Sola Sound - Tone Bender Mark I (1965)  [schematic]

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Re: Sola Sound - Tone Bender Mark I (1965)

Postby sickman82 » 25 Jul 2013, 21:55

Thanks Lowbrow, I'll give it a try. I plan on plugging in most of my transistors tomorrow morning, should be fun since I have around 500 lying around!
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby sickman82 » 26 Jul 2013, 10:52

I've nailed it. It took a lot less time than I expected too. Although, it was by pure chance that I got it sounding as it should.

I was trying a bunch of low gain/high gain, low leakage/high leakage transistors in the three stages.. trying to do it methodically, referring back to this thread and a few others for tips and so on. I was getting mixed results, and some really bad results too. After a while of doing this, I began to get frustrated.. so I just thought, to hell with it, let's try something that (according to what I have read) really shouldn't work. I pulled out a bag of Russian MP16B's (low gain and super low leakage - sound great in a FF circuit), and stuck the first one I grabbed in to the second stage. BAM! The thing fired up, no sizzle, no noise, great sounding high gain MKI tone that I have been chasing since October last year. The sweep of the Attack pot is there.. Mild fuzz, ungated.. all the way to thick, compressed and gated fuzz.

First thing first, I had to jam with it.. I spent the next hour noodling away, finding the sweet spot on the Attack pot. After that I thought, right.. I need to write down the voltages/hfe/leakage for the guys at FSB. There was something making me nervous about removing these transistors to measure them though! I didn't want to lose that sweet sound I'd been hearing the past hour. Anyway, I took a deep breath and unplugged them one by one to measure hfe/leakage. Then put them back in to measure voltages.. here is what I got.


Q1 - HFE 174 - Leakage 0.94mA (AC125)
Cv -9.47 -9.40 -9.39 -9.36 -9.36
Bv -2.31 -2.20 -2.17 -2.17 -2.17
Ev -3.44 -3.26 -3.24 -3.24 -3.24
Q2 - HFE 57 - Leakage 0.06mA (MP16B)
Cv -8.77 -4.95 -3.58 -3.55 -3.53
Bv -0.10 -0.16 -0.16 -0.16 -0.16
Ev 0.00 0.00 0.00 0.00 0.00
Q3 - HFE 176 - Leakage 0.88mA (AC125)
Cv -9.09 -9.01 -8.98 -8.97 -8.97
Bv -0.10 -0.10 -0.10 -0.10 -0.10
Ev 0.00 0.00 0.00 0.00 0.00

From left to right - 7 - 9 - 12 - 3 - 5 - o'clock on the attack pot. The circuit has the stock 180k resistor, and the 2m2 has been swapped to 1m for added output. Other than that, it is the stock circuit.

It's summer, and quite warm where I am at the moment, we've had a bit of a heat wave.. although it is a bit cooler now. So, come winter, I'm kinda expecting to have to do this all over again. I just had to rebias a germanium FF circuit I built last winter because of the recent heat wave. It's getting up to about 33C in my flat as I have huge south facing windows. Yuk!

I'm hoping this helps some others that are struggling to get this circuit down. Although, it seems that each circuit is totally different to the next, and relying solely on voltages and transistor values won't get you where you should be. I'm happy that I removed the 10k trimpots though, that seemed to help a lot.. made things much more simple.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby LucifersTrip » 26 Jul 2013, 12:30

that sounds great...hope it stays that way!

the only thing a bit confusing is how you have a high voltage on Q3C with such a high leakage.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby lowbrow » 26 Jul 2013, 13:10

Congrats! Two questions. Is that milliamps or microamps? And, I was under the impression stock collector resistor for Q2 was 470k? I thought the 180k was a modification David Main does to make biasing easier. I seem to remember photos of the few original units out there all show a 470k...but its early yet and I haven't caffeinated to sufficient levels yet :D
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby Electric Warrior » 26 Jul 2013, 13:31

The unit Dave documented with his schematic (the "Sola Sounds" one) has a 180k, but he was using a 470k in his clone and therefore put that in the schematic.
Vintage units with 470ks and 240ks do exist. There might have been other values in use as well. I know of one unit that has two resistors of unknown value in parallel.

Most (but not all) vintage units seem to have a narrow sweet spot on the attack pot between gating and chirping.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby sickman82 » 26 Jul 2013, 14:16

Could you attribute the high voltage on Q3c to interaction with the previous two stages? I'm no electric wizzard, but from playing with this circuit it seems that not only is each stage dependant on the right transistors, but each stage is also interactive with the other.. altering measurements accordingly. I believe it is this that makes this circuit so hard to get right. I could be totally wrong of course! What do I know!

I measured the leakage in milliAmps Lowbrow. From what I've seen.. the 180k was a stock value, but Electric Warrior may well have better knowledge than me.

