Adding Vox top boost circuit to AC15 amp

[beatnik]

Hi everybody,

I am doing an organ amp conversion into guitar amp, basically following the VOX AC15 circuit.

I would like to implement the Vox top boost circuit originally intended for the AC30 model.

I have a simple question regarding the 220K mixing resistors after the top boost circuit, R9 and R7.
I believe these were intended because there are two input channels on the AC30.
Since the AC15 has a single EF86 input, do I have to omit the mixing resistors, or maybe change the value of the treble pot ?

I have attached the schematics for quick reference.

[Dave H]

I guess you don't really need the 220k mixing resistors but I'd be inclined to leave them in (connect the unused input 220k to ground) to make a voltage divider as it will have far too much gain with the EF86 and the added TB circuit and is almost bound to oscillate. You may need to reduce the value of the grounded 220k to reduce the gain sufficiently.