Film-Tech Forum ARCHIVE: External 6-channel interfacing of two sources

This is topic External 6-channel interfacing of two sources in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Michael Schaffer (Member # 1204) on 05-12-2006, 04:11 AM:

Anyone know an interface board which accepts two DB25 and features relay switching between the two inputs, routing them to one DB25 output (to go into the corresponding 6-channel in, of a CP650, for instance, or a DB25-to-terminal-strip breakout board, for the CP65)? To switch between, for instance, input from a DA20 or DTS-6D and a 6-channel out from a digital cinema server.

Posted by Steve Guttag (Member # 268) on 05-12-2006, 06:50 AM:

Michael, Look into DTS' "CP200" interface for the XD-10. It can do just that. It requires 12VDC to power the relays and is an active-low device for switching (uses a transistor so the switching is low-current). I forget its number off-hand but it should be listed in the XD10 manual.

Steve

Posted by Brad Miller (Member # 2) on 05-12-2006, 08:55 AM:

If it doesn't have to be automated, just go to the computer store and purchase two DB25 switchboxes. Have your projectionist flip both to "A" for SRD or both to "B" for dts. Works like a charm...but it's manual.

Posted by Michael Schaffer (Member # 1204) on 05-12-2006, 09:30 AM:

Thanks! I vaguely remembered there was that DTS product, but I just couldn't remember what exactly it was. What voltage levels does the "CP200" interface board need for switching? Can it also be held by a dry contact closure or does it need +4VDC and 0V?

Posted by Frank Angel (Member # 248) on 05-12-2006, 12:45 PM:

FSR, Inc. also makes very sweet switching modules that are fairly inexpensive. They are pretty compact and live on a small footprint PC board. They are designed for switching stereo inputs. Get yourself three of them and you can either use automation or go manual with a single pushbutton switch (lighted too!).

You might also look into one of those KVM swithches (for switching computer keyboard, monitor and mouse between two or more computers). There should be more than enough conductors for + - and Shield for your application. You would just have to make the break-out cables, which is easy enough. Only thing you would have to check is if the isolation circuit in a KVM switch will impact the audio signal. I seem to remember the last time I opened one of those boxes up, I did see few diodes and resistors, but I believe those were just used to block any DC and to make sure there was no crosstalk between connections. If that doesn't impact the audio signal, these would be nice in that it would be a single switch instead of two for a projectionist to have to deal with. The couple we use have mechanical indication push buttons as well, i.e., a little bright thing flips up in the button to show which is active....nice.

You might also want to go with a simple multigang rotary switch -- can't get any more simple than that.

Posted by Steve Guttag (Member # 268) on 05-12-2006, 01:50 PM:

Michael, the DTS product is the E557 board. It requires 12VDC for power. There is a 3-pin Molex KK series connector for the logic. Use your relay or switch to connect the middle pin to "ground" and the relays will pull in.

Note, the board comes with a 25pin Dsub for the output and the "B" input (normally the XD10). The A input is just the normal JM11 pins of the CP200. However, the board will accept a normal 25pin DSub connector if you are willing to solder one on.

FSR does make good products (to back up Frank)...RDL does as well (they have logic controlled relays as well as "silent switches" in their line up.

If you are interested in active solutions and the ability to deal with balanced sources, there is Panastereo's MP64s. They can be loaded with "Line Input" cards (up to 4 per unit). They are 6-channel cards so you can do a 6-channel A/B system with just two modules.

There is also Wohler but they are more pricey...then again, they go beyond even 6-channels on each input.

Posted by Michael Schaffer (Member # 1204) on 05-12-2006, 11:29 PM:

Thanks for all the tips!

Posted by Gustav Viem (Member # 3750) on 06-01-2006, 03:05 PM:

Cine Project have a nice box called Soundguard.
It has two 6ch inputs on 25pin contacts, and one on RCA-contacts.
The inputs are marked ROWO/Server, DTS/DA20 and AUX. The output is also 25pin Dsub connector. It also has an automation in/out to control the cinema processor(also 25pin con)

We connect 6ch sound from the PC that runs the commercials on one input, and a DTS-player to the other. In another theater we connect the commercials-PC and a D-cinema server. The output of the Soundguard goes into the 6ch input on Dolby CP650.
The AUX input we use for connecting HDCAM, DVD-player or whatever we need. On the AUX input you can also adjust the level.
The automation connector will set the CP650 to input 11 (6ch input) when selecting ROWO or AUX. It is also possible to program the function of the automation.

