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Author Topic: 70.7 volt to line level converter???  (Read 7453 times)

Matt Tudor

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70.7 volt to line level converter???
« on: September 13, 2010, 02:59:05 pm »

We're looking at putting together a small system in the basement Fellowship Hall at our church. Currently the room is covered by 6 70v speakers on a 70 volt line from the main PA upstairs in the sanctuary, but we are looking to add a local mic and multimedia stuff on the computer specifically for this room. I'm thinking small mixer/amp with a mic input, an audio feed from the computer, and a feed from the sanctuary for the occasional times when it's needed. Unfortunately, the only cable coming down from the sanctuary is 16/2 speaker line.
I'm hoping for a simple black box solution, like a step down transformer, that I can pick up off the speaker line and pad the signal down enough to hook it into the line inputs on a mixer. worst case, would a multi-tap transformer at 1/8 or 1/4 watt tap work?
I did check on the ability to run a new line level feed but there is no balanced output from the mixer upstairs and the only conduits I can find between upstairs and down are full of silicone or fire caulk. Mad
TIA
Matt
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Mark Mattocks

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Re: 70.7 volt to line level converter???
« Reply #1 on: September 13, 2010, 05:05:12 pm »

Matt -

Both Radio Design Labs and Audioplex offer products to pull a line output from a 70v line or you can build your own with the handy schematic form Jensen - http://www.jensen-transformers.com/as/as059.pdf

Have a peaceful day!
Mark
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Hal Bissinger/COMSYSTEC

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Re: 70.7 volt to line level converter???
« Reply #2 on: September 14, 2010, 01:00:41 am »

Why would you want to do that? A simple DPDT switch is all that's needed to switch the speakers between the sanctuary feed and the 70v output of your new amp. I've never been a fan of using the output of a power amp to supply the input of another anyway.

-Hal

Matt Tudor

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Re: 70.7 volt to line level converter???
« Reply #3 on: September 14, 2010, 09:57:56 am »

Hal Bissinger/COMSYSTEC wrote on Tue, 14 September 2010 00:00

Why would you want to do that? A simple DPDT switch is all that's needed to switch the speakers between the sanctuary feed and the 70v output of your new amp. I've never been a fan of using the output of a power amp to supply the input of another anyway.

-Hal


Hal,
I considered this but the current system has no local volume control downstairs. One of the side benefits of installing the new system downstairs will be getting local volume control. If I do a switch, then the feed from upstairs still has no volume control and I'm gonna get a lot of questions like "why don't the volume knobs work for upstairs stuff?"
That being said,  and assuming I install a proper converter device to pad down the signal like the RDL unit that Mark pointed out, what is your concern with driving the input of a mixer with the output of an amp?
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Joseph Macry

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Re: 70.7 volt to line level converter???
« Reply #4 on: September 14, 2010, 12:02:15 pm »

RDL's TX-70A oughta work.
Passive transformer piece.
http://www.rdlnet.com/product.php?page=162
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Joseph Macry
Austin TX

Hal Bissinger/COMSYSTEC

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Re: 70.7 volt to line level converter???
« Reply #5 on: September 14, 2010, 01:27:48 pm »

If I do a switch, then the feed from upstairs still has no volume control...

Put an AT-10 on the wall someplace, matter of fact you can get a wallplate to gang the switch and volume control. Lock the amp away so it won't be tampered with.

As an old timer, using the output of a power amp to feed the input of another amp has always been a big no-no. Amps are much cleaner than they used to be but there is still no getting around that output used to drive speakers is always going to be the worst part of the chain in terms of noise, hum and distortion. Use it to supply the input of another amp and it's kind of like making a copy of a copy on a copy machine. You are going to make whatever noise and hum is coming from the first amp worse. Maybe it's not a big deal with simple PA, I know of installations such as mall stores or store departments that have their own music source but must also carry the mall or store wide announcements. That's what those matching devices are for.

Also, knowing churches like I do I would want to keep things simple. Keeping the amp on all the time and expecting people with no knowledge to adjust levels is a bit much to expect. A switch and knob on the wall anybody can understand.

-Hal

Matt Tudor

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Re: 70.7 volt to line level converter???
« Reply #6 on: September 14, 2010, 04:42:10 pm »

Hal Bissinger/COMSYSTEC wrote on Tue, 14 September 2010 12:27

If I do a switch, then the feed from upstairs still has no volume control...

Put an AT-10 on the wall someplace, matter of fact you can get a wallplate to gang the switch and volume control. Lock the amp away so it won't be tampered with.

As an old timer, using the output of a power amp to feed the input of another amp has always been a big no-no. Amps are much cleaner than they used to be but there is still no getting around that output used to drive speakers is always going to be the worst part of the chain in terms of noise, hum and distortion. Use it to supply the input of another amp and it's kind of like making a copy of a copy on a copy machine. You are going to make whatever noise and hum is coming from the first amp worse. Maybe it's not a big deal with simple PA, I know of installations such as mall stores or store departments that have their own music source but must also carry the mall or store wide announcements. That's what those matching devices are for.

Also, knowing churches like I do I would want to keep things simple. Keeping the amp on all the time and expecting people with no knowledge to adjust levels is a bit much to expect. A switch and knob on the wall anybody can understand.

-Hal


I like the idea, and the AT10 and a switch shouldn't be any more than the $30 dollar RDL unit. Thanks for the tip, and thanks to everyone else who replied.

Matt
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Al Clayton

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Re: 70.7 volt to line level converter???
« Reply #7 on: September 27, 2010, 02:52:28 pm »

I use these all the time in situations like you describe. I like the fact that there is control over the output level.

I pay $36.00. from Anixter

http://www.valcom.com/techsupport/enhancement_ts/v1095.htm

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