[sdiy] can I make this circuit change?

[Oren Leavitt]

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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