In another post here, member 'mcabe' talked about changing the 500pf first-stage blocking cap in a Vox Top Boost preamp for a larger value, such as 1200pf. http://www.tdpri.com/forum/amp-tech-center/573075-vox-top-boost-circuit.html I am interested in this idea. I have a home-built version of an AC30, with the 500pf cap. I also have an unused slide switch available. I am considering running a 750pf cap to this switch, and using the switch to enable/disable this cap in parallel with the existing 500pf. This should, in theory, give me a choice of 500pf or 1250pf. That's theory. I wonder how the tone may - or may NOT - be affected by parallel caps at this point in the chain. Anyone have any experience, knowledge, or advice to share here? And does anyone know if using different types of caps within the network will cause any problems? I expect to use silver-mica... but I might try whatever I can dig out of my parts box if there is no reason not to.