My Tone Bender Voltage Correct?

[Arcane Analog]

Not having any leakage in Q1 is strange to send out as a kit. Q2 and Q3 are not as picky but I always like to have some leakage in Q1.

Not strange at all. The Impex transistors Sola Sound was using sometimes have hardly any leakage at all. They set those up with hfes of Q1 and 2 in the 20s or 30s and Q3 in the 2 or 300s. Not all that easy to set it up. I've tried several transistor types with no success. It tends to oscillate and I didn't get the sustain it should have.

Not strange? So the fact that you cannot get several different low leakage/HFE transistors to work in Q1 is attributed to some other cause?  

With all due respect you have it backwards. Q1 requiring some leakage to work properly in the circuit is the norm. What is stange is that the odd ball transistors with low leakage/HFE work. You posted that finding yourself.

[Arcane Analog]

You know, I've built other tonebenders and the generaguitargadget that I've built had a set of OC75s.  It had no trimpots and just used the resistor values that smallbear sent with the transistor set and it is LOUD, unity was about 9:00 and it cleaned up like and overdrive with the guitar's volume control.  When turned up, its full singing, sweet fuzz sustain.  

Steve (SB) sends his trios out with Q3 having the highest gain. It will work fine this way although I have built them both ways and I usually use Q2 as the highest as it tends to reduce unwanted noise.

[Electric Warrior]

Not having any leakage in Q1 is strange to send out as a kit. Q2 and Q3 are not as picky but I always like to have some leakage in Q1.

Not strange at all. The Impex transistors Sola Sound was using sometimes have hardly any leakage at all. They set those up with hfes of Q1 and 2 in the 20s or 30s and Q3 in the 2 or 300s. Not all that easy to set it up. I've tried several transistor types with no success. It tends to oscillate and I didn't get the sustain it should have.

Not strange? So the fact that you cannot get several different low leakage/HFE transistors to work in Q1 is attributed to some other cause?  

With all due respect you have it backwards. Q1 requiring some leakage to work properly in the circuit is the norm. What is stange is that the odd ball transistors with low leakage/HFE work. You posted that finding yourself.

What works for Q1 and what doesn't also depends on the other transistors. The kind of setup I described can work, but I found it hard to make it sound good with the transistors I had. High leakage types like OC75s and AC125s sure make things much easier.

[mac]

Q1:
Q1 needs some leakage to autobias since there is nothing coming from vcc to the base, but a 100k sending current to ground!
The voltage drop across the 10k increases with leakage.
A simple example.
Let's say you have a NPN germ having hfe: 50, leaking 100ua=0.1ma, and Vbe about 0.1v.
The current across the 100k is 0.1v/100k = 0.001ma.
Note that this current comes from the base, and goes to gnd. It's the base current and it is negative!
So there is a negative collector current given by ic = hfe*ib = 50*(-0.001ma) = -0.05ma = -50ua.
The total current across the 10k is ic + leakage = -50ua + 100ua = 50ua,
and the collector voltage drop is 10k*50ua = 0.5v.
The collector will sit at 8.5v.

Another way to look at this is to think that the 100k is stealing leakage and sending it to gnd. It is an anti-leakage device which I used in some FF I built for friends to use germs that were a bit leaky.

So if you have a germ you can estimate the collector voltage drop
dVc = -hfe*Vbe/100k + leakage

Now, remember that near Vcc, say 8.5v to 8v, you get less gain but some kind of 8-up effect. And at lower voltages gain and volume increases.
Q1 voltage is a matter of salt and pepper.
I prefer Q1 biased near Vcc since I'm from the 60s 

Q2/3:
IMHO Q2 must be low leakage. This helps to bias Q3 and to minimize thermal runaway.
If Q2 leakage is big you need a big resistor at Q3, and if you do not scale up the 470 resistor you will notice a lack of volume.
And again Q3 collector voltage is a matter of taste.
I suspect that originals had q3 biased well above 4.5v because of the use of a 100k at Q2 instead of a 33k used in FF.

mac

[Electric Warrior]

Q1:
Q1 needs some leakage to autobias since there is nothing coming from vcc to the base, but a 100k sending current to ground!
The voltage drop across the 10k increases with leakage.
A simple example.
Let's say you have a NPN germ having hfe: 50, leaking 100ua=0.1ma, and Vbe about 0.1v.
The current across the 100k is 0.1v/100k = 0.001ma.
Note that this current comes from the base, and goes to gnd. It's the base current and it is negative!
So there is a negative collector current given by ic = hfe*ib = 50*(-0.001ma) = -0.05ma = -50ua.
The total current across the 10k is ic + leakage = -50ua + 100ua = 50ua,
and the collector voltage drop is 10k*50ua = 0.5v.
The collector will sit at 8.5v.

