Tube Driver Bottom PCB layer parts placement and bias mod How does it sound? I did not care for it - but then I have been spoilt by a real tube overdrive ( 250v dc plate load feed as opposed to this 12v beastie) I think you may be able to improve it's sound by using a higher spec op amp such as the excellent Burr Brown OPA2134 and by using better quality metalised polyester or polystyrene film capacitors - who knows?Īnyway - big drum roll. Good luck if you want to build it - it uses a double sided circuit board. It uses a TL072 op amp and 47k plate load resistors and many other subtle changed components - more later. I have not redrawn the schematic yet - it should be up in the next few days - it is not the same as ANY of the many schems floating around on the net by the way. The additional bias control pot is mounted above the input socket on the rear panel - I preferred it without the additional bias resistance and capacitance - but others may find this B K Butler mod useful. There is no mojo components in here - just cheap mylar greencaps and standard metal film resistors - so It won't sound very good - tell David Gilmour and see if he cares - he has two of these exact same pedals in his Pete Cornish pedalboard The earth pin on the input socket is connected by a parallel connected 100 ohm resistor and a cheap 100n mylar capacitor to the chassis near the front of the case. The input and output sockets are isolated from the chassis by plastic insulating spacers. You will need a suitable 12vAC power pack for this pedal - the original has a small toroidal mains transformer fitted internally near the front of the case. This was traced from a recent B K Butler pedal and has the bias pot modification which alters the voltage on the cathodes of the 12AX7 tube.
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