volume with switch ONLY

There are no comercial units (AFAIK) that do this, but wiring it should not be particularly difficult.

 

There is a hidden problem in output impedance - the output impedance of the attenuator will NOT be 0 ohms, and in all likleyhood will not even be particularly low. 

 

Some headphones resopond VERY poorly to this (high output impedace=low damping factor) where others are fairly indifferent to source impedance, and others work better! Its a crap shoot. 

 

If you do decide to do this, use a dual 500 ohm pot, perhaps a 250 ohm pot depending on your headphones and whether your soundcard can drive it. If the soundcard can drive your headphones directly, it can probably drive the 250ohm pot. I'm not sure whether to use a linear or audio pot. I'd personally lean towards a linear pot, channel matching will be better, and when you load the pot with such a low impedance (Im assuming you are using 30-60ohm headphones, although even 300ohms applies) weird things happen anyways.

 

Assuming you dont want to try the pot, the next more expensive solution is to use a nice analog attenuator like you describe with an active amp after it. Nice and simple Cmoy or szekers amp FTW. 

Edited by nikongod - 9/7/10 at 1:49pm

There is a project in the Headwize library that is sort of like what you're describing.

 

http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=cmoy7_prj.htm

 

 

But I would agree that you're better off building a CMoy amplifier insted.

 

 

http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=cmoy2_prj.htm

http://tangentsoft.net/audio/cmoy-tutorial/

 

 

 

 

RCA is nominally for transmitting line-level signals. It's just a dumb plug, but this is the implication. What matters is the source.

 

Personally, I'd just say fudge it and build a low-end desktop amplifier. The CMoy design is a fine start, but you'd probably want to modify the power section (which could get a little involved).

Why do you need a pot? If your computer has an internal volume control, do you need another?

You could just run a male-to-female extension cable from the back of your computer so you wouldn't have to reach around back. You could also build a box with a jack and a switch if you wanted.

If you go with an amp, you'd feed it with the sound card's line out jack anyway. Problem solved. It also keeps you from hooking the two up in parallel via a splitter or whatever, which is not something you should ideally be doing.

You'd be surprised how many bizarre specs throughout history originated because someone already had some bit sitting around that they wanted to reuse.

 

You can just go with a passive attenuator, but there are problems. For example, power output of your average soundcard is underwhelming to begin with. Also in a hypothetical loop where this could work, you would probably be driving the sound card into a higher-noise regime. It's better to go line-out if possible then amp, even if something simple for the amp like CMoy topology.

 

What sound card is this? An optical plus a 3.5mm TRS headphone jack is kinda...minimal. Most onboard sound adapters give more than that.

I'm having a hard time imagining a worse spot then inside a computer for a headphone amplifier.

The thread linked below should point you in the right direction if you really want to try it.

 

http://gilmore2.chem.northwestern.edu/ubb/showpage.php?fnum=3&tid=4508

 

I have done many silly things, but one of the silliest was the lengths I went to to do this.

 

OTOH, the convenience factor is outstanding.