4
\$\begingroup\$

I have a friend who is permanently deaf in one ear but has normal hearing ability in his other ear.

When he listens to music with headphones or earbuds, he can't hear one of the channels which degrades his listening experience.

I'd like to build him a compact stereo to mono converter. Ideally, it would have an input 3.5mm stereo jack and an output jack that delivers the converted mono sound.

I've tried the simple circuit below using two jacks where I connected the channels using resistors, however, his devices detect the short circuit and won't play the sound. Using sufficiently large resistors I can get past this, but the volume is too low to be usable.

enter image description here

I think I should use an op-amp, but I am not sure which configuration is the best. Should I use a summing amplifier? Do I need a 9V battery to supply power, or could I run this on AA or AAA batteries using rail-to-rail op-amps? Which op-amps should I look for / avoid when it comes to audio quality?

I don't have many restrictions on what I can do. I'm an Engineering Physics student and I have access to nearly any circuit component, a 3D printer, a machine shop, and a PCB mill through my university.

\$\endgroup\$
5
\$\begingroup\$

I think, before over-complicating stuff with an op-amp, try this: -

enter image description here

It could be that the short circuit detection is using DC to decide whether it is shorted. The dc blocking caps shown are 10uF and in case these do not allow enough bass, be prepared to raise their value to 47uF.

You might also need to have bleed resistors from each input line to shield just to activate the output - try 10k on these.

\$\endgroup\$
0
\$\begingroup\$

Putting an op-amp after the high-value resistors with an appropriate feedback resistor will raise it back to audible levels and create a mixer. Use an audio amp such as a LM386 or a LM4951.

\$\endgroup\$
-1
\$\begingroup\$

The simplest solution is a stereo to mono adapter... Im not sure but you may need a mono to stero adaptor to use standard head phones to drive the correct speaker

\$\endgroup\$
  • \$\begingroup\$ maybe I got lucky but there wasn't a need for active components when I did this for my Gran 15 years ago. \$\endgroup\$ – Spoon Jun 7 '13 at 8:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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