How to wire the Crackatwoa as a straight amp

[Rory]

I’d like to use my Crackatwoa with one source that has a variable output, so I no longer need the selector, balance and volume controls.  I imagine that removing these from the signal path might improve the sound, but would it?  Also, while it seems straightforward to remove them, I’m wondering if there’s more to it than simply bypassing the components (using shielded cat6 wiring routed along the perimeter). Do I need to include some impedance in the path? Is there a way to calculate the optimal impedance based on my preamp device (an iFi  ZEN One Signature)?

[Paul Birkeland]

I imagine that removing these from the signal path might improve the sound, but would it?

Not particularly.  It will remove a substantial amount of value from the kit if you ever go to resell it.

Also, while it seems straightforward to remove them, I’m wondering if there’s more to it than simply bypassing the components (using shielded cat6 wiring routed along the perimeter). Do I need to include some impedance in the path? Is there a way to calculate the optimal impedance based on my preamp device (an iFi  ZEN One Signature)?

Yes, you need some kind of grid leak resistors so the grids of the 12AU7 are tied to DC ground.  100K is a fine value for this.

[Skipperrik]

I'm following this with interest since I have bypassed the controls on my Crackatwoa. I'm wondering if this is the cause of a ground hum that has developed. Where exactly should the resistors be placed?

[Paul Birkeland]

Where exactly should the resistors be placed?

They need to go from grid to ground on the 12AU7.

[Skipperrik]

I'm finding conflicting pin numbers. One source says pins 2&8, another says 2&7. I believe it's 2&7. Is that correct?

[Paul Birkeland]

8 is a cathode.  2 and 7 are grids.

[Skipperrik]

Thanks!