Sola Sound - Tonebender Mark II Professional  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...

Re: Sola Sound - Tonebender Mark II Professional

Postby sickman82 » 13 Oct 2016, 19:34

Dragging up the old Tone Bender thread!

Built a MKI a few years back, and a Supa Fuzz around the same time. The MKI was a real pain, but got there in the end. The Supa Fuzz worked out ok.. but I should have spent more time biasing it. Neither are in my collection any longer so I figured I'd have a go at a MKII.

I'm using Tungsram AC125's.. hfe's are Q1 70, Q2 95, Q3 132. I have a 100k Q2C bias pot and it seems to play nice around 8v on Q3C. Q1 is around 8.5v with the stock 10k Collector and 10k on the base. Q2C is around .3v.

The fuzz is pretty damn musical, I always judge a fuzz by how it makes me play.. if I'm inspired to come up with a new riff or whatever. It happened with this build straight away. I'd just like it if it was a tad sharper.. seems pretty wooly as it stands. Do I mess with the transistors to see if I can tease a little more top end out, or do I reduce the input cap and have at it?
“Birds scream at the top of their lungs in a horrified hellish rage every morning at daybreak to warn us all of the truth, but sadly we don't speak bird.”
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Re: Sola Sound - Tonebender Mark II Professional

Postby ivan H » 15 Oct 2016, 10:45

Hi, do you have the 0.01uf cap to ground on the input fitted to your build? I have it on a switch so I can switch it out which makes it brighter. Even with it switched in though its not whoolly. Mine has three OC75's & the bias trimmer (20k) is on q3's collector. IIRC, I have around -7.6v on the collector. Cheers
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Re: Sola Sound - Tonebender Mark II Professional

Postby sickman82 » 15 Oct 2016, 12:57

Yes, I have that 10n on the board. That's a good idea for a switch.. I might put a different input cap on the same switch for a bright mode.

I started with all three collector as trimpots.. but Q2 seemed the most effective after a bit of playing around. I'll out that as an external pot with a series resistor for the most useful range when I box it.

I guess it depends a lot on how you set your amp.. I have the front end of my amp fairly dirty.. but if I clean it up, the MKII is definitely brighter and gives that Yardbirds type fuzz tone. Really digging it so far.
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Re: Sola Sound - Tonebender Mark II Professional

Postby Electric Warrior » 15 Oct 2016, 18:45

Cutting the 0.01µF definitely is a good idea if you want a little more high end.

Q2C is a great spot for a bias trim pot, as it biases Q2 as well as Q3. Unless you're using very differently spec'd transistors for Q2 and Q3, that's exactly what you want.
Q1B can be used to bias the first stage, but the voltage at its collector is fine already.

Q2C measures a bit high. You could try getting Q2C down to around -0.15V and see where you end up with Q3C. -8V is fine there, but you should be able to get away with a higher voltage. Maybe it will cut a little better then - or maybe not. Easy enough to try and hear for yourself.
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Re: Sola Sound - Tonebender Mark II Professional

Postby Duggers » 28 Dec 2016, 01:18

noelgrassy wrote:Dude, they posted copious photos of Page in action, on stage [w/ Pork Pie Hat, no less] rockin' that very box.
If you see the two disc Led Zep DVD, the jam in the Netherlands, on a TV stage, has him using it as well.

:scratch:Sometimes I get the feeling more musicians than just Billy Gibbons have a way of telling none truths.


You also have to consider that perhaps Jimmy is trying to save us money by telling us he didn't use some devices. Think about it. If he stated "I used a XXX device." then XXX devices cost would skyrocket!
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Re: Sola Sound - Tonebender Mark II Professional

Postby agiant » 14 Jan 2017, 00:50

Hi! first post! :applause:

I got these old miniwatt transistors:

oc71:
leaks=77 Hfe=67.9
leaks=91 Hfe=32.5
leaks=141 Hfe=51.6
leaks=163 Hfe=49.5
leaks=209 Hfe=42.8
leaks=211 Hfe=62.7
leaks=212 Hfe=57.5
leaks=242 Hfe=76.4

oc72:
leaks=192 Hfe=39.4

ac128:
leaks=180 Hfe=75
leaks=183 Hfe=61.3
leaks=194 Hfe=60
leaks=137 Hfe=57.3
leaks=154 Hfe=55.6
leaks=129 Hfe=52
leaks=136 Hfe=50
leaks=130 Hfe=51.5
leaks=147 Hfe=48
leaks=140 Hfe=47
leaks=113 Hfe=37
leaks=130 Hfe=44
leaks=119 Hfe=44
leaks=134 Hfe=35
leaks=198 Hfe=33

I followed the Keen method to measure them.

Which ones would you pick for a mkII?

Thanks! :wink:
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Re: Sola Sound - Tonebender Mark II Professional

Postby Electric Warrior » 15 Jan 2017, 01:34

Try these and let us know the collector voltages:
OC71:
leaks=211 Hfe=62.7
leaks=212 Hfe=57.5
leaks=242 Hfe=76.4

Maybe just drop them in and measure the voltages. The leakage may be a little low for the OC75 bias setup, but I can't be sure. They may bias just fine.
Once we know you're in the right ballpark you can swap them around or substitute for other transistors to find out what sounds best to you.
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