Another way to look at this is to think that the 100k is stealing leakage and sending it to gnd. It is an anti-leakage device which I used in some FF I built for friends to use germs that were a bit leaky.

So if you have a germ you can estimate the collector voltage drop
dVc = -hfe*Vbe/100k + leakage

Now, remember that near Vcc, say 8.5v to 8v, you get less gain but some kind of 8-up effect. And at lower voltages gain and volume increases.
Q1 voltage is a matter of salt and pepper.
I prefer Q1 biased near Vcc since I'm from the 60s  

Q2/3:
IMHO Q2 must be low leakage. This helps to bias Q3 and to minimize thermal runaway.
If Q2 leakage is big you need a big resistor at Q3, and if you do not scale up the 470 resistor you will notice a lack of volume.
And again Q3 collector voltage is a matter of taste.
I suspect that originals had q3 biased well above 4.5v because of the use of a 100k at Q2 instead of a 33k used in FF.

mac

OC75/Impex units had a 10k at Q1's base and a 47k at Q2's collector instead of the 100ks used in OC81D units. Q3 C is usually above 8V in either variant. And they don't sound like they have an 8-up effect going on..

[Arcane Analog]

I have yet to stumble accross any report of voltages of an original MKII variant - regardless of transistor type or bias network - that approaches 4.5V. There are many knowledegable people that have been kind enough to share their voltages and not a single person has produced any evidence that the MKII variants should see anything but the 7-8+ V range.

Likewise, I have never heard of any MKII variant having the 8up effect. I have no idea where that suggestion came from.

[Arcane Analog]

There is nothing wrong with biasing a MKII at 4.5V if that floats your boat. However, if you are going for the MKII tone then you must bias as it should be and approach 8V.

[Electric Warrior]

It's likely to sound buzzy and will be rather quiet, though.

Speaking of vintage Sola Sound made MKII Tone Bender voltages: here's what I measured in my Supa Fuzz:

Battery: -9.67V

Q1 C -9.02 B -0.03 E 0
Q2 C -0.17 B -0.08 E 0
Q3 C -8.44 B -0.17 E -0.11

[fuzzymuff]

It's likely to sound buzzy and will be rather quiet, though.

Speaking of vintage Sola Sound made MKII Tone Bender voltages: here's what I measured in my Supa Fuzz:

Battery: -9.67V

Q1 C -9.02 B -0.03 E 0
Q2 C -0.17 B -0.08 E 0
Q3 C -8.44 B -0.17 E -0.11

This is from an actual Supa Fuzz or a clone?  If it is an actual one, then the voltage is dounble what is recommended.  Do you know if the original fuzz faces had voltages that high? 

[Electric Warrior]

It's an original unit, Sola Sound made version:



I've seen measurements of several other units and they're all in the same ballpark. My clone is no different. It's just what you get when you put OC75s or OC81Ds into stock MKII circuits. Q3 C won't go anywhere near 4.5V unless you tweak the resistor..

[Pyr0]

Q1:
Q1 needs some leakage to autobias since there is nothing coming from vcc to the base, but a 100k sending current to ground!
The voltage drop across the 10k increases with leakage.
A simple example.
Let's say you have a NPN germ having hfe: 50, leaking 100ua=0.1ma, and Vbe about 0.1v.
The current across the 100k is 0.1v/100k = 0.001ma.
Note that this current comes from the base, and goes to gnd. It's the base current and it is negative!
So there is a negative collector current given by ic = hfe*ib = 50*(-0.001ma) = -0.05ma = -50ua.
The total current across the 10k is ic + leakage = -50ua + 100ua = 50ua,
and the collector voltage drop is 10k*50ua = 0.5v.
The collector will sit at 8.5v.

Another way to look at this is to think that the 100k is stealing leakage and sending it to gnd. It is an anti-leakage device which I used in some FF I built for friends to use germs that were a bit leaky.

So if you have a germ you can estimate the collector voltage drop
dVc = -hfe*Vbe/100k + leakage

Now, remember that near Vcc, say 8.5v to 8v, you get less gain but some kind of 8-up effect. And at lower voltages gain and volume increases.
Q1 voltage is a matter of salt and pepper.
I prefer Q1 biased near Vcc since I'm from the 60s 

Q2/3:
IMHO Q2 must be low leakage. This helps to bias Q3 and to minimize thermal runaway.
If Q2 leakage is big you need a big resistor at Q3, and if you do not scale up the 470 resistor you will notice a lack of volume.
And again Q3 collector voltage is a matter of taste.
I suspect that originals had q3 biased well above 4.5v because of the use of a 100k at Q2 instead of a 33k used in FF.

mac

This is interesting, so looking at Electric Warriors voltages from an original unit, is there any way to determine the leackage of each device ?

