ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 [All]   Go Down

Author Topic: Diagnose 70v System?  (Read 18443 times)

Sean Lehman

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 95
Diagnose 70v System?
« on: December 05, 2011, 03:41:11 pm »

Hi, What is the practice to diagnose a 70v system to make sure it is not shorting out or damaging the amplifier?  70v amplifier is feeding about 15 to 20 rooms and each room has two speakers that are transformer tapped. Is there a way to test the load at the amplifier end or will a continuity test suffice if I know everything is within spec? what's the best way to go about this?

thanks for your help,
Sean
Logged

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16235
  • Hickory, Mississippi, USA
    • Resotune
Re: Diagnose 70v System?
« Reply #1 on: December 05, 2011, 04:26:07 pm »

For serious debugging they make AC impedance meters that can measure the actual load, while in general an actual short should be easy enough to see with an VOM.

JR
Logged
On the internet people tell you everything "they" know, not the answer to "your" question.....  http://circularscience.com/

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 8725
  • Atlanta GA
Re: Diagnose 70v System?
« Reply #2 on: December 05, 2011, 04:55:21 pm »

Hi, What is the practice to diagnose a 70v system to make sure it is not shorting out or damaging the amplifier?  70v amplifier is feeding about 15 to 20 rooms and each room has two speakers that are transformer tapped. Is there a way to test the load at the amplifier end or will a continuity test suffice if I know everything is within spec? what's the best way to go about this?

thanks for your help,
Sean
You really need to do an impedance test-across the entire bandwidth-not just at 1Khz.  Then convert that impedance to watts and see how it lines up with the amp power rating.

An Ohm meter will be seeing the DC resistance of the wire (speaker wire and transformer windings) only.  If there is a short on the other side-you will not be able to see it with an ohm meter.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16235
  • Hickory, Mississippi, USA
    • Resotune
Re: Diagnose 70v System?
« Reply #3 on: December 05, 2011, 05:09:30 pm »

Yup,, To measure loading wrt 70V amp you need AC Z and then do the math. I built that measurement capability (20-20k) into my old Loftech TS-1 , but it seems a few spot (midrange) audio frequencies will tell you enough. 



JR

JR
Logged
On the internet people tell you everything "they" know, not the answer to "your" question.....  http://circularscience.com/

Tom Young

  • Global Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 620
Re: Diagnose 70v System?
« Reply #4 on: December 05, 2011, 05:54:28 pm »

Yup,, To measure loading wrt 70V amp you need AC Z and then do the math. I built that measurement capability (20-20k) into my old Loftech TS-1 , but it seems a few spot (midrange) audio frequencies will tell you enough. 

JR

The Dayton Audio WT3 impedance measurement software should do the trick.

http://www.daytonaudio.com/index.php/wt3-woofer-tester.html

and:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-804
Logged
Tom Young
Electroacoustic Design Services
Oxford CT
203-888-6217

Sean Lehman

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 95
Re: Diagnose 70v System?
« Reply #5 on: December 06, 2011, 02:00:23 pm »

thanks for the replies and info. appreciated.
Logged

Steven Barnes

  • Full Member
  • ***
  • Offline Offline
  • Posts: 232
    • SBTS Inc.
Re: Diagnose 70v System?
« Reply #6 on: December 25, 2011, 12:33:03 am »

The Dayton Audio WT3 impedance measurement software should do the trick.

http://www.daytonaudio.com/index.php/wt3-woofer-tester.html

and:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-804

This is what I have been using with great success
Logged
Audio Engineering, Design, Consulting
SBTS Inc.
www.sbts-inc.com

David Sturzenbecher

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1521
  • So. Dak.
    • Sturz Audio
Re: Diagnose 70v System?
« Reply #7 on: December 26, 2011, 09:00:52 pm »

This guy does impedance measurements across multiple frequencies...and is a great signal generator.

