Mind confirming a pcb blunder, please?

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boji

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Edit: Rewriting post since I'm still a bit confused....

Does the forward voltage of a diode create an impedance issue in low-voltage control/led signals?
I ask because the circuit in question works fine with the dcom diode in place, it just requires a little more voltage to get the same overall led brightness.

Thanks for your input in advance,
-Boji

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You need to figure about 0.7V  drop for a diode, so yes it would affect things. If in series with a resistor and LED you would need that extra bit of voltage to get the same current to drive the LED. Or you could also lower the series resistor. Similar for control voltages, they usually have a threshold which you would now need to exceed by an additional 0.7V.

(I'm just using 0.7V as nominal, the actual voltage would be dependent on the diode used, the current through it, and temperature)
 
Thanks 12ax.  I can imagine it would be bad indeed if the diode was inline an audio reference path. I will replace it (along with 23 other channels) with a shunt as penance for the mistake.

Moamps:  In a word, protection.  CR3 should have been bridged off of dcom return, with the cathode put to 12v, I believe.
 
boji said:
In a word, protection.  CR3 should have been bridged off of dcom return, with the cathode put to 12v, I believe.

Protection of what? Reverse voltage?
Voltage drop of 0.7V on CR1 and 0.7V on CR3 will significantly lower 5V power supply.
 
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