c326-18@alberta.uucp (Keen Jeffrey Alfred) (11/11/89)
We all know that is 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 sound expansion
connector that most stereo cards use. The pin outs are as follows:
1 Analog to digital in
2 Analog ground (case ground)
3 Waveform out
4 Channel address zero
5 Channel address one
6 Channel address strobe
7 Channel address two
The analog in doesn't consern 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 purchase all the componets costs about $20
canadian which I feel is not bad considering the price of stereo card (most
of which do more like allow digitizing). If anyone has the equipment and
time to design and make a PC board I would be interested in hereing how it
go's. Please forgive the messy apearance of the circuit diagram it not
esay drawing these in ascii. 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 | |output |
Pin 3--/\/\/\--o-|- \_ | | | o-|____|------------o----|stage |----FL
| \__o | | | 1/4 IC5 |_______|
o-|+ _/ | | | |\ 1/4 IC7
| | _/ | o---|-|---o--| >o---o
| |_/ | | | | | |/ __|___
_|_ | | o-|---|-------|____|--o _________
/// | | | | __|___ 1/4 IC5 | |output |
| | | o-|____|------------o----|stage |----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 | |output |
|__ 4|--------------o | o-|____|------------o----|stage |----BL
Pin 6----|EN | | | | 1/4 IC6 |_______|
|____| | | | |\ 1/4 IC7
o----|-|---o--| >o---o
| | | |/ __|___
o-|---|-------|____|--o _________
| __|___ 1/4 IC6 | |output |
o-|____|------------o----|stage |----BR
| 1/4 IC6 |_______|
|
_|_
///
Typical of out output stages.
C2
o----||----o
| R3 |
o--/\/\/\--o
o----o | _ |
| v | | \_ IC3 |
----o--/\/\/\--o-|- \_ |
R7 | \__o---------
o-|+ _/
| | _/
| |_/
_|_
///
R1 - R6 : 1.2k ohm
R7 - R10 : 2k ohm trim
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
brianw@microsoft.UUCP (Brian Willoughby) (11/15/89)
In article <1989Nov10.175249.9131@alberta.uucp> c326-18@jasper.UUCP (Keen Jeffrey) writes: > We all know that is 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. > >IC2 : 74F139N dual 2 to 4 decoder >IC5 - IC6 : 4016 cmos SPST analog switch >IC7 : 4069 cmos hex inverter Keen, 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). Happy circuit hacking... Brian Willoughby UUCP: ...!{tikal, sun, uunet, elwood}!microsoft!brianw InterNet: microsoft!brianw@uunet.UU.NET or: microsoft!brianw@Sun.COM Bitnet brianw@microsoft.UUCP