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Author Topic: Dropping 100v speaker signal down to line input  (Read 2126 times)

Gary Fitzpatrick

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Dropping 100v speaker signal down to line input
« on: June 02, 2018, 12:02:53 pm »

Hi,

So I have a few projects coming up where I need to get an audio feed into a camera. The easiest and shortest cable run would have me connecting into the 100v speaker lines going to the speakers in the church. Is it okay to use a standard 100v 8/16 ohm transformer to drop the signal down?
 


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John Roberts {JR}

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Re: Dropping 100v speaker signal down to line input
« Reply #1 on: June 02, 2018, 02:19:23 pm »

Hi,

So I have a few projects coming up where I need to get an audio feed into a camera. The easiest and shortest cable run would have me connecting into the 100v speaker lines going to the speakers in the church. Is it okay to use a standard 100v 8/16 ohm transformer to drop the signal down?
 



It might still be a little hot depending on how many watts it is tapped to deliver (less watts is better).
 
JR
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Gary Fitzpatrick

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Re: Dropping 100v speaker signal down to line input
« Reply #2 on: June 02, 2018, 03:19:16 pm »



It might still be a little hot depending on how many watts it is tapped to deliver (less watts is better).
 
JR
Thanks For the reply JR. what would you recommend for dropping it down? I see quite a few of these systems coming on board (it is for streaming church services) so I wouldn’t mind doing it “right”

Gary


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Geoff Doane

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Re: Dropping 100v speaker signal down to line input
« Reply #3 on: June 02, 2018, 04:02:37 pm »

1W into 8Ω is about 2.8 Vrms.  If you allow 6 or 7 dB for the crest factor of the signal, that takes you down to an average level of just about +4 dBu.  Chances are the crest factor is higher than that (average level is lower), but it looks like you'd be in the right ballpark, using the 1W tap on a transformer designed for an 8Ω speaker.

GTD
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Gary Fitzpatrick

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Re: Dropping 100v speaker signal down to line input
« Reply #4 on: June 02, 2018, 04:06:13 pm »

That’s great...thanks for the advice.

Gary


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John Roberts {JR}

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Re: Dropping 100v speaker signal down to line input
« Reply #5 on: June 02, 2018, 05:36:36 pm »

Cheapest and easiest is a resistor pad, but a transformer will give you isolation which could be useful.

Try it and see... A wrong size (too hot) transformer can still be combined with a resistor pad to dial it in, while keeping the transformer isolation.

JR
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Gary Fitzpatrick

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Re: Dropping 100v speaker signal down to line input
« Reply #6 on: June 02, 2018, 06:02:56 pm »

Cheapest and easiest is a resistor pad, but a transformer will give you isolation which could be useful.

Try it and see... A wrong size (too hot) transformer can still be combined with a resistor pad to dial it in, while keeping the transformer isolation.

JR
Do you mean like a 100v rotary attenuators? Like this one?

http://cpc.farnell.com/unbranded/p605d/line-attenuator-switch-12w/dp/AR71993

Gary


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John Roberts {JR}

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Re: Dropping 100v speaker signal down to line input
« Reply #7 on: June 02, 2018, 07:04:58 pm »

Do you mean like a 100v rotary attenuators? Like this one?

http://cpc.farnell.com/unbranded/p605d/line-attenuator-switch-12w/dp/AR71993

Gary


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no.. don't know what that does.

JR
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TJ (Tom) Cornish

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Re: Dropping 100v speaker signal down to line input
« Reply #8 on: June 02, 2018, 08:55:06 pm »

Hi,

So I have a few projects coming up where I need to get an audio feed into a camera. The easiest and shortest cable run would have me connecting into the 100v speaker lines going to the speakers in the church. Is it okay to use a standard 100v 8/16 ohm transformer to drop the signal down?
 


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100v systems are only 100v at full-tilt boogie; in practice you're probably a lot less than that.  Even if you are operating around 100v, that's still not a particularly big deal.  A isolation transformer box or DI box with a 20dB pad would get you from 100v at clipping down to around 6 volts at clipping, which should be well within the capabilities of a professional-level line-level input.  If you need to drop it for a consumer-level input, you might need more gain reduction, but there are DIs that have larger pads than that.  The Rolls Matchbox DB25 comes to mind, and has a selectable 20dB and 40dB pad.

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John Roberts {JR}

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Re: Dropping 100v speaker signal down to line input
« Reply #9 on: June 03, 2018, 10:42:54 am »

100v systems are only 100v at full-tilt boogie; in practice you're probably a lot less than that.  Even if you are operating around 100v, that's still not a particularly big deal.  A isolation transformer box or DI box with a 20dB pad would get you from 100v at clipping down to around 6 volts at clipping, which should be well within the capabilities of a professional-level line-level input.  If you need to drop it for a consumer-level input, you might need more gain reduction, but there are DIs that have larger pads than that.  The Rolls Matchbox DB25 comes to mind, and has a selectable 20dB and 40dB pad.
Check with the DI mfr before putting 100V into a DI.

I am not very confident about doing that.

JR
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Re: Dropping 100v speaker signal down to line input
« Reply #9 on: June 03, 2018, 10:42:54 am »


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