I have a stereo line level rca feed from my Mbox 2 output. Ideally the signals would enter into a box I would easily build, then pass through a stereo potentiometer, then continuing into 2 identical outputs per stereo channel. I'll probably use 1/4' jacks and adapters because I have many. Critical audiophile integrity is not the goal...just a useful desktop control knob.

I understand some small amount of signal drop can be expected. The 2 sets of line level outputs would feed my powered desktop speakers, as well as a stereo subwoofer, both controlled by the same pot. That would be the goal. Everything is typical line level I/O.

My question would be about the resistance value of the potentiometer in order to drive the 2 sets of inputs. A good useful range of value so there is not much load up. There won't be any active components as part of this small cheap build. Would any additional resisters be needed after the pot?

Thanks
Greg

 

My question would be about the resistance value of the potentiometer in order to drive the 2 sets of inputs. A good useful range of value so there is not much load up. There won't be any active components as part of this small cheap build. Would any additional resisters be needed after the pot?

10K should be suffcient for the pot. Additional resistors not needed.

 

Thank you.

 

It depends on the input impedance of your desktop speakers and subwoofer. Typically audio amplifier input impedance equals 47 kOhm. If this is the case, then each gang of your potentiometer would see 47 kOhm in parallel with 47 kOhm for a combined load of 24 kOhm. To achieve a smooth volume control, then resistance of the potentiometer in this case should be 5 kOhm or about one-quarter times the load put on the pot.

You could use a pot with higher resistance by placing a resistor in-series with the wiper of the pot, but then you have inserted some constant attenuation.

 

The max impedance of a 10K pot is 5K || 5K = 2.5K. That should be fine to drive two audio inputs.

 

It depends on what You have for a "Stereo"-Sub-Woofer,
which really don't exist, except in some fake, cheap, "consumer-grade" type stuff.
And You never really know what you're dealing with.

Get some Headphones from Walmart, some of them are fairly high-quality.
.
.
.

 

How close to a linear variation do you want?? I did that with 100K pots, but that was for tube amps a while back. 50K will work well, don't go less that 10K because that will be a load on the driver. Probably cable capacitance could be a high's cut with 100K, I had not thought much about that.

 

It depends on what You have for a "Stereo"-Sub-Woofer,
which really don't exist, except in some fake, cheap, "consumer-grade" type stuff.
And You never really know what you're dealing with.

Get some Headphones from Walmart, some of them are fairly high-quality.
.
.
.

This would be a decent component subwoofer that has a L/R inputs. Not a cheapy one. The desktop speakers have done ok for a long time. I've had to use a splitter to send a signal to the sub. That's not a proper ideal setup for sure. I just want to indulge in a "better than it was" setup. Because I'm using speakers, there is no reason or purpose to use headphones. I have some good headphones for when needed. And those plug into the Mbox2.

 

This would be a decent component subwoofer that has a L/R inputs. Not a cheapy one. The desktop speakers have done ok for a long time. I've had to use a splitter to send a signal to the sub. That's not a proper ideal setup for sure. I just want to indulge in a "better than it was" setup. Because I'm using speakers, there is no reason or purpose to use headphones. I have some good headphones for when needed. And those plug into the Mbox2.

And now for the slight change...my laptop only has the small headphone output jack. I really should incorporate it's output into an additional set of stereo inputs on this box that I'll make. I'll use a proper switch to switch between the Mbox2 signal (desktop computer), and the laptop's headphone signal. Maybe that will get weird for driving small line level inputs of the speakers.

2 sources (1 headphone level), switchable, into 2 sets of inputs. I'm curious if that will need any resistors for the headphone level signal.

 

I would get a good USB sound 5.1 device with a decent mixer frontend for the laptop.

 

2 sources (1 headphone level), switchable, into 2 sets of inputs. I'm curious if that will need any resistors for the headphone level signal.

Not if both signal levels are appx the same which you should be able to adjust via the laptop.

 

I would get a good USB sound 5.1 device with a decent mixer frontend for the laptop.

Well the Mbox2 is a USB outboard I/O for all things sound related on my old mac. All I need from the laptop is basic stereo as well. My surround sound days were a while back.

To me, proper hookup is when given just a typical musical analog stereo signal, both channels do supply equal amounts of low end information. If only one channel is routed to the sub, then it's technically missing some low end information. Maybe not noticeable as much, but again I just wanted to give it a shot to see if it makes any difference.

I have time to fill these days.

 

Not if both signal levels are appx the same which you should be able to adjust via the laptop.

I tested the headphone output of the laptop going into the speakers & sub. It will work fine by keeping the laptop at a lower level, as you mentioned. Thanks again.

 

The "Totally NO Compromise" scheme will to have two subwoofer s, one for each channel. No mixing losses at all.