Passive 5.1 volume controllers

[The Red Bladder]

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?

[Hugh Robjohns]

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.

H

[Mixedup]

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...

[The Red Bladder]

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.

[Hugh Robjohns]

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).

H

[The Red Bladder]

... 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.

[Mixedup]

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.

[Hugh Robjohns]

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...

H

[The Red Bladder]

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!

[The Elf]

Give me balanced in and out and I'll place my order too!

[The Red Bladder]

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!
_________________________________________

This has nothing to do with anything, but I am watching a red squirrel have a go at the bird-nuts in one of those wire basket things right now. He's been there for the past 20 minutes. He (or she?) is such a beautiful and small, delicate creature. The sun is belting down and the whole scene is just fantastic.

His cheeks stuffed with peanuts, he has now legged it for the woods in front of the studio.

[Hugh Robjohns]

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...

H

[Mixedup]

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?

[The Red Bladder]

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.

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.

[Hugh Robjohns]

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.

H

[The Red Bladder]

Just another one of the many problems that will need to be solved!

I am painfully aware of this and it is all part of the prototyping process - assuming that I can get 6-gang pots at a price that makes sense. A possible supplier has been found, prices are not yet set.

[Mixedup]

Hmmm... I suspect the market is dmaller than you think. DVD players have volume controls. Interfaces have volume controls/software separate from the DAW. Cubendo offers a dedicated control room facility to avoid the problem you describe... And it seems you're talking about a sector where even if spending isn't lavish a basic active system could do the job perfectly well within a reasonable budget. Don't get me wrong, I wish you luck but I think it's a risk if you need to a big production run to hit a desired price point.

[The Elf]

Without balanced connections I'm no better off than I am now, feeding my 5.1 outputs to a consumer-grade AV amp and using passive speakers.

[The Red Bladder]

I wrote to a manufacturer of potentiometers in the Guangdong Province of China, that I want one hundred 6-gang, 10k, log pots.

They have now queried why I want a six-speed, wooden saucepan!

[The Korff]

FYI, SM Pro's monitor-controller range has now been Harmanised, and they've all got new JBL badges on them:

LINK

...but so far no sign of the surround-sound one... yet...

[tomekpener]

is this controller passive?
I have just received this controller today
and struggles with determining who's the manufacturer, and what
are its specifications.

for any help, I am very grateful.
regards

[Hugh Robjohns]

I've had to edit your links to make the images appear. You need to paste in the direct image BB codes which are provided by your image host website below the uploaded images.

is this controller passive?

A passive controller doesn't usually need power. I suspect this is an active device, partly because it appears to have a power LED on the front panel, and partly because it obviously takes unbalanced inputs and delivers balanced outputs -- which is most commonly achieved with active circuitry.

I have just received this controller today and struggles with determining who's the manufacturer, and what are its specifications.

I don't recognise the manufacturer logo or product name I'm afraid. Hopefully someone else will recognise it.

But it's not really a 'monitor controller' in the usual sense of the term since none of the usual controller controls are provided (overall volume, dim, channel solo/mutes etc). Instead, this appears to be a simple multi-channel precision trimmer which is presumably intended to help adjust the relative volumes of speakers in a 5.1 array.

Since it doesnt have rack ears I would assume it was designed for use in a hifi system, perhaps taking the outputs from a multichannel disc player to feed to professional speakers.

[Drew Stephenson]

Not even the typo in the model name triggers a search result.

[Kwackman]

Ignore- Blind Drew got there before me.
Any passing mod - feel free to delete this.