Sola Sound - Tone Bender MK1.5

The Sola Sound Tone Bender MK1.5 was introduced in 1966 with a view to replace 1965's Tone Bender MKI. With a new sand cast enclosure and a two transistor circuit (which was much easier to build and bias!) it would seem Sola Sound were onto a winner and ended up with an effect which is still casting it's influence on guitar music today!

Here's a quick look at a gut shot from an original Tone Bender MK1.5:

You can see the two Mullard OC75 germanium transistors which are the heart of the circuit. Also note the vero board construction. The tone of this circuit is less saturated than the MKI Tone Bender and produces a tone much similar to the original Arbiter Fuzz Face, and here's why:

The schematic is identical in structure to the original Arbiter Fuzz Face which was released in late 1966 - it is rumoured that the Tone Bender MK1.5 circuit was essentially nicked by Arbiter after they borrowed a Tone Bender unit for inspection. Also of note is the fact that is was this circuit (with a few value tweaks) that Vox used in their Italian made Tone Bender design.

Here's a demo video of the Tone Bender MK1.5 circuit in action (Note - this a D*A*M rebuilt circuit):

Here's a great vero layout by Sinner of www.turretboard.org:

OK, so what transistor HFEs work? The standard Fuzz Face values of 80-90Hfe for Q1 and 110-130Hfe for Q2 are fine, but as usually feel free to tune to your own tastes!