Sola Sound - Tonebender Mark II Professional  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
User avatar
Electric Warrior
Diode Debunker
Information
Posts: 737
Joined: 23 Feb 2009, 03:37
Has thanked: 23 times
Been thanked: 104 times

Post by Electric Warrior »

It's too little leakage for your bias setup, at least if you're going for the OC75/OC81D style thing. You could try 100k on Q1's base and 100k on Q2's collector. I hope that gets you close. They were biased to around 0.16V on Q2C. Hiss is not much of an issue in this voltage range. It's more prone to gating, but the gating can sound quite good.

That said, your Q1C looks like it could be in the right ballpark with the 10k, but I guess your battery voltage may be rather low.

User avatar
Rocket Roll
Solder Soldier
Information
Posts: 249
Joined: 27 Mar 2008, 08:25
Location: Belgrade
Has thanked: 19 times
Been thanked: 44 times
Contact:

Post by Rocket Roll »

Electric Warrior wrote:It's too little leakage for your bias setup...
Well, that's exactly the greatest part of the problem - those are the transistors that are supposed be selected to work well in a ToneBender by the good people in BYOC, right? If so, why aren't they?
Electric Warrior wrote:They were biased to around 0.16V on Q2C.
Great info, thanks!
Electric Warrior wrote:That said, your Q1C looks like it could be in the right ballpark with the 10k, but I guess your battery voltage may be rather low.
Forgot to mention - all measures taken with a laboratory supply at exactly 9.00V.

User avatar
Electric Warrior
Diode Debunker
Information
Posts: 737
Joined: 23 Feb 2009, 03:37
Has thanked: 23 times
Been thanked: 104 times

Post by Electric Warrior »

I guess it wasn't all that well known when they started out and they followed the general recommendations at that time. As you can see from the schematic, they had no chance to get this right.

Considering your supply voltage, Q1C is rather high. I'd definitely use a bigger resistor on its base.

User avatar
Rocket Roll
Solder Soldier
Information
Posts: 249
Joined: 27 Mar 2008, 08:25
Location: Belgrade
Has thanked: 19 times
Been thanked: 44 times
Contact:

Post by Rocket Roll »

Electric Warrior wrote:Considering your supply voltage, Q1C is rather high. I'd definitely use a bigger resistor on its base.
Thanks! Any recommendations? Which voltage do I aim for?

User avatar
Electric Warrior
Diode Debunker
Information
Posts: 737
Joined: 23 Feb 2009, 03:37
Has thanked: 23 times
Been thanked: 104 times

Post by Electric Warrior »

Around 90 to 95% of the supply voltage, so between 8.1 and 8.55 V would be dead on.
If the 100k on Q2C does the trick, A 100k for Q1B should be alright.

User avatar
Rocket Roll
Solder Soldier
Information
Posts: 249
Joined: 27 Mar 2008, 08:25
Location: Belgrade
Has thanked: 19 times
Been thanked: 44 times
Contact:

Post by Rocket Roll »

I'll try. One question, if I may...
Electric Warrior wrote:It's too little leakage for your bias setup...
I've got a small stash of germanium transistors that I can experiment with. Given the above numbers, what kind of leakage (IC and/or ICE0) am I looking for?

User avatar
Electric Warrior
Diode Debunker
Information
Posts: 737
Joined: 23 Feb 2009, 03:37
Has thanked: 23 times
Been thanked: 104 times

Post by Electric Warrior »

You could try around 0.35 mA. Whatever gets you in the right ballpark. Higher leakage should bring down the voltages on Q1C and Q2C, while the one on Q3C increases.

User avatar
Rocket Roll
Solder Soldier
Information
Posts: 249
Joined: 27 Mar 2008, 08:25
Location: Belgrade
Has thanked: 19 times
Been thanked: 44 times
Contact:

Post by Rocket Roll »

I've seen that SmallBear now stocks Amperex 2N281 transistors which are made in Holland, and according to this excellent read (https://sites.google.com/site/transisto ... rs/philips) they should correspond to Phillips OC72 type. I've ordered a set and received this:
Amperex 2N281 Flying Dutchman Smallbear.jpg
SmallBear The Flying Dutchman Transistor Set 12.2017.jpg
The Flying Dutchman Smallbear Set Schematic ToneBender MKii Pro.jpg
SmallBear measurements, as written on the bags:
Q1 - hFE 60, L(eakage) 125
Q2 - hFE 92, L(eakage) 158
Q3 - hFE 158, L(eakage) 181
Chinese transistor tester measurements:
Q1 - hFE 54, ICE0 67uA, ICEs 5uA
Q2 - hFE 96, ICE0 .20mA, ICEs 8uA
Q3 - hFE 186, ICE0 .33mA, ICEs 11uA

I've dropped them in a ToneBender MKII OC75 schematic, without any resistor substitutions, and got this:
In-circuit measurements, taken at 8.99V:
Q1, E 0.00, B 0.02, C 8.86V
Q2, E 0.00, B 0.08, C 0.15V
Q3, E 0.08, B 0.15, C 8.20V

The sound? It fuzzes allright, but let me put it this way: if I were someone who listened to all of the ToneBender lore and then got introduced to this sound, I would've thought that I'm simply not a fuzz person.

