Here are some facts about the drawer – the control panel – of a Mk V Ondes Martenot.
Two swichtes (1, 2) are missing and the touche d’expression is absent as well. No fear, they are kept warm and cosy.
The switches are built from Pertinax (laminated paper) which has suffered over the decades, so that I will drop genuinity in favour of reliability and combine the old nice levers with 2013s switches.

The controls in detail, from right to left:

– switch C/R (rightmost) : selects between clavier (keyboard) and ruban (ribbon)
– three metal knobs : that’s for the circuit benders amongst the ondistes – here your finger becomes part of a series connection with a small capacitor,
directly influencing the oscillator.
– two transparent push buttons left from the C/R switch : transposes down by some amount (only in ribbon mode)
– the big rectangular hole normally hold the touche d’expession, the main volume control button of the Ondes
– switch 1 : adds a LC low pass into the D1 output (red – in, white – bypass)
– switches 2, 3 : some kind of tone control applied to the output amplifier (red – filter, white – off)
– switch 4 : determines the amount of 2&3 (red – full, white – attenuated)
– switch 5 : controls the gain of the pre-amplifier tube – probably into limitation, so a sine will become somewhat rectangular
– switch 6 : adds a filter to the metallic speaker (D2)
– switches D1, D2 & D3 : select the speaker(s) used. D1 is the main speaker, D2 the metallic (gong) speaker, and D3 the palme (with the strings)
– switch 8: adds a bridge rectifier into the signal for speaker D1, thereby doubling the frequency

The wheel numbered I..V : volume control for the main speaker (D1) – to adjust the balance between D1 and D2/D3