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Author Topic: Understanding Hi-Z direct drive amplification.  (Read 2141 times)

Nitin Sidhu

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Understanding Hi-Z direct drive amplification.
« on: April 14, 2016, 01:12:13 pm »

Hello all!

Direct drive from high powered amps.
Understood that a 600w amp at 8ohms can drive 70v lines. Similarly a 2000watt x 8ohm amp could drive a 125v line.

On speakers with built in transformers, selection is for 70/100v taps, with each 70v tap having a corresponding 100v tap also.. If an amp has the potential to drive 125v, then does the 100v tap on the speaker becomes relevant ? But why not the 70v ?

Trying to understand how the step down transformers on the speaker end work, will they step down to 70v irrespective of voltage they are getting ? That was my impression. But for every 70v tap there is an equivalent 100v tap too.

My next query would be regarding amp loading and speaker gauge. But this first.

Thank you all for your time.
Thanks to Ivan and Jonathan and others for already helping me with this.

Regards,
Sidhu
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John Roberts {JR}

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Re: Understanding Hi-Z direct drive amplification.
« Reply #1 on: April 14, 2016, 02:02:05 pm »


There are many white papers on the internet, probably one from every manufacturer of 70/100V equipment.
Hello all!

Direct drive from high powered amps.
Understood that a 600w amp at 8ohms can drive 70v lines. Similarly a 2000watt x 8ohm amp could drive a 125v line.

The proper way to think about this is that amplifiers that can output 70v or 100v can generally be used to drive a 70/100V line. If this was such a good idea all the manufacturers wouldn't put output transformers in their amps. That market is cost sensitive.
Quote

On speakers with built in transformers, selection is for 70/100v taps, with each 70v tap having a corresponding 100v tap also.. If an amp has the potential to drive 125v, then does the 100v tap on the speaker becomes relevant ? But why not the 70v ?
because 100v is closer to 125v.
Quote
Trying to understand how the step down transformers on the speaker end work, will they step down to 70v irrespective of voltage they are getting ? That was my impression. But for every 70v tap there is an equivalent 100v tap too.
the 70v is a nominal voltage, in use the voltage varies just like every other audio amp in the world.

A step down transformer uses different turns ratios to drop down the 70V to a more sensible power per speaker.
Quote
My next query would be regarding amp loading and speaker gauge. But this first.
Higher voltage supports smaller gauge wire all else equal.
Quote
Thank you all for your time.
Thanks to Ivan and Jonathan and others for already helping me with this.

Regards,
Sidhu
Seriously read a white paper or two, that might clear up a few things. This as an old very mature technology, and just because you can skip the output transformer doesn't mean you should. 

JR
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Mac Kerr

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Re: Understanding Hi-Z direct drive amplification.
« Reply #2 on: April 14, 2016, 02:08:45 pm »

Hello all!

Direct drive from high powered amps.
Understood that a 600w amp at 8ohms can drive 70v lines. Similarly a 2000watt x 8ohm amp could drive a 125v line.

On speakers with built in transformers, selection is for 70/100v taps, with each 70v tap having a corresponding 100v tap also.. If an amp has the potential to drive 125v, then does the 100v tap on the speaker becomes relevant ? But why not the 70v ?

Trying to understand how the step down transformers on the speaker end work, will they step down to 70v irrespective of voltage they are getting ? That was my impression. But for every 70v tap there is an equivalent 100v tap too.

My next query would be regarding amp loading and speaker gauge. But this first.

Thank you all for your time.
Thanks to Ivan and Jonathan and others for already helping me with this.

Regards,
Sidhu

The transformers on a 70V speaker are labeled in watts to make it easy to add up the number of "watts" that are on demand if the amplifier is driven to full output. What they really do is change the impedance of that device. A lower impedance device will draw more current, and so more watts, at any given voltage. Voltage is what amplifiers actually put out. By using the watts terminology it is easy to do the math and see if you have tapped speakers to more than your amp can deliver. That would mean you are loading the amp to a lower impedance than it is designed to operate into.

A 600W 8Ω amplifier can be tapped to about 540W (600W-10% safety factor), at which point it will be seeing a load impedance of about 8Ω. A 100W 70V cannot be loaded as low as 8Ω, as it is designed to operate into a load impedance of about 50Ω.

Mac
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Craig Hauber

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Re: Understanding Hi-Z direct drive amplification.
« Reply #3 on: April 14, 2016, 03:55:39 pm »

Hello all!

Direct drive from high powered amps.
Understood that a 600w amp at 8ohms can drive 70v lines. Similarly a 2000watt x 8ohm amp could drive a 125v line.

On speakers with built in transformers, selection is for 70/100v taps, with each 70v tap having a corresponding 100v tap also.. If an amp has the potential to drive 125v, then does the 100v tap on the speaker becomes relevant ? But why not the 70v ?

Trying to understand how the step down transformers on the speaker end work, will they step down to 70v irrespective of voltage they are getting ? That was my impression. But for every 70v tap there is an equivalent 100v tap too.

My next query would be regarding amp loading and speaker gauge. But this first.

Thank you all for your time.
Thanks to Ivan and Jonathan and others for already helping me with this.

Regards,
Sidhu

The taps are just different impedances with the "watt" labels being simple convenience.

A tap of 'z' impedance when presented a 70V signal will equal approximately 'x' "watts"
that very same tap when presented a 100V signal will equal a higher number of "watts"

add up all the tapped speakers impedances in parallel to get the total impedance on the line.
For a 600W at 70.7v on a direct 8-ohm amp you need to make sure your total line impedance is 8-ohm or higher then the watt labels on those transformer taps would be close to accurate.

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Stephen Swaffer

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Re: Understanding Hi-Z direct drive amplification.
« Reply #4 on: July 09, 2019, 01:02:14 pm »

Sorry to resurrect a zombie thread.  I need to replace a paging amp.  I think my current 100 watt amp has been overloaded-upgrading to a comparable 250 watt paging amo is north of $900 when I can purchase a Crown XLI 800 for under $300.  What's the downside?
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Mike Caldwell

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Re: Understanding Hi-Z direct drive amplification.
« Reply #5 on: July 19, 2019, 09:22:47 am »

Sorry to resurrect a zombie thread.  I need to replace a paging amp.  I think my current 100 watt amp has been overloaded-upgrading to a comparable 250 watt paging amo is north of $900 when I can purchase a Crown XLI 800 for under $300.  What's the downside?

In bridged mode it would just meet the 70 volt spec.

What is the total tap wattage on you system?
Was the old paging amp just an amp or did it include any mixing functions?
What is this system used for?

Remember somewhere along the way you need to apply a high pass filter in a 70 volt system, smaller the speakers, smaller the transformer, higher the high pass filter frequency. 70hz minimum is a staring point.

You amp could have been "overloaded" because of the lack of a good HPF in the system and someone wanting to crank the bass.

When the transformers get hit with too much low frequency and saturate the more or less present a dead short to the amp.

ProSoundWeb Community

Re: Understanding Hi-Z direct drive amplification.
« Reply #5 on: July 19, 2019, 09:22:47 am »


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