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?
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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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Re: Sola Sound - Tonebender Mark II Professional

Postby sickman82 » 21 Jul 2017, 12:22

I revisited my build today because to get it to bias with the AC125's I had at the time I built it, I ended up having to stick a resistor across Q1 to simulate leakage. I had a search through my stash the other day and found some pretty leaky AC125's and put the circuit back to stock MKII and plugged in some different trannies. Here's what I get now voltage wise:

Battery 9.47v

Q1 C -8.25v B -0.04v E 0v (hfe 109, 0.32mA leak)
Q2 C -0.08v B -0.07v E 0v (hfe 131, 0.40mA leak)
Q3 C -8.45v B -0.09v E -0.05v (hfe 105, 0.32mA leak)

It's pretty gnarly, plenty of volume on tap. It gets very gated when rolling the volume down on my guitar. I mean, it sounds good to my ears.. but the Q2 voltages look low to me? :hmmm: I have other more leaky AC125's.. some that are in the 0.6-0.8mA range, I plugged them in and it made not a whisker of difference. Don't really wanna fork out for some random OC75's on evilbay either. :scratch:
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Re: Sola Sound - Tonebender Mark II Professional

Postby Bret608 » 21 Jul 2017, 18:50

Those voltages look really close to what Electric Warrior posted for his original Supa Fuzz at one point. I'd be curious what happens if you swap Q2 and Q3. I think the slightly lower leakage could get your Q2 closer to 0.15v on the collector, which may make it gate less when you roll back your guitar's volume knob. I feel like your Q1 collector may be slightly low, but am not sure if it really matters. A leakier one in that spot could bring it up a bit.

I'll be building attempting to build one of these using some AC128s or 125s soon, so will be really curious to hear you results! :)
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Re: Sola Sound - Tonebender Mark II Professional

Postby sickman82 » 22 Jul 2017, 09:28

I lowered Q2's collector resistor to 39k which has given these more respectable readings now..

Battery 9.26v

Q1 C -8.85v B -0.03v E 0v (hfe 109, 0.26mA leak)
Q2 C -0.18v B -0.09v E 0v (hfe 127, 0.30mA leak)
Q3 C -8.22v B -0.18v E -0.11v (hfe 113, 0.27mA leak)

Interesting how the temperature alters the transistor readings too.. much colder here this morning.

Bret.. you'll enjoy building a TB circuit.. you learn a lot. The MKI is a real bitch, MKII is much easier. Both are fun in their own right. I think I may start a MKI build again soon.
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Re: Sola Sound - Tonebender Mark II Professional

Postby Electric Warrior » 23 Jul 2017, 00:53

Right. As leakage increases with the temperature, the voltages on Q1C an Q2C decrease while the one on Q3C increases.

0.08V on Q2C is a little low. Just out of the range I've seen in vintage units.

The gating not only depends on the voltages, but also on the interactions between transistors from what I understand. With higher leakage on Q2 the gating increases, but somehow sometimes I end up with a low voltage on Q2C but decent clean up. :scratch:

A little gating sounds great with this circuit. My vintage unit sometimes cleans up well and sometimes it doesn't. It can be pretty random. I don't think they considered good clean up a priority.
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Re: Sola Sound - Tonebender Mark II Professional

Postby sickman82 » 23 Jul 2017, 10:15

Just to satisfy your curiosity Bret, I switched Q3 and Q2. Q3's collector was then around -7.2v and Q2 around -0.32v. Had I also put the 47k back on Q2's collector then the voltages may well have been in range.

EW.. I actually like the gated clean up sound. It's got a lot of texture, and depending on how I have my amp set it produces different results. Do you prefer to play in to a clean, clean-ish or dirty amp? I usually have mine set clean-ish.
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Re: Sola Sound - Tonebender Mark II Professional

Postby Bret608 » 28 Jul 2017, 14:15

Interesting! Thanks for sharing. I bet it would have been in the vintage range. As it is with the 39k, you got very similar voltages to what I had on my first MkII attempt, where I used transistors that were not leaky enough. Still sounded really good; it just didn't quite have that magic that that bit of gating seems to provide.

I've tended to go clean-ish/edge of breakup on these vintage fuzz builds. Not sure if that's the preferred scenario in every case, but it's worked well up to now (both the MkII I mentioned and a Mk I-like circuit I did).

Cheers,

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Re: Sola Sound - Tonebender Mark II Professional

Postby Electric Warrior » 28 Jul 2017, 23:31

sickman82 wrote:Just to satisfy your curiosity Bret, I switched Q3 and Q2. Q3's collector was then around -7.2v and Q2 around -0.32v. Had I also put the 47k back on Q2's collector then the voltages may well have been in range.

EW.. I actually like the gated clean up sound. It's got a lot of texture, and depending on how I have my amp set it produces different results. Do you prefer to play in to a clean, clean-ish or dirty amp? I usually have mine set clean-ish.


Clean-ish-

0.32V on Q2's collector is in the vintage range. Units with Impex S31T transistors can measure like that - looks like a MKII built with a just a little less leakage, but they actually used transistors with extremely low leakage (close to 0) and low gain (in the 20s and 30s) for Q1 and Q2 and extremely high gain for Q3. I wasn't able to make it work properly using transistors with similar specs, though.

I have a strong preference for the range in which OC75 and OC81D units were biased as the gating sounds ace there if you like it. And those who don't can dial it out easy enough. Lots of great tones to be discovered here.
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Re: Sola Sound - Tonebender Mark II Professional

Postby sickman82 » 31 Jul 2017, 13:58

Interesting info EW.. and Bret, that gating does make this circuit what it is.. I've realised that now.

I used it almost exclusively at rehearsal the other night; got my Marshall Super Bass just on the edge of breakup and kept the MKII on and just riding the volume gave everything I needed.. I love it with the volume backed off just a hair on my Strat. It's a gnarly fuzz tone that just sizzles, gates just enough and cuts through the mix like nothing else right in that sweet spot.
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Re: Sola Sound - Tonebender Mark II Professional

Postby Electric Warrior » 31 Jul 2017, 16:59

sickman82 wrote:Interesting info EW.. and Bret, that gating does make this circuit what it is.. I've realised that now.


The whole point of the first stage may have been to make the gating more useable. The MK1.5 farts out easily in warm weather as it's biased a little too hot. I suspect the MKII was Sola Sound's fix for this problem.

I don't think the gating is absolutely necessary. It can sound huge and still have a nice clean up at the same time when done right. Picking a transistor for Q2 that biases in the sweet spot between gating and hiss at room temperature would be a good way to set a good range of temperatures in which it is usable.
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