19.012 How can I get 'regular Apple sound' (like BEEPs, etc.) to play through my Mockingboard's outputs?
Description
This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
19.012 How can I get 'regular Apple sound' (like BEEPs, etc.) to play through my Mockingboard's outputs?
I recently got a Mockingboard C, which, it turns out, has a plug and cable
specifically for connecting in sound from the Speaker! (Most likely, the MB A
has a similar connection.)
----------------------------
By: Rubywand
Evidently, older Mockingboards (like our Sound II) do not include the
built-in Speaker connection; so, users with these boards will need to do a
simple mod.
The Apple II speaker is in the Collector circuit of the sound output
transistor-- one end of the spkr goes to a resistor and capacitor connected to
the output transistor Collector and the other goes to +5V (not ground). To get
an audio output signal, the spkr must be in place; or, you can substitute a 1
watt resistor-- something in the 22-39 Ohm range.
The output should come from the side of the spkr (or 1 watt resistor)
going to the resistor & capacitor connected to the transistor-- i.e. the side
which is not the +5V side. The output goes through a coupling capacitor to
the center lead of your RCA plug. The Ground side of the RCA plug goes to
ground.
"Ground" is DC ground = any motherboard trace area which is connected to
the ground side of the power supply. For example, the outside "shell" of the
composite video output is soldered to ground.
Here is a rough picture ...
+5V side
|
|
[]< Speaker or 27 Ohm resistor
|
|---------------------|(--)|------------------------ Output
| 10uF 10uF to Amplifier
| 2 caps connected as bi-polar capacitor
|
Transistor _________________ Ground
side |
DC Ground
You can get a bi-polar coupling capacitor at Radio Shack or make one by
connecting two 10uF caps neg end to neg end. The value is not critical, a 2uF-
5uF bipolar cap or two 5uF caps connected back to back is fine. Voltage rating
should be 10V or better.
----------------------------
By: Michael Mahon
For the vast majority of connections to external amplifiers, a non-
polarized capacitor is not required in this circuit, precisely because the
transistor side of the capacitor never goes below ground. A 4.7 uF capacitor,
with the (+) side toward the transistor collector and the (-) side toward the
amplifier will do the job nicely.
By: Mitchell Spector
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