Supa Fuzz Mk.II too low gain

[MoldyJuice]

Hi everyone, I recently built a clone of a Marshall Supa Fuzz Mk.II using some transistors I got at a local parts store. The clone sounds great but the only problem is it's very low gain sounding more like a fuzz face on low than a supa fuzz/tonebender. Even with the attack and volume all the way it only generates a light fuzz. The transistors it's using are two 2N281 and one AC128, I have tried installing a bias pot on the collector of Q2 and it has improved it slightly but it's still too low. Could this be because the transistors are too low gain?
Thanks


Sent from my iPhone using Tapatalk

[Electric Warrior]

Do you have any idea how high or low the hfes are?
With the bias pot on the collector of Q2 you're setting the voltages for Q2 and Q3. Q1 could still be off. Voltage readings would tell us more.

[MoldyJuice]

Do you have any idea how high or low the hfes are?
With the bias pot on the collector of Q2 you're setting the voltages for Q2 and Q3. Q1 could still be off. Voltage readings would tell us more.

Unfortunately I don't know the hfe of them, is that something I should find out? Also how would I find out if the q1 is off? Thanks

[MoldyJuice]

Also here are my voltage
Q1 c 9.2 b 0 e 0
Q2 c 0.5 b 0 e 0.2
Q3 c 5.3 b 5.5 e 5.2

Q1 and Q2 2N281
Q3 AC128




Sent from my iPhone using Tapatalk

[Chugs]

Check that the cap between lug 2 of the Attack pot and ground is connected correctly. If it is not, gain will be low

[Electric Warrior]

Also here are my voltage
Q1 c 9.2 b 0 e 0
Q2 c 0.5 b 0 e 0.2
Q3 c 5.3 b 5.5 e 5.2

Q1 and Q2 2N281
Q3 AC128

Sent from my iPhone using Tapatalk

Ok, your transistors seem leak too little for your bias setup. Try a larger resistance on Q2C. The collector voltage should be quite a bit lower, around 0.15V. That will also bring up Q3C considerably.
Q1 may or may not be alright like this, depending on your battery voltage. In most vintage units it measures around 8.5V. You could try a larger resistor on Q1's base to bring it down a little.

Here are voltages from my vintage unit for reference:

Battery: 9.67V
Q1 C -9.02V B -0.03V E 0V
Q2 C -0.17V B -0.08V E 0V
Q3 C -8.44V B -0.17V E -0.11V

Q1C is a little high in this one. The rest is pretty close to average.

I don't think your voltages are off enough for it to have too little gain, though. Fuzz Faces have plenty of gain when biased to 0.5/5V. Finding out your hfes would be a good idea if correct biasing and Chug's idea about the cap don't work out.

[MoldyJuice]

Also here are my voltage
Q1 c 9.2 b 0 e 0
Q2 c 0.5 b 0 e 0.2
Q3 c 5.3 b 5.5 e 5.2

Q1 and Q2 2N281
Q3 AC128

Sent from my iPhone using Tapatalk

Ok, your transistors seem leak too little for your bias setup. Try a larger resistance on Q2C. The collector voltage should be quite a bit lower, around 0.15V. That will also bring up Q3C considerably.
Q1 may or may not be alright like this, depending on your battery voltage. In most vintage units it measures around 8.5V. You could try a larger resistor on Q1's base to bring it down a little.

Here are voltages from my vintage unit for reference:

Battery: 9.67V
Q1 C -9.02V B -0.03V E 0V
Q2 C -0.17V B -0.08V E 0V
Q3 C -8.44V B -0.17V E -0.11V

Q1C is a little high in this one. The rest is pretty close to average.

I don't think your voltages are off enough for it to have too little gain, though. Fuzz Faces have plenty of gain when biased to 0.5/5V. Finding out your hfes would be a good idea if correct biasing and Chug's idea about the cap don't work out.

I double checked all the connections of the cap and brought the bias down to .15 v on Q2 collector the only thing I seem to notice that's out of place is that q3 has about 5v on its collector emmiter and base is this normal?


Sent from my iPhone using Tapatalk

[Electric Warrior]

Whoops, sorry, I totally missed that. I must have been blind this morning. 
You're right, that's ain't normal. C, B and E are in a similar range. Maybe they're shorting out? Also, Q2e should be 0.