PSU with automatic switching for active/passive instruments

[row-she]

hello there,

I recently got into stompbox building and made some effects/utilities for friends.
lately a friend of mine keeps asking me if I could build him a PSU to power his active bass from his pedal board
so he wont have to keep changing batteries. I thought of kinda phantom-powering it through the ring-connector of a
stereo-jack. (as have others too apparently  )
so... thats not the problem.
here is one: my friend plays an active bass as well as a passive one and he asked me if he could plug that into this stompbox
I'm going to build as well? I said sure... as long as you're using a stereo cable - but then i thought... what happens if you
accidently plug in a mono cable? you would short the connection between the +9v and GND. which seems to be bad.

so i'm thinking about building a power supply with some kind of "relay-fuse" that automatically switches the +9v off when a
mono-cable is connected and shorts the ring and sleeve connectors. at the same time it could re-route the signal path either straight through
or to an attenation-circuit (active/stereo mode) since his amp hasn't got separated inputs for active/passive instuments - so he could match
the instuments via a pot on the stompbox.

I'm thinking about running the +9v from the standart PSU on his pedal-board first through a step-up transformer (so it has a higher voltage
like... let's say 12v) then build in a regulator for 9v (and maybe a filter) inside the bass-guitar (to get a steady 9v) and connecting a relay (designed for 12v opperation)
between the ring and sleeve connectors. that way, if you should short the terminals by plugin in a mono-cable, the relay would autmatically turn off the
power on the ring-connector and switch to passive mode. the only problem is that it would instantly switch back since there would be no power any more.
so... here's the freaking vicious circle!

any ideas, solutions?
i'm thankful for any reply / help.

thanks!

[duck_arse]

hello and welcome, row-she.

there was a thread recently along similar TRS detection lines.

http://www.diystompboxes.com/smfforum/index.php?topic=108232.0

[row-she]

thanks duck_arse for the link!

didn't find that one using the search-function.
couldn't find a solution there though.
but I'll see what I can make of that.
still... got some new ideas/aspects to play around with now.

so..thanks again.

if anyone has got an idea, I'm still open to suggestions of course 

[PRR]

> switches the +9v off when a mono-cable ...shorts the ring and sleeve

"Foldback regulator".
http://en.wikipedia.org/wiki/Foldback_%28power_supply_design%29

> running the +9v from the standart PSU on his pedal-board first through a step-up transformer

Can't transform DC that simple.

> then build in a regulator for 9v (and maybe a filter) inside the bass-guitar (to get a steady 9v)

Why not just use GOOD 9V power to start with?

There are very-very good 9V pedal supplies.

Also 9V relays if you must do a relay.

But in general, I think all these ring-switching schemes will run into some odd combination of plugs and devices which you didn't anticipate, and do a Wrong Thing. At that point you may have wished you had got a deal on a 25-pack of simple 9V batteries.

[row-she]

hello PRR,

thanks for that link. and...

> Can't transform DC that simple.

there you're absolutley right. forgot that I have DC here.

> Why not just use GOOD 9V power to start with?

well... that might be the best idea. I wanted to use 12 V in my original plan to have two different voltages
for a relay to compare. but I see why this might not be the solution.

> But in general, I think all these ring-switching schemes will run into some odd combination of plugs and devices which you didn't anticipate, and do a Wrong Thing. At that point you may have wished you had got a deal on a 25-pack of simple 9V batteries.

can't really argue with that. it's a pain in the ... but I don't want to give up on this. not just yet 
it has got to be doable! I'm even considering putting a freaking microcontoller in there.

There's still something absurdly attractive to me about a pedal that can tell what kind of cable is plugged in, so I'll continue to pursue that path for now.