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Old 22nd April 2004, 12:07 AM   #1
jonz is offline jonz  Canada
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Default some questions on PA amp(pics)

I know I asked questions before on this subject but I just wanted to be sure..I picked this amp up at an auction and it appears new..I was wondering if I could use it to power a subwoofer..it appears it is rated at 360 watts....

Click the image to open in full size.

the pic below has a 4 ohm tap..is this where I can hook up sub?

Also there is a DC switch..what is that for?On the switch it reads "rated ouput 720 watts" does this mean anything...and could I convert it by installing a binding post?

Click the image to open in full size.


thnks guys..
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Old 22nd April 2004, 01:10 AM   #2
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Hi Jonz,

I think this is a real PA/public-address amplifier, I can see a output transformer for high ohm/volt speaker distrubition system and probably intended to use for department store, hotel, school, hospital sound system installation.

The DC switch function are if you want to run the amplifier from a battery or emergency power source.

May be it is not so good for Hi-Fi or sub bass.

--Bo
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Old 22nd April 2004, 01:28 AM   #3
sam9 is offline sam9  United States
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I had an idea like that once. Thought I could at least salvage the transformer but even that didn't work out as the current available was too skimpy for the the voltage unless you used an other transformer to step it down. I also concluded that the power ratings on PA amps don't seem to translate very well to audio expectations.

Maybe there is someone here who knows a lot about PA amps who can explain all this better -- all I know is what i thought would be good deal turned out to be of little practical use. Unless I was going to make a speach at the Lions Club, of course.
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Old 22nd April 2004, 01:38 AM   #4
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I cant quite make out the markings barrier strip, but it looks like there may be a 4 ohm output in addition to a 35 and 70 volt tap.

I'm thinking that the amp is set up to be used as a paging amplifier and can either use the 35/70 for distribution or the 4 ohm for a local driver.

You should be able to run a sub.
Binding posts shouldn’t be a problem either.
I agree that the DC power is for battery backup. Lots of building codes now require fault tolerant paging systems.

The second transformer, the E-Core one, is likely the transformer for the 35/70 outputs. With a little care you should be able to pull it out and still have the 4 ohm output.

Take a couple of 15" 8 ohm drivers in parallel for your sub, that should match your 4 ohm output just fine.

Is it audiophile? Tuff to say from my where I'm listening, but I might not be too picky either.

Id forget about that DC input, unless your looking for a big thumper in the trunk of your car. (might need more than 12 volts for the DC, 24/48 aren’t uncommon for DC backup) The PC card to the right of the transformers looks like it could be a charger/inverter for the battery supply. You can likely loose that too.

Find a schematic if you can. Most of this shouldn’t be too tuff to noodle out.
There’s a bunch of assumptions here on my part. Take’em for what they are worth.

Have fun!

(starring at the PCB on the right, it looks to have some other PS functions to it too, it likely cant be scrapped)
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Old 22nd April 2004, 02:08 AM   #5
jonz is offline jonz  Canada
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Here's a couple of more pics

Click the image to open in full size.

Click the image to open in full size.
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Old 22nd April 2004, 02:35 AM   #6
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Is it a Bogen?

Yah, I still think should be able you should be able to drive a 4 ohm driver btween the common and 4 ohm screws.
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Old 22nd April 2004, 02:45 AM   #7
jonz is offline jonz  Canada
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It's a Torttech.....
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Old 22nd April 2004, 03:06 AM   #8
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Default I think it is

Quote:
Originally posted by jonz
It's a Torttech.....
Tortech

some Teac and other brands use Tortech stuff but meanwhile I think they have stopped production
I used to have a link to them but it does not work anymore
http://home.echo-on.net/~tortech/home1.html

J-P

(in france Bogen and Tortech used to collaborate in cabling large phonesystems)




J-P
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Old 22nd April 2004, 06:14 AM   #9
Eva is offline Eva  Spain
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Taking into account the 24V supply option, It's probaby a bridged topology

Depending on the exact topology, the circuit may or may not be able to work without the output transformer. Some 'lower distortion' circuits drive the transformer in a push-pull fashion through a dual primary and take the feedback from an auxiliary winding, so the transformer is required. Other 'high coloration' circuits are independently bridged class B amplifiers driving a single primary of the transformer, so you are free to remove it

You should supress that transformer since It's designed to allow maximum power output on vocal frequency range only, and to allow full range output [20Hz-20Khz] only at low [ambient music] levels. Below 100Hz the transformer usually saturates below the power rating of the amplifier [the lower the frequency, the lower the output needed to saturate it] thus making it useless for subwoofer use

Take into account that manufacturers usually play with the 'primary impedance' of the transformer so even the 4 ohms output is usually stepped-up through it. Assuming 360Wrms output and a sagging 24V supply, transformer primary may provide about 2 ohm load to the amplifier to be able to develop the rated power. This means you should use two 4 ohm drivers in paralell

You may also think about building a new circuit using the case, toroidal transformer, heatsinks, fan, power resistors and maybe output devices
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