[Help] channels footswitch!

HeaD · May 26, 2005, 01:21:02 PM

Hi all!!! I have built this Footswitch to select the "Reverb" and "drive" channels of a laney amplifier:

It works but the green LED doesn't light up! I have tried to replace the LED and wire the circuit in various ways, but it keeps doesn't light up!! Why?

Thanks to all!

JimRayden · May 26, 2005, 01:23:29 PM

You might have the resistor on the wrong pin of the LED.

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Jimbo

HeaD · May 26, 2005, 01:44:17 PM

err... sorry, I have mistaken to draw it!!

other ideas? :?

HeaD · May 26, 2005, 04:41:39 PM

please help me!!

petemoore · May 26, 2005, 04:57:15 PM

I'm don't see a power supply for the LED's.
The schematic looks like the type used as 'short to ground' for internal switching [in the amp] but with LED's and resistors added in each STG 'channel'.
With those switches a simple STG switching and LED's can't be done....AFAIK, you'll need at least DPST switches...maybe I'm missing the whole idea as I can't see the 'rest'...[not that I would make heads or tails of the amp schem]...but assume that the switches are what is used in a factory dual switch [Reverb/Dist, each short to ground to activate internal routing...Jfet or CMOS signal switching done internally] like comes with modern amps...simple short to ground type switches.
To add LED's to indicate reverb or Ch1/ch2, a Battery [or long PS wires[ for the LED power, and 'upgraded' switches [with two poles each] will be needed. The actual STG switching remains the same, simultaneous but separate [as in double pole] LED power on/off would be used to switch the LEDs on and off.

HeaD · May 26, 2005, 05:04:42 PM

Quote from: petemooreI'm don't see a power supply for the LED's.

...stereo jack is connected to the suitable amplifier output. this footswitch don't need any power supply

Anyway, red led works but not the green one!

KORGULL · May 26, 2005, 09:47:33 PM

Did you try lowering the resistor value for the green LED? Maybe not enough current is reaching it?
I took apart the footswitch for my amp last week to see what was in there - it uses LED indicators, but had no resistors on the footswitch PCB. Maybe the current limiting is done at the amplifier's end and adding more resistance within the footswitch is overkill?

niftydog · May 27, 2005, 12:23:58 AM

So, you're relying on the amplifiers footswitch jack to provide the power for the LEDs? This would seem to me to be a mistake... unless the amp is designed to work this way, which seems unlikely.

Usually, as Pete said, you need a separate power source for the LEDs. The switching of the channels is effected by simply grounding the appropriate signal.

The fact that one of the LEDs is working is probably purely due to luck. The circuit is managing to provide just enough power to light the LEDs, but again I doubt it is designed to do so.

LEDs have a specific voltage drop across them when they are powered. This voltage drop may be close to the swtiching "threshold" point of the amps circuity. Should the voltage be high enough, it may stop the footswitch from working because the LEDs voltage drop would prevent the signal voltage from being pulled to ground (or close to ground).

My advice is to go with a more conventional design or forget about the LEDs entirely.

HeaD · May 27, 2005, 02:47:04 AM

thanks to all....

i've found this other schematics: http://www.superchamp.dk/papers/Footswitch%200017007000.jpg .

It use dpdt switches, this one don't need a power supply (there are 6.2V from amp). btw i can't use it... because there are 2 stereo jacks, and this amplifier have only one stereo output (jack tip for drive and jack ring for reverb)... how can i do?? :/

Bagge · May 27, 2005, 02:47:08 AM

I don't see any power supply either. The reason for the red LED working could be, that there are voltage on tip of the stereo jack. That is, the amp delivers power through the tip, but not the sleeve.

?

niftydog · May 27, 2005, 03:16:20 AM

ok, that schematic appears to be for an entirely different amplifier to your Laney. It should not be relied apon as the basis for you design, but it might give some clues.

First up, while I understand that only one LED works at the moment, does the channel switching work properly?

You need to measure the tip and the ring to make sure the 6.2V is present at both pins. My guess is that it's only coming from one or the other.