Strand Dimmer Identification

[boatman]

... and here's how much they cost in 1976!

 

[Ashley R]

It might be worth a post on the ALIA forum as well. There may be similar installations in other parts of Oz.

 

At my school they have got a similar set of dimmer to control the houselights but we have a small bank of 3 push buttons, One for up, one for down and a preset. And when I visited another small theater that was still decked out in Strand gear they had an identical dimming system.

 

Well at lest I think they are the same, ill have to have a look.

[oilyspark]

To control them from your desk you will simply need a demux to generate an ordinary Strand analogue 0 to -10V control output for each dimmer you want to control, and diode-add it to the output of the preset control card. This is basically a set of latches that is put into one of its three states (off, on, preset) by a contact closure at the pushbutton, sending respectively 0V, -10V or the preset level to the dimmer circuit itself. The latter is a regular trigger card as used in any *TM series dimmer, the silver (early) and green (later) units will have different trigger cards but the operation is identical.

 

It makes sense that you only have three separately controlled areas, since only the silver units are PTUs (evidenced by the knobs). My guess is that the green TU dimmers have been added later to increase the available load capacity, and slaved off two of the PTU control cards. You would be able to control all five dimmers separately from your demux if you diode them in separately. As an alternative you might be able to feed your demux outputs into the control cards in place of the preset pot wiper, and have the three pushbuttons on the wall function as off, on and demux-controlled.

 

FWIW with the few capacitors changed that usually need changing by now, these things will last almost forever.

 

Lucien

[David A]

as each dimmer is independent you can run it + or - control by simply switching over the 2 control wires on the dimmer module, I have lots of old Strand circuit diagrams as I used to install them.

[fliggygeek]

Any chance of the circuit diagrams mysteriosuly being posted of PM'd to me? I'm new to the whole demux setups and all that but am perfectly happy with digital circuitry and some analogue circuits. my other interest pount is with the analog control system, to my knowledge its a HTP system, meaning that if we had a fixed manual switch where the current one is, we could have non DMX control as well as the DMX control, bearing in mind that we make sure the manual override is in the OFF position before shows.

as each dimmer is independent you can run it + or - control by simply switching over the 2 control wires on the dimmer module, I have lots of old Strand circuit diagrams as I used to install them.

 

A concurrent post has been automatically merged from this point on.

 

I grabbed the STM maintenance manual off the strand archive, this is one page im interested in. It clearly shows the control inputs for the dimer, but from what I hear from you, ill be wanting to bypass the trigger cards for in order to use the full dimming capacity of the dimmers. Is this right?

http://imgur.com/qprAP.png

To control them from your desk you will simply need a demux to generate an ordinary Strand analogue 0 to -10V control output for each dimmer you want to control, and diode-add it to the output of the preset control card. This is basically a set of latches that is put into one of its three states (off, on, preset) by a contact closure at the pushbutton, sending respectively 0V, -10V or the preset level to the dimmer circuit itself. The latter is a regular trigger card as used in any *TM series dimmer, the silver (early) and green (later) units will have different trigger cards but the operation is identical.

 

It makes sense that you only have three separately controlled areas, since only the silver units are PTUs (evidenced by the knobs). My guess is that the green TU dimmers have been added later to increase the available load capacity, and slaved off two of the PTU control cards. You would be able to control all five dimmers separately from your demux if you diode them in separately. As an alternative you might be able to feed your demux outputs into the control cards in place of the preset pot wiper, and have the three pushbuttons on the wall function as off, on and demux-controlled.

 

FWIW with the few capacitors changed that usually need changing by now, these things will last almost forever.

 

Lucien

[Tomo]

It clearly shows the control inputs for the dimer, but from what I hear from you, ill be wanting to bypass the trigger cards for in order to use the full dimming capacity of the dimmers. Is this right?

No, you don't bypass the trigger card!

The trigger card is the bit that's doing the dimming calculation and firing the triac.

 

You land the demux output on the control input of the dimmer, with diodes to allow HTP merge with the Preset card if you want to retain the existing Preset function.

 

The two control lines D and E may be the relevant pins, though I'm not sure of that as it's been a while since I looked at analogue dimming systems and I've never worked on the Strand range so there may be a bit more upstream of that pair.

[David A]

on the dimmer module E is positive and D is negative, on early models E was connected to earth, later models used an isolated common but it was then called control earth, in effect contol common.

[fliggygeek]

It makes sense that you only have three separately controlled areas, since only the silver units are PTUs (evidenced by the knobs). My guess is that the green TU dimmers have been added later to increase the available load capacity, and slaved off two of the PTU control cards. You would be able to control all five dimmers separately from your demux if you diode them in separately. As an alternative you might be able to feed your demux outputs into the control cards in place of the preset pot wiper, and have the three pushbuttons on the wall function as off, on and demux-controlled.

 

FWIW with the few capacitors changed that usually need changing by now, these things will last almost forever.

 

Lucien

 

I'm guessing that all the preset control circuitry is in the PTU dimmers as opposed to being down FOH where the pushbuttons are, in which case the idea of having on off and demux would be a great idea.

As regards the capacitors, what needs doing there, are there any howtos on doing this?

 

Regards, David

[Don Allen]

They are JTM dimmer modules, usually 5KW, in individual cases for house lighting. Inside the case will be a low voltage mains trasformer to supply the control card and for the master dimmers, an Up Down Preset card, with only momentary contact switches being remoted, usually on multi core telephone cable. The slave dimmers have their control volts in parallel with the master.

