Showtec Demux with Permus dimmers

[Biskit]

Hi All,

I've searched for similar topics and I know this area has been covered before - but not one specific point...

I've been asked to look at an existing school install which is a 24 channel Strand Permus rack with analogue control.  They want to have DMX control.  Simple solution - the Showtec Multiexchanger demux and an appropriate break-out lead from the 25-pin D connector to 4 x DIN.  I know it works, as I've done it as a temporary basis in the past.

However my question is: how would people suggest powering the demux? The two options essentially are - 1. power it from the dimmer rack, so that when powered up, it just comes on and is ready to go, or 2. power it separately, which means the power-on can be sequenced (demux first) HOWEVER in reality I know the school staff won't do this, and it just adds another thing to go wrong which means I'll get a phone call saying it's not working.  I'm keen to go for option 1, however I've noticed in the past these demuxes can sometimes spit out a 'blip' of all channels @100% when powering up, and I've known this cause nuisance tripping of dimmer racks in the past.  Has anyone else experienced this, or am I likely to get away with it?  I think the rack in question is actually on a distribution circuit with fuse protection, rather than breakers, however I'd be interested to know what experience others have had with this kind of setup.

As ever with schools... simplicity is key.  One of the teachers actually told me to specify 'prison grade equipment' haha

Thanks in advance!

Edited November 21, 2022 by Biskit

[sunray]

4 hours ago, Biskit said:

Hi All,

I've searched for similar topics and I know this area has been covered before - but not one specific point...

I've been asked to look at an existing school install which is a 24 channel Strand Permus rack with analogue control.  They want to have DMX control.  Simple solution - the Showtec Multiexchanger demux and an appropriate break-out lead from the 25-pin D connector to 4 x DIN.  I know it works, as I've done it as a temporary basis in the past.

However my question is: how would people suggest powering the demux? The two options essentially are - 1. power it from the dimmer rack, so that when powered up, it just comes on and is ready to go, or 2. power it separately, which means the power-on can be sequenced (demux first) HOWEVER in reality I know the school staff won't do this, and it just adds another thing to go wrong which means I'll get a phone call saying it's not working.  I'm keen to go for option 1, however I've noticed in the past these demuxes can sometimes spit out a 'blip' of all channels @100% when powering up, and I've known this cause nuisance tripping of dimmer racks in the past.  Has anyone else experienced this, or am I likely to get away with it?  I think the rack in question is actually on a distribution circuit with fuse protection, rather than breakers, however I'd be interested to know what experience others have had with this kind of setup.

Yes I've been there, the school had 4x 6 channel analogue dimmers and insisted they wanted to keep them in service, first thing was to repair the selection of faults then fit 2 12channel demuxes, as mentioned they outputted 100% during powerup and yes they did trip the 50A MCB. My horrible solution was 6x 4pole relays which operated at power up and off again after a couple of seconds to interupt the control lines. Not pretty but it was a solution.

4 hours ago, Biskit said:

 One of the teachers actually told me to specify 'prison grade equipment' haha

That is the most important part of supplying kit to schools😉

[richard_cooper]

On 11/21/2022 at 8:38 PM, Biskit said:

I'm keen to go for option 1, however I've noticed in the past these demuxes can sometimes spit out a 'blip' of all channels @100% when powering up, and I've known this cause nuisance tripping of dimmer racks in the past.  Has anyone else experienced this, or am I likely to get away with it?  I think the rack in question is actually on a distribution circuit with fuse protection, rather than breakers, however I'd be interested to know what experience others have had with this kind of setup.

I did it once, many (~17?) years ago, and seem to remember that issue. Yes I remember an issue with the Multiexchanger in -10v mode where it would snap every channel to full briefly on start up. The natural flow of the venue was to power the dimmers on before the desk. This may be a non issue in this specific case, we had the issue that the supply breakers to the dimmers could not take the inrush of basically every channel fully loaded (among all sorts of other issues that we couldn't get sorted!). We had to ensure the Multiexchanger was powered up before the dimmers. I think we tried having them power up together and seem to remember that reducing this happening to about a 50% random occurrence. This was with 2x24 channel Permus racks.

That was a long time ago, and I think it was the Botex version of the Multiexchanger, so it's possible that that issue has been fixed by now, but doubt it's changed.

[sandall]

If you're looking for "prison grade" why not go for something like Zero88, rather than cheap Chinese.

 

[ianknight]

9 hours ago, sandall said:

If you're looking for "prison grade" why not go for something like Zero88, rather than cheap Chinese.

 

Except Zero88 no longer offer a demux 😞

It might be possible to find Demux 24's on eBay as used/previously enjoyed or their might be a dealer with one left on the shelf as 'new old stock' but you won't get one 'new out of the box' these days 😞

(Don't be tempted to buy a used Demux 48 either unless it's been well looked after - they don't age well if the battery has leaked at any point 😞)

[sandall]

2 hours ago, ianknight said:

Except Zero88 no longer offer a demux 😞

That's rather sad. They were still listed last time I looked (obviously longer ago than I though🙁).

[ianknight]

13 minutes ago, sandall said:

That's rather sad. They were still listed last time I looked (obviously longer ago than I though🙁).

It is sad -  noticed it dropping off the price list about 18 months ago - now a legacy product 😞

Some dealers may have odd ones in stock or hire stock - whether they're happy to sell off though...

Luckily I have 3 (don't ask me how!) in my loan/slave stock 🙂

[alistermorton]

With the cheap and  easy availability of microcontrollers (once supply chains stabilise again) and the relative ease of both DMX interfacing and analogue output, it would seem there might be a cottage industry opportunity for someone.

[J Pearce]

There are a few boards available for upgrading 6ch dimmers. I’m not aware of a larger board for 24/48/72 ways.

[sunray]

2 hours ago, alistermorton said:

With the cheap and  easy availability of microcontrollers (once supply chains stabilise again) and the relative ease of both DMX interfacing and analogue output, it would seem there might be a cottage industry opportunity for someone.

Indeed, I know of 2 π based demuxes, both homebrewed as an education project and installed in said establishments, one school, one college.
 

[graemeftv]

We now manufacture a demux and can easily adapt, make negative out. Change the code for delay startup etc. get to powerup from the low voltage supply from the dimmers etc.just ask

https://ultralightsound.co.uk/product/24-channel-DMX-to-analog-demux-convert-dimmers-to-DMX-control/

[Biskit]

On 12/1/2022 at 2:23 PM, graemeftv said:

We now manufacture a demux and can easily adapt, make negative out. Change the code for delay startup etc. get to powerup from the low voltage supply from the dimmers etc.just ask

https://ultralightsound.co.uk/product/24-channel-DMX-to-analog-demux-convert-dimmers-to-DMX-control/

That sounds interesting - are you saying it would be possible to have one of these powered directly from an existing Strand Permus rack (either from the mains feed, or at a lower voltage)?  And that it wouldn't send a surge on start-up, meaning it could safely and reliably be powered up simultaneously with the dimmer rack?  That sounds like a good solution to my problem here.