Do i understand this pre-amplifier circuit correctly?


Joined Apr 5, 2008

How did you connect the inputs of the TDA8932?
The - input needs to go to ground using a capacitor.
The + input will be for your input signal, also using a capacitor.


Thread Starter

Aivaras Andrijauskas

Joined Aug 26, 2019
I originaly connected it like you said, a mono guitar jack input, + to the + terminal, ground to the - terminal on the chip. just without capacitors. Mono jack input, works with a guitar, just need 2-3 times more volume. which is what the preamp is for.
What value caps should i put on the + (signal) and - (signal ground), on my TDA8932?

And a question i have, is that if i connect the ground of my preamp to the signal ground, the preamp has two grounds, does it not? one from the DC power source, and one from the TDA chip. Because only the DC+ connection is ilustrated in the circuit, i thought the other power supply wire is the -/ground connection. but then there's two grounds, is that fine?

Or should a single wire be connecting the preamp and amp circuit? Because, as i ilustrated here, i do have the both the ground connected, i was told to do this when building my first preamp, and that one works.


Joined Dec 20, 2007
An audio amp needs a signal input wire shielded by the ground input wire. The ground/shield wire connects from the guitar pickup to the amplifier input ground terminal.

The Jfet preamp does not need an input coupling capacitor and is biased at 0V by the magnetic pickup.

The transistors preamp is no good for a magnetic guitar pickup.