volume with switch ONLY
Sep 7, 2010 at 4:12 PM Thread Starter Post #1 of 12
Skoobs

Skoobs

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i want to make something to go on my desk so that i dont have to fumble around plugging in my headphones into the back of my computer every time i want to use them. i was thinking RCA input on the back, then a potentiometer with a switch on the front (for volume control so that i can leave my computer volume at 100%), with a 3.5mm jack next to it. all i want is to be able to keep my headphones plugged in but not have power going to them until i turn on the potentiometer and turn up the volume.
 
anyone know of a product like this?
 
i would really like to make it myself, so if anyone can give me pointers on which potentiometer to use, i would appreciate it. theres so many different ones, from 1ohm to a billion ohm. i have no idea what to use.
 
all i want to do is keep the signal from my sound card, which i very much enjoy, and just pass it through a little box with volume control. unchanged except for volume.
 
thanks in advance if anyone gives me any pointers. ill check back this evening!
 
Sep 7, 2010 at 4:47 PM Post #2 of 12
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. 
 
Sep 7, 2010 at 5:39 PM Post #3 of 12
Sep 7, 2010 at 5:45 PM Post #4 of 12
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).
 
Sep 7, 2010 at 7:34 PM Post #5 of 12
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.
 
Sep 8, 2010 at 5:14 PM Post #6 of 12
i want to be able to leave the phones plugged in and turn off/down the volume without changing the system volume. i always forget my headphones were the last thing i use and have to figure out why my speakers are so quiet haha
 
Sep 8, 2010 at 5:58 PM Post #7 of 12
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.
 
Sep 8, 2010 at 11:17 PM Post #8 of 12
my sound card has an optical out, and 3.5mm out which is what i use for my headphones... im not sure what is being wired in parallel or split... i just wanted to keep it simple. out of headphone jack at full volume, variable resistance to taste, out through 3.5mm jack to headphones. i dont know why i owuld need a full amp to do that. but i guess ill just build a cmoy.
 
Quote:
gimble said:
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).
Click to expand...


the cable i was going to use would be a 3.5mm to rca jack just because i have a nice one sitting around. a 3.5mm would work just the same. i have no intention of using a line out signal. (so i could follow a cmoy guide to the T.)
 
 
 
 
Sep 9, 2010 at 4:27 AM Post #9 of 12
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.
 
Sep 9, 2010 at 3:39 PM Post #10 of 12
it is optical + 7.1 SS 3.5mm + a mic. it is a sound blaster titanium NON fatal1ty series. in the settings, you can change the 7.1 SS so that the second 3.5mm plug is full stereo only. the optical line out is already going to a speaker amp.
 
speaking of line-out though... could i use the front panel connector to run internal wires to a cmoy that i build to fit in one of the 5.25in drive bays??? that would be super awesome. could the power supply be used to power it? i would have to draw up my own CDs to account for the different voltage (as opposed to single or dual 9v batteries...)
 
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