19.002 Is there a way to output quadrphonic sound on a IIgs?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
19.002 Is there a way to output quadrphonic sound on a IIgs?
We all know that the "S" in GS stands for sound. Stereo cards abound but
the GS is capable of much more. The following circuit uses the same technique
as stereo cards to decode stereo but decodes quadrophonic. Inside the GS by the
memory expansion slot exists the J-25 sound expansion connector that most
stereo cards use. The pin outs are as follows:
J-25 Connector
1 Analog to digital in (end nearest front of computer)
2 Analog ground
3 Waveform out
4 Channel address zero
5 Channel address one
6 Channel address strobe
7 Channel address two
The analog in (pin 1) doesn't concern us here. The waveform out is the
important signal. The contains the output of all oscilators one after the other
in quick succession (the DOC only handles one at a time). When the DOC is
outputing the waveform from an oscilator it puts the channel address from the
DOC register $A0 + osc (most significant four bits) on the three channel
address lines and pulls the channel address strobe low. (The DOC realy has four
lines but only three are connected in the GS).
The circuit below uses the first two lines the decode the channels
(creating 4 unique channels) and breaks the signal into four parts depending on
the address using cmos single position single toggle wired as dual position
single toggle switches. Then the chopped output is smoothed with an active low
pass filter with a corner frequency of 17.7KHz.
Because most programs only use stereo the second channel address in
normally low so this circuit will also decode stereo and this will turn up at
the front two outputs. I have built this circuit on a bread board but need to
make a PC board to make a better sounding circuit. Also the output impedance
should be set to 75K ohms but I haven't yet gotten around to it.
To make sound in stereo or quad all you have to do is place the binary
address of the channel you wish the sound to have in the control regsister for
the ocsilator (the tools can do this) and there you have it.
C1
o----||----o |\ 1/4 IC7
| R2 | o-----------o--| >o---o
o--/\/\/\--o | | |/ __|___
| _ o-|-----o-----|-------|____|--o
R1 | | \_ IC1 | | | __|___ 1/4 IC5 | *
Pin 3--/\/\/\--o-|- \_ | | | o-|____|------------o---[O]--FL
| \__o | | | 1/4 IC5
o-|+ _/ | | | |\ 1/4 IC7
| | _/ | o---|-|---o--| >o---o
| |_/ | | | | | |/ __|___
_|_ | | o-|---|-------|____|--o
/// | | | | __|___ 1/4 IC5 | *
| | | o-|____|------------o---[O]--FR
IC2 | | | | 1/4 IC5
______ | | | | |\ 1/4 IC7
| | | | o-|-|---o--| >o---o
Pin 4----|a 1|-------------o | | | | | |/ __|___
Pin 5----|b 2|---------------o | o-|---|-------|____|--o
| 3|-----------------o | | __|___ 1/4 IC6 | *
|__ 4|--------------o | o-|____|------------o---[O]--BL
Pin 6----|EN | | | | 1/4 IC6
|____| | | | |\ 1/4 IC7
o----|-|---o--| >o---o
| | | |/ __|___
o-|---|-------|____|--o
| __|___ 1/4 IC6 | *
o-|____|------------o---[O]--BR
| 1/4 IC6
|
| *Notes: [O] = Output Stage
_|_ FL = "Front Left"
/// BR = "Back Right"
... etc.
Typical Output Stage [O]
C2 - C5
o----||----o
| R3 - R6 |
trim pot o--/\/\/\--o
o----o | _ |
| v | | \_ |
----o--/\/\/\--o-|- \_ |
R7 - R10 | \__o---------
o-|+ _/
| | _/
| |_/ 1/2 IC3 - IC4
_|_
///
R1 - R6 : 1.2k ohm
R7 - R10 : 2k ohm trim potentiometer
C1 - C5 : 47pf
IC1 : LM318 high speed op-amp
IC2 : 74F139N dual 2 to 4 decoder
IC3 - IC4 : TL072 dual op-amp jfet input
IC5 - IC6 : 4016 cmos SPST analog switch
IC7 : 4069 cmos hex inverter
----------------------
By: Brian Willoughby
While there is nothing wrong with your circuit, I thought that I would
mention that the functionality of IC2, IC5, 6 & IC7 are combined in a few
standard CMOS chips. It turns out that your circuit is so useful in many
applications that you can easily find it in one chip, thus saving wiring and
lowering noise.
Look for a Siliconix DG506 or any make of 4058. I'm not absolutely sure
about the number 4058, but just check in any CMOS 4000 series list for an 8-
channel to 1 analog multiplexer/demultiplexer (not the digital type, they won't
handle audio/sound signals).
----------------------
By: Seth D. Kadesh
One of the chips Brian refers to is a 4052. Both the LM318 and the 4052 can be
purchased from B.G. Micro (214-271-5546). Cost for both was $3.75 USA.
The other parts can be purchased from Radio Shack.
By: Rubywand
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