CGS real ring modulator

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Cgs photo cgsrr1.jpg
Cgs photo cgsrrv11.jpg

CGSRR the CGS real ring modulator is a traditional diode and transformer ring modulator.

Please note: This is not a guitar effect where you can "plug in your guitar and get a sound out". Extra circuitry is absolutely essential, either directly wired, or as parts of other equipment. If you need to ask how to use it, then it's not for you.

Four quadrant multipliers have more or less replaced ring modulators in synthesizers, even though they still bear the label "ring modulator". The distortion in these is lower than that of a true diode ring modulator, because the diode voltage drops have been eliminated. This leads to better specifications, though in a noise maker, this is not always desirable. For years I have been building various four quadrant modulators, and have been satisfied with none of them. Not one of them had the raw sonic beauty of the traditional ring modulators I made when I was first starting out in synthesizer building. For that reason I present here the "Real Ring Modulator".

Carrier suppression is good, but not complete, so a compressor-expander could help if better suppression is required.

How it works

The schematic of Real Ring Modulator. Above is the standard diagram used for a ring modulator, if for no other reason than it is easier to work out what is going on by looking at it. Below the diode ring has been "unfolded" to make it clear that it is a diode ring, not a diode bridge.

Construction

The component overlay for the VER2.1 PCB. Click through for an enlarged, printable version. Print at 300dpi.
Wiring the ring modulator. The center input is the carrier input. In and out are interchangeable. The wiring remains the same for the later version of the PCB.

Parts list

  • Transformers:
    Mouser 42TM018-RC 10KCT-10KCT
    Altronics in Australia. M0222 3kCT - 3k
  • Diodes: 1N60 or 1N34A, or any other germanium diode. It is best if they are matched for voltage drop. Schottky signal diodes could also be used, e.g. BAT48.

Notes

  • It is best to use a transformer with an impedance of 3k or greater, though lower impedance coils will work. Note that the DC resistance of the coils is much lower than the specified impedance. If the transformer you buy has both coils center tapped, just ignore or cut off the center tap wire on one coil. The KT-211P transformers used in one of the photographs were junk-box transformers I had to hand. They have a lower impedance than recommended.
  • To match diodes, measure the voltage drop across the forward biased diode junction using the diode-test function of any good digital multi-meter. Pick diodes that have readings that are as close as possible to each other. The greater the number of diodes you have to hand, the greater your chance of getting a well matched set. Important! The diode voltage drop is affected by temperature. You must measure all of your diodes in one session, and you must not handle them with your fingers during the process. It is easiest to measure them while they are still on the tape on which they are usually supplied. Stick that to a piece of paper, and write the voltage down beside each as you measure them.
  • Early PCB info: 0.6" x 2.3" with 3mm mounting holes 0.15" in from the corners.
  • V1.1 PCB info: 1.0" x 3.0" with 3mm mounting holes 0.15" in from the corners. Has pads for a greater range of transformer footprints

CC-BY-NC

Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.

See also

References

External links

Suppliers