A/V Switcher

[BraveSirRobbin]

I guess I really don't understand what good an 8x8 multiplex switch is if you can't truely MULTIPLEX the inputs and outputs then. What am I not understanding here? Why would anyone want the 8x8 units then?

 

[smee]

The idea would be to control the six sources, the AVS 8x8 and the Volume Control remotely either by IR or serial port/Main Lobby or a combination of both. I was thinking about experimenting with Buffalo Electronics IR distribution equipment which is now carried by Automated Outlet.

I'm using a Xantech-based system to control some of the A/V sources connected to my matrix (VCR, DVD, MediaMVP). A single IR zone gets signals from 2 IR receivers and a USB-UIRT connected to my HS machine.

The switch is controlled over ethernet as described previously (from HS).

Zone volume control is handled locally - through local A/V receivers. I would move to replace these with smaller amps and volume controls as mentioned previously, but then I'd need to find a place to store at least one of the receivers.

I have wiring for 2 additional IR zones. These have been used in the past and could be used now to control the power/volume/etc. of the receivers. I find, however, that local control with a remote is my preferred method of control.

 

[BraveSirRobbin]

Edit:

Rereading your post Smee, I intend to switch the audio and video (keep them together) on the eight sources. As a matter of fact, I will probably not even switch video for the first go around.

So say we threw video out of the picture here for the purpose of this discussion. I could then have audio input (stereo) one going to audio output one and two, while having audio input two going to audio output three and four and audio input three going to audio outupt five (as an example of how I would want this matrix to work).

 

[Guy Lavoie]

Smee, I remember discussing this unit during the Friday chat a few weeks ago. Nice project.

 

[smee]

I guess I really don't understand what good an 8x8 multiplex switch is if you can't truely MULTIPLEX the inputs and outputs then. What am I not understanding here? Why would anyone want the 8x8 units then?

I think the problem is in my explanation, not in the switch.

As far as I can tell, the HACS unit is a true 8x8 crosspoint. Any of the 8 outputs can be connected to any of the 8 inputs. The limitation is that an input or output is defined as one composite video connection and 2 audio connections. I think it will do exactly what you want it to do.

The difference between the HACS unit and mine is that mine is essentially two separate crosspoint switches - one for audio and one for video. One of mine is a 16 input/8 output video crosspoint. The other is a 16 input/16 output audio crosspoint.

Most of the time, I operate exactly the way the HACS does. But, through a different set of commands, I can get more control. For my hardware, the command "V1,4;" will connect input 4 (composite and stereo) to output 1. But, if for some reason I want to see the video from input 4 but hear the audio from input 7 in output zone 1, I would send the command "C1,4;A1,7;" - I can switch video and audio separately. I can go one step further and control left and right audio separately - the crosspoint is really a 16x16 analog switch - not two 8x8 analog switches. Using this, I can mix up left and right from any number of sources to my heart's content - not that there is much use for this.

But the total package would let me do things like route 16 security cameras (with video and mono sound (since I can treat left and right separately)) to 8 monitors with stereo sound (even though left and right outputs would come from the same mono input).

 

[smee]

Edit:

Rereading your post Smee, I intend to switch the audio and video (keep them together) on the eight sources. As a matter of fact, I will probably not even switch video for the first go around.

So say we threw video out of the picture here for the purpose of this discussion. I could then have audio input (stereo) one going to audio output one and two, while having audio input two going to audio output three and four and audio input three going to audio outupt five (as an example of how I would want this matrix to work).

Yes. That's exactly what you could do.

It's no fun without the video . How else do you control the behind-the-mirror bathroom LCD screen?

 

[BraveSirRobbin]

Thanks for the explanation smee. I agree switching the video would be cool, I was just trying to understand how that matrix switcher worked using just audio as an example.

Do you have any good suggestions on how to remotely control volume? I know John Wilson uses independent amplifiers/receivers and control them via IR for his NetRemote, which sounds like a good method, I was just trying to keep the component size down.

I wish there was some sort of preamp (line level) remotely controlled volume device that could be controlled via IR. Know of any good products/suggestions for this application.

BTW: Very cool project you got going there on your matrix switch!

 

[smee]

I'm sure that there are remotely-controlled line level volume controls out there, but I've never looked for them - figuring I'd just make one myself.

A potentiometer can be used as a very simple line-level volume control. The quality and losses of the sound depend on the quality of the pot. At line level, you don't need to worry too much about the power going through the pot. [1]

I figured my first attempt at line level volume would use a digital potentiometer [2]. These are chips which implement a digitally controlled pot (typically with up to 64 steps of control). Maxim (Dallas) makes several, among other manufacturers. A microcontroller of some sort, a little programming, and a serial (or other) interface and you are all set.

There are also some fancier chips out there which add in bass/treble/balance/loudness/etc. control. I'm aware of one that uses potentiometers for inputs but handles everything on a single chip. You could use digital pots to control this. I'm sure there are all digital ones out there.

All of these chips are a few dollars each, so it's not too expensive to build something to see how well it works. Maybe someday I'll pull it off the back burner.

[1] Maybe a simple, servo-controlled pot. An RC servo rotating a mechanical potentiometer and you are all set. It would need to be a stereo pot (two pots on the same shaft).

[2] Using a digital pot will probably make audiophiles cringe. A good mechanical pot (read "good" = "very expensive") or a high-quality switch and discrete resistors will probably offer better sound quality.

 

[smee]

I don't know anything about it, but something like this is what you would need:
www.hometech.com RCLL1

May be a bit expensive for multiple zones.

{edit}
OK, here's a cheaper alternative. Again, I don't know anything about it:

Volume control kit

 

[rocco]

. . . Using a digital pot will probably make audiophiles cringe. . .

. . . as well as us non-audiophiles.

I've used digital pots to set the brightness and contrast of LCDs, to tune servo loops, to auto-terminate video lines, for programmable power supplies, and a few other products that I don't remember. They usually work well. One place they don't work well is in audio.

Maybe it is their course resolution, maybe it's the way they work internally, or maybe it's the way I was using them, but they would always pop or tick when I used them to adjust volume. Very obnoxious. I now use programmable-gain amplifiers or multiplying DtoAs for audio, or something like this:

http://www.cirrus.com/en/products/pro/detail/P2.html

 

[smee]

. . . Using a digital pot will probably make audiophiles cringe. . .

. . . as well as us non-audiophiles.

I've used digital pots to set the brightness and contrast of LCDs, to tune servo loops, to auto-terminate video lines, for programmable power supplies, and a few other products that I don't remember. They usually work well. One place they don't work well is in audio.

Maybe it is their course resolution, maybe it's the way they work internally, or maybe it's the way I was using them, but they would always pop or tick when I used them to adjust volume. Very obnoxious. I now use programmable-gain amplifiers or multiplying DtoAs for audio, or something like this:

http://www.cirrus.com/en/products/pro/detail/P2.html

I've played with them before and found the same thing. But, there are some from Maxim (Dallas) that I'd like to play with. They say that the value is changed during a zero crossing to minimize this. I'd like to see if it works.

I'll take a look at the Cirrus chip, though.

 

[huggy59]

Great discussion and lots of good info here! And don't forget that there is always old TV/radio/studio gear up for auciton on eBay. in case anyone wants this kind of stuff and can live with the cast-off non-state-of-the-art units. (ie. me!)