In this particular setup, they do not show more than 10% of the ToneBender potential. The sound is velcro-ish, octavey, gated. It is very present and "real", but not really pleasant.

If I haven't already completed two ToneBenders and somehow got crazily lucky with them (they sound very "Marshall in a box"-like, gainy and creamy, almost BigMuffish), I would've thought that ToneBenders are simply not my cup of tea, and that any zVex Fuzz Factory could do a number of such tricks, without the mythology attached.

So, do I change the transistor order and try to coax something out of this circuit as it is, or do I change the resistors - that is the question now...

User avatar
Electric Warrior
Diode Debunker
Information
Posts: 737
Joined: 23 Feb 2009, 03:37
Has thanked: 23 times
Been thanked: 104 times

Post by Electric Warrior »

Right.. voltages are one thing. Tone is another.
You've got a really wide spread of gains here, which probably makes things more complicated than they need to be.
Also, Q1 obviously has too little leakage.

Why don't you go through your stash of germaniums and see what works well for you?

User avatar
fuzzbunny
Information
Posts: 46
Joined: 09 Jan 2012, 18:12
Has thanked: 59 times
Been thanked: 14 times

Post by fuzzbunny »

@Electric Warrior

I just wanted to say that you are an awesome individual. So many times I have seen you step up and offer your valuable knowledge on vintage germanium circuits. Thank you!

User avatar
tonycaster
Information
Posts: 6
Joined: 12 Jun 2017, 01:02

Post by tonycaster »

What do you guys think about using a 33 k on Q2 collector? I've done that in few tb mk2 i built and i think it gives me much more 'range', i can use the fuzz even when it's super hot cos the 33k it's balancing with the leakage when increasing.
The sound is never gated.
At room temperature the bias on Q2 collector is 0.6v

User avatar
Rocket Roll
Solder Soldier
Information
Posts: 249
Joined: 27 Mar 2008, 08:25
Location: Belgrade
Has thanked: 19 times
Been thanked: 44 times
Contact:

Post by Rocket Roll »

I've ordered a ToneBender set from diyguitarpedals.com.au - http://www.diyguitarpedals.com.au/shop/ ... ducts_id=6

The transistors look the part:
AC125 01.jpg
AC125 02.jpg
It came with these marked values:
Q1 Collector current (IC) 828, Leakage (ICL) 159, hFE 73
Q2 Collector current (IC) 818, Leakage (ICL) 146, hFE 73
Q3 Collector current (IC) 1182, Leakage (ICL) 185, hFE 108

My meter tells me this:
Q1 hFE 71, IC 1.0mA, ICE0 .25mA, ICEs 12uA
Q2 hFE 74, IC 1.1mA, ICE0 .30mA, ICEs 15uA
Q3 hFE 102, IC 1.4mA, ICE0 .32mA, ICEs 14uA

I haven't measured the voltages, but by ear, after I've replaced the first SmallBear's "Flying Dutchman" (2N281) in my BYOC build with the middle AC125 (the one with hFE73), the sound got fuzzier, which is to say less like distortion and more like fuzz ("mushier", "looser", "spongier"). It's a pleasant sound alltogether. I'll leave that transistor there for the time being.

User avatar
Ocular Dawn
Information
Posts: 1
Joined: 07 Jun 2015, 12:46
Has thanked: 1 time
Been thanked: 1 time

Post by Ocular Dawn »

Hey Rocket, I have the same BYOC E.S.V. Tone Bender which came with 3 VAL OC76. Mine were very hissy and as a result are still in my parts drawer. Luckily I had a few others to try. Think I settled on a trio of GT402B which worked really well and the thing roared into life. Anyway I scored a 100 of those AC125's you have and they tend to drop in nicely for all Tone Benderesque circuits I have built. Try putting the lowest hfe in Q1 - highest Q2 - and the remaining in Q3 if you haven't already. While there is a plethora of variable's to consider (leakages / voltages / luck), I've found that transistor setup has been kind to me in the past.

User avatar
andregarcia57
Cap Cooler
Information
Posts: 572
Joined: 16 Nov 2008, 15:42
Has thanked: 72 times
Been thanked: 108 times

Post by andregarcia57 »

Hello guys, I got some Germanium NPN and I want to mount a Tonebender, which schematic version do you recommend?

What better trio to get a great tonebender?
Follow report with Geofex tester
Item - HFE - LEAKAGE mA
01 - 116 - 0.082

02 - 113 - 1.015

03 - 79 - 0.566

04 - 113 - 0.607

05 - 69 - 0.562

06 - 90 - 0.983

07 - 97 - 0.672

08 - 121 - 0.716

Thanks 🤜🤛
Attachments
20220122_112049.jpg

Post Reply