A/B Box to choose between tape and digital recorders

idylldon

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I recently picked up an MCI JH-24 tape machine and plan to integrate it into my setup, which now consists of a Neotek Series II console and an Alesis HD24XR.

I'd like to have the tape ins and outs from my console hardwired into a routing box and then be able to choose between the HD24 and the MCI machine; that is, I'd like to flip a switch have the router send input and outputs of the console to either recording medium. Kind of an A/B setup.

Can I use a simple relay layout for this or will it cause some problems? I've read about the coils in relays inducing noise into signal lines, but if I'm careful on layout could I eliminate this possibility?

I suppose I could just manually plug/unplug connections, but having something that'll work with a flick of a switch would be much easier.

Cheers,
--
Don
 

pstamler

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You should be able to do this. Use DC relays, caps across the switches and reverse-biased diodes across the coils to get rid of back-EMF problems from the coils. While the relay's engaged, with DC coils, you should not have any noise problems; it's only while switching that you may encounted pops.

Do keep a careful eye on grounding, though.

Peace,
Paul
 

Boswell

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Should be fine. You probably need only switch the tape/hd24 outs - the ins could be permanently wired in parallel. What maximum input levels do you normally run into the JH24? The HD24 has a 0dbFS of +19dBu, so you may need to fit attenuators in one or other of the JH24 or HD24 ins and outs to balance up the levels at the desk.
 

pucho812

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your making it way harder then it needs to be. Better off to just wire up a pannel with elcos from the console to the pannel for sends and returns to the multitrack. Then wire from each multitrack elco to inputs and outputs. Then patch them in at the pannel as needed. do 90 pin elcos so you have 24 in's on one and 24 outs on the other. :thumb:
 

idylldon

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Thanks for all the advice.

Yeah, using Elco connectors and just plugging in whatever recorder I'm using at the time is surely the path of least resistance, but it sure would be nice to have it switched electronically.

Cheers,
--
Don
 

SSLtech

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I've done it this way before now, and it's super-easy:

A box full of changeover relays, with the coils all wired in parallel. Can be 12V, 24V or whatever. Then I just run a wall-wart into ALL the relay primaries. Plug the wall-wart in, and I'm using the analog machine. Unplug the wall-wart and I'm using the digital machine.

As a further folly, I plugged the wall-wart into a socket which was run through a light-switch; -you know, the sort proveided for a table lamp or whatever. then I labeled the lightswitch "digital" in one position and "analog" in the other.

It really is the coolest thing to have a switch next to the light dimmers, to chage the room over from analog to digital... you REALLY ought to try that one... it feels so wierd, it's RIGHT! (very risky if you have a cleaner or a spouse though... they want more light, and they chenge modes for you!!! :green: )

Keef
 

idylldon

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[quote author="SSLtech"]I've done it this way before now, and it's super-easy:

A box full of changeover relays, with the coils all wired in parallel. Can be 12V, 24V or whatever. Then I just run a wall-wart into ALL the relay primaries. Plug the wall-wart in, and I'm using the analog machine. Unplug the wall-wart and I'm using the digital machine.
Keef[/quote]

This is what I had in mind. Do you prefer any particular brand and model of relay? I've used Omron in the past with good luck, but I'm always interested to hear if there are better ones out there.

Cheers,
--
Don
 

SSLtech

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Omron make good ones and bad ones, but this isn't a "thousand times a session" switchoiver, like a punch-in relay might be, so most all of their relays will be fine. -If you can get 4-pole changeover, 12 relays will do a 24-track balanced changeover, but if you can only get 2-pole, you'll need 24 of them.

I actually wired my box with a male Elco 120-pin output connector and 2x female Elco input connectors, so it could go anywhere. The connectors are not vital, so you can make a hardwired unit and save some dough, but strain relieve the cables well.

Keith
 

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