I'm building a Stepped Tone Generator (AKA Atari Punk Console (APC)) based circuit, which is not a stand alone device, but which will feed into a number of subsequent stages/circuits.
The majority of the schematics out there show the audio output referenced to GND, like so:
However, I have come across three schematics (1, 2, and 3), which have the sleeve (and ring) of the jack, or speaker (as in the original design by Forrest M. Mimms), connected to the +V line:
- The tip/pin of the jack in this case is connected to the +V and the sleeve to the output
- The sleeve (and ring, if jumpered) is to +V and pin to the audio output
- The speaker, in the original circuit, is connected between the output and +V.
I understand that the DC bias of an audio signal is irrelevant, and is blocked by C3
TL;DR
- In the first example, with +V connected to the tip, the effect output is effectively the "right way up", but with a moving ground, as the signal is now the ground, especially if connected to an amplifier (where the amplifier's input sleeve is connected to GND).
- In the second example the signal would appear to be inverted, as the ground is now +V.
- Why did Forrest M. Mimms not connect the speaker between the output and GND?
- Shouldn't the GND line be used, especially if connecting the APC to another piece of grounded audio equipment, such as an amplifier?
- Does it make a difference, if +V or GND is used, as the DC bias of the signal is not relevant?
- Are there any advantages to doing this (using +V en lieu of GND)?
I am confused, but that could just be due to my conditioning that signals should be referenced to GND. I have never seen (or maybe noticed) this +V referenced type of signal/circuit before. Is this related to virtual-grounding?