CGS delay development board

CGS44 the CGS delay development board has been designed to allow people to experiment with the Princeton Technologies PT2395 Enhanced Digital Echo IC. The delays produced by this chip are quite long, suitable for various forms of echo. As it stands it is not appropriate for use in chorus units or flangers, though it may be possible to achieve this by dropping address lines. Other areas such as the feedback network also need improvement over what has been suggested on the application notes for this device, thus this board, to give an easy starting point for such experiments.

A little on how it works
The board is made up of several distinct blocks, some of which are not connected in any way.
 * A buffer for boosting the output signal up to levels suitable for synthesizer use.
 * A basic compressor and
 * A basic expander to reduce noise generated by the delay chip.
 * The delay block itself.
 * An experimenters area.

The delay circuit is based on the application note for the PT2395, and I recommend you seek out the appropriate file. The desired file is called "PT2395.pdf" and is 519k in size. Note that there are a number of errors in this app, note. It is even contradictory in places. There are several other versions of the app. note/data sheet, but all are cut-down versions, and are more or less useless.

Construction


This is one of those PCBs than can be assembled in a number of different ways to suit the builder's needs.

On the first run of boards, a track is missing. It runs between pin 4 of the NE570 and AGND (0 volts).

One builder says he got better results by adding a 10k resistor between pin 12 of the NE570 and ground (thus in parallel with the internal 30k resistor).

Note that some chips a mounted in the opposite direction to others on this board. Large arrows on the overlay make this clear.

There is a development area to the right end of the board, allowing a 74HC4046 and associated components to be fitted, including two 4024 divider chips. The theory is that voltage control of the delay can be achieved using the 74HC4046, and frequency dependent delays achieved using the phase-locked-loop. At this point this area has not been developed, and is up the individual experimenter to use or ignore as s/he sees fit.

Before you start assembly, check the board for etching faults. Look for any shorts between tracks, or open circuits due to over etching. Take this opportunity to sand the edges of the board if needed, removing any splinters or rough edges.

When you are happy with the printed circuit board, construction can proceed as normal, starting with the resistors first, followed by the IC socket if used, then moving onto the taller components.

Take particular care with the orientation of the polarized components such as electrolytics, diodes, transistors and ICs.

When inserting ICs into sockets, take care not to accidentally bend any of the pins under the chip. Also, make sure the notch on the chip is aligned with the notch marked on the PCB overlay.

Parts list
This is a guide only. Parts needed will vary with individual constructor's needs.

Ooops.... missing

Suppliers

 * The delay chip can be purchased from Small Bear Electronics.