Cobalt Drive

Chas Grant

Well-known member
Just finished up a Cobalt Drive pedal, it sounds GREAT! It's a stock build per the doc since this is the first time I built this one. I'll give it a few months and then look up some mods on it and see how they sound. The pedal went together with no problems, The PedalPCB layout is awesome and easy to work with! First time I tried this finish and I'm pretty happy with it. A water slide decal straight on a sanded box then 5 thin coats of lacquer gives it a nice look with a small bit of depth.
 

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Chuck D. Bones

Well-known member
Tayda has some that you'd have to hard-wire to the board. Small Bear has B250K dual, which will work fine, the bottom-end of the range will be a little more sensitive. Or you can use an A500K dual and either enjoy the extra 12dB of gain at the top end or add a 470K resistor from pin 1 to pin 3 (two places).
 

Urshurak776

New member
Looks great. I'm building one also (waiting on parts.) I can't find that dual pot anywhere (right angle pins.) Tayda doesn't carry them. Bought one with solder lugs, hopefully I can wire it. Worried about clearance issues. I'm doing the Keeley MOD also.
 

Chuck D. Bones

Well-known member
By Keeley Mod, you mean replacing two of the clipping diodes with 1N4002 and retuning the TONE control, right? Are you thinking PHAT mod too?
 
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Urshurak776

New member
Yes, the PHAT mod. Maybe saying Keeley isn’t the right description. Not sure.

Oh, R24 in diagram should be 10K. The guy that did it made a typo.
 

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Chuck D. Bones

Well-known member
Sort of. My read of the Keeley mod as applied to the PedalPCB board is:

Change C20 to 10uF 16V Tantalum.
Replace C14 with 33nF. For Keeley PHAT mod, add a switch that connects a 68nF in parallel with C14.
Jumper D2, replace D1 with 1N4002. OR remove D1 & D2, connect 1N4001 from D1-A to D2-K.
Change D3 to 1N4002. This makes no sense to me because D5 & D6 should never conduct. The original BD-2 used a different opamp and it might have made a difference then. But who am I to 2nd guess Robert Keeley?
Replace ceramic caps with SM (or film).
R24's value is not critical. 2M would have been a problem with aluminum for C20. With tantalum, it doesn't matter.
 
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