HP/Agilent 34401A low beep sound level

Question

I want to modify the internal beep sound pressure level of this bench DMM and make it louder.

I have a problem with my ears and I won't be able to hear the the beep sound well when making continuity measurements. The beeper is small (well, not so small, is a Murata piezo speaker.) Looking at the schematic, the Murata is continuously receiving 5VDC, and when you use the continuity mode shorting the probes, the circuit sends around 2.4VDC, with a mixed square wave to make the beeper/speaker beep noise.

I was thinking of using a kind of simple design using an opamp (the 34401A has a 12VDC rail inside,) or maybe with a couple of transistors will be better.

Maybe I'm getting deaf, but the only DMM I can hear is the Fluke 87, which uses a differend kind of beeping sound, bi-frequency, not a "piiiiiii" one (which, if you vary your head's position with respect to the DMM you won't be able to hear it well)

PD: Here is the part of the schematic which shows the piezo speaker:

Answer 1

You could try something like this, only 5 jellybean parts:

^{simulate this circuit – Schematic created using CircuitLab}

If it's too loud, add a resistor in series with C1. This gives about 21Vp-p rather than about 5Vp-p across the piezo.

It will function (at least for a time) without C1/R4 but C1 and R4 maintain ~0Vdc across the piezo when not active, which is recommended by manufacturers to prevent silver migration in the element, and subsequent failures.