I'm stumped, what would these resistor values be?

[Dutchman]

I got info from Peavey to build a footswitch for the Peavey Ranger I hauled outa the garbage in nonworking condition. All tube 120 watts. It sounds fantastic. I decided to build a pedal board for it as Peavey said they had a schematic. My question is what are the values of the resistors in the circled box? The White and Orange appear to be the supply for the LED's.

Standard drop 150 ohm? I asked Peavey no response so far.

Edited Sunday at 12:05 PM by Dutchman

[BoogieMKIIA]

If you can find the voltage driving the LEDs (12V?), assume an operating current, say 20 mA. Then solve V/I=R, with a typical diode drop of 0.7V.

(12 - 0.7)/0.020 = 565 ohms.  Of course, more resistance means lower current and lower brightness. If you could find the LED spec you would have all but one variable.

Different color LEDs have different specs, that why you can see different resistor values.

 

 

[Dutchman]

Thanks!

3 hours ago, BoogieMKIIA said:

If you can find the voltage driving the LEDs (12V?), assume an operating current, say 20 mA. Then solve V/I=R, with a typical diode drop of 0.7V.

(12 - 0.7)/0.020 = 565 ohms.  Of course, more resistance means lower current and lower brightness. If you could find the LED spec you would have all but one variable.

Different color LEDs have different specs, that why you can see different resistor values.

 

 

I wondered if I took the voltage of the white and orange then I would know what voltage the supply would be. Then replace all the current leds so I have a known value. Then calculate the voltage required using the formula you provided! 

[BoogieMKIIA]

I assumed individual squares were the LED and just noticed they are dual color LEDs. Is that your assumption or info from Peavy? This means it’s likely there are several resistor values. Different color LEDs have different current specs to get a specific brightness.  From the way it’s wired I would guess two different colors. What are the amp functions for each LED.

I don’t understand the diagram so well. There is a wire (Bare Wire?) that is common to all 4 LEDs, seems it would be ground and not power. The fourth LED has both “control” pins going to the bank of three resistors associated with the White wire. Both LED elements in that device always on. Doesn’t seem right for what looks like the Channel LED. Could be that the voltage on the orange and white wires are switched in the amp. The middle leg of some 3 terminal LEDs is often ground.

If you have a DC bench supply, you can use that with a known resistor to determine a good LED current. Look at the LED as you increase voltage until it looks bright enough. Measure the resistor voltage and you have the LED current. Then, use the voltage you measured to find your resistor value. If 20 mA typical is correct, you should be somewhere near it. Also note the LEDs could be rated lower, you could get from 2 to 20 mA.

If your current is much higher or lower, you can plot the current curve using the DC bench supply. Or, look for the turn on voltage (with DC bench supply and known R). From one generic diagram, the operating point was about 0.7 V above turn on voltage. 

It would help to have the schematic to the rest of the circuit, maybe there is one on the web. But I think you will figure it out if not already done.

[velorush]

I found this thread on mylespaul.com discussing just this "terribad" schematic. The poster came up with a much better schematic after reverse engineering another footswitch. This is what he came up with:

Hope this helps.

[BoogieMKIIA]

3 hours ago, velorush said:

I found this thread on mylespaul.com discussing just this "terribad" schematic. The poster came up with a much better schematic after reverse engineering another footswitch. This is what he came up with:

Hope this helps.

I thought the “LEDs” might be relays, now it makes sense. The 20V and 1K resistors means around 20mA per LED.