[sdiy] LED Drops

[Roy J. Tellason]

On Sunday 09 December 2007 16:02, mike ruberto wrote:
> Ok this is cool, the catalog has alot of good info.
>
> LOL "WE PUT THE "DIE" BACK IN DIODE" That website is a trip!

I didn't run across that bit,  but the online rendition of the printed catalog 
is really quite impressive!  Or was,  until my browser crashed for some 
reason.

> I want to build this circuit...
> http://www.jlmaudio.com/JLM%20Hybrid%20Opamp%20circuit.pdf
>
> but all I have is a green LED.

Oh my.  In that particular case I really wouldn't substitute...

> It seems the green have a higher voltage drop than the red.

Yes,  somewhat.

> So it looks like I'll have to play around with resistors or a combo of
> regular diodes. 

I acquired a whole bunch of (mostly red) LEDs by buying a couple of assortment 
packs.  Years ago now, and I haven't come anywhere near using them all up.  I 
also take LEDs out of stuff being scrapped,  and snagged a bunch from a guy 
who was disposing of a lot of old computer cases,  which is handy in that 
they have the leads with connectors attached.  Surely you can pick some up 
somewhere...?  I don't suppose it would be that big of a deal to drop one or 
two into an envelope?

Most similar circuits I've seen had _three_ diodes in there,  not two.  Two of 
them just compensate for the base-emitter drop of the transistors,  and that 
leaves the drop across the emitter resistors to overcome -- if you don't have 
a bit more bias than two diodes would give you,  you'll end up with somewhat 
more crossover distortion than what you probably want.

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