Steve Eddy
Member of the Trade: The Audio Guild
Aka: TempAccount555
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- Sep 28, 2003
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Steve , thanks for replying. I have several more questions.
Sure. And first my apologies for taking so long to reply. Got a bit sidetracked.
If the first resister is to be in series to reduce the overall out voltage and allow to increase our volume pot. Does this effect factor damping factor.
Well, for dynamic headphones, which don't have a nice flat, resistive impedance curve, it can effect frequency response. But for orthos, which is the subject of this thread, the concept of "damping factor" isn't really relevant. The impedance curve of orthos is flat and virtually purely resistive so the resistor's only effect is signal attenuation.
Second question. I am assuming the resister in parallel with the headphones is to match the nominal imp of that particular headphone.
No, it's not to match the impedance of the headphone, but rather to allow the headphone to see a lower output impedance from the amp than it would see if just using a series resistor.
Let's say you're using a 100 ohm series resistor. Then the impedance seen by the headphone would be 100 ohms. But add a 10 ohm parallel resistor and now the headphone sees an impedance of 100 ohms in parallel with 10 ohms which comes to about 9 ohms.
Of course you could do all the attenuation with just a parallel resistor, but it may end up being of such a low value that it could end up having to dissipate a fair amount of heat. So a series/parallel pair is a good compromise to give you a lower output impedance while not having to dissipate much heat.
Third question . Would it be better to have the resister as like 8 ohms. And resister in series from there to antenna the the output voltage and the final resister in parallel with headphone matching the headphone . At the speaker terminal the amp would see a nominal load of 8 ohms .
Well, as I said above, the purpose of the parallel resistor isn't to match the headphone impedance but rather to have the headphone see a sufficiently low output impedance that it won't have a significant effect on its frequency response.
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