Making a headphone amp mono

[juan_felt]

Hi people!!

I want to use this schematic for a headphone preamp, but in mono.

http://www.redcircuits.com/Page119.htm

My idea was to use only one side of the opamp, but I wonder if I have to do anything with the lugs that are not being used.

As usual, thanks!

[induction]

You can always just use a single op-amp. But if you use a double, then tie the unused inverting input to the unused output and tie the unused non-inverting input to the half-rail voltage. If you don't want to use two extra resistors to make the half-rail voltage you can just leave it tied it to the junction of R2 and R3.

In other words:
- get rid of P1B, C6, R5, R6, C7, and C8.
- Put a jumper where R6 used to be.
- Done

Source

Relevant quote:
"Two conditions are required to properly terminate an uncommitted op amp:
   The op amp inputs must be actively held within the input common-mode voltage range of the device.
   The op amp output must be set within the output voltage swing range of the device. "

[PRR]

Feed the same signal to both inputs.

If you are clever, skip the dual-pot, use a single pot, its wiper to both inputs.

(Me, I'd keep the dual-pot and use a Y-cord to put mono to both sides; then if I ever had a Stereo source I'd be set.)

Further simplification "is" possible. But in this case:

'5532 is made to drive loads over 300 Ohms (per half)
At lower voltage it may not suck with somewhat loawer loads
Many headphones are 32 Ohms

So a single 32-Ohm ear on each half may be acceptable, but two 32-Ohm ears on one half may be disappointing.

Since '5532 is easier to find, easier to use, and as-cheap or cheaper than the single-amp '5534, use the '5532 and give each ear to one half.