The 1N4148 has leakage x1000 the input of TLC BiFet so the drive to the OA input is very well defined and is a convenient way of implementing a peak h old without using an extremely large valued resistor. Also, anyone can see the LEDs are intended to avalanche. The OP didn't think a 12V supply was im portant, so it caught up with him. The circuit is very clever and works wel l for audio frequencies.
Except that it doesn't, per the OP. It's a complete hairball. Just for openers, avalanching a LED doesn't make it light significantly. (Try it.)
Build that circuit with lead-free solder and water soluble flux, and all those resistances become uncertain by two or three orders of magnitude.
Every once in awhile you run into a good reasons to rely on untested parameters of some part or another, but blinking a LED to the music isn't one of them.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
)
That's what they say...there's something they're not telling us about those LEDs.
We don't know what the original circuit called for, the hobby cultists star ted circulating the schematic assuming it was all they needed to know, but the Elektor article probably called for standoff mounting and flying leads.
I think it's supposed to be used to set drive levels to things like amplifi ers and not for some kind of light display synchronized to music. The only strange part about the circuit is separate positive and negative peak thres holds adjs, you would think they should be the same.
On Thursday, February 13, 2014 10:41:06 PM UTC-5, snipped-for-privacy@gmail.com
fiers and not for some kind of light display synchronized to music. The onl y strange part about the circuit is separate positive and negative peak thr esholds adjs, you would think they should be the same.
Errr...left and right channel...
well.
I disagree. It is a lot better than the first circuit. It sees both positive and negative over excursions. C5 is a pulse stretcher.
?-)
A surprising number of LEDs spec their abs max reverse bias at 3V. This means many LED driver chips stress the LEDs.
If you actually avalanche them, they will become leaky.
I think this is just laziness on the part of LED manufacturers. I haven't found an LED that avalanches at less than 20V. (But if you have actually tested some, then please post a part number.)
Well in my experience if you limit the current such that the total power disipation is less than ~50mW (whatever the forward biased max power is.) then there is no harm done.
George h.
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Aarghhh...
Careless problems with the front end; sorry 'bout that. :-(
I'll post the fix some time this weekend. :-)
John Fields
Prepare for PAL with HUB attack, engineering honesty is not tolerated and will be subject to derision. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
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