I've been checking over a Uher VG 840 amplifier (part of the Uher Miniline stack) and would like some insight as to why the headphone output is not loaded by a resistor, and instead has a small capacitor to ground.
I thought this was normal to avoid untoward noises when headphones were plugged in when the unit was on, so I'd like to know what the designer had in mind here. I'm sorry for the quality of the snippet, but I've included one channel of the headphone output so you can see what I mean.
The headphone output is driven by an LA4170 IC, and the circuit follows the datasheet circuit which doesn't have a resistor.
Is the capacitor to decouple any high-frequency pick-up from the headphone lead?
Would I see any benefit from adding a load resistor in parallel with the headphone output?
I thought this was normal to avoid untoward noises when headphones were plugged in when the unit was on, so I'd like to know what the designer had in mind here. I'm sorry for the quality of the snippet, but I've included one channel of the headphone output so you can see what I mean.
The headphone output is driven by an LA4170 IC, and the circuit follows the datasheet circuit which doesn't have a resistor.
Is the capacitor to decouple any high-frequency pick-up from the headphone lead?
Would I see any benefit from adding a load resistor in parallel with the headphone output?
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Most solid state amps need no idle loading, but here a resistor to ground on the output would serve to keep the output capacitor's output side at ground, avoiding plug-in cracks and thumps. 100k would do for that. The capacitor to ground acts as Zobel network in combination with the 47 ohm resistor I think.
Note this circuit will have a large switch-on thump if the 'phones are left plugged in.
Note this circuit will have a large switch-on thump if the 'phones are left plugged in.
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