jeffbro

Multitrack changeover box
« on: June 14, 2020, 10:52:54 AM »
Like MrClunk, I am contemplating building a 24 track tape machine changeover box, only in my case the design goal is to switch among not 2 but 3 machines.  That's a lot of expensive relays!

Surely the problem of simultaneously switching 24 line level signals to multiple destinations has been solved in the studio,  communications, or network broadcasting industries.   Anybody have any ideas or pointers to solutions that use FETs or analog switches rather than relays or manually re-plugging EDAC connectors?

JB


JohnRoberts

Re: Multitrack changeover box
« Reply #1 on: June 14, 2020, 11:57:03 AM »
Like MrClunk, I am contemplating building a 24 track tape machine changeover box, only in my case the design goal is to switch among not 2 but 3 machines.  That's a lot of expensive relays!

Surely the problem of simultaneously switching 24 line level signals to multiple destinations has been solved in the studio,  communications, or network broadcasting industries.   Anybody have any ideas or pointers to solutions that use FETs or analog switches rather than relays or manually re-plugging EDAC connectors?

JB
I've done some low distortion  2-way electronic switches for 20+ channels electronically (decades ago)... One of three could be done with commensurate complexity increase.

Relays would be easier to design.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Rob Flinn

Re: Multitrack changeover box
« Reply #2 on: June 14, 2020, 12:22:26 PM »
I use three of these boxes

https://www.ebay.co.uk/itm/Kentek-DB25-2-Way-Manual-Data-Switch-Box-RS-232-Parallel-Serial-D-Sub-25-Pin/223973147827?hash=item3425d704b3:g:7q0AAOSw~ttekEE7

They do a version I think that switches 4 ways.    They are normally only a few pounds to buy.
regards Rob

jeffbro

Re: Multitrack changeover box
« Reply #3 on: June 14, 2020, 01:17:09 PM »
Good idea, but I can only find 3 way switches in 1's, mostly used, on eBay. 

Oddly, 4 way switches still seem to be available in normal retail channels.  That's more capability than required but would solve the problem at  minimal cost.

Rob, I assume you are satisfied with signal integrity and crosstalk levels?

JB

squarewave

Re: Multitrack changeover box
« Reply #4 on: June 14, 2020, 02:56:46 PM »
Just spit-balling here but dp3t slide switches are (can be) inexpensive and individual channels could be switched to different machines. You could also go so far as to use dp4t or more but they start to get more expensive. Although they're usually pretty small so you have to feel them switching and they're not designed for long term use. But if you need a pro solution then use relays. Analog gates would probably work just fine but I would be little weary about source / load impedances without buffering. If the source impedance was like 600R, that's not completely insignificant depending on the Ron of the gates.

Rob Flinn

Re: Multitrack changeover box
« Reply #5 on: June 14, 2020, 02:58:17 PM »
Good idea, but I can only find 3 way switches in 1's, mostly used, on eBay. 

Oddly, 4 way switches still seem to be available in normal retail channels.  That's more capability than required but would solve the problem at  minimal cost.

Rob, I assume you are satisfied with signal integrity and crosstalk levels?

JB

I haven't personally had a problem with them. The internal wires are obviously not screened pairs. However they are computer data switches so are designed to be used with high speed digital signals.  The price that I paid for them on ebay compared to what a 25 pole 2 throw switch would cost new makes them a good low cost solution.

Another way I have seen this done is with a 96 way edac patchbay, but that would be a lot more expensive.
regards Rob

ruffrecords

Re: Multitrack changeover box
« Reply #6 on: June 14, 2020, 05:06:09 PM »
Back in the 70s at Neve we used to do this kind of think with what I think are called T-bar relays. Huge Christmas tree like things that can switch 24 balanced lines with one relay. Don't know if they exist any more.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Youngwhisk

Re: Multitrack changeover box
« Reply #7 on: June 14, 2020, 05:43:50 PM »

PRR

Re: Multitrack changeover box
« Reply #8 on: June 14, 2020, 07:38:11 PM »
Or https://www.surplussales.com/Relays/tbar.html

However at these prices you can hire a guy/gal to sit behind the rack and manually change-over.