Yep, the sweet spot is pretty narrow.. but once you get it, it's sublime. There really is no other fuzz like it. On to the Supa Fuzz next!
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby LucifersTrip » 27 Jul 2013, 20:47

sickman82 wrote:Could you attribute the high voltage on Q3c to interaction with the previous two stages?


you pretty much answered that question with the voltages you gave above. look how little Q1/Q3 voltages change when you made a big change to the voltages of Q2
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby themerman » 08 Aug 2013, 09:05

That is a strange reading. 5ua leaking to the base - I'd expect 8v or less at q3c.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby JustinFun » 14 Aug 2013, 14:01

I was getting sick of continually failing to build a satisfactory MKI, despit trying scores of different transistors and layouts, so I decided to make a cheats 'tweakable' SMD-based layout.

It features 1M trimmers for faking leakage on all 3 transistors (and dialling in 'correct' voltages) and 1k trimmers on the emmitters of Q2 and Q3 for taming squeals and chirps.

Don't know if it's really a magic 'use any transistor you like' solution, but it worked right off the bat with 3 AC176s - this is after weeks of trying other methods. I'm really pleased! It's not a purists version, but it's good enough for me.

Layouts below in case anyone else fancies a go.
MKIsmdtweakerlayout.png


MKIsmdtweakermask.png
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby soggybag » 29 Aug 2013, 02:22

I just built one of these on the breadboard. Fired up the first try. I used some random AC128s. All of the transistors seem to measure in the 90 to 100 hfe range. Not sure about leakage. Will have to experiment more and see if different transistors make a difference.

I built his from the Hurst schematic. The extra resistor on the Attack pot makes that control more useful.

Early posts suggest using a lower gain transistor for Q1 works best, while later posts seemed to get a good sound with a high gain in Q1?

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Re: Sola Sound - Tone Bender Mark I (1965)

Postby phibes » 29 Aug 2013, 15:26

I'd go with the 98 in Q1, 80 in Q2 and 104 of Q3. You can swap the 98 and 104 for Q1 and Q2 but you probably won't notice a dramatic difference unless one leaks a lot more than the other. If you measured those transistors without factoring the leakage though, the actual value will be different.

The attack pot is just a bias pot. It's meant to set and forget. I think that's what really confuse people about the MKI. If you can get a good sound somewhere on the sweep, you got yourself a finely working MKI. Spitting and some squeal also normal. An MKI that doesn't sound like a mean bitch isn't a MKI. The nastier the better I say!
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby Liquids » 29 Aug 2013, 16:44

I'm not super techie...but in a circuit that is transistor based...here is my understanding....

Hfe only tells you so much. Maybe the circuit was designed around a certain understanding of the transistors being used...and then, given how variable old components like GE transistors are, and how tuned into audio we are...people find ones that 'sound good' and note something like the HFE...or even the 'measured' component values, voltages etc...

All that info is good. But barring a transistor being biased into it's extremes, if one finds a higher gain transistor of the desired time when they want a lower gain transistor given a certain circuit, or likewise wants higher gain from a lower gain transistor...

Within reason...tweak the biasing resistors. A higher value resistor from B+ to the collector will increase gain. Compensate with a high value collector resistor if you want to make "voltages at the transistor" the spec to be duplicated while you tweak gain...

Certainly changing compoent values will influence other things...but feeling 'stuck' with a certain transistors Hfe does not mean you are powerless to tweak, and it's not sacrelidge to change resistance values to use the transistors you have.

Even leakage can be simulated a little by starting with high value resistors (1MEG is a starting point, but higher may be applicable, as may lower values) connected from collector to base, that can effectively duplicate some of what leakage does. Likewise with caps for tonality.

All of these things interact. Minimally (Say, compared to tubes), but noticably, a higher collector resistor will cause more loading of the signal out of the transistor stage...may smooth the sound...and a lower value collector resistor may lower the gain, but increase high frequencies. A resistor from collector to base may simulate leakage, but as you go down in value, input impedance of the transistor may be affected. Likewise, bias point will be affected by it...which can be used to get things more in the "voltage" zone for the transistor that one is looking for, or need to be adjusted for...
Biasing is a moving target...but, hey, so is finding the perfect GE transistor...and biasing is a lot more controlable than searching the world over for the perfect vintage transistor for location X in circuit Y...it does, however, take some knowledge-based tweaking, or, even just enjoyment of blind expirimentation...

In short, having the (GE) transistors one has on hand, but wishing they had a different Hfe is rarely something that must hopelessly resign on to searching for another transistor with a different Hfe. There are other things one can do, if one doesn't consider the component values sacred, or, for any number of reasons, wants to use what they have on hand and knows they can do so to audio success.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby phibes » 29 Aug 2013, 20:47

Liquids wrote:I'm not super techie...but in a circuit that is transistor based...here is my understanding....

Hfe only tells you so much. Maybe the circuit was designed around a certain understanding of the transistors being used...and then, given how variable old components like GE transistors are, and how tuned into audio we are...people find ones that 'sound good' and note something like the HFE...or even the 'measured' component values, voltages etc...

All that info is good. But barring a transistor being biased into it's extremes, if one finds a higher gain transistor of the desired time when they want a lower gain transistor given a certain circuit, or likewise wants higher gain from a lower gain transistor...

Within reason...tweak the biasing resistors. A higher value resistor from B+ to the collector will increase gain. Compensate with a high value collector resistor if you want to make "voltages at the transistor" the spec to be duplicated while you tweak gain...

