Technics piano - Sustain pedal

[MarkOne]

I friend of mime has acquired a Technics piano that came without a sustain pedal. He tells me it requires a DIN connection. And on further investigation, it seems to need a 4 pin mini DIN.

Does anyone know if the Technics pedals were continuous controllers, or just switches?

I'd be happy to sort out a standard sustain pedal and solder on the right sort of connector if I knew the pinout. (and could get the right plug)

[Hugh Robjohns]

I found an article here that might shed some light.

http://www.m0wye.radiouk.com/PEDALS.PDF

It seems the 4-pin plug is for use with a traditional three pedal set up, with one pin for each pedal, plus a pin to provide power... possibly. A common ground is via the shell.

It suggests the pedals are normally closed microswitches....

Good luck!

[MarkOne]

Thanks Hugh! Those 4 pin mini DINs were used to connect S-VHS signals. I remember making up a lead to go through our ceiling space from the AV Receiver at the front of the lounge to the projector on a ceiling mount at the rear.

It was a ba$7@rd of a lead to make. Mulitcore, containing s-vhs, RGB phonos and a screen motor control mini-jack. And all soldered while standing on top of a pair of steps.

I'll see if my friend wants to get the bits and offer to make it up.

[sonics]

I'd make up a breakout cable to sockets rather than a single pedal and 4-pin plug. You never know...

[MarkOne]

I found an article here that might shed some light.

http://www.m0wye.radiouk.com/PEDALS.PDF

It seems the 4-pin plug is for use with a traditional three pedal set up, with one pin for each pedal, plus a pin to provide power... possibly. A common ground is via the shell.

It suggests the pedals are normally closed microswitches....

Good luck!

Hmmm. The wiring diagram is a little... er... vague. The sustain pedal goes to pin 3 of the 5 way connector, and from there to pin 1 (I think of the mini DIN). pin 4 of the mini DIN goes to pin 4 of the 5 way strip and thence to nowhere. - but I suspect this might be a common switch return for all three pedals, but that's not what's shown! and then pin 5 goes to the ground shell of the mini DIN.

[Hugh Robjohns]

Hmmm. The wiring diagram is a little... er... vague.

Yeah, I know... but it's a start that you can check out with a meter and some test switches... It's better than nothing, and all I could find...

...pin 4 of the mini DIN goes to pin 4 of the 5 way strip and thence to nowhere. - but I suspect this might be a common switch return for all three pedals, but that's not what's shown!

If you read the blurb, he suggests the common switch return ground is on the shell, and pin 4 is suggested to be a power rail from the keyboard.

A multimeter would figure it out...

What I didn't get is that he suggests the switches are normally closed, which presumably means their respective lines are grounded when the pedals are up.

But if that's the case, unplugging the pedals would be the same as pressing all the pedals... and that doesn't seem likely!

I suspect the description is backwards, and its more likely that a ground is needed to activate the pedal input...

... but equally, it might be that there really is power on pin 4 and the pedals apply power to the inputs.

Either form would leave the keyboard functioning normally when the pedals are disconnected.

But step one, for me, would be to measure for voltages on the Din pins (ref the shell ground). If there are volts on all three inputs then they're probably pull-ups and need a ground to activate.

If there are no volts then they probably need a voltage (from pin 4) to activate...

If you can track down the keyboard service manual on line it might make things clearer.

[forumuser931182]

There does appear to be a number of components on the pedal pcb so there may be more to it than just the switches. Will require a schematic to confirm but may be a common pedal for numerous technics models.

[forumuser931182]

Actually the schematic here ( not necessarily your model ) :
https://www.manualslib.com/manual/11744 ... =53#manual

Pin outs for connector page 53
Schematic for pedal page 65

All looks pretty straight forward.

[Hugh Robjohns]

Here's the pedal schematic from page 65...

[MarkOne]

Here's the pedal schematic from page 65...

20240328_011207.png

Thanks Hugh! Really useful.

[MarkOne]

Hmmm.
The plot thickens.

I sorted out a suitable pedal for my friends keyboard, with the correct pin wired to the connector shell via a 4k7 resistor and the switch normally closed.

I took it over to his place and plugged it in. Nothing,

Ok now here’s thing. The pedal board is supposed to offer the keyboard a normally closed circuit and when you press the pedal it is a 4k7 ohm resistance.

The wrinkle is, that with no pedal connected, the keyboard is playing with no sustain. (I.e. an open circuit on the pedal input) I’d have thought that an o/c pedal input would have been interpreted as pedal pressed.

This is a very old piano, and the psu input board has also seen some diy, so I’m suspicious there might have been some diy to bypass the pedal inputs along the way.

[Hugh Robjohns]

Have you had a poke around with a voltmeter to find out if the switch pins are pulled high or low? If not, that's where I'd start to fathom this out.

If the plug terminal is low I'd expect the pedal switch to pull it high, or vice versa — the latter probably being most common (plug terminal held high with pedal switch pulling it low).

I'd be surprised if psu mods affected the pedal inputs... unless the +ve feed to the socket has gone missing