The Crank - dual pot log or lin?

[blues123]

Hi,

Anybody know if the dual pot in the crank is log or lin?
Mark, one for you I think!!

[Mark Hammer]

I *think* its linear.  Most dual-ganged pots are for things like treble and bass controls on stereos, and those are always linear.    Certainly log will not prevent functioning, but my hunch is that the change in gain will be a little strange with log since the opposite-direction wiring of the pots means you're going in the log direction for one half and anti-log for the other.  Stick with linear.  It should yield the smoothest gain change.

Also:

• change the 6k8 fixed resistor in the second stage to 5k6, and the .47uf cap to 1uf to get more gain and more bass
• stick a 1k resistor in series with the diodes in stage 2 to soften whatever distortion/coloration is produced

... and consider seriously the insertion of a SWTC ( http://img.photobucket.com/albums/v474/mhammer/SWTC.gif ) using a 50k pot and .01uf cap to ground between the 10uf cap and output level pot.  A 1k fixed resistor also goes between the 10uf cap and 50k pot to produce a maximum treble point.

[Paul Marossy]

I used a linear in mine.

[blues123]

WOW, that was fast. You guys never cease to amaze me.

Mark & Paul, thanks for putting me straight. I really appreciate the extra info as well. I look forward to including these extras/mods in my pedal.
By the way, just finished the Roseyray. Man, thats one mean box!!!!

Thanks
Steve (UK)

[Mark Hammer]

Were you able to avoid the nasty little low freq oscillation in the Roseyray? When I first made it, I was testing it out on a 386-based headphone amp with a 3" speaker so I didn't hear the oscillation.  It was fixed by providing an AC only path between the 2nd stage output and 2nd stage non-inverting input.

And yes it IS mean isn't it?  I normally don't lean towards such things, but I kinda like it.  I might point out that it responds VERY nicely to a wah in front of it.  Definitely Steve Vai territory.

[blues123]

I am getting some oscillations at really high gain settings, but I put that down to the fact that I haven't trimmed the wires yet or boxed it up.

It was fixed by providing an AC only path between the 2nd stage output and 2nd stage non-inverting input.

So you're putting an extra cap in there?
What sort of value would you suggest?

Thanks again Mark

[Mark Hammer]

Yep, that would be it.  Turn the gain up, and rotate the tone/head control over to the bluesier side an you get no problems.  Rotate the tone/head control over to the more metallic side and you can't turn the gain up very far without producing oscillations.

I imagine layout may also have something to do with it too, but you need to have caps on the two outputs so that bias vltages are not fed back to the 2nd stage input.  Somebody recently posted a redraw with the added caps, but I forgot who.  Check the archives.