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Passive 5.1 volume controllers

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Passive 5.1 volume controllers

Postby The Red Bladder » Mon Feb 29, 2016 5:05 pm

Now that SM-Audio no longer makes their passive 5.1 volume controller, following their acquisition by Harmann, am I right in thinking that nobody sells such a thing anymore?
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Re: Passive 5.1 volume controllers

Postby Hugh Robjohns » Mon Feb 29, 2016 5:26 pm

I can't think of any entirely passive 5.1 controllers. The nearest is probably the Coleman Audio SR5.1 MkII, which has active input buffers and output drivers, but a passive signal path between them!

http://www.colemanaudio.com/cntrl.htm#m3lnk

The level control is via a rotary switched attenuator which guarantees very accurate channel tracking at all levels, with attenuating trimmers to fine tune the balance across all six channels, if required. It also has individual input (not output!) mutes, and active fold-downs to mono and stereo with further fine trimmers.

I've used one and it sounds very good and works well... with the possible exception that the mono mode is arranged as phantom across LR rather than all to C. Mr Coleman always manages to find some frustrating way of stuffing up an otherwise brilliant product! ;)

However, I suspect you want passive for cheapness... and the Coleman lists at £850 ex VAT from KMR.

https://www.kmraudio.com/coleman-sr5-1-mkii.php#productTabs2

The vast majority of surround controllers are active, of course, because that is fundamentally the right way to do it...

The SPL SMC 2489 is probably the cheapest and best made alternative at around £550. Switching on inputs between two 5.1 or two stereo sources, and between 5.1 or stereo monitors. They have changed the design (and model number) slightly since I reviewed it, but it's essentially the same thing. I note they still have a bonkers channel assignment on the D-type connectors, but that is manageable in most situations without too much trouble.

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Re: Passive 5.1 volume controllers

Postby Mixedup » Mon Feb 29, 2016 5:44 pm

Did you want passive simply due to cost, or due to an aversion to active electronics?

The SPL Volume 8 is not passive, but it's not badly priced. Ditto the SPL2489.

Though if the passive side of things is really important and you're not into DIY, I'm sure you could get a man in a shed (Orchid Electronics?) to knock up a passive one for cash or favours...
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Re: Passive 5.1 volume controllers

Postby The Red Bladder » Mon Feb 29, 2016 5:57 pm

Well, I was hoping you would chip in Hugh, as you are the guy who would know if there was such an animal.

No, nothing to do with price! Obviously the right way to do it is actively and then one simple control can work as many channels as you want and of course balanced. A balanced passive controller would have to either be done with stepped attenuation and then you have to faff about with trimmers, as Mr Coleman has done, or you go unbalanced.

Given that you are dealing with short cable runs and voltages high enough to withstand the slings and arrows of being unbalanced, a passive box should give no real disadvantage.

It just struck me that the home studio boys and those sound designers who want to take their work home with them, might appreciate such a product, if one made it cheaply enough, but used solid components and stripped it of pointless options that they have anyway in their DAWs, such as mono summing and channel solo.
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Re: Passive 5.1 volume controllers

Postby Hugh Robjohns » Mon Feb 29, 2016 6:04 pm

The Red Bladder wrote:It just struck me that the home studio boys and those sound designers who want to take their work home with them, might appreciate such a product, if one made it cheaply enough, but used solid components and stripped it of pointless options that they have anyway in their DAWs, such as mono summing and channel solo.

That was the market the SM Pro was going for... and the fact that it is no longer available suggests the market was too small to support it (since it had no real competition).

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Re: Passive 5.1 volume controllers

Postby The Red Bladder » Mon Feb 29, 2016 6:12 pm

Hugh Robjohns wrote:... and the fact that it is no longer available suggests the market was too small to support it (since it had no real competition).


It had no competition because getting good 6-gang pots with the right values was difficult. I believe it worked as well with stepped attenuation and I do know that loads of them broke, as they were made too cheaply. I suspect that Harman binned it as it caused too many problems and possibly competed with other products they own.

As I said, if you strip away all the unnecessary guff, you can bring the price tag right down to a level where the RRP could be below £20.
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Re: Passive 5.1 volume controllers

Postby Mixedup » Mon Feb 29, 2016 6:14 pm

Hugh Robjohns wrote:the fact that it is no longer available suggests the market was too small to support it (since it had no real competition).

Possibly... although it could equally mean that Harmann preferred to fry other fish, having acquired SM Pro largely for their console. Admittedly, they've since brought out rebadged versions of some SM Pro stuff in their other lines (eg Dbx), and this isn't amongst them.
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Re: Passive 5.1 volume controllers

Postby Hugh Robjohns » Mon Feb 29, 2016 6:14 pm

The Red Bladder wrote:As I said, if you strip away all the unnecessary guff, you can bring the price tag right down to a level where the RRP could be below £20.

