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Old 20th March 2013, 01:36 PM   #11
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Location: Athens GREECE
Forgot to mention that in the output of these devices we installed one amplifier and 4 speakers on it covering a distance with speaker cables then of about 100 m

When we run out of speakers in the output of the device we drive 4 active speakers and after we went with balanced cables in to out and so on

Mixing the system resolved the cable issue since part of the system was done with speakon while the rest was made with balanced so my company didnt run out of cables ( other gigs was going on at the same time )

Kind regards
Sakis
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Old 20th March 2013, 04:07 PM   #12
JMFahey is offline JMFahey  Argentina
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Dear Sakis, as you see I hit the nail right in the head, both with the amount of powered speakers (which you had not stated), the distribution system, the driving with a power amp (I fact the boosterI suggested was a bridged TDA2030, which both provided balanced output and could drive down to 8 ohms), etc.
Only we used balanced cable and part of the profit was keeping 40 30 meter balanced cables.
You wonder how I was so sure?
Ahem!!, look at a couple of my jobs
Any similarity between Argentina and Greece is *not* a coincidence.
Including both being Mediterraneans and having a *long* history of economic crisis:
In the first one you see one "head" of the Carnival street, with added line array systems on both sides of the stage.
There sits the Province Governor, the Mayor and Press, plus the Judges who choose the most beautiful girls.
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Old 21st March 2013, 03:54 AM   #13
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Simple method

Use one amp with 100 volts output and one 100 volt speaker at the end to load the amp.

Now, use one stepdown transformer for each active speaker for deriving audio of 1 volts. You may find that the signal is dropping as the distance increases. So use 100:1 transfomer for the nearer ones and use 110/3vct for the further ones. Use a pot/resistors to set the input level to the actives.

Gajanan Phadte
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Old 21st March 2013, 07:22 AM   #14
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Or someting between a line-driver and a 100V amp:
Use an ordinary small stereo amp and drive on echannel inverted. That way you will be able to drive a long cheap speaker cable which you use to feed your active speakers (maybe using resistive voltage dividers). Small series resistors at the output help keeping the amp stable with the capacitive loading of the long line. Maybe soem termination at the end would be good as well.
If there is any chance that you get this job several time I would also build a smal IC amp as line driver.

Regards

Charles

P.S: This job would be quite a bit of work for the amount of money you will get !
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Old 21st March 2013, 10:28 AM   #15
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both ideas are dirt cheap and correct still the winner is any possible solution that features any type of trafo .... ground isolation when you have 10 different spots of mains power supply is mandatory

Kind regards
sakis
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Old 25th March 2013, 01:00 AM   #16
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I put your query to an engineer friend of mine (Doug Ford www.dfad.com.au) and he came up with a similar method. His reply follows.

"1/ Use cat5 cable to reticulate the signal.
Cost = AU$57/305m (WES components 'economy' CAT5).
Parallel the twisted pairs at the source, and at each drop-point, to reduce series resistance (although capacitance will rise).

2/ Drive the cable with a cheap, second-hand stereo amplifier connected for bridge-mode.
I'm sure they'd have an old 20+20 amp hanging around somewhere.
They may need to connect (say) a 2.7-ohm resistor between the amp outputs and the cable, to assure amp stability.
Distribution signal levels of around +20dBV (10Vrms) should easily be attained, with plenty of headroom.
If you want, terminate the cable with 120 Ohms at the far end (will increase cable attenuation, but will also give better stability & flatter response).

3/ Use screw terminal blocks at each drop-point.
These can be weatherproofed with an inverted cut down plastic milk or drink bottle.

4/ At each weatherproofed drop-point, connect a small 240V:24V transformer.
These cost about AU$8 each.
When used as an audio transformer, these have quite acceptable frequency response.
The 10:1 stepdown ratio, combined with (nominal) +20dBV line transmission levels, will provide a clean 0dBV signal at each drop-point.
The powered speakers should handle this level quite nicely.

5/ Variations in amplitude along the cable due to cable resistance are easily accommodated by the volume knobs on the powered speakers.

6/ Total cost (AU$):
Drive amp = Zero cost
Cable = 4 x $57 = $228 (1200m)
Screw connectors = 20 x AU$1.00 = $20.00
Transformers = 20 x AU$8.00 = $160.00 (if purchased new!)
Waterproof housings = Zero cost
TOTAL = AU$408 = 250 euro (approx)."
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Old 26th March 2013, 06:10 AM   #17
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well done .... i ve done the exact same thing using actually single cheaper telephone cable but better audio grade transformer / circuit

The grate fun in this story was that since the set up was in a public place and a a lot of people was there obviously some of them belonged to the competition and they come over actually for industrial spying ....all of them wondered how i managed and all of them wondered ( and asked my people there ) about the ""magic boxes "" ....You see ...car stereo items are not really known to PA people ...

Kind regards
Sakis
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Old 28th March 2013, 04:58 AM   #18
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And now they can read it here and improve upon.

Gajanan Phadte
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