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headphone volume


Matrix12x
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The mixed output isn't a headphone output, it's just passive mixed with 10K resistors, hence very low output level. Not much I could do about that, no room on the PCB for a headphone amp, plus I heard (perhaps incorrectly) that the audio outputs swing up to 9V, making a single supply amp running on 9V difficult or impossible. I don't really know, though. Perhaps using PSU Option B (generating a 12V supply) combined with 8580/6582 SIDs (which will output 9V max) is a scenario suitable for a headphone amp supplied with 12V.

If someone comes up with a good circuit, please share it! :)

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Most cheap headphones are about 600 Ohms am I correct? I thought the low impedance ones were about 100-150 ohms.

I figure a simple circuit using a dual opamp like a 5532, a 1uF DC block to a 10K ohms on the non inverting input, 10K to gnd as R1 at the inverting input, 100K as Rf, and a 56 pF cap in the feedback to limit the BW, and maybe a 100-150 ohm series output resistor feeding a 1uF DC block to my headphones. I'll probably play with the feedback resistors value to match it to the gain I need. I have used this IC with as little as +/- 5VDC. A voltage divider to float the audio signal on the input at some offset will allow single supply operation.

I'll breadboard something next week and let you know the results.

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A voltage divider to float the audio signal on the input at some offset will allow single supply operation.

you could either remove the electrolytic cap at the audio out that does AC couple the signal, or if the gain of the transistor circuit is too high (didn't bother to investigate this) you could even grab the output signal directly from the SID output (I think I remember it does swing around 4.5V with not too much of amplitude, maybe look up the datasheet), buffer it with an opamp and do a complete active preamp/mixer stage. In the last case, better solder the wires instead of a connector, the SID doesn't like hot-plugging on its output very much.

S

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Most cheap headphones are about 600 Ohms am I correct? I thought the low impedance ones were about 100-150 ohms.

Most cheap headphones i know of are usually under 60 (Sixty) Ohms, maybe thats what you meant?

You'd really need an impedance that low for use with mp3 players, otherwise they'll be far too quiet,

and will require a headphone amplifier to get a decent amount of volume.

Edited by Smithy
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