From apm@zeppelin.abl.caWed May 24 11:24:55 1995 Date: Wed, 24 May 1995 14:06:48 -0400 (EDT) From: Andrew Paul Marriott To: bode Cc: analogue@hyperreal.com Subject: A simple ring modulator Since there seems to have been a lot of discussion about ring modulators recently, I thought I would take the time and create an ASCII schematic of the Digisound 80 ring modulator which is based on the MC1496 balanced modulator. This schematic is probably copyrighted but since Digisound don't seem to exist anymore, I don't think I have violated too many rights by reproducing it here. Any questions about the schematic, please ask. I have construced this (as a dual ring modulator on a signle board) and it works fine. Enjoy. Paul. Digisound 80 Ring Modulator (1 channel shown) Specification: inputs: 10V peak-to-peak nominal (can range from -10V to +10V) carrier feed through from X input better than -50dB signal feed through from Y input better than -40dB output 10V peak-to-peak nominal output impedance 1k Components: R1 200k R2 1k0 R3 1k5 R4 1k5 R5 1k0 R6 100k R7 1Meg R8 200k R9 10k R10 10k R11 100k R12 1Meg R13 13k R14 1k2 R15 1k2 R16 13k R17 100k R18 100k R19 100k R20 1k0 all resistors 5% or better metal or carbon film RV1 100k cermet multi turn RV2 100k cermet multi turn C1 470n polyester C2 470n polyester C3 220n polyester C4 22u electrolytic C5 220n polyester C6 4u7 electrolytic C7 4u7 electrolytic IC1 MC1496 (or equivalent) IC2 TL081 (or equivalent) C3 __R1_ >--||-----|___|---+ X in | o-----------o------------o +15 | | | --- C1 o +15 | --- | | | |-| | o-----------o-----------+ Ground | |R4 | | | | | | --- C2 --- | | | --- - |-| | | | | o-----------o------------o -15 | | | __R5_ | +---o---|___|--(----o---------> To pin 8 | | | | | | | |-| | | | | |R6 | | | | | +| | | |-| C4 === | __R2_ | | --- o---|___|--o----o---------> To pin 10 | | | | |-| |-| | | |R3 | |R7 | | | | | | |-| |-| | | | +---o | --- | - __V__ -15 o--|___|--o +15 RV1 C5 _R8__ >--||------|___|-o-----o---------> To pin 4 Y in | | |-| |-| R9| | | |R11 | | | | |-| |-| | | --- | - | | +----------o---------> To pin 1 | | |-| |-| | |R10 | |R12 | | | | |-| |-| | | | | --- | - __V__ -15 o--|___|--o +15 RV2 _R17_ +-|___|---+ | | C6 _R16_ | |\ | from pin 12 >---#|------|___|--o-|-\ IC2 | + 2| \ | |TL \ | _R20_ |081 >--o-|___|----> OUT C7 _R18_ 3| /6 from pin 6 >---#|------|___|--o-|+ / + | | / | |/ |-| | | | |R19 |-| | --- - o -15 o +15 | | | | +------------+ |-| | 14 | | |R14 | | | | | | |-| | | | >----|8 12|-----o----> | | | | >----|10 6|-----o----> | IC1 | | | | |-| | MC1496 | | |R15 | | | | | | |-| | | | | | | | | o +15 | | >----|4 5|-----+ | | | | | |-| >----|1 | | |R13 | | | | | | |-| | | | | | --- | 2 3 | - +------------+ | | +----+ Also connect all the positive power pins on the ICs to the decoupled +15V power supply and all the negative power pins on the ICs to the decoupled -15V power supply. Calibration: Some setting up is required to minimize the signal and carrier feedthrough. Apply a 1kHz sine or triangle wave to the X input. Connect the output to either an oscilloscope, a sensitive AC voltmeter or an amplifier. Adjust RV2 until the output signal is a minimum. This setting is critical and hence a multiturn trimmer should be used. Now connect the 1kHz sine or triangle to the Y input (nothing connected to the X input). Perform the same procedure by adjusting RV1. After setting up the ring modulator, repeat the procedure after a few minutes. It is important that a stable power supply is used. It should be possible to trim the feedthrough to be around 10mV (-60dB, ref 10V input) for the X input and around 40mV (-48dB, ref 10V input) for the Y input.