0
\$\begingroup\$

I have a cheap bluetooth audio module (with no documentation) that outputs a signal greater than line-level. It was probably designed to be connected directly to small speakers, since the ground on the output signal is floating.

I'm trying to connect it (as line-level) to the input of a more powerful amplifier. I assume that a potentiometer is a reasonable way to adjust the signal level, but should I put it before or after the isolation?

In other words, should I do it like this:

schematic

simulate this circuit – Schematic created using CircuitLab

Or like this:

schematic

simulate this circuit

Or some other way entirely? Assuming that I'm on the right track, what value of potentiometer should I be using?

\$\endgroup\$
2
  • \$\begingroup\$ Lose the transformer and use a 50k logarithmic pot. \$\endgroup\$
    – user207421
    Mar 28, 2015 at 0:22
  • \$\begingroup\$ How does that guard against shorting the floating ground to actual ground? \$\endgroup\$
    – Ian
    Mar 28, 2015 at 0:54

1 Answer 1

3
\$\begingroup\$

Drive the transformer from a low impedance.

The source impedance and the transformer's primary inductance form an R-L high pass filter which determines the LF rolloff of the circuit.

So with the attenuator ahead of the transformer it'll be all about the treble ... no bass.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.