Sola Sound Tone Bender MK1 build

[planchette]

Hello stomp-box freaks!

First time poster, long time lurker here. As the title suggests, I want to start piecing together an MK1 build. I've read over the original posting here, which yeilds a lot of useful information. I figured I'd start a new post that is specific to mine and see if anyone has since attempted this build. I want to stick to the original circuit, but I've seen other schematics floating around. For example, this site has several variations of the MK1, with different component values and one with a bias resistor (which sounds very useful). If anyone has any tips or insight on this circuit, it would be greatly appreciated!

Also, I'm looking to obtain some transistors for this (OC75 & 2G381). Can someone steer me in the right direction?

Bless!

[planchette]

No one wants to chime in?

I've sourced all the components and have 3 OC75 Mullards, a pair of AC128s & pair of AC125s on the way! I will experiment with different transistor combinations until I hit that sweet spot. I'll probably try and build point-to-point, which will be a first for me..

[GuitarMatt]

Hi there, I'm by no means an expert here, but I'm also attempting to build a MK1. I hope you'll keep your progress documented in this thread, maybe I'll learn something from you!

From what I've researched, the MK1 can be picky about transistor gain and leakage (it requires more-than-usual leakage to work, from my understanding). You might need to build the GeoFx transistor-tester to get proper info about the hfe and leakage for each one you've ordered. The tester is found here: http://www.geofex.com/Article_Folders/ffselect.htm

[bmsiddall]

Hi Planchette.

Possibly one reason you haven't been inundated with replies is that there are extensive old threads here and elsewhere covering the circuit already (it's also good practice to include the schematic in your thread as well).  EDIT- sorry dude, reread your post and I completely forgot the links you provided. Apologies! /EDIT

About a month ago I completed my first germanium Mki (used NPN transistors) - I used that info as the basis for what i ended up with.

Q1:  leakage of 400 µA+ to get emitter voltage to 2 V.  Recommended HFe 50-70, but I'm not sure this matters too much?  I ended up with hfe about 70.
Q2: I used HFe 127 and moderate leakage of about 250 µA
Q3: I wanted an ill behaved, rude, bacon crackle fade mki, so i aimed for >8V on the collector.  Low leakage appears to be the key on this transistor to get collector voltage to about 8.3- 8.5 V.  Ended up with HFe 101 and 50 µA leakage.  Gains up to 135+ don't seem to matter much.

I tried both 470k and 180k for the Q2 Vc-base bias resistor.  To get a decent sweep of the attack control, I fiddled with the rail-based resistor (470 K).  Full attack was a little touchy and very close to anticlockwise with 180 K.  Ended up compromising at 470//470 K and also changed 50 K attack pot to logarithmic.  Nice sweep from barely on (anticlockwise, 7 on the dial) through full attack (approaching 12 ) then various amounts of gating to 5.  Q2 collector voltages range from >8v to <0.5v (most gated). I'm generally using it around 3 on the dial, which gives a slightly thinner sound but more gating.  Absolutely fantastic sound, with aggressive fuzz, decent sustain and bacon sizzle decay.

Cheers,
Brett

[JebemMajke]

Yello

This is what i did ( bias wise ) and it worked out great for me, it is the best fuzz i have and i love it.

I had offers which went over 500e for it and I kept it.

So my transistors are

oc75,oc71,oc45 ( 45 to give it a bit of gloom, but 71 worked great in this position too ). I have never measured leakage and I don't care, it sounds great.

The first and the second 8k2 are trimpots and 15 k ( above q3 ). And there is a 470k above second 8k2.

Tune first 2 to your liking and use the last one for the volume/gating and other things.