transistors which distort, and increasingly clip and compress as input signal level increases.
  Cuts [tear's?] away everything except a 'slice' of the input signal swing.
  Anywhere just off bias line starts getting clipped. Clipping starts very early...etc...as soon as the transistor starts swinging the collector voltage in response to input, it starts running out of room to swing.
  May sound 'pinched'...lol.
  Very 'different' approach = different Fuzz Sound...cool !
  Anyway, with such a small bias voltage, if anything 'moves' like say a transistor drifts or...the small opening of the window gets closed completely.
  @@R@te That's my take on the design approach or result.
  I'ts kind of a 'wierd' sound for a distorter, at first...seems too wierd...wierd tone can be cool once you adjust your pallete and acquire a taste for it, adding 'spices' to this dish...spices it up too. Slamming the input with more voltage via other Boost or Fuzz being one way to spice it up.
  Can sound like an 'octave -the octave', gnarly Fuzz, nasty fuzz,
  If it's real bad gatey and you'd like a little more signal to swing through...I'd mess with 'opening up' the bias a little or a little more..., as Gus and others have done.

[analog kid]

Hey all, If any are still interested in this I finally got around to messing with my original Fuzzrite some more (delicately as possible)
But first , and this pertains to one of the last posts here. I got the "stompbox" book by Art Thompsom from my wife for Christmas (it was my second choice If I couldn't get Mike's book ; ) I was very pleased with it btw far as the historical front. And I was very surpised to read in the section on MOSRITE , a little quote from the founder / creator of the Fuzzrite that  " Only the first 250 Fuzzrites were made with Germanium trannies, when i discovered that they wouldn't fuzz right (haha) when set on cold concrete", "we then switched to silcon transistors for production" 
so as far as I take that at least, the one I own , being the Germanium equipped model , Is actually ONE of the original 250 made , and only ones to ship with the germ's in there!!!  that would make it even more of a collectable.        On to the issue I have with it , which makes my findings even more depressing as i think that tranny has problems
  I did get around to pulling up the Collector lead  on the Q2 since the Base was already disconnected I figured if I pulled the B and C I could leave the Emitter to ground and it wouldn't matter , then I could make a little "in circuit test jig " to solder in other PNP's and test the circuit around Q2.
Well first off I dropped in a 2907 sili pnp and right off  the voltages become substantial !!!  I got a vltg of 1.2v for Collector and  apprx  .550v for Base.    So this alone prob tells me that the original 408germ is no longer good (with it's 70mv C and 55mv B)  anyway I also noticed , and I didn't mention this before , that the squealing / oscillation that I sometimes would get when I switched On ,which was also controlled in pitch and volume by both pots,  seemed to be gone.      Now there is definitely still misbiased/gating with that tranny I dropped in but that's likely to be expected.
So IF it's now obvious that the Germ Q2 was bad , would the best way to go about it IF i wanted to replace it , to just leave 'test jig' wires there and try soldering in several different pnp Germaniums till I find one that biases out pretty well ? rather than just picking one and then worrying about the resistor values.           and  if so and looking at the schematic... a Higher gain or Lower gain for Q2?  I assume not the hfe like a normal fuzz face?
        THANKS AGAIN

[analog kid]

Well another discovery! maybe the original q2 isn't bad?
While I was clipping in other trannies for Q2 I found that any Ge I put there was still getting those horribly low C/B readings ( 30mv-80mv range) with less than 10mv or so drop between them.
  BUT it wasn't til I sort accidentaly struck the strings (fuzzing) while the probe was at the collector, that I realized I WAS getting  a higher voltage there!!  so I checked this way and where I got  70mv C and 60mv B  while "idling" ... I was seeing around 3-4volts Collector and 1-2volts Base WHEN THE STRINGS WERE HIT!!!   and yes, even with the original Ge in the circuit!
  So , besides the posibility that the tranny wasn't bad , what does this tell us? Looking at the schematic I linked to, what could possibly be the cause (IF this isn't a normal occurance  that is) of this ? and so far as I could tell Q1 doesn't do this , it reads proper vltg regardless.  AND when I had a silicon rigged in there for Q2  it also seemed NOT to matter if the strings were struck or not. I got same 1 bias voltage regardless.
         thanks

[petemoore]

Well another discovery! maybe the original q2 isn't bad?
While I was clipping in other trannies for Q2 I found that any Ge I put there was still getting those horribly low C/B readings ( 30mv-80mv range) with less than 10mv or so drop between them.
  BUT it wasn't til I sort accidentaly struck the strings (fuzzing) while the probe was at the collector, that I realized I WAS getting  a higher voltage there!!  so I checked this way and where I got  70mv C and 60mv B  while "idling" ... I was seeing around 3-4volts Collector and 1-2volts Base WHEN THE STRINGS WERE HIT!!!   and yes, even with the original Ge in the circuit!
  Generally bias is taken with the transistor having no real input. I wondered if the bias voltage didn't rise on the collector when signal 'pushed' on the base.
  So , besides the posibility that the tranny wasn't bad , what does this tell us? Looking at the schematic I linked to, what could possibly be the cause (IF this isn't a normal occurance  that is) of this ? and so far as I could tell Q1 doesn't do this , it reads proper vltg regardless.  AND when I had a silicon rigged in there for Q2  it also seemed NOT to matter if the strings were struck or not. I got same 1 bias voltage regardless.
  I would guess everything might be close to 'right' with your circuit, this would mean that the voltage on Q2 collector rises with signal input to circuit.

[analog kid]

Well thanks for your input on it.  If this is normal operation than this is definitely something I've never seen before in a Fuzz crkt.  Though yes It does make theoretical sense.
  I really do need to whip up this crkt  ASIDE from my vintage unit so I can check things out.  but I just am a bit short on jacks etc.. right now ( I HATE Salvaging from other projects even if they're not being used as that usually means in my case that there's little chance they will be again : )
   BUT I WOULD need to wire up the bypass switchign the same as it is on the stock unit (which is very unique if you recall , with  Battery + and ground going to one outside lug and Q1/2 Emitters 'grnd  tied to the middle two lugs ...Input/Output at the opposite side lugs.  Anyway i will need to do it this way to see how it behaves I think.   the switching may be what is causing some of my problem with the big dying animal screeching sound  charging / discharging with the switchi!
I obviously just hate to try another switch in there  , If I had an old Carling DPDT to put in I likely would though

[8mileshigh]

Hey all !

I finally got around to tackling the misbiased Q2 in my Ge Fuzzrite clone built from Andy's vero layout.  I did as Gus suggested and replaced R3(the 1M resistor between the Collector and base and threw in a 2.2M (pretty much all I could find).  The old DC V readings were :
Q1
C=2.77v
B=0.1v

Q2
C=0.2v
B=0.08v

With the new resistor in place:
Q1
C=3.15v
B=0.1v

Q2
C=0.35v
B=0.08v

This mod has definately got my Q2 distorting nicely but I have no idea if this is optimal because there isn't much of a tonal difference between Q1 and Q2 right now.  I also believe I have lost some output from the circuit.  I'll have to install a pot and do some fine tweaking but I'm happy that I've improved the sound of the box.  I have no idea if any of this will be of any help to Analog Kid or not.  Thanks to Gus for the suggestions.

Chris