Help recovering volume loss (super fuzz)

[DiscoVlad]

Apologies if it sounds like I'm being argumentative for the sake of doing so, it's certainly not my intention.

Regarding devices of low Hfe:
I've just now measured two batches of 2n2222A transistors.
The ST Micro ones in TO-18 metal cans were all hfe around 60-70 (batch of 20), while the dozen or so Fairchild devices I have in TO-92 packages were all hfe 150-170.

The datasheets for 2n2222a from both of these manufacturers have identical hfe figures for Vce=10V, over the same range of base currents and these levels I've measured are both within specs .

Bias Voltages:
Looks like I've misunderstood you there with how they sound.

Here's a picture showing what's going on (click for larger):


At the 7.2V collector, the transistor is just starting to turn on so the gain of the device doesn't matter (as borne out by your testing) and it sounds the same.
While at 2.1V the transistors are saturated, and they sound different because the two transistors have different amounts of collector current through them, which is related to the transistor's hfe.

[StevenJM]

Well i changed Q2 and Q6 and it still has the same readings... nothing new... i'm ready to give up.  I'm really not sure what i'm doing at this point, its just getting really frustrating.

[StevenJM]

After seeing this picture... I think some YO-YO swapped out some of my 10uf electrolytic caps with .047uf caps.  thats gotta have an effect on the output... ugh this thing has just been a huge PITA.

[joegagan]

ya, steven , don't give up. don't take anything for granted when a pedal is this old. no telling how many yahoos have been goofin around inside there.
when you get it working as it should, you will be glad you stuck with it.

[StevenJM]

but then i find this one that looks pretty much identical to mine.

(the .047 looking green caps instead of of the 10uf electrolytic caps)

I just don't even see a single .047 cap in the schematic so that just makes it even more confusing.

[StevenJM]

So now that I've replaced the electrolytic caps and a hand full of transistors, my volume is still low (while audio-probing, I get good volume and good fuzz before Q6).  It kind of 'pops' when i pluck a string and then the sustain of the fuzz is pretty crappy (again, not present when i'm audio probing prior to Q6...

Here's my current readings, with the values from SolidHex's original in (Parenthesis)

Q1
C=5.58 (6.01)
B=0.69 (0.66)
E=0.13 (0.12)

Q2
C=8.94  (8.88)
B=5.59  (6.01)
E=5.04  (5.41)

Q3
C=6.28  (6.23)
B=3.00  (3.27)
E=2.62  (2.72)

Q4
C=2.73  (3.10)
B=1.53  (1.70)
E=0.93  (1.11)

Q5
C=2.73  (3.10)
B=1.53  (1.67)
E=0.93  (1.11)

Q6
C=0.26  (5.75)
B=0.83  (0.98)
E=0.19  (0.36)

So the only number that is drastically different is the Collector of Q6, so going off of this schematic, what could be giving me such a low number? http://www.experimentalistsanonymous.com/diy/Schematics/Fuzz%20and%20Fuzzy%20Noisemakers/Shin-ei%20Fuzz%20Wah.gif
... my board had a .047uf cap after Q6r instead of a 10uf electrolytic cap, so i replaced that, however it made no change.  The 10uf cap at the input was a .047 cap as well, so i also changed that out to a 10uf electrolytic cap.  also no difference.

Based off that schematic, how can i tell for sure whats the + or - of the cap?  is the short line the negative, or vice versa?  I tried them both ways and didn't notice any difference.

Should I try replacing the passive capacitors?  all of the resistors i've tested still seem to be working. 

I'm just not getting it.  I might give up and try taking it somewhere to get fixed.  I tried reflowing all of the solder on the board, the pots, and the jacks... I've spent so much time just staring at this thing hoping for something to jump at me.   

[DiscoVlad]

Do you have a picture of the trace side of the board around q6? Maybe there's a short?

How about breadboard up a copy of the circuit between the balance pot wiper and the output, and compare?

[joegagan]

forgive me for asking, but is Q6 possibly in backwards? i agree with discov, you still have some sort of problem around the biasing of Q6, bad trans ( i know you've replaced it), something.

[StevenJM]

I don't think the transistor is in backwards, since the emitter should be connected to the 1K, and then to the ground.

I don't notice any shorts, do you guys notice anything that stands out from the bottom of my board?

[joegagan]

well, different  trans part numbers can sometimes have different pinouts. forgive my memory, was the part you put in the same part number as stock?

[StevenJM]

Yea, the transistors are the same... the 2SC828... so the E,C,B pin layout should be the same.  Theres only so many parts around Q6, a 10K resistor in front of the collector and the 10uf electro-cap after (last thing before the output of the board) and a 100K a little further down the line.

[joegagan]

if i was working on it i would lift one leg of each of the 5 resistors surrounding Q6 and measure each one. at that age, one of them may be slightly cracked or who knows what.

[StevenJM]

if i was working on it i would lift one leg of each of the 5 resistors surrounding Q6 and measure each one. at that age, one of them may be slightly cracked or who knows what.

cool, i'll give it a try.  I'm willing to try pretty much any suggestion at this point.  even throwing it at a brick wall.   

[StevenJM]

all the resistors are checking out...

Looking specifically at the collector of Q6, there's a 10K resistor between the power and the collector.  So I get a 8.8K reading before the resistor, and only .26 after... does that seem right?  that just seems like way too big of a drop in voltage, yet the resistor is checking out at 10k.

[LucifersTrip]

I'm willing to try pretty much any suggestion at this point.  even throwing it at a brick wall.   

did you read the part in my earlier post regarding voltages:
http://www.diystompboxes.com/smfforum/index.php?topic=97888.msg854759#msg854759

I doubt it's the problem since your Q6C voltage is so far off (at this point you probably should post a large closeup pic of Q6 and the surrounding components), but it's worth a shot...

Try altering 15K from base to ground and see what happens. If using a 235 hfe with a 17K gave me 2.1v and 10K gave me 7.2v,
what will you have to lower the 15K to to get 5.75v?

Q6 (hfe 235)
17K (2.1v)
10K (7.2v)

[StevenJM]

A swap to a 10K resistor gives me

C=1.93
B=0.76
E=0.15

So the collector is a little higher.

Should I maybe try a different transistor too?

[StevenJM]

I plugged it in and it is working now.. So that's pretty awesome.  Maybe the 15K was just too strong for that transistor.  Should I try a resistor lower than 10K now, to try and raise the collector even more?

[LucifersTrip]

A swap to a 10K resistor gives me

C=1.93
B=0.76
E=0.15

So the collector is a little higher.

I plugged it in and it is working now.. So that's pretty awesome.

excellent!

Should I maybe try a different transistor too?

Should I try a resistor lower than 10K now, to try and raise the collector even more?

A lower gain transistor will give you higher collector voltages....but, you should sub a pot for the 15K and adjust it while playing

[StevenJM]

I don't have any spare pots at the moment, but plenty of resistors... I put in a 8K2 resistor and that bumped my collector up to 6.09... That might be too high now, but I'll play with it, if anything I can go back to the 10K.

I'm just SO glad it works.  I jokingly told my gf "today's gonna be the day that I get this thing working" now I can relax and actually play the thing.

[LucifersTrip]

I don't have any spare pots at the moment, but plenty of resistors... I put in a 8K2 resistor and that bumped my collector up to 6.09... That might be too high now, but I'll play with it, if anything I can go back to the 10K.

I'm just SO glad it works.  I jokingly told my gf "today's gonna be the day that I get this thing working" now I can relax and actually play the thing.

cool...like I always say, "excellent...one more fuzz in the world"

6.09V is very close to the Solidhex mark, so should sound pretty damn good.