EFM Wildcat rev 1 & rev 2

last update: october 17th, 2004
The EFM Wildcat is a single board modular synthesizer designed by Tom Gamble at EFM. For a very low cost it is possible to build a very efficient and powerful modular synthesizer. This page describes the progress of the assembly of my Wildcat system. Because I purchased a pre-release board (rev.1) a lot of PCB design errors had to be corrected. It took me some time but it was part of the deal (reduced price for the rev-1 board) and also part of the fun. I really had a good time at tracking the bugs and troubleshooting these. In some way, I brought a modest contribution to the release of the rev-2 board that is now available. I also purchased a rev2 board in which most of the bugs have been fixed.
I also made some improvements to the original design : purer waveshapes, hum noise rejection and so on...
The current status is :
  •  The rev1  & rev 2 boards are fully populated
  •  The modules have been tested, fixed when required and adjusted.
What is still to be made :
  • Some daughter boards such as : octave range switches for the VCOs, buffered control voltage dispatchers, a joystick controller.
  • A nice panel (I will try to make it entirely : no Front Panel Designer, no Schaeffer Apparatbau), I know it is going to be challenging.
  • A decent wood cabinet.
To conclude, I must say that the now defunct EFM_SYNTH list was very helpful! There's always somebody in the list to help you sorting out electronic problems. Thanks very much to Harry Bissell, Dave Magnuson, Rich Hess and Tom Gamble for their helpful advices.
Rev1  board
click to magnify

left rev 2, right rev 1
click to magnify

In order to cut down costs, 1% resistors were used only for those modules where accuracy and reproducibility were an issue. That is, for the VCOs, the balanced modulator and the staircase generator.
I used cheap 5% 1/4W resistors, elsewhere.
Also, I used mostly LM13700 ICs as substitutes for LM13600s. I tested the circuits either with LM13700 and LM13600 : I didn't see or hear any difference except for the Moog VCF1 module where the LM13600 is very much recommended. Therefore, you may use LM13700 in all modules with the exception of VCF1, they are easier to find than LM13600 and cheaper as well. 
Power supply : I used ML9 heat sinks with a thermal resistance of 6°C/W  for the +12V and -12V supplies and a ML26 heat sink (15°C/W) for the 5V supply.


Here you will find the corrections to the rev1-PCB tracks of the VCOs and the mods I made to improve the waveshapes (rev1 & rev2).

VCF 1 - Moog ladder

From my various experiments I highly recommend to use LM13600 for U2 you will get much higher and punchier levels than if you used a LM13700.
more to come...

VCF 2 - MS20

more to come...


more to come...


The Wildcat has four VCA's based on OTAs. The design is quite classical, though some resistor values need to be changed in order to improve the dynamic range. Here you will find my mods of the VCAs. These mods are also valid for Wildcat rev2.

Noise generator

The noise generators of my rev1 and rev2 boards tend to be contaminated by some 100Hz hum. As a matter of fact this hum is hardly earable when listening to the raw white noise signal but becomes more perceptible as soon as the noise signal is injected in a VCF. Go here to see the modifications I made to the noise module.

Ring modulator

I was not really happy with the Wildcat's Ring Modulator : poor modulation and carrier nulling, high distorsion level. By adding a few resistors (5) and changing the value of a single resistor the ring modulator now behaves the way I expected. Click this link to view the modifications. These modifications also apply to the rev1 and rev2 boards and to the EFM RMP1 module as well.

Sample & Hold

This module behaves more like a Track & Hold circuit rather than a Sample and Hold circuit! To have it behaving the way I expected, I made a few modifications. Click this link to view the modifications. These modifications also apply to the rev1 and rev2 boards
Enveloppe Generators

more to come...

The behaviour of this module depends heavily on the brand of LM358 IC that is used for U . The choice of the LM358 IC is critical because it has to handle voltages that very close to the power rail value. A way to cure this problem would be to power up this module from a separate +/-15V power supply.
Among those I have tested, I recommend to choose either the LM358N from ST Microelectronics or the LM358N from Motorola. Avoid LM358A or LM358NA !

Wildcat housing
The cabinet
coffret cc cc cc
l1 l2 Click on the images to blow them up

 The front panels

The left panel (sized 500x300mm) will host the the control knobs, switches and other controls, and the right panel (sized 300x300mm) will be the patch panel hosting jack sockets. They will be made of 3mm thick aluminium plates. The marking of these panels is still an issue...