A much early Christmas present for all you Tone Bender lovers... :)

[petemoore]

  Is it better than other pedals or just rare?
  It is the same as other pedals, except different.
  We are just now discussing these differences, when some are actually built and tested, more information about the 'unique' circuit will be floating around.
  Long explanations about subcontexts and opinions, amps, speakers, guitars and preferences [all have to do with ones perception of a circuit]..and short story is that 'better' doesn't 'play right', [and implies 'worser' to other circuits, many of which the designers frequent this forum, so is indirectly 'pitting against' other pedals and can easily become an insult] but there is always 'different in certain ways I like'...which doesn't really say much, about the right amount.
  Anything else like player, guitar or pickups or cable changes, the change of the 'effect' can easily be confused with the 'peripheral' items in the signal chain, including the ears of the listener.
  And..with this circuit, the consistancy from one to the next is sure to be low, as such each one is almost certain to 'work' differently, part of the 'coolness', but makes it difficult to comment in a matter which would necessarily be consitant with your build.
  I'd build the 'other pedal' first...might be the 'wrong order'...I haven't heard a MkI in action.

[ISC]

Looking at R10 2M2 in series with the 500K volume pot I would think that this pedal was not very loud and was probably louder in bypass.
Perhaps Mr Hurst included this value to save loading the pramps on the valve amps that would have been used. Shorting out R10 will unleash the true gain of this circuit but the result may not be so good. Any good sound samples of this anywhere ? I suspect the later versions of this yield better sonic results and were more than likely the pedal used by Beck and the others. I'll wait to see the other MK1 versions before I build this one  .

Regards
Trevor

[tcobretti]

Vanessa, you rock!  I will be building this next weekend, and sound clips will be forthcoming.

[brett]

Hi
thanks Vanessa.  Very cool.

First: the circuit is capable of plenty of output (at a quick guess, I'd say about 1V p-p, or 10 times the bypass voltage).

A feasible way of overcoming the bias issue is to use low-leakage PNP germaniums (e.g. Japanese 2SB124 ??).
These often have the right hFEs (60 to 120) and very low leakages (often one fifth to one tenth of early AC128s etc).
With these transistors you simply add a resistor from the transistor's base to the supply, to bias the transistors in the same way as in most modern circuits.
The tone might be altered a little, but at least it would work.

If old mate has a working circuit, it would be really useful to take voltage measurements at the bases and collectors of those transistors.
cheers

[R.G.]

If old mate has a working circuit, it would be really useful to take voltage measurements at the bases and collectors of those transistors.

... and to remember that the meter he uses has to have a high impedance compared to the 1M pulldown resistors, so a VTVM (!?!) would be really appropriate there. Ordinary 1M to 10M DVMs can pollute these measurements a lot.

[vanessa]

Vanessa, you rock!  I will be building this next weekend, and sound clips will be forthcoming.

Don't thank me thank David Main of D*A*M. David provided the schematic. His was a little hard to read and I also wanted to make sure both he and Gary Hurst got credit for posterity so I redrew it so it could be easier to read.

BTW: David tells me he is producing  a very limited run of MKI's (only 20) to the exact spec of the originals. He makes very well made pedals. If you are looking for one of these you might want to put in an order before the info goes public.

[ISC]

Brett I agree with you that there should be plenty of gain through the transistors but my point was that it is being strangeled by the 2M2 in series with the volume pot. Even when the 500k is maxed = zero ohms you still have 2M2 on the output. I dout this pedal would be loud enough for a live gig, studio or bedroom maybe. I would need to hear a decent sample before I was convinced.

Regards
Trevor

[mac]

In my experience with MK-II I found that, for example, at Q1 which bias in a similar way, a Toshiba 2SA49 hfe=68 leak=27uA was not as good sounding as a Matsushita 2SB102 (BA) hfe=61 leak=124uA. Toshiba low leakage was detrimental. The 102 biased a little lower than the 49. On the other side, low leakage was ok at Q2 and not decisive at Q3.
In the 3 knob version, Q3 needs a very low leaky device even though the leakage bias.

In this case I'll try 100 to 200uA.

mac

[mac]

Maldita sea, I can not sleep...

A glass of milk and the breadboard... Some voltages using 3 different good Jap Ge. All same hfe?75 but with different leakage:

Toshiba 2sa52 leakage=30uA, Matsushita 2sb175 leakage=115uA, Hitachi 2sb77 leakage=260uA

Battery=8.73V

Ge	Q1	Q2 1k8	Q2 47k	Q3
2sa52	0.12v	8.70v	6.00v	8.59v
2sb175	0.65v	8.64v	5.53v	8.49v
2sb77	3.03v	8.42v	4.10v	7.69v

I hope my cheap chinese ddm did not lie.

My guess is, and it is 3:12am, that Q1 must be between 3.5v and 4.5v, Q2 near vcc when Re=1k8 and 5.5V to 4.5V when Re=50k, Q3 around 7V. But it depends on the hfe of the original transistors so this values maybe not the real ones. I should try hfe=150 with different leakages. Hope some may find this useful.

mac

[brett]

Hi

Brett I agree with you that there should be plenty of gain through the transistors but my point was that it is being strangeled by the 2M2 in series with the volume pot. Even when the 500k is maxed = zero ohms you still have 2M2 on the output.

The 2M2 isn't such a problem for circuits like this that have substantial output voltages. 

