DMX Polarity?

[Robertdazzler]

I am about to do a one off job and am considering using my Strand MX DMX desk with the Zero 88 DMX dimmer system in stalled in a school but am uncertain about DMX line polarities. I have an idea from the past that Strand is at odds with Zero 88 or does the latter not care. Any advice will be welcome. if essential I can easily make a" line swap" adaptor.

[Andrew C]

DMX is DMX.

 

You may be confusing old Strand kit that used -10V as an analogue control voltage when Zero (and the rest of the universe) used +10.

[pscandrett]

Um, reversed polarity is a thing on DMX, surely? If pins 2 and 3 are swapped, most devices won't recognise the data and indeed some older units and fixtures were pins 2+3-, I think, rather than the conventional 2-3+. It's more rare now I think, but @Robertdazzler that's all you need to do in a swap adaptor if you want to make one up to be prepared.

Edited November 15, 2021 by pscandrett

[timsabre]

Reverse DMX polarity is a thing but (barring weird installation errors) will not be a problem between Strand and Zero88 products. Random chinese disco lighting, maybe.

Also (going way back) Strand had a control system called D54 which used 3 pin XLR. I have once nearly been caught out by an old installation which I thought was DMX but on further investigation turned out to be D54. Definitely way before the days of Strand MX though.

 

Edited November 15, 2021 by timsabre

[DrV]

The MX does have a D54 output as well as DMX and AMX. AMX is neat to look at on a scope - you get a sync pulse followed by a load of variable height pulses which correspond to the channel levels. If you move the faders up and down you can see the peaks go up and down in sympathy. Completely useless info, I know, but it looks pretty!

[Don Allen]

The main area or reverse polarity or more correctly reverse phase was early Martin disco lighting and movers. I still have a phase reversal lead in my tool kit but have not needed it for a long time. If you have a look at the back of small Showtec lighting desks they have a DMX polarity reversal switch which causes problems when people change it when trying to troubleshoot a situation.

[sunray]

27 minutes ago, Don Allen said:

If you have a look at the back of small Showtec lighting desks they have a DMX polarity reversal switch which causes problems when people change it when trying to troubleshoot a situation.

Been there, I did a run of 4 days panto. The whole of the control position was on a single 13A socket so the power down/up routine was switch off socket/switch on socket, push power buttons on CD & MD machines. Lighting, intercom and amplifier was on a dedicated consumer unit so main switch off/on.

I couldn't do 3rd show, when I turned up to do 4th everything had been turned off with it's switch (That's every device, consumer unit main switch and mcb's, each dimmer pack socket[had to get a ladder out for that] etc). I had everything going except the lighting and only tried the polarity switch with an almost full house.

Edited November 15, 2021 by sunray

[Kazeja]

I seem to have a fuzzy recollection that back at the tail end of the last millenium, there may have been some compatibility issues between Strand DMX and Z88 betapacks using high(ish) DMX addresses, but believe that to have been resolved.  I have used my MX into BPs without problems.  OK, so the BPs were addressed below 50 but I'm sure others would have commented by now if there were any outstanding compatibility issues.

K.

[Stuart91]

On 11/15/2021 at 12:54 PM, timsabre said:

Also (going way back) Strand had a control system called D54 which used 3 pin XLR. I have once nearly been caught out by an old installation which I thought was DMX but on further investigation turned out to be D54. Definitely way before the days of Strand MX though.

The Strand MX has a D54 output on a 3-pin XLR. It seems to be the primary/default interface, as in certain circumstances the desk can reset itself and output is via D54 rather than DMX. It's changed via a menu setting, but had me panicking at one show back in the day. 

Since I haven't come across a D54 installation in the wild, I ended up repurposing the 3-pin XLR to DMX by adding jumpers across from the 5-pin socket. Did the same on our Act 6 dimmer packs. 

[tonytech]

On 11/15/2021 at 2:07 PM, DrV said:

The MX does have a D54 output as well as DMX and AMX. AMX is neat to look at on a scope - you get a sync pulse followed by a load of variable height pulses which correspond to the channel levels. If you move the faders up and down you can see the peaks go up and down in sympathy. Completely useless info, I know, but it looks pretty!

Oh nice. I showed some of our stage crew DMX signals on a Picoscope (computer oscilloscope) I thought it was interesting, they not so much.

The trace showed a bit of noise (mostly due to my dodgy wiring), but I explained how the noise could cause weird effects and why using DMX to trigger pyro requires careful consideration.

[J Pearce]

My electronics tutor at 6th form used the college's MX48 D54 output to demonstrate Time Division Multiplexing. (He also used the college's PA horns in a class once because he thought we all needed help hearing him)

There's still a few venues running D54 behind a DMX converter, to run old strand dimmers.

[paulears]

Yep, that's us. 72 channels down D54 still running fine. D54 could catch you out when you used miswired mic cables - that was always a head scratcher!

[TomHoward]

On 11/15/2021 at 2:35 PM, sunray said:

I couldn't do 3rd show, when I turned up to do 4th everything had been turned off with it's switch (That's every device, consumer unit main switch and mcb's, each dimmer pack socket[had to get a ladder out for that] etc).

That has just reminded me of a lockup security guy we used to have who was obsessed with turning everything off. We have several racks with power sequencers at the bottom, he would start at the top and turn off each piece of equipment individually, and at the end switch the power sequencer to shut off supply to all the items.

Restarting it you used to get all the 'clunks' of contractors with absolutely nothing happening.

[sunray]

On 11/17/2021 at 11:21 PM, TomHoward said:

That has just reminded me of a lockup security guy we used to have who was obsessed with turning everything off. We have several racks with power sequencers at the bottom, he would start at the top and turn off each piece of equipment individually, and at the end switch the power sequencer to shut off supply to all the items.

Restarting it you used to get all the 'clunks' of contractors with absolutely nothing happening.

We used to find that in night clubs...      Oh except the amp room was supposed to be locked to prevent tampering.

[Robertdazzler]

Thanks all for the confident answers that all should be well. It's really raised some serious nostalgia and anecdotes.