1
\$\begingroup\$

I have an audio amplifier and one of those cheap Chinese Bluetooth audio receivers.

The output of the receiver is way above audio line level, about 7V peak to peak.

When using that as input for the amplifier, it starts clipping.

Now, I could just attenuate the receiver signal with a resistor voltage divider or potentiometer to 1V peak-peak line level.

However, I was wondering what would be the simplest way to attenuate a signal of arbitrary level (say somewhere between 2V and 10V peak-peak) to a fixed 1V, ideally without opamps?

\$\endgroup\$
6
  • 1
    \$\begingroup\$ It's called a "compressor" or "automatic level control". It would be possible, but not easy to do it without opamps. It would depend on your specific requirements with respect to accuracy and audio fidelity. \$\endgroup\$
    – Dave Tweed
    Oct 2, 2023 at 16:06
  • 1
    \$\begingroup\$ Having an automatic gain control seems to be what you ask, but using an AGC to say 1Vpp means all loud and silent passages have equal amplitude no matter what you play, which I guess is not the point of what you want to play, and you would not be able to control the volume at all, not even on your mobile phone as Bluetooth transmitter, as your analog circuit would scale everything to 1Vpp no matter how loud or silent you send audio digitally over Bluetooth. \$\endgroup\$
    – Justme
    Oct 2, 2023 at 16:37
  • 1
    \$\begingroup\$ Depending on current, a tungsten-filament lamp in series can act as a compressor. You might try a "grain of wheat" 1.5 V lamp in series, and four Si diodes (two in series in each direction) across the output... but expect distortion, too. \$\endgroup\$ Oct 2, 2023 at 16:39
  • 1
    \$\begingroup\$ You could expect the bluetooth module output to be reasonably consistent. I'd go with the fixed resistive divider! \$\endgroup\$
    – Neil_UK
    Oct 2, 2023 at 17:02
  • \$\begingroup\$ Thanks for the input, automatic level control is what im looking for. "No opamps" isn't really a requirement, i just wondered if it was possible without. In this case i could indeed just use a fixed divider, but that wouldnt work in a more general case where the source signal level might vary. \$\endgroup\$ Oct 2, 2023 at 17:11

1 Answer 1

1
\$\begingroup\$

Audio compressors have been in service for many years. The question is restricted to a simple circuit, not using opamps. A circuit can not get much simpler than this one valve/tube circuit from 1953.

https://www.preservationsound.com/2015/01/a-simple-one-tube-compressor-circuit-c-1953/

Into the transistor era and there were simple circuits such as: https://www.electroschematics.com/mini-audio-compressor-schematic/

A more modern IC circuit is: https://freecircuitdiagram.com/4588-compressor-circuit-with-570571-compandor-ic/

\$\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.