Excellent. Go for it. I'll place my order with you for one right now. ;) You could even make it £20 plus VAT if you like...

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Re: Passive 5.1 volume controllers

Postby The Red Bladder » Mon Feb 29, 2016 6:50 pm

Unfortunately, a minimum production run would be 1,000 pieces, as the pots would have to be built to order.

I am pricing stuff up as we speak!
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Re: Passive 5.1 volume controllers

Postby The Elf » Mon Feb 29, 2016 7:52 pm

Give me balanced in and out and I'll place my order too!
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Re: Passive 5.1 volume controllers

Postby The Red Bladder » Tue Mar 01, 2016 11:33 am

The Elf wrote:Give me balanced in and out and I'll place my order too!

Unless you go for all that faffing about that Coleman does, with silly stepped attenuation, doofus trim pots that would have to be set up just about every time you use the damn thing, balanced passive is almost impossible.

If you want a pukka volume control, but passive, the only other way would be to have transformers going in and transformers coming out - that's 12 audio transformers at a wholesale price of £35 each, making the RRP at least £1,000 if built to order and if I use conventional calculations for mass production, about £4,000 (or use cheap Chinese transformers that drop down 6dB at 10kHz and cost just $1 each!)

Balanced active means a more complex CE certification process, power supplies, control LEDs, larger and more robust housing, more expensive plugs/sockets, op-amps and line drivers, etc., etc. If you want balanced, £500 for that SPL box is about right!
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Re: Passive 5.1 volume controllers

Postby Hugh Robjohns » Tue Mar 01, 2016 12:17 pm

The Red Bladder wrote:Unless you go for all that faffing about that Coleman does, with silly stepped attenuation, doofus trim pots that would have to be set up just about every time you use the damn thing, balanced passive is almost impossible.

A passive balanced surround controller using a twelve-level pot is clearly impractical. Not only would the the tracking accuracy be non-existent, but the cost of such a unique control element would be prohibitive.

However, it is possible with a multi-layer switch and a resistive attenuator chain, which is why Coleman takes that approach. And it would be possible with a simpler switch and relay-switched attenuator chains... but then you're into power supplies again upping the cost. And if you have a power supply you might as well go active and do all the level control with unbalanced circuitry between balanced input buffers and output drivers.

I can assure you that the level trims on the Coleman don't need resetting every session, so that's one concern ruled out. ;)

I'd still be utterly astonished if you can build an unbalanced passive surround controller with decent tracking between channels for anything like £20. -- but I've put a note on the side under a pot just in case... ;)

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Re: Passive 5.1 volume controllers

Postby Mixedup » Tue Mar 01, 2016 12:40 pm

I see the old M-Patch and so on are out under the JBL moniker now. I wonder if the SM Pro surround one will follow...

I may be missing something but... if it's all about doing it on the cheap, and you're happy to leave all the frills like mono buttons and so on to the DAW... why not leave the surround volume control to the DAW too... and just map a single rotary encoder to it. The most you'd need in the analogue domain is a panic-mute button. That's got to be cheaper even than what you're proposing here, no?
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Re: Passive 5.1 volume controllers

Postby The Red Bladder » Tue Mar 01, 2016 2:28 pm

Hugh Robjohns wrote:I'd still be utterly astonished if you can build an unbalanced passive surround controller with decent tracking between channels for anything like £20. -- but I've put a note on the side under a pot just in case...

I make no promises! At that price level, it would have to be six-in, six-out RCA/Chinch connectors only.

Mixedup wrote:why not leave the surround volume control to the DAW too... and just map a single rotary encoder to it.

It's not just about DAWs. There are other applications, such as between a DVD/BR player and active speakers, or indeed any other situation where you want to control a 5.1 system with a single knob.

In every post production room I've been in, they have something like that SPL box and there are literally dozens and dozens of active 5.1 and 7.1 controllers and even some Atmos + everything else controllers from folks like Genelec, but these can only be used with their newer digital speakers.

There are good and practical reasons to have a volume control OUTSIDE of the DAW, for example, because we want to alter the volume without altering the settings in the DAW as we intend to store and possibly render at that particular volume.

With the so-called 'democratisation' of the music and video markets, there has to be a market slot for a cheap solution to an old problem.

Once we have solved the problem of a decent 6-gang pot, we can start to think about adding source selection switches, to flip between DAW, BR player, Freeview decoder, TV set, etc. and add off-the-shelf D-A decoders for fibre and HDMI.
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Re: Passive 5.1 volume controllers

Postby Hugh Robjohns » Tue Mar 01, 2016 2:38 pm

The Red Bladder wrote:At that price level, it would have to be six-in, six-out RCA/Chinch connectors only.

Sure... but is that really a practical solution. You're talking about using it with active speakers, so you're instantly opening a huge can of ground-loop worms by running unbalanced audio with common grounds everywhere to (presumably) class-1 grounded active speakers.

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