Shin-Ei Fuzz Q2 Biasing.

[Toney]

I have been messing around with the Shin-Ei this evening.
Doesn't sound half as good as I 'remembered'. So, after checking the trannie voltages, I find the collector voltages a bit odd - Q1s is at 1.7v. and Q2's is at only 0.8v

Build as per this http://fuzzcentral.ssguitar.com/schematics/shineify2schematic.gif
I checked in with the build info at GGG and he has the Q2 suggested voltage as 6.6v?? (note GGG reverses Q1 and 2s numbering - I am referring to the linked schem from Fuzzcentral)

A bit of a forum search suggests people with a range of Q2 voltages or perhaps onlt people with a stuffed build post Lol.
Anyways so, if someone has a working well one, a voltage reading off Q2's collector would be good. 

[Toney]

Right, well I just found another thread here...... http://www.diystompboxes.com/smfforum/index.php?topic=77319.msg634521 and Pete posts voltages identical to my own with an equally underwhelming sonic results...
Which leads me to assume that the voltages in this GGG document are just wrong?

http://www.generalguitargadgets.com/pdf/ggg_secf_instruct.pdf

I'm going to play with the bias reistors on Q2, that collector voltage (0.8v)  is too low...it sounds gated too.
I can't believe this is right.

[El Heisenberg]

I got the collector voltages exactly as on the GGG document by messing aroung with different transistors. I ended up using two 2N5133s thay measured 90 hfe each that got me the exact voltages.

But i thought it sounded horrible. In every way i played it. With every trannie combo it was just
different, not great. Only reason i settled on the pair of 5133s was to get the voltage right. Maybe id like it later. But i still dont.

Maybe im doin somethin wrong. Not scrappin it yet.

[Gus]

What would help is if people that have "good sounding" Shin EIs would post some voltage points referenced to ground.

Power supply voltage
Collector voltages
Base voltages

hfe might help as well.

[kupervaser]

The sound is so personal, someone who like one sound can hate something else.

But it is a good idea to post some shin ei sounds and than compare the circuits.

[Mark Hammer]

I have an original.  With a fresh battery that gives a V+ of 9.78VDC, I measured the following:

Q1:  E - 0v,  B - .59v,  C - 3.40v

Q2:  E - 0v,  B - .55v,  C - .9v

[El Heisenberg]

But the Hfe of the trannies...theres the voodoo. What did the originals
measure?

[gigimarga]

But the Hfe of the trannies...theres the voodoo. What did the originals
measure?

Mark said in another topic that the hFEs are around 250, if i remebered well.

[Mark Hammer]

Yeah, nothing really extraordinary.

[gigimarga]

I measured the voltages on my clone (http://ustomp.com/?p=13) in which I used BC546B with the hFEs around 300 I obtained these values (using a 8.90V battery):

Q1: E=0.00V     B=0.59V     C=2.89V
Q2: E=0.00V     B=0.54V     C=0.79V

As you can see, the voltages are pretty close to Mark's.
I made very much tries with the transistors in this clone (hFEs from 120 to 700!!!), confused by the GGG's voltages as you, and I can say that almost it doesn't matter.

[Toney]

I have an original.  With a fresh battery that gives a V+ of 9.78VDC, I measured the following:

Q1:  E - 0v,  B - .59v,  C - 3.40v

Q2:  E - 0v,  B - .55v,  C - .9v

Thank you Mark.
Well that confirms it folks.

BTW I used 2n5088s HFEs ~ 400 AND the original part 2sc536 but new manufacture HFEs ~230
So... it's just  a bit of a gated pooey sounding circuit.
I will do that bias messing around today. I'm sure turning on Q2 more will improve things.

[Gus]

Using the voltage readings from Mark H. and fuzz central schematic (Q1 has the 22K collector resistor).

Q1
9.78 VDC - Q1 collector voltage 3.40 = 6.38VDC
6.38VDC/22K = about .29ma Ic
3.40VDC -.59VDC =2.81VDC across the 2.2meg bias resistor
2.81VDC/2.2meg=1.27 ^-6 amps or .00127ma Ib

.29ma / .00127ma = about 228 about the hfe not exact because the Ib is added to the Ic but Ib is small to Ib so close enough to say the hfe is 228.  Note hfe vs Ic curves in spec sheets, hfe changes with Ic so a DMM measurement of 250 might be good enough because of the current the DMM tester uses.

I did the same math for Q2 and got hfe about 250.  Ic is 8.88VDC/147k .06ma Ic

Looks like it was designed with Q2 close to sat.

Try resistor values like 470K to 3.3meg etc for the 1.2meg at Q2 to see what happens with the collector voltage.  Try different hfes with fixed resistor values note what affects the operation points.

work out the hfe with gigimarga voltage reading and compare.  I would try a 2n2222 2n4401 etc. at about 200hfe at Q2

Note all I used was Ohms law and some simple math.  I suggest to do the math with this circuit the fuzzrite the mastro and all the other two transistor fuzz with mixing circuit like these to figure out the hfe range they were design for stock and then how to change it.

Maybe a "tech of" is needed?

[petemoore]

Maybe a "tech of" is needed?
  I've tried a few 'Stretch Bias' circuits like this. They are not pop the parts in 'n go type builds.
  For this one, thanks for the suggest Gus, it wasn't too hard [I used `tricks] to get a more 'centered' bias by `converting it to a Foxey Lady circuit.

[Toney]

Pete, what set up did you do with in the end re Q2?

Gus, I'm going to add a 1m pot plus a fixed at the collector to base and 100k at the collector.
I'll try the tune it in method and I'll go through my trannies for some ~ HFE 200.

[petemoore]

Pete, what set up did you do with in the end re Q2?
  Proportional to the Foxey Lady's base bias string, IIRC something like 470k/1meg., whatever I had in there on the base stayed in there, and a large resistor about 1/2 it's value was added between base and Gnd.
  There's also a resistor between E and Gnd. [IIRC], for that I bent the E lead of the transistor up and poked the E resistor into the socket, soldered it right in there.
  Of course it's a different sound, but gone was the gating, the bias came into 'focus' better.