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Red LED substitution questions

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well, i would like to substitute those leds to try something that would work there in that ccs better.....:) the problem is that i am not sure if adding LM336-2.5 instead of the red led would cause some non-stabilities...... i will calculate resistors but don't know about the stability of the ccs....
if i use LM336-2.5 - would it be stable and would it be good to use little (few pF) capacitor in paralel with the LM336-2.5 if i use it there....???

:confused:
 
this is the one
 

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o.k. thanks.......

can you sugest something maybe to substitute that ccs ....something that will be arround 25mA, and that would not be the design from mr. Pimm (not that i don't like it (i value his work a lot) - the problem is to find LND transistors - and i also would like to have it on a solid state without tubes in ccs)....this ccs was my only choice for now.....
something better would be nice - since this ccs is sounding very good....
 
:D -i am trully sorry - i did not know that this word is that hard.... i looked in the slang dictionary and found what is the correct meaning :eek: :blush:....that is what you have when you learn english from the films that our children are looking too:rolleyes: ;)
oh well.... i admit i am ashamed and i am sorry.....so lets proceed quickly to the problem that is presented here :)
 
Ex-Moderator
Joined 2003
Given that your circuit is preceded by a volume control, I assume that the signal level is fairly healthy. Changing things in the reference chain of the CCS will only affect noise/hum, but you have enough signal not to need to worry.

If you had a smaller signal you might be worried. The LED is quiet but even if you manage to find the old low brightness LEDs, the internal resistance isn't all that low (5R or so) so you don't get particularly good attenuation of power supply hum from the potential divider formed by the LED's internal resistance and R2. Replacing R2 with a crude CCS (DN2540N5 plus two resistors) can help considerably.
 
EC8010 - thanks .... the problem is to use those exotic parts like DN2540N5 and LND150.... i am living at the end of the galaxy (hm, well it is maybe the begginning actually :) ):D so i can't obtain those parts... but i can use normal ccs with BC550/560 - this would also help i think :confused:........

LED diodes that i have are from some not known type and i have tried to pair them so i have 2 pairs (4 pieces) - one that is brighter and the other that is not that bright.... i would like to avoid that problem by putting something better - not to have those LED's - that was the reason for the original question.... oh well - i might try to find something that is bright and red.....in fact i like their look in the preamplifier - everything is glowing all around....tubes LED's :D yes, yes - that is what i like - but want to boost the quality if possible (using right now 12B4 tube in that configuration).....
i might also use some capacitor to put in paralel with the LEDS - lets say >10uF......??!!


opinions? :D
 
Ex-Moderator
Joined 2003
OK, if you have trouble getting parts, then use an MJE340 as a crude CCS in place of R2. There's no need to fuss matching LEDs - and you don't want good ones! You want the cheapest nastiest oldest dimmest red LEDs you can find. The nice bright new ones have a much higher internal resistance...

There's no need to put a capacitor in parallel with the LED. Assume 5R internal resistance and that you want the capacitor's reactance at 100Hz to be equal to the LED's internal resistance. That's 330uF. It's hardly worth the trouble.
 
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