Dean Markley Overlord to B K Butler Tube Driver

So, I've got one of these and I've got to admit - I agree with the advert - it's ugly as sin but it does sure cook an amp nicely, but it could be better. It's the Dean Markley Overlord Tube Overdrive pedal. Using a REAL 12AX7 vacuum tube it creates realistic tube overdrive and distortion tones! It has some close relatives:

Now check out the schematic for the Overlord:

Now, as I stated earlier it has some close relatives, not only looks wise but circuit wise too. Here's the B K Butler Tube Driver:

Now there are plenty of variations on this design from B K Butler himself, Chandler and Tube Works among others. I took a look at various schematics with a view to modifying the Overlord to full-fill it's true potential:

Tube Works - Real Tube

Tube Works - Blue Tube

Tube Works - 303 Smooth

Chandler - Tube Driver (4 Knob)

And the newly updated Tube Driver itself (with the "Bias" mod):

New version B K Butler Tube Driver

And another version by Bajaman - The Real Tube Overdrive with a regulated power supply and simplified tone control:

Baja - Real Tube Overdrive

Now what I want to do is combine the best parts of each of these variations into one and modify my Overlord into the ultimate tube overdrive pedal... So, what am I planning to do:

1 - Make this thing True Bypass; the bypass switching currently employed by Overlord is terrible, a switch to true bypass will greatly improve the bypassed tone.

2 - Incorporate the "Bias" mod, here's a description of what the bias mod actually does from the B K Butler website:

"The Bias control is very helpful as it adjusts the amount of current applied to the cathode of the tube. Eric Johnson used to spend a lot of time looking for perfect tubes to use in his standard Tube Drivers, but now he can just set the bias easily with the stock tube. Just go up or down a few clicks and he nails what he wants. The Bias control also adds dynamics and allows you to custom match your Tube Driver for any particular pickup/amp combination.

Technically it varies the electrical 'strength' of the tube and that affects gain, texture and dynamics. It does not change the EQ directly but because the way the tube responds can be varied; you will hear EQ differences at various settings.

Most players find a 'sweet spot' about 2:30 - 3 o'clock on the control.

All in all, it is a 'pro tool' type of control that each player can set to their own subjective taste."

3 - Remove the in chassis power transformer and utilise a 16VAC adaptor with a modified regulated power supply a'la the Baja Real Tube Overdrive to reduce hum and circuit noise.

4 - Modify the stock component values to match the re-issue B K Butler Tube Driver. The "Mids" control will be sacrificed and replaced by the Bias control.

5 - Upgrade poor quality components to higher quality equivalents and use shielded wire for all signal carrying off-board connections to ensure this thing sounds as good as it can!

So after all that what am I going to end up with? Well, hopefully a super clean and cool version of the well known (and widely used) "Tube Driver" circuit. Check back here to see my build/mod report shortly :-)