The DUP (DownUpPreset) card was made by Rank Australia in Melbourne and has up rate, down rate, pre rate adjustments, to provide a fade up to full, fade down to off and fade up to preset.

The JTM dimmers only weakeness is the axial electrolytic capacitors, available from RS in Australia and the skeleton preset pots, replace them with sealed types such as Piher and the dimmers will just keep going.

As others have said, just diode-or the 0 to 10v dc from a demux to convert to DMX. You can even but DMX demux pcb's that will fit into the dimmers.

[oilyspark]

as each dimmer is independent you can run it + or - control by simply switching over the 2 control wires on the dimmer module

 

This is easy without the pushbutton controls. However in this case the result would be that the entire control system of each channel including the pushbutton wiring around the building rides up and down on its incoming control volts from the demux, as that would take the place of ground. It might work but there is considerable potential for weirdness. If the common to the pushbuttons has been shared between the units then it is impossible as they would no longer be at the same voltage. I would say it's better to get a -ve output demux or make a little converter - you can do four channels with one quad op-amp IC and eight resistors.

 

all the preset control circuitry is in the PTU dimmers as opposed to being down FOH where the pushbuttons are

 

Yes, the PTU responds to momentary switch contact closures; any number of pushbutton stations can be wired in parallel across the terminals on the unit.

 

As regards the capacitors, what needs doing there

 

Depends what version of cards you have. Post pics and we can point out the suspects!

 

to my knowledge its a HTP system

 

If you make it so - at the moment there is only one source, the selected output of the up/down/preset control card. Any number of analogue sources can be combined using signal diodes between that and the input to the trigger card and so long as each has a diode the dimmer will respond to the highest voltage without the sources interfering with each other. When adding diodes, it will be necessary to adjust the zero and span presets to get the proper dimming curve. This is easy and should be checked after tinkering wth these things anyway.

 

Lucien

[fliggygeek]

as each dimmer is independent you can run it + or - control by simply switching over the 2 control wires on the dimmer module

 

This is easy without the pushbutton controls. However in this case the result would be that the entire control system of each channel including the pushbutton wiring around the building rides up and down on its incoming control volts from the demux, as that would take the place of ground. It might work but there is considerable potential for weirdness. If the common to the pushbuttons has been shared between the units then it is impossible as they would no longer be at the same voltage. I would say it's better to get a -ve output demux or make a little converter - you can do four channels with one quad op-amp IC and eight resistors.

 

all the preset control circuitry is in the PTU dimmers as opposed to being down FOH where the pushbuttons are

 

Yes, the PTU responds to momentary switch contact closures; any number of pushbutton stations can be wired in parallel across the terminals on the unit.

 

As regards the capacitors, what needs doing there

 

Depends what version of cards you have. Post pics and we can point out the suspects!

 

to my knowledge its a HTP system

 

If you make it so - at the moment there is only one source, the selected output of the up/down/preset control card. Any number of analogue sources can be combined using signal diodes between that and the input to the trigger card and so long as each has a diode the dimmer will respond to the highest voltage without the sources interfering with each other. When adding diodes, it will be necessary to adjust the zero and span presets to get the proper dimming curve. This is easy and should be checked after tinkering wth these things anyway.

 

Lucien

 

Ok. Once again thankyou for this information. To confirm the device ID thing, the green boxes are in fact TU units and the silver ones PTU. I found some hidden ID plates on the green ones.

 

Ill be going back up to the theatre sometime later this week, so ill remove the covers and give you guys some dimmer pr0n to cast your eyes over.

 

My plans thus far are to have the preset buttons putting the dimmers into DMX mode, and replacing the existing pots with the demux. as to how well this will work im not sure, I suppose tis will depend on the results on my checking of the system later this week.

[church]

Done that already, just waiting for a response.

 

Can't say for certain, but I suspect these may possibly have been a special from Strand. Can't see anything obvious in the Strand Archive pages, but it might be worth contacting Jon directly to ask if he has any ideas. (His e-mail at the bottom of the archive pages)

 

Strand often package their standard dimmer modules in custom pacakges for specific applications - no doubt inside the box you will find a standard dimmer module. Also note that the STM and JTM dimmer modules were built for local markets in Canada and other countries and the standard circuit design would be modified for local requirements and gicen a unique code. Here in canada the STM was sold as the CTM.

[fliggygeek]

I'm considering using This as the demux, the link is the tech sheet. it says that it does up to +- 15v so I think ill be ok with the voltages.

[Ynot]

I'm considering using This as the demux, the link is the tech sheet. it says that it does up to +- 15v so I think ill be ok with the voltages.

 

Er, tried your link and got

Whoops! - it's a 404 Error!

 

We've had a complete overhaul of our website, and the page you have requested no longer exists.

 

You should easily be able to find the new version of the page you are looking for, but please let me know if you have any problems finding it.

 

Gerry.

[fliggygeek]

I'm considering using This as the demux, the link is the tech sheet. it says that it does up to +- 15v so I think ill be ok with the voltages.

 

Er, tried your link and got

Whoops! - it's a 404 Error!

 

We've had a complete overhaul of our website, and the page you have requested no longer exists.

 

You should easily be able to find the new version of the page you are looking for, but please let me know if you have any problems finding it.

 

Gerry.

 

That is odd, ive just verified the link with two separate browsers and it still wont work when added to a post. Anyway, its in the DMX512 section, DMX-USB-RX-A8