Danelectro Tuna Melt Mod - Rate LED help needed

[ediblefoliage]

Hello, long time reader, first time poster.  Wondering if someone knows how to solve an issue I'm having with this pedal:

I've rehoused this pedal and added an additional LED in series with the LED that interacts with the LDR (to use as a rate indicator).  Everything works perfectly except for when the pedal is in "soft" mode.  As I turn the depth knob down, the overall brightness of the the LEDs gets darker, resulting in less volume.

Now I've seen this thread already, but I'm not sure if this solution would help in this situation as well. (schematic can be found at that link as well):
https://www.diystompboxes.com/smfforum/index.php?topic=121977.msg1149137#msg1149137

Anyone have insight to this?

Thanks!

[willienillie]

Not an expert on this, but I think you would want the added LED to be in parallel, not in series, with the existing one.  You might have to tweak some resistor values (R107, R104 and/or R106).

But wait for one of the smarter folks here to chime in before you do anything.

[Kipper4]

Welcome lurker.

Willies right the indicator led needs to be in parallel.
Doesn't solve the issue of is there enough current/voltage to drive both leds. I suspect there's enough.

So you get a drop in level from bypass level when in soft mode with the depth down.

Would suggest you might need to increase the gain of the output stage (IC102 Hollis drawing, your linked thread) when you are in soft,depth down.......
To do so you might put a pot in place of the 17k5 (r102) maybe try an A50K.
Might not be practical since you already rehoused it.

I hope you find a solution
Rich

[Kipper4]

Or just leave the 17k5 and add a series A10K wired as a variable resistor.

[Kipper4]

Figure 3 R3 style

[PRR]

Parallel will only work if the LEDs are "matched". Otherwise the lower-Voltage LED will steal all the current.

If the LDR and "eye" LEDs come from the same bag, that's probably close enough. If the LDR LED was built into a factory opto-coupler, probably you can't find a close-enough eye LED.

Current-share resistors would help. However I'd want to see a schematic *with values* to even begin to guess what those resistors would be.

A current mirror is a "correct" technique but more parts.

However: do you really need the eye LED to follow the Depth? Eye is not a great judge of brightness. You probably want to see Rate. You can tap the raw oscillator wave this way:

[ediblefoliage]

I had tried wiring them in parallel previously and it did not work. It's possible I  was doing it wrong though. I will try again and see if it helps.  Thanks all for the tips!