DPDT LED indicator, no more lugs

[Ric046]

HI, I've been wrecking my brain all day and I can't seem to come up with a solution as to how to attach an LED indicator to a DPDT switch when there are no lugs available.

In the schematic, when switched to the 1k position (lugs 3&2), you get a boost in gain from the j201s. So I'd like to make it so that an LED comes on when switched to boost. Obviously to wire up an LED for lugs 1&2 position would be easy, but it seems counter intuitive to me to have the LED come on for UNBOOST.
I've given up thinking about it a few times today but just keep getting this niggling feeling it can be done.

I can't use a 3DPT because I simply don't have the room on the PCB.
I know a 3PDT can be substituted for a DPDT when used with an optocoupler for bypassing so maybe there's something down that road. I've tried putting both 1ks from the two j201s to the same lug, therefore only using one pole of the switch and freeing up the other, but I'm not sure what it's doing to the sound. I'm going to investigate that a little further tomorrow but until then I was hoping you guys might have an idea? Or at least put me out of my misery.

Cheers
Ric

[solderfumes]

Perhaps something based on the Millenium bypass?  You could hook up a transistor with the base connected to the "off" position lug and to a resistor to +9V (or whatever your supply is).  When the boost is off, the base is pulled to ground and shuts off the LED; then, when the boost is on, the base is left at +9V and the transistor turns on.

[Ric046]

That sounds like a great idea. I did consider the millennium bypass for a time. But I think I may have over complicated it in my mind. The only thing that concerns me is will it short the circuit if I GND the base?

[solderfumes]

If you're using a standard NPN bipolar junction transistor, and the emitter is also grounded, I think it should be OK as no current will flow from base to emitter, and so no current will flow from collector to emitter either.  Someone please correct me if I'm wrong though!

But: won't the extra transistor/resistor/routing take up as much space as the extra row of lugs on the 3PDT switch?

[Leevibe]

Everything you are trying to accomplish involves switching to ground. It looks to me like you can just hook the cathode of your LED to lug three of one of your switch poles (not forgetting to have a CLR in series with the LED).

[Leevibe]

Actually, I see that my idea can't work because of the voltage coming through the LED in unboosted mode. Duh.

[Ric046]

I've used a 2n3904 I found lurking in my stash, (which is a NPN transistor). I've wired it up in a millennium bypass fashion with the switched GND going to the base.

It works great. LED comes on when I want it to. None of the componets are burning out, sound doesn't alter, voltages stay the same throughout and there's no shorting of the circuit.

The reason I'm not using a 3PDT isn't because of lack of space on the PCB, but more because of the positioning of the switch. It's being placed right at the top of the PCB just above a pot. A bigger 3PDT would mean I'd have to move the pot down further and then the pot below that down further and the way it is at the moment, (with the DPDT) it just about fits the height of the PCB.

[Leevibe]

Would a compact 3pdt fit?

[Ric046]

Perhaps, but I've already got my DPDTs and I've got my method thanks to the help of 'Solderfumes'

Thanks anyway

[solderfumes]

Cool, glad it worked   I actually thought you'd put the LED and CLR between the collector and +9V, but that's good too.