Category Schematics

Equipment Repair, Mods and More

We’ve got a lot of experience repairing and modding audio gear here at the studio and the soldering iron is always hot.

If your gear needs repair or restoration and you don’t think you have the skill, confidence or money to get the job done, give us a call.

We can bias your amps, diagnose many common issues, and replace out-of-spec and worn components with the extensive inventory of components on ...

Alembic F-2B Inspired Preamp Clone

I’ve always wanted one of these so I built one.

Until then, I never realized how great sounding and versatile this amp is. It’s now a studio staple. We use it for everything; bass, guitar, organ, DI.

In many ways, it’s the sound of rock and roll. It’s Bootsy Collins, Phil Lesh, Jerry Garcia, David Gilmour, and Stanley Clarke in a box.

The circuit for this preamp has been around forever...

Leslie 825 9-Pin Connector Wiring With Motor Controller Switching and External Preamp Input

This setup can easily be mounted in a 1590B Hammond box  with IEC connections for power, a 1/4″ TS audio input, and even a TRS jack for a remote footswitch.

Don’t forget the fuse in your build! The main Motor switch on the schematic is optional but could be useful if you want to use the Leslie without rotation otherwise the Leslie will always spin.

The 9-pin connector we used came from our stock...

MTI Rotophaser with Footswitch Schematics and Images

The MTI Rotophaser is a rotating tremolo horn speaker system made in Italy in the 1970s. It is similar to the top half of a Leslie cabinet.

These are somewhat uncommon to find and often the footswitch has been lost or damaged.

Since the Rotophaser won’t work without the foot switch and its tangle of cable,

I’ve drawn up some schematics for the MTI Rotophaser footswitch and posted them on this page...

Shure M67 Microphone Mixer Preamp Mods


The Shure M67 is a vintage four channel microphone mixer commonly modified for use as a four channel preamp in recording studios. First manufactured in 1968, these became a standard in the broadcast industry. The M67 was used to record Woodstock and many a tv news program. Still readily available on the used market, they remain relatively affordable...

Cordovox Accordion Amp Conversion with Schematics


Converting a 1962 Cordovox Accordion Amp to a guitar amp…

A brief build summary:

  • Tone Generator Cabinet gutted.
    • Components parted out and scrapped.
  • Tone Generator Cabinet used for build.
    • Chosen for existing control panel cutout.
    • Cabinet modified with 2×12 speaker baffle.
  • Original Jensen C12R Speakers relocated.
  • Amplifier
    • Chassis moved to tone generator cabinet.
    • Circuit traced ...