Not all green LEDs have the same Vf

Chuck D. Bones

Chuck D. Bones

Circuit Wizard
I was running some breadboard tests with a soft clipper using green LEDs. The circuit was basically the gain stage from a Tube Screamer. With 5mm super bright green LEDs installed, the opamp (TL071) was saturating under high-drive conditions. I removed the LEDs and tested them on my CCTT (Cheap Chinese Transistor Tester). The Vf (measured at around 5mA) was 2.74V, very high for a green LED. Those were from EG, unknown mfgr. Then I tried some 5mm super bright green LEDs from Tayda. They measured 2.44V, also high for green. After that I tried a 3mm and a 5mm "regular brightness" LED. They measured 1.97V and 2.00V. Those measurements are what I would expect for a green LED. So why were the super brights higher Vf? Turns out that making high brightness green LEDs has been challenging, so the LED manufacturers resort to a technique called phosphor down-converting. They make a blue LED and coat the die with phosphors that absorb the blue light and re-emit green light. This same technique is used to make white, aqua and pink LEDs. Different phosphors emit different colors. That explains the higher Vf; the diode part of the super bright green LED is blue, not green. I replaced the super bright LEDs with 3mm diffuse green LEDs and everything was good. To get a little more headroom, I replaced the TL071 with a CA3130.
 
https://imgur.com/k6uZyxs

https://imgur.com/q6wlhFf



This TS is so super smooth...especially when playing thru old glass Amprex , Mullards.....i dont know but this one is super fine ...your recommendation !

Should have named it Pay Dirt....man is this one awesome it ticked all the boxes

LEDs are from Tayda....But if you cooked up a better Version of a TS , ill buy another PCB....i dont think i have the CA3130 tho...

Mike
 
Mourguitars said:
LEDs are from Tayda....But if you cooked up a better Version of a TS , ill buy another PCB....i dont think i have the CA3130 tho...

Mike
Click to expand...
I am not cooking up another TS, I think there are more than enough of those already. This thing I'm messing with at the moment is a highly modified Brownout (Subdecay Variac). The Brownout is a nice pedal as-is, I'm just experimenting to see if there is a different way to do the 3rd stage and that's where I ran into headroom problems. The jury is still out on whether what I have done is worthwhile. In any case, you don't need a CA3130 for a TS build.

Nice build, BTW!
 
LOL...Gotcha !

I have a lot of reading to catch up on....

Feral Feline said:
I knew the superbrights had a higher Fv, but it's super-cool to get the low-down on why. Thanks CDB!


@Mourguitars Great name for an OD pedal, "PAY DIRT"!
Click to expand...


Im a OD junkie.....Over Drives...clear that up a little !

Every one you play acts and sounds differently ......Chuck suggested i put some Green LEDs in there i socketed them....Man ...thats it ..Pay Dirt...or Play Dirt !...im mean thats butter smooth in that build !

Mike
 
I was just reading another thread where CDB posted a handy dandy chart on this subject, guess I should be more discerning about my greenies! I had a quick question; will the size, like 3mm and 5mm, have an affect on the related Vf readout? Maybe, but not as much as the color? Also, I put some green LEDs in my last TS build and they didn't light up as in Mourguitar's picture. Is that because they were maybe high Vf blue LEDs in disguise, or indicative of something going wrong? It seemed to have the intended sonic effect, and I'm pretty dang sure I put em in the right way, but they didnt light up even when driven hard which I found suspicious.
 
Untro said:
I was just reading another thread where CDB posted a handy dandy chart on this subject, guess I should be more discerning about my greenies! I had a quick question; will the size, like 3mm and 5mm, have an affect on the related Vf readout? Maybe, but not as much as the color? Also, I put some green LEDs in my last TS build and they didn't light up as in Mourguitar's picture. Is that because they were maybe high Vf blue LEDs in disguise, or indicative of something going wrong? It seemed to have the intended sonic effect, and I'm pretty dang sure I put em in the right way, but they didnt light up even when driven hard which I found suspicious.
Click to expand...
Shouldn’t be a difference based on the size— that’s just a matter of how much plastic they encase it in.
 
Untro said:
Also, I put some green LEDs in my last TS build and they didn't light up as in Mourguitar's picture.
Click to expand...

Take another look at Mourguitar's pic. Nothing is plugged into the pedal. No power, no guitar, nada, zilch, bupkess. That light you see in the green LEDs is a reflection of the camera flash.

It is very common for the clipping LEDs in a pedal to not light up, or if they do , it's pretty faint. Super bright LEDs will light up more, but then you have the higher Vf thing to contend with. If it sounds good, then it's working the way it's supposed to work.
 
Mourguitars said:
Im a OD junkie.....Over Drives...clear that up a little !

Every one you play acts and sounds differently ......Chuck suggested i put some Green LEDs in there i socketed them....Man ...thats it ..Pay Dirt...or Play Dirt !...im mean thats butter smooth in that build !

Mike
Click to expand...
The TS is a green pedal, so it stands to reason that green LEDs are the way to go. :rolleyes:

Actually, I tried 'em in my Frost Drive and they sounded good. Different pedals need different LEDs. Higher Vf diodes will provide more clean headroom before they start clipping.
 
Chuck D. Bones said:
The TS is a green pedal, so it stands to reason that green LEDs are the way to go. :rolleyes:

Actually, I tried 'em in my Frost Drive and they sounded good. Different pedals need different LEDs. Higher Vf diodes will provide more clean headroom before they start clipping.
Click to expand...


That is so correct !

That was my 1st mod...well not really mod ...just something different to do per your recommendation...again Wow !

Lol

Mike
 
Chuck D. Bones said:
Take another look at Mourguitar's pic. Nothing is plugged into the pedal. No power, no guitar, nada, zilch, bupkess. That light you see in the green LEDs is a reflection of the camera flash.
Click to expand...
D’oh! 😅 Guess my monkey brain only sees shiny! I was also thinking of the Gov’nator build, which has very visually obvious and kinda fun LED clipping, but i guess the difference is hard vs soft clipping? Thanks for the continued information, I always had a suspicion that the green ones were my favorite!
 
Ive been reading Wamplers DIY pedal mods book i forgot i had when i migrated to my new mac...He use green LEDs in a lot of his mods ...thats a pretty informative book for beginners
 
You must log in or register to reply here.
Back
Top