Happy Frog, Sad Pearl?!?

[Stuart91]

Interesting problem reared its head at Saturday's gig.

 

Our crew had gone in and rigged all the lighting for the gig the night before. The rig consisted of a bunch of generics (run from 2 x Beta packs and 2 x Strand ACT6) and four Miniscan HPEs. We used our own Fat Frog desk to run the rig for testing and focussing and it all ran perfectly - no problems or glitches.

 

The following day, the band's LD arrived, bringing his Pearl with him. I think it's a 2008 model (said so on the surface) although I'm not too familiar with Pearls. First up, he had real trouble getting it to talk to the dimmers. We had two DMX lines running between desk and dimmer land. Neither of them seemed to want to work, from any of the Pearl's outputs. He wound up sending the signal down a line on our audio multi and that seemed to work OK.

 

Then we tried to get the Miniscans to work. The four scans were connected in a chain on the truss. For some reason

the last two in the chain worked fine, but he couldn't get any response out of the first two, no matter what we tried. (Cycling the power, changing addresses, etc.)

 

Let me underline for extra emphasis - all the lights worked perfectly on the Frog, and we only had problems when the Pearl was connected. At several points I swapped back over onto the Frog, the lights would work, then plug back into the Pearl and they don't. In the end he ran generics from his Pearl, and the scans from the Frog.

 

Things that confuse me about this:

 

Why would the Pearl have problems with the standard DMX cables we were using? (Van Damme 2 pair cable, proper XLRs etc.) Especially since it ran happily down a mic cable? Something to do with the Pearl putting multiple universes out on the 5 pin XLR?

 

How come the two scans wouldn't work, when the other two did? I'm fairly certain we can rule out cable issues, since it was the first two scans on the chain that the Pearl couldn't see, the latter two ran fine. Even setting the uncooperative scans to the same addresses as the working ones didn't give any improvement.

 

I'm pretty sure the Pearl is working correctly (i.e. not broken) - it was apparently running 12 heads the night before without any problems. I'm not suspecting operator error either - he knew his desk and had no problems getting things addressed etc.

 

 

Have I uncovered a strange fault with Pearls? Or is there some flaw in my DMX chain that trips a Pearl up, but Frogs ignore it?

[niclights]

I'm not sure what might have been wrong but my only guess is it is related to the split universes. This has been scrapped in the Expert.

 

What happens to your DMX at stage end? Does it go through any splitters/converters etc?

[quinch]

From what I remember the PEARL send lines 3 and 4 down pins 4 and 5 of its DMX outputs. This only becomes a problem when manufacturers use these last two pins on their fixtures for some non-standard purpose. CP seem to be one of these...

 

As you correctly pointed out, the problem goes away when using an audio multi, because you are filtering out the conflicting lines. Its not really a fault with the Pearl, or the miniscans, but two manufacturers taking advantage of a hole in the DMX spec in different, incompatible ways. The safest thing to do is to make a Y split for the Pearl and always use it, even if you only want the first two lines.

[Stuart91]

What happens to your DMX at stage end? Does it go through any splitters/converters etc?

 

Nope, nothing fancy. Just a straightforward chain from device to device.

 

It might be worth mentioning that, whilst the main runs from FOH to stage were two pair, every other bit of cable on the rig was single pair. (The two mains runs are loomed together with the audio multi and an AC run, and I figured 2 pair would be more future proof)

[johnhuson]

Only thing I can think of is that the two outputs on the Fat Frog are the same universe of DMX, just two optically isolated outputs of the same data stream. Where as the outputs on a Pearl are separate universes so maybe a patching issue?

[danjshelton]

One other thing that it could have been (well the dimmer part of the problem) is the speed of the DMX Signal transmission. I've had problems before with Pearls talking to Alphapacks, and it is because the DMX Transmission rate is too high.

 

To solve this simply go into the user settings (Avo + B off top of head) and change the DMX Rate to a lower rate. I'm not sure of the transmission speed of the Frog but I know that Pearl's default speed is above specfication.

 

Cheers

 

Dan

[Stuart91]

One other thing that it could have been (well the dimmer part of the problem) is the speed of the DMX Signal transmission.

 

I'm not sure of the transmission speed of the Frog but I know that Pearl's default speed is above specfication.

 

Interesting - this was something that had crossed my mind briefly, but I couldn't word it. I wonder if there's a chance that, for example, two of the scans that were used were slightly older and wouldn't cope with the Pearl's speed, but the other two would?

[niall]

Hey,

 

I've used the miniscans in question (with the same band/multi, different venue) on a Pearl 2004 and they ran fine. My first idea as to why they didnt work would be that the wrong personality files were used, so there could be some discrepencies in the DMX channels.

 

The only other thing is that I'm not sure that the Scans are self terminating (I know our CP stage 300s and Zoom 1200s arent) so some amount of bounce back could've been affecting the signal.

 

No idea what the dimmer problem could be, as I used the Pearl on two of your strand dimmers at the same gig and they worked fine!

[niclights]

I also run MiniHPE's and have no problems. I do have them terminated. Double-check the wiring of the FOH runs and the single pair runs that follow. So long as all are wired straight pin-pin, with the single pairs using pins 1,2 & 3 there should be no problem. The Pearl combines universes A&C on output 1 and B&D on output 2 where the earth is commoned on pin 1. Univ. A/B are on pins 2/3 and Univ. C/D on pins 4/5.