[sdiy] can I make this circuit change?

[db]

Interesting. So you say instead of having r105, c16 and q102 go to ground, 
they go to a negative supply instead?

I do have a -15 available, but will that now create for too much voltage at 
that LED?

(I have 16 channels to do, so am trying to avoid a bunch of op amps.)



At 1/17/2009 09:20 PM, you wrote:
>Hi db,
>
>For the LED overload indicator:
>The problem is that the darlington connected transistors are going to 
>require at least +1.2V (two Vbe drops) on the input to turn on and light 
>the LED as they are now..
>You might try referencing R105, C106 and Q102's emitter to the V- rail 
>instead of ground. Then tweak R104 for desired LED threshold.
>Do not go too low with R104 because the Vbe juctions of the transistors 
>will "short" or clip the output of IC1b when they are biased on.
>
>OR...
>
>You can use an op amp comparator or op amp full wave rectifier to drive 
>the LED when any signal appears.
>
>Hope that helps,
>- Oren
>
>
>db wrote:
>>
>>On the schematic here:
>>http://workingdistance.com/temp/mixer.jpg
>>I lowered to r104 to 1k, and even then still not quite enough to light 
>>the led on regular signal levels. :(
>>I normally keep input gain (VR101) all the way down.
>>I don't really understand how in this circuit the gain knob affects the 
>>led - it looks to me like the signal to the led circuit would be the same 
>>regardless of gain setting.
>>What am I missing?
>>Anything else I can try in this circuit to get some more ooomph to the leds?
>>I have 16 channels to do so I'm hoping for simple..
>>  >I have a mixer with an input led for *overload*.
>>  >I was going to add LEDs for showing signal is present in the input, 
>> but seems easier if I just make this led signal regular input instead of 
>> overload.
>>
>>dennis.barton:skylab2000[socal]
>>
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dennis.barton:skylab2000[socal]