INMC 80 News


October–December 1981, Issue 5

Page 22 of 71

Sound Board

The PHG Electronics Programmable Sound Generator

A review by D. R. Hunt.

A couple of weeks ago a new, some what noisey, goodie appeared on the home computer front. It is the PHG Electronics Programmable Sound Generator (PSG for short). The PSG is supplied built, using a good quality single sided pcb about 4″ square, and fitted with a 3.5″ loudspeaker. The pcb is drilled for mounting pillars to support speaker and the card itself, but no pillars are supplied. The card was terminated with a ‘gold flashed’ single sided edge connector, the connector being supplied, but the lead to the Nascom PIO is not. There aren’t many components on the board, the chip that does all the work is the General Instrument AY-3-8910 three channel synthesizer, and there are three other support chips, including a small power amp chip to drive the speaker. A few electrolytic capacitors, and a couple of resistors complete the components. The PSG comes with two manuals, a well produced and printed instruction manual of about 12 pages, and a 64 page booklet produced by GI giving very detailed operating instructions for the AY-3-8910 chip. No circuit diagrams were supplied. A demonstration tape recorded in Nascom 2 format at 1200 BAUD was supplied, this assumes that Nascom Basic and 16K of RAM are available.

Connecting the Nascom PIO lead to the connector is straight forward and well illustrated in the PSG manual, and short lengths of heat shrinkable sleeving are supplied to insulate and strengthen the connections. The PSG requires a single rail +5 volt supply, and this is drawn from the Nascom via the PIO cable. Adjacent to the connector is a 4 pin stripline connector, and as supplied, a plug is fitted connecting the four pins together. The manual describes this as the output and phones connector, and appears to parallel all three channels and connect them to the onboard audio amplifier. Although this is described in the manual with an illustration showing links, the layout is slightly confusing as the links are where the output coupling capacitors are fitted, and the description does not tie in too well with the way connection is intended. It is a pity no circuit diagram was supplied, as it would have shown quite clearly what was intended. To be fair, this, and the lack of circuit diagram are the only criticism that can be leveled at the PSG.

On plugging the unit into the PIO, and loading the tape, the PSG performed well. The demo consisted of five effects. The first, John Brown’s Body, gave a pretty fair imitation of a harmonium, and was followed by some birds twittering. The third was very short, and would be a ‘must’ in any Space Invaders program, consisting of a missile flying across the screen, and hitting it’s target with a commendable explosion. This effect could drive anyone not playing Space Invaders nuts within minutes. This demonstration was convincing because it showed how, given instruction, the PSG will continue to generate sound until updated by the program, allowing the computer to manipulate the graphics to suit. The graphics were fast, very impressive, particularly as the graphics were manipulated by Basic. The fourth demo was a bit of Bach’s 4th Brandenburg Concerto. The program was written in three parts, each separate channel handling one part. Following the instructions for fitting stereo phones, the effect was very impressive. The tone of the music was definitely ‘electronic’, but Walter Carlos wouldn’t have worried. It showed the programmer wasn’t neccessarily a musician, as there were at least three bum notes in the Brandenburg (easily corrected in the program). The last demo was Frere Jaque programmed as a three part ‘round’.

The demos were good and gave an idea how the PSG performed. Now how about trying it for yourself? The manual gave examples of adapting the demo program to allow you to compose you own music and this was easy. Given a modest amount of patience it was easy to program recognisable tunes, and by presetting the noise register, other simple effects as well. Anything more elaborate required careful reading of the AY-3-8910 booklet, along with a reasonable

Page 22 of 71