Sola Sound LTD - Tonebender MKI / Hornby Skewes - Zonk Machine / D*A*M - FZ-673

The Sola Sound Tone Bender MKI was one of the first fuzz pedals available in the UK. Designed by Gary Hurst it was the British response to the American made Gibson Maestro Fuzz Tone FZ-1. Although the circuits are similar (Gary Hurst based the circuit around the FZ-1 structure) the Tone Bender has a much longer sustain and a more powerful "all out" tone due to the modifications that Hurst made to the circuit - 9 volt power instead of 3 volts in the FZ-1 and a tweak of the transistor bias.

Now, there are a few reasons why the Tone Bender MKI is interesting - The Beatles used one, Jeff Beck used one, Pete Townshend of The Who used one aaaaaaannnnnddd Mick Ronson used one too! That tone that Mick gets? Yeah, it's his MKI Tone Bender...

Here's one in action:

So what's inside one:

And, thanks to David Main of D*A*M (and those who donated their original pedals!), here are some schematics of original units, firstly a Sola Sound Tone Bender MKI and a Gary Hurst Model:

Sola Sound Tone Bender MKI schematic

Gary Hurst Tone Bender MKI schematic

RnFR over at freestompboxes.org produced this vero layout for the Gary Hurst MKI (You can also build the Sola Sound version on here by leaving out the extra Gary Hurst components and substituting the required values):

Here's an alternate Sola Sound Tonebender MKI vero board layout from IVIark, this version has trim pots to make biasing the circuit a little easier: http://tagboardeffects.blogspot.co.uk/2011/01/tonebender-mki.html

And here's IVIarks Gary Hurst vero layout: http://tagboardeffects.blogspot.co.uk/2011/01/gary-hurst-tonebender-mki.html

And here's a turretboard layout by Sinner (note - this layout has the 180k bias resistor on Q2, most people use a 470k here):

Now, before you have a go at this there's a few things you need to know - the MKI ~Tonebender is a right bugger to build, it's the most tempermental circuit I've ever messed around with. However, if you get it right the rewards are worth it. For more info and biasing tips check out this article on Geofex: http://www.geofex.com/Article_Folders/zonkmach/zonkbst.pdf (I know it's for the Zonk Machine but they are the same circuit!).

Finally, here's a couple of videos showing you how one is built (some useful tips here and worth a watch if you are going to build one):

If you wanna ask some questions here's the freestompboxes.org forum topic for the MKI Tonebender: http://freestompboxes.org/viewtopic.php?f=19&t=406

Next - the (almost as famous) Hornby Skewes Zonk Machine is an almost identical replica of the Tone Bender MKI. Made in Leeds, Yorkshire, England between 1965 and 1966:

And here's a few schematics for various versions of the Zonk Machine:

Here's another version as pointed out by Jonaz:

And here's a schematic he drew up:

And a further alternate schematic for yet another original Zonk Machine that was traced:

He also has some advice regarding transistor gains he used in his build and some further advice to other builders: "The transistor gains for Q1-Q3 are as follows: 70, 116, 97....

Tips for other builders interested in the Zonk Machine:

1. Socket all transistors because you’re likely to go through a bunch of them before you find some that work well.

2. The Zonk is very bright. Play around with the input cap and try values between .001uF and .01uF. Maybe even set up a three way switch to toggle between different values.

3. Definitely use a log/audio taper “Fuzz” pot. I used linear at first but it greatly limits the useful range of the pot. The name “Fuzz” is a bit of a misnomer as it doesn’t really fulfill most people’s definition of a fuzz control. It essentially adjusts the bias of Q2. The Sola Sound Tonebender Mk1, which is a topographically identical circuit (sans the 33K resistor), called this pot “Attack” which is a bit more appropriate IMO.

4. Set up an SPST switch to bypass the 2.2M resistor for nasty, all-out craziness!"

As you can see the structure of the circuit is identical to the Tone Bender MKI (with smaller input/output caps and a few resistor tweaks). Here's another vero for you, this time for the Zonk Machine (Many thanks to Sinner and www.turretboard.org):

However, if you want to build the Zonk Machine though I'd go for one of these sweet little machines:

The D*A*M FZ-673, a small custom run of a modified Zonk Machine circuit with an input cap blend, it sounds damn awesome:

And here's a layout from Sinner (turretboard.org):

I just need to thank Sinner of www.turretboard.org for the layouts in this post - cheers Sinner!

Here's the freestompboxes.org forum topic for this one: http://freestompboxes.org/viewtopic.php?f=7&t=12720