|
AM2500 Module - Eµ VC Clock
Overview This module is a clone of
the rather special Voltage Controlled Clock module in the Eµ Systems Modular Sequencer. It is a very close replica with the minor changes to use modern analog components.
The VCC is the core of the sequencer as it enables all the
other modules to be driven from a wide range low frequency VCO. The frequency and pulse width are voltage controlled, and pulse and saw waveforms are available, with synchronous gating. The oscillator can be gated on and off and the pulse
output can be switched between 2 separate outputs. The clock has a range of 100,000, from once every 5 minutes to 500Hz.
Original Circuit
The original Revision 1 design dates back to December 1973. A Revision 2 is documented in a set of schematics in 1980, and it's this later version I have cloned. The different between the revisions is probably minimal, maybe the use of contemporary Op Amps, etc.
The core of the circuit is a sawtooth low frequency oscillator built around a couple of transistor pairs and a bi-polar Op Amp with a discrete FET input stage. The oscillator is not temperature compensated, but this is rather
unnecessary for non-pitched LFO. The transistor pairs are AD820 and QD402's and the Op Amp is a 556. The pulse shaping circuit and gating in built around the core using CMOS logic chips.
Specifications:
- Frequency input has approximate 1V/Octave sensitivity
- Frequency range 0.002 to 500Hz (typically 0.001 to 1KHz)
- Pulse Width input has approximately 10%/V sensitivity
- Pulse Width variable from near 0 to near 100%, but a pulse is always generated
AM Circuit The AM circuit is exactly the same except for:
- Modern matched transistor pairs (SSM2210, SSM2200)
- The ITE4340 FET transistor is replaced with a 2N4340 FET
- Option of using a modern FET Op Amp or the original Dual FET transistor 2N3958 and a bi-polar Op Amp
- Modern blue and aqua 5mm LED's
The front panel is similar to the original, although I have fitted it into a narrow panel and
laid out the gating controls rather better (IMHO). There is no trimming.The module needs +5V for the CMOS logic, so a simple 5V regulator is on the PCB. It also drives the LED's and effectively splits the analog and digital power.
Front Panel The front panel is a standard AM design, 90mm wide and 4U high, with black lettering. Controls knobs are standard Eµ Modular designs.
Build History
The schematic was transferred into Eagle CAD in the summer of 2005 when I was on holiday in the Peak District (UK). The circuit has been laid out over 2 80x100mm PCB's and a prototype will be tested in the Spring of 2006.
|
Site Options
Resources
* AM FAQ's 