what green LEDs for General Tso?

[Chuck D. Bones]

My LDR experience is limited. What I have figured out is that putting more light on an LDR than is needed by the circuit is counter-productive. In both circuits, the gain is proportional to LDR resistance. As the guitar signal decays, the compressor reduces the LED current so that the LDR resistance will rise and increase the gain. If the LDR was over-dosed with light, the LDR resistance will not rise quickly enough to maintain a constant, or near constant signal level at the output. The result is that the guitar signal fades and then recovers.

The short answer is you don't want a bright LED and as long as the LDR resistance gets low enough during the attack, the color of the LED doesn't matter either. Use what's in the BOM and don't obsess about getting every photon onto the LDR. If you get enough compression and sustain and it all works smoothly, then you did it right. If the compressor over-reacts and cuts the guitar signal too much immediately after the attack, then too much light is landing on the LDR.

 

[cooder]

Great advice Sir Chuck! I'll give it a whirl...

 

[jubal81]

Chuck's right. You're going to want a low-brightness LED there. With that super-bright LED and GL5516, the sustain and tone controls might as well have been switches. It wasn't working properly, but I gotta say I had a lot of fun with it like that.

Found another LED I'm going to grab on my next Mouser order - a 30 MCD clear, green, flat top (link). I also ordered some GL5528s from eBay to try.

 

[lcipher3]

Aside from cost - any reason not to just use a VTL54C?

VTL5C4
1mA = 784 ohms
5mA = 354 ohms
11.5mA = 220 ohms
20mA = 168 ohms
41mA = 120 ohms

TAYDA GREEN A-1553 - LED top pointing at LDR inside a 5mm shinksleeve
1mA = 7.7k ohms
5mA = 2.1k ohms
10mA = 1.2k ohms
20mA = 835 ohms
43mA = 577 ohms

TAYDA YELLOW A-1583 - LED top pointing at LDR inside a 5mm shinksleeve
1mA = 846 ohms
5mA = 320 ohms
11.5mA = 204 ohms
20mA = 155ohms
40mA = 126 ohms

 

[jubal81]

So after some digging in my closet, I actually found some diffused 5mm Tayda LEDs - green (A1-1553) and yellow (A-1555). These must be 4-5 years old, so I can't be sure it's what they're still selling.

With the stock values (1K5), the current for the LED drivers is limited to about 5ma. At which, I got:
Green: 3.2K
Yellow: 860R

So I made some new couplers with the Tayda green, swapped back in the standard 1K5 CLR and voila, sounds great and controls work just as you'd expect.

So, 5516 and Tayda green and I'd say you're set. And I'd wager you're getting a better response with that combo than the VTL5C4.

 

[jubal81]

@Icipher: I think to best answer your question, all 3 of those will work and it's going to be a matter of taste, so I'd recommend experimenting and comparing to find out which you prefer.

The Tayda diffused green works really well for me and I think if people want to just build it with that and 5516, they'll get good results. On their website, they characterize it as 2,000 to 3,000 MCD, which is off my a factor of 100 I suspect.

I do recommend this build, though. It can't do everything my Cali76 can do, but with the tone control, and how I actually use compression, I prefer the General Tso - don't need that switch, though.

 

[cooder]

Super, thanks for sharing your findings, jubal81!

 

[lcipher3]

@Icipher: I think to best answer your question, all 3 of those will work and it's going to be a matter of taste, so I'd recommend experimenting and comparing to find out which you prefer.

Yeah I have it all built up except for the LDR socket - just been lazy lately! I have the AION version (w/o the treble pot) and it sounds amazing with VTL54C .
I figure either the TAYDA GREEN A-1553 or Yellow (or VTL) will all work great.

Did you couple LED side to cell, or LED top to cell?

 

[jubal81]

Yeah I have it all built up except for the LDR socket - just been lazy lately! I have the AION version (w/o the treble pot) and it sounds amazing with VTL54C .
I figure either the TAYDA GREEN A-1553 or Yellow (or VTL) will all work great.

Did you couple LED side to cell, or LED top to cell?

I have them touching face-to-face. I got some little round PCBs to solder the LED and LDR to fit perfectly in a milkshake straw, which I then cover with heat shrink. But if I do my own layout, I think I've got an even easier solution worked out. Stay tuned.

 

[cooder]

I have them touching face-to-face. I got some little round PCBs to solder the LED and LDR to fit perfectly in a milkshake straw, which I then cover with heat shrink. But if I do my own layout, I think I've got an even easier solution worked out. Stay tuned.

That's next level sh#t....

 

[lcipher3]

very nice work