DIY and Hi-Fi Audio Schematics DIY and Hi-Fi Audio Schematics. This is our collection of DIY and Hi-Fi Audio Schematics. Feel free to send us your hi-fi audio schematics and we will add them here. If you have built any of these circuits, we would love to hear from you so send us your comments. Many of these diy Audio Books contain schematics. Amp Mods - Rob Robinette Amp Protection Mods Protect your amp from expensive damage. Using the Ground Switch Hole for Mods Be careful, it's noisy over there. Add a 6" Practice Speaker to your amp head. Tremolo Cut Switch Add gain by disconnecting the tremolo circuit. Slow the Tremolo Slow is good. Eliminate Tremolo Ticking Add one cap and it's gone. Vox AC30 + EF86 channel in a different way Nov 11, 2013When your triode/pentode switch is in the EF86 position, the cathode follower grid has no ground reference - the cathode follower gets its bias voltage from the anode of the preceding triode. It might work if you removed the d coupling capacitor between the EF86 anode and the switch.