DPDT diode switching confusion !!

MartyMart · August 14, 2006, 08:51:36 AM

Lost the "plot" on this one ... sorry guy's

Someone set me straight, I'm going in a large "stupid" circle !

Here's what I want to do :
Use a DPDT footswitch to add diodes to ground at the back of a circuit.

Here's what I have :

Bottom two lugs joined - as in normal bypass switch
Middle two lugs carry circuit section input and output at either side ( normal )
Top two lugs connect to 2 x 5mm LED's , one side anode one side cathode, the other two
ends of LED's join and have a wire to ground .

So "bypassed" the circuit works as normal - fine

Switched, I get a total circuit "cut" - nothing ... silence !

I know, it's me being "very stupid" but I jusr cant see what , obviously the "whole signal" is
being puled to ground ....

HELP !!!

MM.

Seljer · August 14, 2006, 09:01:10 AM

By bypassing the diodes with a wire you're shorting it directly to ground. I think you could remove that wire and it'd work fine.

edit: this is what you want to be doing, you basically only need 2 lugs of the switch

MartyMart · August 14, 2006, 09:05:13 AM

Wont the diodes just be "in line" with signal then ... there's no "to ground" connection !

MM.

Torchy · August 14, 2006, 09:07:15 AM

Quote from: Seljer on August 14, 2006, 09:01:10 AM
By bypassing the diodes with a wire you're shorting it directly to ground. I think you could remove that wire and it'd work fine.

No, by wiring like that youve effectively split the output signal across the switch. The signal is effectively shorted to ground via the first diode, the second never comes into play.
I think you want this ...

Seljer · August 14, 2006, 09:08:50 AM

Yeah, i Just realised I misunderstood they way he described the wiring, i was thinking vertically instead of horizontally.

just short out the middle 2 lugs

MartyMart · August 14, 2006, 09:15:29 AM

So let me try and understand this :

Circuit in/out of middle lugs AND shorted across those lugs
Remove my jumper across the "other" set of lugs
Put back the diodes "as was" like your diagram on the third set of lugs ??

So one switch effectively "does nothing" as circuit is connected anyway
Other switch , switches in the diodes to ground.... BINGO

MM.

PB Wilson · August 14, 2006, 09:27:22 AM

So you could also put another set of diodes on the top two lugs and switch between them, right?

GibsonGM · August 14, 2006, 09:35:46 AM

Sounds like you got it, Marty! What really helped me when I was sort of a 'noob' was to check each set of terminals with my DMM, set for continuity...hearing that "BEEP" reinforces what's actually going on inside the switch!! The center posts, because they're jumpered, are always connected. If it's a toggle switch, they'll be connected to the bottom posts if flipped up, and the top posts if flipped down. In this config, the top posts aren't going to be used; you're only going to remove the diodes from the signal path.

Since the diodes are parallelled, they only tap off the switch at 1 place (the jumper is overkill) - you could use a SPDT or SPST for this, too, and save the good switch for something else! The DPDT is actually 2, 2, 2 switches in one. Sometimes switches will drive you nuts, LOL. It's really cool once you get it working, tho!

** you definitely could use that to switch between diodes, PB. You'd never get a "no diode" situation from that arrangement, but if the distortion is always on, then that's fine! **

All you're really doing is adding the diodes from signal to ground, as if you 'tapped' them off with a jumper cable

MartyMart · August 14, 2006, 10:02:57 AM

Still isn't working !!
I thought it may be the 5mm leds so changed 'em for 3mm reds ... no change when engaged

Bugger it, I'll use the switch to add in a boost or something.

MM.

WGTP · August 14, 2006, 01:32:33 PM

Maybe the clipping threshold is too high with the LED's for you to hear the change. Try SI/s or GE's just to see if it is working. If you use an on/off/on switch, couldn't you have 3 choices with the middle being no diodes?

Torchy · August 14, 2006, 05:10:17 PM

Marty - which circuit are you putting the diodes across ?

MartyMart · August 14, 2006, 06:09:40 PM

Quote from: Torchy on August 14, 2006, 05:10:17 PM
Marty - which circuit are you putting the diodes across ?

It's at the back end of my Classic 30 jfet sim, it's not a real high gainer, nor a serious boost
so perhaps the threashold just wasn't being reached !
It was just an idea

I've built a tiny little full range booster using an MPSA13, so I'll pop that in in a few days to
use the other switch location, with a preset gain boost.
I must have had it wired correctly a couple of times, just wasn't distortin' !

MM.

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DPDT diode switching confusion !!