[sdiy] Socket schematic symbol question

Harry Bissell harrybissell at wowway.com
Thu Oct 28 19:01:32 CEST 2010

Jacks with an isolated switch that closes when the plug is inserted
are a bit more rare. Most jacks have 'break' switches... and the switches that
close may be physically larger (not good for a guitar pedal.

Using the stereo jack is the standard approach, otoh I don't like
passing battery current through the plug. there may (should) be a capacitor in there
that might draw a lot of current on charge, and cause pitting of the finisg
of the jack...

of course its probably less damaging than dropping the jack on a floor full or beer...

H^) harry

----- Original Message -----
From: Donald Tillman <don at till.com>
To: Ben Lincoln <blincoln at eventualdecline.com>
Cc: Synth DIY <synth-diy at dropmix.xs4all.nl>
Sent: Thu, 28 Oct 2010 12:37:58 -0400 (EDT)
Subject: Re: [sdiy] Socket schematic symbol question

On Oct 28, 2010, at 8:55 AM, Ben Lincoln wrote:

> Would you see something like either of these designs used in the TRS connectors for the inserts on a mixing board, or would those have break connections on more than one of the pins?

Yes, a stereo jack with the switch on the tip will work well for an insert on a mixing board.  The send signal goes to the tip, the receive signal comes off the ring, and the switch shorts the two if there's no plug inserted.

And Mackie style, if you insert the plug half way you can tap off the send signal without breaking the chain.  (I don't know if Mackie does anything special for that feature, or if that's the way it's always been and they were the first to document it.)

> Alternately, are one or both how (some?) guitar pedal manufacturers wire up the input jack so that the pedal is powered off when nothing is connected? I would think those would use mono connectors, but maybe some manufacturers use stereo jacks for some reason?

For a guitar pedal, the minimalist approach is to use a simple stereo jack, and connect the ring connection to the negative side of the battery.  With nothing plugged in the battery is disconnected, and when you plug in a guitar cable the negative terminal of the battery connects to ground through the ring connection.

That's not really professional, though.   It fails for stereo cables, and the battery connection has to go through several points of contact in series.

So it's best to have a jack with an actual switch there.
  -- Don

Don Tillman
Palo Alto, California
don at till.com

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