http://www.cine-project.de/118.0.html?&L=1

Posted by Alban Birch (Member # 4121) on 01-24-2007, 12:54 PM:

Hello
I found a cheaper and maybe better Switch
It is from FTT in Germany , it is called MA-6 witch 2 inputs and MA-6 MkII with 3 inputs. Inputs and Outputs are DB25. They have isolating Transformers to avoid Groundloops. The Input 3 has a single trimpot to match levels of none cinemamaterial.
There is even a relay to cut the SR-sensing/pulse-Line on a DA-20.
Switching is done by pulsed or permanent 12V. There is one multicolour-LED to show the Status.
The Unit is 1U high, weighs 2,5 kg and 265 mm deep.
Pricetag 595€ for the MA-6
and 795€ for the MA-6 MkII
I don't know the price of this one but sounds interesting too, it is non-cinema-material

Edited
Sorry, my bad

[ 01-24-2007, 07:18 PM: Message edited by: Alban Birch ]

Posted by Mark Gulbrandsen (Member # 72) on 01-24-2007, 04:46 PM:

Alban,
Neither of those links are working....

MArk

Posted by Frank Angel (Member # 248) on 01-26-2007, 09:39 AM:

Wow, that Zector sounds like it might be a solution for switching 4trk mag head signals between two projectors. Our original mag system was an Altec tube preamp which used a single preamp using 12AX7 tubes -- the preamp was very well matched to the heads and had a sweet, rather warm sound. BUT the system did change-overs with relays rather than using dual preamps. Switching very low level mag head signals is a BAD idea -- it's almost impossible to avoid noise. Even though the system had a mute-before-make relay which actually shorted all inputs while the four audio signals were being switched to the other projector, you still heard a big THUMP -- you might as well have been shouting out the booth port "CHANGE-OVER!"

We switched to an Inovonics solid state preamp that was orginally designed for 4 track Ampex and Scully tape transports. It was better, but no cigar -- the thud was reduced, but the sound was harsh, probably because it was not perfectly matched to the mag heads. And that preamp picked up hum from motors.

The Zector switch might have been a good solution. Now we've junked the single preamp idea and use two SMART mag preamps -- no problems. That switch would have been a cheaper solution.

Posted by Joel N. Weber II (Member # 3530) on 01-27-2007, 01:49 AM:

quote: Frank Angel
You might also look into one of those KVM swithches (for switching computer keyboard, monitor and mouse between two or more computers). There should be more than enough conductors for + - and Shield for your application. You would just have to make the break-out cables, which is easy enough. Only thing you would have to check is if the isolation circuit in a KVM switch will impact the audio signal. I seem to remember the last time I opened one of those boxes up, I did see few diodes and resistors, but I believe those were just used to block any DC and to make sure there was no crosstalk between connections. If that doesn't impact the audio signal, these would be nice in that it would be a single switch instead of two for a projectionist to have to deal with. The couple we use have mechanical indication push buttons as well, i.e., a little bright thing flips up in the button to show which is active....nice.

Analog video cards typically have 8 bit DACs. The keyboard and mouse signals are purely digital.

Whereas good digital audio is typically at least 16 bits.

So the tolerable noise floor for video is probably substantially higher than for high quality audio.

The frequencies used might also be an issue. A single cycle of a sine wave going to a subwoofer can take longer than 1/60th of a second, whereas the less frequently updated monitors typically have hundreds of thousands of pixels redrawn in the space of 1/60th of a second.

When you ``block DC'', you are actually picking some appropriate cutoff frequency, and even if you're just repurposing a PA microphone mixer to mix subwoofer signals, I think you might need to watch out for what the cutoff frequency on the DC blocking is.

Posted by Eric Robinson (Member # 2966) on 01-27-2007, 01:56 AM:

Here's a very versatile product:

From Agilent URL:
Agilent 3499 switch control unit

quote:
Ideal for mid-sized systems, the Agilent 3499A can accommodate up to five plug-in modules, routing up to 200 channels in a test system. With various switch modules, it can scan at rates up to 350 channels per second, or open/close 200 channels in less than 0.1 second. The 3499A is compact, requiring only 2U height in a full rack width mainframe unit.

Or you can go for the 3488a which is discontinued but is available on EBay from about 50 to 200 bucks.

Posted by Mark Gulbrandsen (Member # 72) on 02-05-2007, 04:11 PM:

quote: Steve Guttag
the DTS product is the E557 board

Steve, Are you thinking of the D-567 board instead???

Mark