[Chet_Summers]

 
Unless you have dual outputs on your sound card or a loop out on your headphone amplifier, it’s difficult to have both your computer speakers and headphone amp plugged in at the same time.  I’ve got the Klipsch Promedia 2.1 speakers and found these maniacs online who have posted the schematics for the entire Klipsch Promedia line.  After staring at the schematic for the control pod for a few minutes I realized that it’s just a headphone amplifier plus a volume control and high pass filter for the sub (which I thought was odd at first, but I guess it’s for DC blocking protection or something).  I thought that my expensive headphone amps should sound way better than the one in the control pod and decided to rebuild the bass volume control and HPF.
 
Check out the schematic labeled “Schematic diagram of Control Pod” on this page: http://www.thompdale.com/bash_amplifier/2-1/2-1_bash_amp.htm
 
You don’t want anything to the left of the HEADPHONE OUT jack, just the stuff in the upper right starting with R519 and R520. Don’t forget the two power supply caps C511 and C512, you need those. I skipped the LED because I don’t like them (R529 and D405).  Thanks to Tangent’s advice, I used an OPA2132PA for U501 instead of the TL074 in the schematic (plus I only needed 2 op-amps, not 4). For the DIN output connector (to be connected to the Klipsch subwoofer cabinet) I used a generic PS2 cable, although the wire colors don’t match exactly with what’s in the schematic (use a multimeter to figure it out as yours will probably be different both than mine and the schematic).  I used a 1/4” jack for the input (to be connected to the expensive headphone amp output). I boxed the finished bass volume control and HPF into a Hammond enclosure shown below. 

Pic below shows the control pod next to my finished rebuild.  

 
End result: Doesn’t sound much different.  I tested with a Headroom Home and Millett Hybrid MiniMAX, sounds about the same as before.  I threw the bass volume control box under my desk, so things are a little bit cleaner, but I guess this whole project is sort of like putting lipstick on a pig.  Always fun to build stuff though, and the volume pots on these control pods are crap, so this is an option if yours dies and you have a headphone amp.  
 

Label​	Value​	Mouser Part #​
R519	5100 Ω	271-5.1K-RC
R520	5100 Ω	271-5.1K-RC
R521	510 Ω	271-510-RC
R522	20.0 kΩ	271-20K-RC
VR502	10 kΩ	688-RK097111080J
U501	OPA2132PA	595-OPA2132PA
R523	10 kΩ	271-10K-RC
C509	0.1 µF	75-715P200V0.1
C510	0.1 µF	75-715P200V0.1
R524	40.0 kΩ	271-20K-RC (x2)
R525	10.0 kΩ	271-10K-RC
R526	5110 Ω	271-5.11K-RC
R527	20.0 kΩ	271-20K-RC
R528	10 kΩ	271-10K-RC
C511	0.1 µF	75-715P200V0.1
C512	0.1 µF	75-715P200V0.1
Input	1/4” cable	172-0108
Output	6 pin DIN
Case	Hammond	546-1455CALBK-10

Parts List

 
 

 

[Rescue Toaster]

Thanks for that link. I have some Promedia 4.1's that have a little noisy volume control, and also any time it's ever unplugged, after plugging it in the speakers make constant static noise for hours and hours, that goes away when I 'turn off' the pod (really just mutes it according to those schematics). So It sounds like if I build a replacement for the pod, I'll be in good shape. I also never use the rear channels (got them in the kitchen on an old 2 channel receiver), so I can remove all that and permanently mute it.