http://www.nti-audio.com/Home/Products/Minstruments/MiniratorMRPRO/tabid/119/Default.aspx
Logged
Audio Systems Design Engineer
Daktronics, Inc.
CTS-D, CTS-I
AES Full Member

Billy Wood

  • Newbie
  • *
  • Offline Offline
  • Posts: 7
    • Audio Visual Professional Group
Re: Diagnose 70v System?
« Reply #8 on: January 02, 2012, 09:19:40 pm »

I have a Fluke and it has a amperage clamp that I use on all kinds of equipment.  You can push a tone down the line (120hz if it is a cheap meter) then get your amp reading.  Then multiply that by the voltage which you can also measure with it.  I know 70v would be logical but I like to measure rather than assume.  That has helped me diagnose a busted Yorkville amp before.  You can get your system wattage from that and know if you are over loading your amp.  Easiest way to fix a overload problem is to change the volume knobs in rooms to bring your total wattage down.  Alot of people buy 100w volume knobs assuming that it is related to its durability and max load but it limits that zone to said wattage.  You can put 1000w worth of speakers on the other side and it will only get 100w.  It is just a multi-tap transformer with a knob on the front to pick the multiple taps.

Ok with that said testing at the amp will ussually show you nothing because you have volume knobs at every zone.  Everything past the volume knob will not show at the AMP.  That is usually where most of your problems lie due to them being above ceiling tiles that everyone and their mom gets into!

Impedance will not tell you much also. 70v is not a impedance based system. That is why it is used in distributed audio.  You need to turn every zone off at the zone controls and then run signal through your system.  If you are getting amperage draw over the hot line at the amp you have a leak to building ground somewhere (ie. - a short). 

The impedance remark is only applicable if you do not have a step up transformer at your amp and it is a transformerless amp system.  This is saying you don't have a regular 2/4/8 ohm amp at the start and a step up transformer feeding your 70v.  I have not ran into this in any recent installations. 


Billy Wood
www.avprogroup.com
The Woodlands, TX
« Last Edit: January 02, 2012, 09:40:21 pm by Billy Wood »
Logged
Billy Wood
www.avprogroup.com
The Woodlands, TX

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16235
  • Hickory, Mississippi, USA
    • Resotune
Re: Diagnose 70v System?
« Reply #9 on: January 02, 2012, 11:24:36 pm »


Impedance will not tell you much also. 70v is not a impedance based system. That is why it is used in distributed audio.  You need to turn every zone off at the zone controls and then run signal through your system.  If you are getting amperage draw over the hot line at the amp you have a leak to building ground somewhere (ie. - a short). 

The impedance remark is only applicable if you do not have a step up transformer at your amp and it is a transformerless amp system.  This is saying you don't have a regular 2/4/8 ohm amp at the start and a step up transformer feeding your 70v.  I have not ran into this in any recent installations. 


Billy Wood
www.avprogroup.com
The Woodlands, TX

"Huh"?    70/100V systems are called "constant voltage" systems, and impedance is indeed a useful measure of how heavily that amp is loaded for that nominal (not really constant) system output voltage..

It is fairly simple math to convert 70V at X watts, into a minimum Y ohms, and unlike your clamp on ammeter you can debug the system when it's turned off or broken.

Of course do what works for you...


JR
Logged
On the internet people tell you everything "they" know, not the answer to "your" question.....  http://circularscience.com/

Billy Wood

  • Newbie
  • *
  • Offline Offline
  • Posts: 7
    • Audio Visual Professional Group
Re: Diagnose 70v System?
« Reply #10 on: January 03, 2012, 12:44:15 am »

"Huh"?    70/100V systems are called "constant voltage" systems, and impedance is indeed a useful measure of how heavily that amp is loaded for that nominal (not really constant) system output voltage..

It is fairly simple math to convert 70V at X watts, into a minimum Y ohms, and unlike your clamp on ammeter you can debug the system when it's turned off or broken.

Of course do what works for you...


