CP650 Slow/Lagging Operation

[Kyle Mikolajczyk]

Well, still on the topic of the CP650, does anyone have an elegant solution to multiple different DB25 cables into the Analogue Input of the CP650? We currently have two cables we swap out, one for Mag 70mm from the Dolby MPU and we have a custom DB25 board that breaks out audio from our Oppo player into the CP650. We will soon have a 3rd DB25 that will need this slot. Any ideas that aren't constantly going behind the rack and swapping?

[Steve Guttag]

A/B (two sources) are easy as one can do that with just relays. when you get into 3 or more, you get into electronic switching or doing things with a "buss."

If you want really elegant, look into Q-SYS and let the CP650 just be a source. Even their "baby" CORE can handle up to 64 channels of input and output. The CORE110 handles up to 128 channels in/out plus it has up to 16-channels of analog input built in.

I don't doubt there are source selectors out there but a 3 into 1 isn't going to be as easy or as cheap as you would hope. Analog audio isn't as popular as it once was so choices will be limited.

[John Thomas]

I've never tried this, but always wondered if one of these would do it:

https://www.newegg.com/p/0ZK-06F4-004X1

[Frank Cox]

I remember using one of those back-when to switch between a laser and a dot matrix printer. There was some reason why we didn't just put two parallel cards into that machine, but I've forgotten what that was now.

[Steve Guttag]

It will work for A/B BUT you WILL get crosstalk. If you look inside one of those you'll see bare wires and with that you'll get inductance across the wires and hence crosstalk. You also will have whatever noise the switch itself brings, particularly over time.

Wohler used to have an entire series of multi-channel analog audio switchers...long gone. It gets trickier as you want 6 and 8-channel switches as that makes the need even more niche.

[Carsten Kurz]

We had a rack mounted relay and transformer based device made by one of the german integrators (FTT MA6). It had a Dolby automation pinout control interface, and could switch between 3 or 5 sources. It is no longer made, but you can find it second hand occasionally.

For a while, we used one of these printer switches to switch between DA20/DTS-6D and our Bluray players 5.1 output towards our CP65. Yes, it is a cheap hack (ours had split flat ribbon cable between switch and connectors). But it was decent for the time. You could probably rewire one of them with ground wires between each signal and improve it a little bit. The bad thing is, you can not automate it. A relay solution with an automation interface is not too complicated to do, though. There are many cheap Arduino or PI related relay boards on ebay.

[Paul Finn]

A "Coleman Audio 7.1 Switch" will do exactly what you want. The four inputs are each 8 channel balanced to a single 8 channel balanced output. The DB25 connectors use the Tascam pin-out format so you may have to use crossover cables to the standard THX/Dolby pin-outs.

Paul Finn

[Marcel Birgelen]

I've never tried this, but always wondered if one of these would do it:

https://www.newegg.com/p/0ZK-06F4-004X1

NEVER use those things for analog signals... at least not signals you actually care about...

[Leo Enticknap]

They increase the risk of dropouts in an AES signal by an order of magnitude, too.

[Marcel Birgelen]

They increase the risk of dropouts in an AES signal by an order of magnitude, too.

You really have to look for what kind of applications those devices are rated. While AES isn't a very high-bandwidth protocol by modern standards, many of those switches are designed with serial or parallel connections in mind, not exceeding a few kilobit a second.

This particular device is rated for serial RS232 connections, so most pins are probably not even patched thru. RS232 on 25-pins D-Sub only uses a few pins, most are simply unused.

[Mike Babb]

I have used the Coleman box mentioned above, works great

[Scott Norwood]

+1 on Coleman Audio products. I haven't used the 7.1 switch, but the products of theirs that I have used are of good quality.

[Scott Norwood]

Also, there's nothing particularly magical about the Dolby preamp cards. They just conveniently have four channels, HF EQ, and changeover logic. But there are plenty of off-the-shelf devices that can do these things at least as well. The Dolby "magic" is in the NR decoding and SRD decoding, and, to some extent the matrix decoding.

[Steve Guttag]

Slit loss correction is not HF EQ. One can sort of mimic it using a high Q PEQ. Its value has probably been diminished with the reverse scan soundheads. A proper optical preamp will also present itself as a very low impedance to cause the "cell" to behave like a current source. The other thing an optical preamp has to anticipate is the DC offset voltage that a normal cell will produce. If you want to see/hear/measure the differences on optical preamps, compare the Panastereo to the Dolby and the SMART and Kintek. You'll see pretty drastic differences using the same soundhead, same test film in both response and phase relationships. This will translate into better 2:4 decoding as well.