[Electric Warrior]

I'm not gonna unsolder the trannies 
But OC75s are rather leaky. 300µA is not uncommon.

[Pyr0]

I wouldn't either, that why I was hoping there was some way of working out some good leakage values from the voltages.

[Electric Warrior]

No way. Apparently the ones with low leakage Impex transistors have Q3 C voltages in the same ballpark...

[Arcane Analog]

This is from an actual Supa Fuzz or a clone?  If it is an actual one, then the voltage is dounble what is recommended.  Do you know if the original fuzz faces had voltages that high?  

Recommended by who?   Are we not talking about MKIIs? The Fuzz Face and the MKII are not the same circuit.

As EW said, you cannot get 4.5V using stock MKII components - you need to really mess with a few values to hit something that low. I have played with the MKII circuit alot and I find 4.5V sounds like crap - nothing like a good MKII. Scrap the Q3 trimmer or set it to ~8k2 and bias from Q2. Get the voltage close to 8V and then tune it by ear.

[mac]

And they don't sound like they have an 8-up effect going on..

I mean that Q1 sounds much like 8-up near vcc, but the FF stage masks this effect, but no completely.

This is interesting, so looking at Electric Warriors voltages from an original unit, is there any way to determine the leackage of each device ?

leakage = dVc + hfe*Vbe/100k

Unless you know hfe there is no way to determine leakage of Q1.
But supossing hfe is between 50 and 100 which is a good guess you can have the lower and upper limit of leakage.

Another way to determine hfe and leakage of an original pedal is measuring dVc = vcc - vc.
Then adding a temporary 1M resistor from vcc to base, measuring dVc again and doing the maths to have another set of eqs in terms of dVc, leakage and hfe.
A kind of RG test in situ 

mac

[fuzzymuff]

man, im hooked on these tonebenders.  Check this out.

[Arcane Analog]

And they don't sound like they have an 8-up effect going on..

I mean that Q1 sounds much like 8-up near vcc, but the FF stage masks this effect, but no completely.

This is interesting, so looking at Electric Warriors voltages from an original unit, is there any way to determine the leackage of each device ?

leakage = dVc + hfe*Vbe/100k

Unless you know hfe there is no way to determine leakage of Q1.
But supossing hfe is between 50 and 100 which is a good guess you can have the lower and upper limit of leakage.

Another way to determine hfe and leakage of an original pedal is measuring dVc = vcc - vc.
Then adding a temporary 1M resistor from vcc to base, measuring dVc again and doing the maths to have another set of eqs in terms of dVc, leakage and hfe.
A kind of RG test in situ 

mac

I have never heard anything remotely 8-up in a MKII and you are the first person I have ever heard suggest that. You might be hearing a little harmonics in there but I cannot see why you would think you hear an octave effect. Are we even talking about the same effect?

Guessing HFE for Q1 is just that - guessing. The only person I have ever heard of actualy measuring the Qs of an original MKII variant found the HFE of Q1 to be 174. Throwing out math is fine and dandy as is making an educated guess. The problem there is that you are long on theory and short on actual data.

[Electric Warrior]

man, im hooked on these tonebenders.  Check this out.

Their MKIIs don't sound like their supposed to. Overly saturated with 100k at Q1's base in the OC75s version. And don't get me started on their "NOS" "OC81D" units.. And then there's the business practices and their reputation for faking stuff...

Guessing HFE for Q1 is just that - guessing. The only person I have ever heard of actualy measuring the Qs of an original MKII variant found the HFE of Q1 to be 174. Throwing out math is fine and dandy as is making an educated guess. The problem there is that you are long on theory and short on actual data.

There are some OC75s with high hfes out there. I have some Valvos that are as gainy as that. But I don't need that to approach the sound of my vintage unit.

A couple of days ago I tried to get in the right ballpark with Valvo AC125s. I only have three of them, but they work really well in that circuit. Here's what I ended up with:

Q1: hfe: 83; leakage: 404µA
Q2: hfe: 65; leakage: 299µA
Q3: hfe: 80; leakage: 388µA

The person who measured hfes of original MKIIs would be David Main of D*A*M. He published hfe and leakage measurements of two Impex equipped units on the D*A*M forum, too. That's where I got the data.

[Arcane Analog]

You missed the point EW - I did not comment on what HFEs are required for a certain sound. I was merely commenting on the fact that mac assumed an HFE between 50 and 100 for Q1 in trying to determine the leakage of the transistors in an original without desoldering them. Assuming that a vintage unit has a low gainer anywhere is simply not going to get the job done when there is evidence out there that HFEs ran all over the place and did not follow the erroneous numbers people commonly use today.