My head ain't sharp... help with pointing it? DIY Monitor section

I've been tasked to build a "Monitoring" device... 3 in 1 out. One big knob for "volume" (attenuation I would suspect) and Mute, and Mono.

Has anyone DIY something like this already, I searched, but didn't turn up much. It seems passive wouldn't work because the output impedance would be affected?

Any help pointing me in the right direction or, well, "pointers"

jwhmca said:

I've been tasked to build a "Monitoring" device... 3 in 1 out. One big know for "volume" (attenuation I would suspect) and Mute, and Mono.

Has anyone DIY something like this already, I searched but didn't turn up much. It seems passive wouldn't work because the out impedance would be affected too much?

Any help pointing me in the right direction or, well, "pointers"

Click to expand...

Igor has passive CRM kit and seems to be releasing another active version soon. 
http://www.groupdiy.com/index.php?topic=29771.0
http://www.groupdiy.com/index.php?topic=42829.0

Also Nielsk seems to be planning one
http://www.groupdiy.com/index.php?topic=42880.0

Other than that, you could just find some console monitor module schematics and improvise on that?

Forget about passive. There are too many landmines in that field.
See attached dgm. I would recommend making the input sections adjustable. You can use THAT line receivers and drivers or your own. Be careful, most EBOS want to see a very low source impedance so you probably want a buffer after the pot.
Speaking from experience, 3 ins is not enough. And maybe you want a -10dBu input for a CD player and another for an i-phone, and another for a soundcard output, well...

EBOS?

How is MONO handled?

jwhmca said:

EBOS?

Click to expand...

Electronically balanced Output Stage.

How is MONO handled?

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As shown on the dgm. The switch connects the Left node to the right one.

So, the signal needs to be de-balanced. Would implementing the de-balancing from the GSSL be the right idea?

Sorry, I guess I'm still not 100% percent on the MONO. You are saying that "un-drawn" left side is just plugged into the right? No buffer resistor or anything.

My head in general is still a little weak on whole world of impedance. But, I think I understand... I was looking at one set of active speakers (something this box would be feeding) they said they had an input impedance of 30k... That's where I get kinda lost. My source feeding them would need to be 30k or that's what they will load down my output to... or did I just say the same thing?

do a little reading on "potential divider"

you want as much of the signal as possible across the active speaker.

The total value of the pot you use will look in parallel like the load your driving (to the source).
The ratio of the pot position and the input impedance of the active speaker will tell you how much signal will be dropped in the pot, and how much in the active speaker.

i'd still go with an active system... as you could use it with any speaker/amp then.

jwhmca said:

So, the signal needs to be de-balanced.

Click to expand...

Yes, so you don't need a quad pot and makes a lot of other things simpler, like Mono and DIM.

Would implementing the de-balancing from the GSSL be the right idea?

Click to expand...

You can use a diff amp, as in GSSL, but a THAT chip is so much better...Beware that is you use a THAT 1646, it has 6dB gain, so you may have to use an input chip that has 6dB attenuation.

Sorry, I guess I'm still not 100% percent on the MONO. You are saying that "un-drawn" left side is just plugged into the right? No buffer resistor or anything.

Click to expand...

There is one; I've shown it between pot and switch.

My head in general is still a little weak on whole world of impedance. But, I think I understand... I was looking at one set of active speakers (something this box would be feeding) they said they had an input impedance of 30k... That's where I get kinda lost. My source feeding them would need to be 30k or that's what they will load down my output to... or did I just say the same thing?

Click to expand...

That means that you're fine as long as the actual source impedance is less than 3k (1/10th of 30k). With a typical THAT chip or a cross-pair EBOS, the impedance is 50-100r so don't worry.