Installing a volume on my front audio. Page 1 / 2

cybertao, Jan 1, 5:03am
Installing a volume on my front audio. I have a stereo hooked up to the soundcard output at the rear. My computer also has a socket at the front I often plug headphones into. Rather than having to change the volume on my computer when I switch between the two, it would be cool to put a knob on the front to change the the volume on the headphones. Looking in my Jaycar catalogue they have two small logarithmic pots available in 10kohm and 50kohm - any idea what value resistance I would need?

gbbrot, Jan 1, 6:29am
Sounds too big.. to me. I seem to recall a figure of 32 Ohms is the speaker/earphone output. Your pot needs to be somewhere around that value.


kevin16, Jan 1, 6:37am
Http://is.gd/ekyF .

swivel, Jan 1, 6:37am
Headphones With volume control would be easyer

deodar, Jan 1, 6:43am
I have volume on the earphones Simple.The headphone out should be
cutting al other output,so speakers
will be silenced.Unless you have a
monitor/playback card for mixing.Or
else your wires are crossed X.

biggal, Jan 1, 6:50am
# 1 Is the h/phone socket at the front on the front panel of the CD drive ??

lostdude, Jan 1, 6:52am
Realtek HD (onboard soundcards) do not cut out if both (front & rear) outputs are connected.

cybertao, Jan 1, 6:56am
No. It's a socket at the front that it connected to the motherboard. I want to put a pot inline and install it in the side of the tower. I'd much rather do that than buy another set of headphones.

cybertao, Jan 1, 7:01am
For those interestedIt's a DFI Lanparty motherboard with a Karajan audio module that feeds the front jacks.

biggal, Jan 1, 7:11am
My way Little box with 1000 ohm log pot inside. Lead with jack at one end and jack socket coming from centre pot connection at other end.

deodar, Jan 1, 7:26am
Disconnect speakers Unless you need both.

cybertao, Jan 1, 7:31am
Thinking more on it. The headphones do provide an impedance of 32ohms. If I simply increase the resistance with a pot, it will mess with the frequency ranges, no?

biggal, Jan 1, 7:58am
NoNo reactance/impedance involved apart from that of the phones

richms, Jan 1, 9:52am
Yes a resistor in line with headphones will stuff it up, it will ruing the damping factor which will change the bass response majorly.

On both machines I have used recently with a realtek hd audio, it has cut off the audio but only when the case had hd audio front jacks, which my old case did not have so they didnt turn off the rear jacks, its an option in the realtek control panel if the rear mutes when the front is connected, and you can make it a seperate audio device which is what I do since it means I can have my headset in there and use it for voip while playing other stuff.

pc_nut, Jan 1, 10:13am
You could make up a stereo headphone amp consisting of a few LM386 amp chips so you can adjust the volume without screwing with the impedance of the headphones or affecting responce ect and assuming you can solder otherwise i could make it and list it as an auction there are circuits on the internet avalible why cant you just use the amp's headphone socket and just adjust the amps main volume?

cybertao, Jan 1, 10:17am
Yeah, that's what I was thinking. Do you know what I need in the way of a headphone driver? I'm not all that concerned about quality, but something simple that would be better than just a resistor. Some sort of op-amp?

cybertao, Jan 1, 10:19am
Ooh, thanks pc_nut. Yeah, I could plug them into the stereo. But I'd like to take the time to kit out the front socket, it would be more convenient and I won't have to rely on the stereo - just to 'future proof' and be more flexible.

pc_nut, Jan 1, 10:23am
http://www.hobby-hour.com/electronics/lm386-power-audio.php

make up two of these puppies and you've got a stereo headphone amp

cybertao, Jan 1, 10:39am
Cool, thanks man. I remember those chips from when I had a dick smith funway kit. I think it was from the second series...many, many blue shaded moons ago.

richms, Jan 1, 1:05pm
Look at the cmoy headphone amp - its quite a popular low cost schematic - I don't know how it would like sharing a ground with the PC power supply tho, that will but your biggest obstacle when dealing with audio between things. Some coupling caps on the input would probably solve it but its being about 10 years since I have looked into anything like that.

deodar, Jan 1, 6:13pm
You could get a Behringer Headphone Amp 1/4" input though.

cybertao, Jan 1, 10:08pm
I was thinking about the amp diagram when I was drifting off to sleep(yeah, I have weird dreams). The input to the amp controls the volume by passing the input siganl...through a variable resistor! So the amp would suffer the same bass frequency dampening. That's why they have the circuit with a bass expander. And using an amp will amplify the noise in the computer like rich mentioned. I'm going to use biggal's suggestion and make an external box to try different things with before I commit to an in-case mod. Thanks for the ideas, guys.

biggal, Jan 1, 11:02pm
# 10 I should have stipulated a double gang pot for stereo, difficult but not impossible.
Damping factor, normally used in reference to spkrs, is a murky subject. The effect on bass response can be easily checked with a mock up of the 32 ohm phones and resistors.

cybertao, Jan 1, 11:05pm
Yes, I realise that. Thank you for bringing it to my attention. I hope my local Jaycar is open today.

cybertao, Jan 2, 6:05am
Sweet as! I got a 10kohm(smallest they had) log pot from Jaycar and wired it inline. It's a bit too high so I don't get much sensitivity from the knob, but I can fix that by adding a couple of resistors to it. A potentiometer has three terminals as it can be used as a voltage splitter, the load on the circuit is always the same, the percentage that goes to the headphones is controlled. Godflesh still has all the bass.B-) Good to read the soundcard documentation as well, it seems there are supposed to be jumpers shorting the two channels for the rear output to work, but if you take them off and plug in the front port the rear is disabled. The cables for the front ports on my case have two plugs per channel, acting as a jumper as well(so both ports are always active. So the next project will be to wire up some transistor gates to disable the rear port while something is plugged into the front port.

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