Best case is feeding a buffer or tube amp, that often have 1M input impedance.  The voltage passed to the next stage will be 1/(1+2.2) = about one third of the output voltage (say 6 V), or more than a volt.  That's a lot more than a guitar produces. 
If, however, the amp or whatever has only 100k of input impedance, the voltage seen by the next stage might be 6 x (0.1/(0.1/2.2) = about 0.3 V, which is only tripple a guitar's output, which is only a mild volume boost.
cheers

[smnm]

David (D*A*M) ... forwarded me some hfe's from a Gary Hurst reissue he had in his shop.

Q1 hfe = ?
Q2 hfe = 120
Q3 hfe = 92

Maybe I'm missing something or Mr Hurst made some other adjustments on the reissues, but according to a datasheet I eventually found the original Q2 and Q3 (2G381) were low power Germs - only about 30 hfe.
BTW I've found a supplier for these but as they want the equivalent of about $10 each for them, I'm passing. No shortage of leaky weak Ge's out there.

We'll see...

[smnm]

OK!
So I was waiting for a stash of ge transistors before trying this and the Soviet GT308Vs arrived from ebay via Bulgaria this week - so I built it today. Don't be put off by the warnings of biasing difficulties - I didn't even measure them, I just picked up 3 at random to see if it was gonna work, and WOW! it sounds GREAT, really spiity/raspy and garage-y, but retaining some bottom end - "Heart Full Of Soul" and then some! Orpheum /Fuzzrite territory. With the 2M2 on the output it was a bit quiet so I just left it out (needed the space on the vero too), so obviously now it's hugely loud. I'll probably go back and try some other trannies - lower gains for Q2 an 3 maybe, just to see what difference it makes, but I'm pretty happy with it as is. Notes on the top E string sound weird and fizzly with irregular decay, I could probably fix that with bias adjustments, but for now I like that randomness.
I realised afterwards that I'd made a mistake - the first electrolytic between Q1 and Q2 is 25uF on the schem but on my layout I used 2.2uF - maybe this accounts for the super raspiness? Anyway, I like it that way, so if anyone asks I'm calling it a mod.

Thanks again to Vanessa and David Main!

[GREEN FUZ]

Alright you`ve whetted my appetite. Where`s the schem?

[smnm]

the schem was in the first post, but has been taken down - here it is again:

[smnm]

just playing it again on a guitar with lower output pickups.
It sounded amazing with my Burns Sonic, but not so hot with the Supro - more fizzy blatty gated misbiased sounds with this...

[tcobretti]

I, meanwhile, had the opposite experience.  I couldn't get mine to work at all, even after much troubleshooting.  I figured it was a bias problem, but maybe I should try it again.

[smnm]

I figured it was a bias problem, but maybe I should try it again.

I tried it with some AC128s and it was barely alive, but the GT308s are great with it! the ebay seller is called orpheus2005 - 50 for $12.

[tcobretti]

Yeah, I had a few different types, but not much of a selection of transistors.  I do have a bunch more now, so I guess I should try it again.

[tcobretti]

So, 6 months later, I went back and figured out what I did wrong.

This is a surprising fuzz.  It's actually pretty thick, yet still somewhat bright.  I tried it with many Ge transistors, and every single one worked; however, some, which I suspect had insane amounts of leakage, generated too much hiss to be usable.  I like it very much.  When I A/Bed it with my TB Mk II I was surprised at how much more full it sounded, and how much more gain it had.  It's hard to describe what it reminds me of.  It almost sounds somewhere between a RM Axis Fuzz and a Ge FF.  That said, what is very different from those pedals is that changing the guitar's volume knob does little to nothing useful.

For a while now, I have believed that Billy Gibbons' classic tone was the result of subtle use of a fuzz pedal, but have never managed to reproduce it with the usual suspect fuzz pedals.  I now believe that it was this one.  Try this: turn the volume all the way up, and then the fuzz all the way down.  Then bring the fuzz up till you are at unity or just above it.  Using the bridge P/U of my Les Paul, the tone I get with this setting is very similar to a fuzz tone he used on many of the early ZZ recordings.  I believe we may finally have uncovered his secret weapon.

Thanks again to Vanessa for digging this up!!

[GREEN FUZ]

Finally got round to making one of these and despite the warnings about finicky biasing it has been one of the most stress-free builds I can remember. I was lucky enough to find some Ge transistors within the recommended hfe tolerances. Namely:

Q1 = 60-70
Q2 = 70-80
Q3 = 110-145

Can`t remember where those hfe`s were suggested but they seem to do the trick.

I ended up using an NKT214F for Q1, a random unidentified tranny for Q2 and an AC128 for Q3. All other values were stock bar the 25uf cap for which I substituted a 22uf.

It is surprisingly quiet in use. No radio stations, crackle, fuss, buzz etc.


I`ve done a short soundclip so hopefully you can judge for yourself.
http://www.aronnelson.com/gallery/main.php/v/album174/TONEBENDER+MK1/moonage2.mp3.html

For the rhythm track in the left speaker the guitar volume was slightly rolled off . I used a live recording as reference and I believe you can hear Mick Ronson turning up the volume as he goes into the lead break which results in some extra saturation. I`ve left room on the circuit board to incorporate a crybaby circuit in order to achieve the %^&*ed wah sounds that were a huge part of Ronson`s sound. All I need now is '68 Les Paul and a Marshall Major amp.


Forgot to mention. Thanks to David Main and cohorts for the research and Vanessa for the schematic.