the output of the AY-3-8910 contains a transistor (that is how the circuit modulates the signal to allow an audible signal). The base pin of the transistor is modulated and amplied thought he transistor.

For an NPN transistor, the collector must be connected to a voltage more positive than the emitter for current to flow through it and allow the base pin to modulate the current flow.

If you connect either the emitter or collector pins to a capacitor, then no currnet can flow though it, the transistor is deemed to be "floating" at this point.

If you use the water valve analogy of a transistor, then mr. waterman can turn the valve (base) but since there is a cap on the end of the hose (capacitor), no water will flow and you cannot modulate the output signal proportional to number of valve turns. Simply, nothing happens.

Review the transistor pages of the eBook on this site.

 

the output of the AY-3-8910 contains a transistor (that is how the circuit modulates the signal to allow an audible signal). The base pin of the transistor is modulated and amplied thought he transistor.

For an NPN transistor, the collector must be connected to a voltage more positive than the emitter for current to flow through it and allow the base pin to modulate the current flow.

If you connect either the emitter or collector pins to a capacitor, then no currnet can flow though it, the transistor is deemed to be "floating" at this point.

If you use the water valve analogy of a transistor, then mr. waterman can turn the valve (base) but since there is a cap on the end of the hose (capacitor), no water will flow and you cannot modulate the output signal proportional to number of valve turns. Simply, nothing happens.

Review the transistor pages of the eBook on this site.

Yes, the base must be high relative to the emitter, but can you point to where it is shown that the output of the D/A converter is a BJT with an open emitter? I can't find that information in my AY3-8910/YM-2149 datasheets.

 

Here' a simulation with and without a 1k load resistor:

 

Yes, the base must be high relative to the emitter, but can you point to where it is shown that the output of the D/A converter is a BJT with an open emitter? I can't find that information in my AY3-8910/YM-2149 datasheets.

It is not in the DATASHEET. There are simply four options of an output on a chip, not all are the same but all will have a transistor internal. The different options are...

(1) open collector (an external pull-up resistor to Vcc is required).

(2) open emitter (an external pull-down resistor to ground is required)

(3) common collector (similar to #2 but resistor is internal)

(4) common emitter (similar to #1 but resistor is internal)

Now, the datasheet does not tell us how the chip is configured with a schematic of the internal circuitry. However, based on these options 1-4 listed above, can you deduce (as I did) which configuration the Ay-3-8910 uses?

You are more than welcome to believe more than one configuration is possible and, if you do believe that, I strongly encourage you to breadboard all options that you believe are more reasonable than the circuit shown on the manufactures datasheet. Let me know what other options end up being more viable.

Cheers.

 

Here' a simulation with and without a 1k load resistor:

View attachment 54986

Interesting: why doesn't the transistor go into cut-off in the case of the green output? Isn't base still at a lower potential than emitter?

It is not in the DATASHEET. There are simply four options of an output on a chip, not all are the same but all will have a transistor internal. The different options are...

(1) open collector (an external pull-up resistor to Vcc is required).

(2) open emitter (an external pull-down resistor to ground is required)

(3) common collector (similar to #2 but resistor is internal)

(4) common emitter (similar to #1 but resistor is internal)

Now, the datasheet does not tell us how the chip is configured with a schematic of the internal circuitry. However, based on these options 1-4 listed above, can you deduce (as I did) which configuration the Ay-3-8910 uses?

You are more than welcome to believe more than one configuration is possible and, if you do believe that, I strongly encourage you to breadboard all options that you believe are more reasonable than the circuit shown on the manufactures datasheet. Let me know what other options end up being more viable.

Cheers.

That was the explanation I was looking for!

 

Herp a derp: I forgot that the output has a coupling capacitor, so I guess that the green output's transistor doesn't go into cutoff because there's some DC bias that's killed off before it gets to the green output. D'oh!