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Stereo to mono summing cable

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Stereo to mono summing cable

Postby Grappa » Wed Sep 06, 2017 6:04 pm

Hi,

I've ordered a Hosa monitor switch which has multiple L & R outputs but want to plumb my second pair of outputs into a single mixcube.

Can anyone point me to a wiring diagram of how to do this as I'm capable of making a cable but have no idea how it needs to be wired. The mixcube can take jack or XLR input so any guidance appreciated.

Thanks,

Simon
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Re: Stereo to mono summing cable

Postby ronmac » Wed Sep 06, 2017 7:09 pm

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Re: Stereo to mono summing cable

Postby Hugh Robjohns » Wed Sep 06, 2017 8:16 pm

Yep, the Rane diagrams work. Figs 3/4 for a balanced mono summer:

Balanced mono summer.jpg


The specific resistor values aren't particularly critical, so you can use 470 Ohms and 22K, values, for example, but the pairs of same values should be close-tolerance -- 1% matched or better.

If you want to get the resistors from Maplin, (1% tolerance, 0.6W, metal film) the order codes would be M470R (x4) and M22K (x1). Getting the resistors into XLR bodies is easy enough, but it will; be more of a challenge with TRS plugs. Just make sure you insulate the wire-resistor joints to avoid short circuits against each other or the plug casing!

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Re: Stereo to mono summing cable

Postby Grappa » Thu Sep 07, 2017 3:11 pm

Thanks very much for the response all.

Much appreciated.

Regards,

Simon
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Re: Stereo to mono summing cable

Postby Scramble » Thu Sep 07, 2017 4:18 pm

It's really hard to find commercial stereo-to-mono cables -- perhaps SOS could sell some for those people who aren't keen on making their own in their special cables section?
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Re: Stereo to mono summing cable

Postby Hugh Robjohns » Thu Sep 07, 2017 4:50 pm

You know, that's not a bad idea... I'll discuss with the bosses.

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Re: Stereo to mono summing cable

Postby Mike Stranks » Thu Sep 07, 2017 6:03 pm

Scramble wrote:It's really hard to find commercial stereo-to-mono cables -- perhaps SOS could sell some for those people who aren't keen on making their own in their special cables section?

You're right of course, but just to amplify ( :D ) it's not at all hard to find loads of 2-to-1 cables that are frequently advertised as 'converter cables' when they're just two plugs connected to one...

... and that's where the fun starts! We've discussed here on several occasions what can happen to some kit when you simply combine left and right in this way.

Far better to get a cable with inbuilt resistors or use a specific 2-to-1 combiner box - which is what I use.
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Re: Stereo to mono summing cable

Postby Sam Spoons » Thu Sep 07, 2017 7:10 pm

And, in the meantime, John at Orchid Electronics will make you one for a very modest price.
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Re: Stereo to mono summing cable

Postby ef37a » Fri Sep 08, 2017 6:53 am

Hi Grappa,
you might consider building the whole thing in a tin with XLR or TRS connectors?

This removes the 'fiddle factor' but also gives you the opportunity to fit a switch so you can do mono/stereo checks. While you are at it you could fit a second, polarity flip switch to check for out of 'phase' wiring.

Maplin do a range of small aluminium boxes.

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Re: Stereo to mono summing cable

Postby Hugh Robjohns » Fri Sep 08, 2017 11:54 am

Scramble wrote:It's really hard to find commercial stereo-to-mono cables -- perhaps SOS could sell some for those people who aren't keen on making their own in their special cables section?

Taking this idea a bit further, can I ask what you (and anyone else who might be interested) would be prepared to pay, please?

If we took this forward, it would be, like the Pseudo-Balanced cables, custom made for us exclusively and to very high standards in the UK. It would use a bespoke PCB inside the male output XLR (to accommodate the high-tolerance mix SMD resistors), and with options for either female XLR or TRS plugs for the two input channels. All Neutrik connectors, of course.

It would need to be an XLR for the output because a TRS plug wouldn't have sufficient room for the cables and resistors -- but I've done a quick check and I think every likely mono check speaker has an XLR input anyway. Obviously, different source devices have different output connections, so offering female XLR or TRS would be sensible and easy to do.

Share your thoughts please gents (and ladies if there are any lurking here)!

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Re: Stereo to mono summing cable

Postby blinddrew » Fri Sep 08, 2017 1:02 pm

Hmmm. Being a cheapskate, anything more than £15/£20 and I'd just make my own.
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Re: Stereo to mono summing cable

Postby Hugh Robjohns » Fri Sep 08, 2017 1:15 pm

It's what I feared. It would probably need to be around £30 or even £35 to be viable commercially.

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Re: Stereo to mono summing cable

Postby ManFromGlass » Fri Sep 08, 2017 1:52 pm

but if it came with a bonus SOS tuned duvet then I'll buy a few......
errr, I'll get my hat and be on my way.....
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Re: Stereo to mono summing cable

Postby Grappa » Fri Sep 08, 2017 5:17 pm

All,

Thanks for posting.

Looking at the wiring it's just too fiddly for a curmudgeon like me. I can hear the cursing now..

I may take the Maplin box route or reach out to Orchid depending on the cost.

Seems strange that these just don't seem to be commercially available.

Regards,

Simon
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Re: Stereo to mono summing cable

Postby Hugh Robjohns » Fri Sep 08, 2017 6:36 pm

The reality is that the market is extremely small, and to make this cable in a way that would be realistic for moderate production runs and be reliable enough and of a quality to warrant the SOS branding, it's actually quite involved. As a result, it would be relatively expensive to make with significant initial design and set-up costs, and that inevitably impacts further on the pricing. So no ordinary commercial cable-making company is going to incur the set-up overheads when the margin per cable is only a few quid...

However, as the SOS boss said to me today, "...sometimes it just looks good to be seen to
be offering useful things" -- which I think is a really refreshing attitude in this profit-driven world of ours. The R&D consultation is ongoing...

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