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The first +3 release had a fatal hardware error: the 128K sound output is completely distorted.

Technical explanation:

On +3, the analog output of the AY-3-8012 sound chip was intended to be amplified by a one stage common-emitter transistor. In practice, they forgot to put a resistor to the transistor’s emitter. The result: the transistor works in pure switching mode, so the sound is converted from analog multi-level amplitude to digitized two-level amplitude, same as the old 48K sound system.

Take a look at the +3 sound diagram .

The second +3 release (the so-called +3B) had the sound circuit fixed. Also, the sound on all +2As encountered by me was ok, however, most of them were Spanish version which are supposed to be released later than their UK counterpart.

If someone wishes to fix the sound of an original +3, there is a better solution: stereo sound output, sometimes referred as “ACB Sound”. The layout comes from Amstrad CPC 464+ computers. I have done this on several +3 and the result is excellent.

With reference to my +3 sound diagram : the stereo sound output described below also makes a sound mix between 128K sound and the old 48K sound (beep). I personally prefer to have the 128K sound separated from the 48K beep. If this is also your case, simply omit the two (unnamed) 100K resistors. The 48K sound can be heard on the TV set or may be amplified separately from the cass out connector.

Assuming you own a first release +3, to build the stereo sound, you have to:

  • !! know precisely what you are doing !!
  • remove C38
  • remove R72
  • cut tracks between pin 1 and 4 & 4 and 5 of IC11 (the AY chip) on the back side of the printed circuit board; here is an example
  • build the matrix resistor around pins 1, 4 and 5 of IC11; note that pin 6 (GND) may be used for the ground point for the matrix; here is an example

You then have to find a way to get the sound out from the inside. One of two solutions:

  1. mount two RCA connectors on the back side of the +3; this is somewhat carcass destructive
  2. use the existing RGB PERITEL for stereo sound output; if this is the case, you have to:
    • remove R42
    • remove R43
    • if you are NOT using the +12V for RGB switching of your TV set, then remove R44
    • if you ARE using the +12V for RGB switching of your TV set, then:
      • leave R44 as is
      • cut tracks between pin 1 and pin 5 of RGB PERITEL connector on the back side of the circuit board; connect a wire between the rear termination of R44 and pin 1 of RGB PERITEL connector, like in this example ; pin 1 remains now the +12V switching pin for the RGB system
      • cut tracks between R44 and pin 5 of RGB PERITEL connector on the component side of the circuit board; the place is somewhat narrow; here is an example from a +3B board
    • make all connections to RGB PERITEL as shown in the +3 sound diagram

You can now use a stereo RCA cable (version 1) or a stereo DIN cable (version 2; pin 3=L, pin 5=R, pin 2=GND) to put the sound to any amplifier (usually the AUX input).

Important: the stereo sound output, as described above, has relatively low output level. If your amplifier has not enough sensitivity, try to connect the +3 to the MIC input of the amplifier, if available. A local amplifier may be build inside the +3, however, this is outside the scope of these technical notes.
Even if not at 1000W acoustical power, Ghouls’n’Ghosts pure sound can be now finally enjoyed !
(I personally like very much Software Creations’s sound music :)

Note: over the time, I read some comments regarding the two 33pF ceramic capacitors I have put on my stereo audio outputs, in that they were considered way too low and, therefore, completely useless; well, not quite: they are used (just) to bypass high frequency energy to ground that might be radiated by the circuit paths, in order to prevent VHF interference on external TV or other similar sensitive devices. For this same reason these should be soldered very close the connector choosed for audio output (rather than near to the AY circuit).


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