Some more detailed information on the Megamodule circuit bend:
Here is the megaphone I used:
(It was available from Amazon Warehouse for about $5 at the time.)
Photos of the circuit board:
In the last photo, the 16k resistor near the lower right corner is the pitch resistor. Its location on the underside is marked in the diagram below along with +9V and 0V traces.
Connections to the board:
- +9V and return side of speaker
- Send side of speaker
- 0V and return side of mic
- Send side of mic
(The speaker connects to the LM386 output and the +9V rail. I replaced with output connections to the LM386 output and the ground rail.)
Toggle switches are the five sets of three connections across the middle: Bottom on each is ground and top two connect to the sound chip.
Schematic of modifications:
Block at left with LED and resistor is vactrol. Blocks at right center are Molex connectors for panel components (not listed, but shown in schematic).