Certainly changing compoent values will influence other things...but feeling 'stuck' with a certain transistors Hfe does not mean you are powerless to tweak, and it's not sacrelidge to change resistance values to use the transistors you have.

Even leakage can be simulated a little by starting with high value resistors (1MEG is a starting point, but higher may be applicable, as may lower values) connected from collector to base, that can effectively duplicate some of what leakage does. Likewise with caps for tonality.

All of these things interact. Minimally (Say, compared to tubes), but noticably, a higher collector resistor will cause more loading of the signal out of the transistor stage...may smooth the sound...and a lower value collector resistor may lower the gain, but increase high frequencies. A resistor from collector to base may simulate leakage, but as you go down in value, input impedance of the transistor may be affected. Likewise, bias point will be affected by it...which can be used to get things more in the "voltage" zone for the transistor that one is looking for, or need to be adjusted for...
Biasing is a moving target...but, hey, so is finding the perfect GE transistor...and biasing is a lot more controlable than searching the world over for the perfect vintage transistor for location X in circuit Y...it does, however, take some knowledge-based tweaking, or, even just enjoyment of blind expirimentation...

In short, having the (GE) transistors one has on hand, but wishing they had a different Hfe is rarely something that must hopelessly resign on to searching for another transistor with a different Hfe. There are other things one can do, if one doesn't consider the component values sacred, or, for any number of reasons, wants to use what they have on hand and knows they can do so to audio success.


Your understandings correct. Shooting for a gain bucket saves a considerable amount of time with the tweaking process. If you go too low or too high, it can get very hard to tweak right, especially when stages in other Germanium circuits play off each other. With Tone Benders, as long you're between 60-100 with little to moderate leakage, tweaking is very minimal.
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby Masuto » 02 May 2014, 06:38

Hi fellow builders. I took on the Gary Hurst Tonebender mki layout yesterday and the day before but after a successful build i had to build another one because the led started zapping (!) in tune with the q1 trannie whizzing. Started from scratch with a new build. Heres the final result:

https://www.facebook.com/photo.php?v=10202584086136398

After testing a veritable bucketload of trannies for q1, lots of whizzing, i decided to go for something high gain. Enter a Texas Instruments 1N1307 measured, hfe 136. Tweaked a bit with a multiturn trimmer..
On q2 and q3, AC128 of around 80-100 hfe. They just sound more "complete" than the various oc76, oc125 etc i tried on this build. Nice vocal trail, a bit of that fart a bit of that harmonics sensation.
Still room for improvement..as i was recording my friend for a guitar solo up the fretboard, it started cutting the sustain a bit in a funny way.
WHAT DO YOU THINK?
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby DrNomis » 03 May 2014, 00:14

I've got a set of 4X AC128 Transistors, and two other transistors marked NKT275, plus 4X GT308A which I might try using to build one of these things, one of the NKt transistors has just over 1mA of leakage, the other a bit less, , I don't think the transistors are bad cause I did a bit of an experiment with some ice cubes and found that the two NKTs and the AC128s seem to be a bit temperature sensitive, I'm going to try using them anyway, will let you know how my build goes..... :thumbsup
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby DrNomis » 03 May 2014, 07:20

Okay, so I've breadboarded the Mk I circuit but I had to substitute a 330k resistor for the 470k resistor, anyway it seems to be working with the three AC128 transistors I selected, geez this circuit has alot of gain, even when feeding in a 1kHz 100mV Peak To Peak sinewave it easily generates a 2V Peak To Peak output, here's a screenshot of the output signal I saw on my Oscilloscope:
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby Masuto » 04 May 2014, 16:38

How do you think mine sounds? Is it how it is supposed to sound?
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby DrNomis » 04 May 2014, 17:48

Masuto wrote:How do you think mine sounds? Is it how it is supposed to sound?



It sounds pretty smooth to my ears, have you tried comparing it with some Mk I videos on youtube?..... :thumbsup
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby DrNomis » 05 May 2014, 18:21

I've finished soldering the resistors, caps, and tinned copper wire links onto the piece of tagboard I'm using to build a Mk I, and I've been trying out each of my 4 AC128 transistors on the breadboard, here's a list of voltages, Hfes, and leakages for the three AC128 transistors I'm going to be using, let me know if these should sound good, note that I'm using stock value resistors, with a 47ok resistor for one of Q2's base biasing resistors:

HFE And Leakage:

Q1: Hfe= 140 / Leakage = 650uA.

Q2: Hfe= 87 / Leakage = 380uA.

Q3: Hfe= 100 / Leakage = 630uA.

Voltages:


Q1: C= 8.72V, B= 0.02V, E= 2.69V.

Q2: C= 5.88 To 8.55V (Depending on 50k Pot Setting), B= 0.04 To 0.12V, E= 0.0V

Q3, C=6.77V, B= 0.04V, E= 0.0V



Here's a pic of the Tagboard:
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Re: Sola Sound - Tone Bender Mark I (1965)

Postby LucifersTrip » 05 May 2014, 21:50

DrNomis wrote:Q3, C=6.77V


should be ~ 8V
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