L.E.D question

[daz]

A friend wants me to make a footswitch for his PRS amp and not having one handy to see how it's wired i just stuck a TRS plug in it and took a LED and touched it to it to see what was what. Turns out it's the common ground and 2 conductors, one for reverb and one for channel switching. The one for channel switch is normal....the LRD lights when the OD channel is selected as is common. The verb however is OFF when the LED is lit. Is there a way to reverse that? I don't see any way but me being as electronically crippled as i amp and most of you here being gurus to a degree that dwarfs other forums, i figure if there IS a way someone here will certainly know. Tanks.

[R.G.]

My best guess without delving through the amp schematic is that it requires bringing another wire carrying power out to the footswitch, which is probably not possible without changing out the footswitch jack on the amp for a different type connector, or putting a battery inside the footswitch to power the LEDs and whatever circuits inside the footswitch make the LED do the right thing.

The central issue is how to power the LEDs and the circuit that tells them "do the opposite".

There are some sneaky ways which would involve using a circuit that steals current from the "off" condition voltage supplied to the switches to charge up a cap, then blinking an LED every second or so to keep the power down. But these are tricky and are compromises.

The more effective way to do this is to modify the amp to reverse the sense of the pedal inside the amp. This would make the pedal do nothing except pull current into the LED when the effect is on, and then the circuit inside the amp would take care of making the amp switch to the right thing by sensing when the LED pulled current. But this is a bit more work, and somewhat more involved. It has the advantage that the stock footswitch would still work if you did it right.

[Mick Bailey]

I've sometimes come across this and my way round it is to ignore any voltages on the cable and wire the functions to DPDT switches. Use the 'unused' side to switch the LEDs on/off via a 9v battery. If you use high-brightness LEDs a relatively high series resistor can be used and still get a good level of brightness - I use 10k Ohm. Use 1 resistor per LED.

The battery lasts a very long time and you can wire on or off to be whatever position you want. I have a customer with a pedal I made that's still on the original battery after more than 2 years.

If the footswitch is on a pedal board it can be fitted with a DC socket.

[J M Fahey]

i figure if there IS a way someone here will certainly know.

Simply invert the Logic in your own brain.

Dirty led shining means Dirty Channel ON, Reverb Led shining means Reverb OFF or MUTE

After all, you just want to know what's happening and there's no doubt about that.

I know, I know, we have all been trained to the Pavlovian reflex that Red means Stop, Green means Walk .... it's just a convention and would work fine if inverted.

Then don't use Green for reverb ("because green means ON") nor Red ("which means Distortion") but some other colour, such as Yellow or even better, Amber .

Brain rewiring is better than hardware wiring because it can be done on software

[daz]

As i figured. Well, i had to ask. Thanks all. I will just use LEDs and tell him to reverse his thinking on the verb

[g1]

Just put a big sticker at that Led that says "kill reverb".
Why would you want to turn it off anyway (unless playing bass)?

[Tooboob]

I think it's wired like that so that the reverb works without the footswitch, with no reverb switch on the amp. Carvin does that too, but they have a switchable effects loop, and it only works if you turn it on with the footswitch, even though it has a bypass if you run it with nothing plugged in. Kinda silly.

You could go all Fender and just leave off the LEDs. I hear their amps are just about perfect. No sense trying to improve on them. It makes people grumpy.

[R.G.]

Boys, I think we've come up with something here that's going to be truly earth-shattering: the inverting LED. We can just make LEDs that are on if you put no current into them, but turn off when you increase the current to a certain level. I can think of all kinds of uses for this! We better head on out to the patent office with this one.

Notice that this is different from the Darkness Emitting Diode (or DED) that actually sucks light out of the surroundings when there's enough current through it.

[g1]

We can just make LEDs that are on if you put no current into them, but turn off when you increase the current to a certain level.

Could we just cobble up something with a 10F cap to do this? Low voltage (2.5V) ones can be had for $5 .

[J M Fahey]

You could go all Fender and just leave off the LEDs. I hear their amps are just about perfect. No sense trying to improve on them. It makes people grumpy.

I guess you should update your Fender files a little

Maybe you are thinking about this:



which used to be their standard footswitch ... some 40 years ago ... but for at least the last 20 years their standsrd footswitch has been something like this:



or this:



Notice the LEDs accompanying each and every switch.

To boot, square .

[Tooboob]

I got this one with my DRRI:



I need to fix it or the circuit in the amp so that I can sell it.

[Tooboob]

National used to have an interesting tech writer or two. I'd get datasheets, dated April 1, for things like the BD1 Battery discharger IC (The extreme efficiency of the BD1 may require the addition of a series resistor). My favorite was the "Confusion Compounder with no Comprehension". Applications included fishing lures, and the characteristics included the note "Except of Fridays, when we drink beer."

They cleaned it up later, but the old linear databook used to have the LH0063 "Damned Fast Buffer" (it had a 6000V/microsecond slew rate). The Warnings section was titled "Achtung!", and it included a pretty dual-log graph of Hz vs. cycles per second. Price was $30 or $60 or something, which bought a small house in those days (except in Silicon Valley).

[Enzo]

The Write Only Memory was a classic.

[The Dude]

Years ago, I managed a pro audio shop. Rane used to send out some interesting cut sheets. I remember paging through the product literature book one day and found this: PI 14 Pseudoacoustic Infector. At first, I thought, " I didn't know Rane made an aural exciter.". Then I started reading and was laughing out loud. They snuck it right in with everything else as if it were the real deal. It's still one of my fav's.

Edit: BTW, it IS worth it to click on the pictures to see the front and rear panels.

[R.G.]

My all-time favorite is the Turbo Encabulator.