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Headphone jack wiring problem
ArcadeBliss:
OK, I followed your plan and used a 100K pot. It is wired as such:
PC -> POT -> Headphone Jack -> PC Subwoofer (powered)
As it should, when I insert my headphones, it cuts out the line going to the PC Subwoofer, which of course was the desired effect. The problem I am having is that the headphone volume ist wayyyyy to low and does not adjust to changes of the pot (twisting the knob). Only when you adjust to pot to full (= 0 resistance) does the volume turn all the way up.
After talking with a few friends of my, the consences seems to be that a 100K pot is way too large for the widerstand found in your garden variety headphone (4 - 16ohm). They suggested I replace the pot with a 1K pot.
What would this do to the connection going to the pc speakers. I have no clue ??? Is this even a choice? How did you solve this problem? (Questions, questions, questions...)
--- Quote from: Zebidee on June 29, 2009, 02:36:07 am ---
--- Quote from: Kevin Mullins on June 28, 2009, 12:12:54 am ---I hope somebody makes some use of the confusion. :laugh2:
--- End quote ---
Likewise! :dizzy:
What I was trying to promote was a a linear or logical approach using discrete components in series. In other words, run the signal through vol pot and/or audio jack before it gets to the amplifier, rather than trying to modify the amp itself or splitting signals (or hairs).
The guide doesn't cover audio jacks because there are many different ways to do this, many of which do not involve actually directly wiring up the audio jack. In fact, my favourite way involves re-using the little front-panel PCBs that many PCs have, mounting that behind a control panel fascia and extending the cable by a metre or so (anything over two metres might start to cause problems).
Maybe I should do a page on making little admin control panels from top to bottom, complete with headphone jacks, volume controls and USB ports. Here is an example of one I installed into an existing hole for a coin mech:
--- End quote ---
Zebidee:
Hmmm
Do you have both speakers wired through a double-ganged 100k pot? Also, I need to know if you have a linear or a logarithmic pot.
I have had your experience. I suspect that you are using a cheap log pot. What this means is that the log pot as two resistance tapers (zones of movement) rather than just one (more expensive log pots have just one element with resitance varying over it's length, and if you graph it you get a logarithmic curve, not a linear (straight) curve, that provides for a smoother transition). This first taper gives slow adjustment, and the second taper (once engaged) allows for fast adjustment at the top-end (this behaviour matches your description). It is clunky and does not sound good at all - and is not what log pots should be.
Although theoretically designed for audio applications, the reality is that they are all made cheap-and-nasty these days and it is difficult to get anything else (manufacturers of quality audio products probably get their own made to spec). I have NOT had good experiences using these and generally prefer the linear pots instead.
More on pots and logarithmic tapers:
http://sound.westhost.com/pots.htm
http://en.wikipedia.org/wiki/Potentiometer
http://www.geofex.com/article_folders/potsecrets/potscret.htm
Taper Old Code New Code
Linear A B
Log C A
Antilog F N/A
You can try other resistance values - anything from 10k to 100k is fine, and I have had probably best results with 50k linear pots. However, 1k would be a bit too small I think. I would recommend that you try a linear 10k-100k pot before a 1k pot. A 10k linear pot is commonly used in button headphones designed for use with PCs (I have pulled sets apart and tested them).
Good luck! Photos?
ArcadeBliss:
Thanks for your reply. What do you mean by both speakers? The left and right signal from the pc (speaker out) is wired to the pot. Just like your setup, I have one (line in) cable that is fee d into the subwoofer. From the subwoofer, the speakers are wired into that. The subwoofer runs fine and reacts to the pot movements.
I have a 100K Linear pot. The writing on the side says 100KB.
I guess pictures are worth a thousand words - here you go.
Let me explain what you will be seeing:
Front.jpg: This is the front of my panel 2 buttons Exit and Tab, 2 USB Ports, 2 Composite Sync Ports, the Volume Pot handle, and 2 headphone jacks.
Back.jpg: (see front.jpg)
input.jpg: the rightmost cable is from the pc and goes to the pot. Next to the pc cable is the subwoofer "line-in" cable. It is feed from the first headphone jack. (see wiring.jpg)
Zebidee:
Looks like your headphone jacks cut the active signals, not ground?
You seem to have a linear pot, but perhaps a 50k or 10k pot would work best, especially if you are finding that all the volume variation happens over a small part of the knobs' rotation (I have seen a little of this with 100k pots too, but never enough to worry me at normal amplifier output levels). I still think that 1k is a bit too small though. I have had the best results using some small B50K dual-gang pots (linear) that I de-soldered from old PC multimedia speakers (I couldn't find exactly the same ones at Jaycar, which is a popular electronics parts shop in Australia).
ArcadeBliss:
OK, I received feedback from the friend of mine too. He advised me to use a 10K pot. I'll give that a try this weekend.