If you are rich: https://www.newark.com/c/switches-relays/relays?brand=t-bar-olympic-controls

squarewave

Re: Multitrack changeover box
« Reply #9 on: June 15, 2020, 12:32:03 AM »
Hmm, I wonder if you could make something like that using 3 layers of PCB, some mill-max spring contacts and a solenoid.


ruffrecords

Re: Multitrack changeover box
« Reply #10 on: June 15, 2020, 02:53:41 AM »
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

pvision

Re: Multitrack changeover box
« Reply #11 on: June 15, 2020, 07:05:55 AM »
Isn't the answer DL plugs?

nielsk

Re: Multitrack changeover box
« Reply #12 on: June 15, 2020, 09:21:23 AM »
What is the purpose?
If it is live recording generally the inputs are fed from a multed source, and a suitable console is either equipped with A/B/C inputs or enough channels
If it is just selecting machines in a studio, there is a big advantage with a MTR patch system (you can dub as well as select machines)
We always used DLs to patch 24 channels at a time, but as everything uses db-25 connectors these days, db patch panels and cables are cheaply available and offer more flexibility.

jeffbro

Re: Multitrack changeover box
« Reply #13 on: June 15, 2020, 04:06:51 PM »
Wow, those T-Bar relays are something, although it makes sense that such things exist.

I'm surprised there has been so little discussion here of electronic switching solutions.  After all, many high quality consoles use FET's and similar circuits to switch audio all the time.

Nonetheless, I'm thinking that, in the end, manual changeover with DLs, EDACs, or D-Subs might be the way to go since whatever solution is chosen, multichannel connectors will necessary to get the signals into and out of the switch box, and with manual changeover no more expensive parts are required.

JB

mrclunk

Re: Multitrack changeover box
« Reply #14 on: June 22, 2020, 06:20:50 AM »
I've ended up using 8 way relay PCBs from JLM audio. I designed my own but as i have zero time for errors i just grabbed the JML PCB.
Very reasonably priced and have been tested!


fazer

Re: Multitrack changeover box
« Reply #15 on: June 25, 2020, 10:51:42 AM »
Why do you need to patch input.  I would just parallel feed inputs from channels to the tape and the DAW.  If your light on channels you decide to playback the tape thru channels or the DAW for traditional mixing.   Seem like Robs DB25 computer switch works fine for this.   Tape has crosstalk that might exceed that of the switch box.   But for me it’s usually one or the other depending on clients need.

Whoops

Re: Multitrack changeover box
« Reply #16 on: June 26, 2020, 09:43:40 PM »
Rob, I assume you are satisfied with signal integrity and crosstalk levels?

Opened one of these boxes one day, pretty cheap switch and bad soldering.
It worked fine when it worked...


Rob Flinn

Re: Multitrack changeover box
« Reply #17 on: June 27, 2020, 09:37:49 AM »
Opened one of these boxes one day, pretty cheap switch and bad soldering.
It worked fine when it worked...



What's so wrong with the switch in your opinion ?  With regards to the soldering it's probably no worse that in a lot of commercially bought Dsub audio cables .........     Lots of people around here use that brand switches on here for attenuators,  frequencies selectors etc.   If you're worrried replace is with an ELNA & watch the price x20.
regards Rob

Whoops

Re: Multitrack changeover box
« Reply #18 on: June 27, 2020, 12:40:39 PM »
What's so wrong with the switch in your opinion ?
Nothing wrong with the switch in my opinion, I didnt say there was something wrong with it

With regards to the soldering it's probably no worse that in a lot of commercially bought Dsub audio cables .........     

I dont know how the soldering is in the Dsub audio cables you refer to, but in these boxes the soldering job is the "fast chinese soldering job" if you know what I mean

If you're worrried replace is with an ELNA & watch the price x20.
I'm not worried at all, I dont use these boxes nowadays,
I actually had 2 almost new ones that I would gladly offer to any of you but I sent them to the skip 1 year ago.

Rob Flinn

Re: Multitrack changeover box
« Reply #19 on: June 27, 2020, 03:20:50 PM »
[quote author=Whoops link=topic=75362.msg957259#msg957259 date=1593276039
I dont know how the soldering is in the Dsub audio cables you refer to, but in these boxes the soldering job is the "fast chinese soldering job" if you know what I mean
[/quote]

I do know what you mean.  I don't solder Dsubs I crimp them, it's a far better connection.
regards Rob


 

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