JR

Sorry JR.  I should have rephrased that.  I was really only addressing a building short.  For example the all to common light fixture placed on top of a cable in some ceiling tiles and has a earthing problem from the wire being smashed but not completely cut.  A handheld or isolated testing equipment would not follow through the building because it is isolated from it.  It would still follow through the wire as if nothing was wrong. But a amp being connected through the same ground as the lighting fixture surely will.  You are completely correct.

And the only reason I mention it is because alot of times I work on 70v the amp is to small or on the other side of a transformer and it will not burn through a cable leaving an open circuit. 

I was not trying to smash you guys at all. I was only answering one side of his question about building short.  A short between hot and nuetral of a system would plainly show near 0 ohms where a building short would not be so apparent.

I find that I never seem to come out and service a distributed audio system when it is simple and we all no electricians never pay any mind to our speaker wire near their light fixtures or a plumber and their fire systems.
Logged
Billy Wood
www.avprogroup.com
The Woodlands, TX

Hal Bissinger/COMSYSTEC

  • Full Member
  • ***
  • Offline Offline
  • Posts: 204
    • COMSYSTEC
Re: Diagnose 70v System?
« Reply #11 on: January 03, 2012, 10:06:17 am »

...Alot of people buy 100w volume knobs assuming that it is related to its durability and max load but it limits that zone to said wattage.  You can put 1000w worth of speakers on the other side and it will only get 100w.  It is just a multi-tap transformer with a knob on the front to pick the multiple taps.

Ok with that said testing at the amp will ussually show you nothing because you have volume knobs at every zone.  Everything past the volume knob will not show at the AMP.  That is usually where most of your problems lie due to them being above ceiling tiles that everyone and their mom gets into!

Impedance will not tell you much also. 70v is not a impedance based system. That is why it is used in distributed audio.  You need to turn every zone off at the zone controls and then run signal through your system.  If you are getting amperage draw over the hot line at the amp you have a leak to building ground somewhere (ie. - a short). 

The impedance remark is only applicable if you do not have a step up transformer at your amp and it is a transformerless amp system.  This is saying you don't have a regular 2/4/8 ohm amp at the start and a step up transformer feeding your 70v.  I have not ran into this in any recent installations. 

 

Billy Wood
www.avprogroup.com
The Woodlands, TX

A direct drive amp (transformerless) is no different than one with an output transformer in that the voltage at the output will be 70.7 volts at the rated output. That's the basis for the constant voltage system.
 
Actually those volume controls are a tapped auto transformer. The taps represent some value 1/10, 1/5, etc of the connected impedance and as such the input will represent the connected load. A 100 watt control is capable of handling a 100 watt load and if you use it to control a 1000 watt load it will deliver the power- until it burns up.
 
Also, with any controls that I have ever seen the highest setting is 1:1 and the autotransformer is bypassed. Since at the maximum setting the control is out of the circuit set all your controls to max while doing impedance measurements.
 
The most sensible way to find a short to ground is to just disconnect the wiring from the amp and use an ohm meter to check each side to ground.
 
-Hal
Logged

Devin Rice

  • Newbie
  • *
  • Offline Offline
  • Posts: 21
Re: Diagnose 70v System?
« Reply #12 on: March 12, 2012, 12:28:04 pm »


Actually those volume controls are a tapped auto transformer. The taps represent some value 1/10, 1/5, etc of the connected impedance and as such the input will represent the connected load. A 100 watt control is capable of handling a 100 watt load and if you use it to control a 1000 watt load it will deliver the power- until it burns up.
 
Also, with any controls that I have ever seen the highest setting is 1:1 and the autotransformer is bypassed. Since at the maximum setting the control is out of the circuit set all your controls to max while doing impedance measurements.
 

 
-Hal

I have had an architect spec for 15w ceiling speakers with a 6w volume control. Does this mean there is underutilization of the system? This is for a 100v system.
Logged

Brad Weber

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2209
  • Marietta, GA
Re: Diagnose 70v System?
« Reply #13 on: March 12, 2012, 01:20:50 pm »

I have had an architect spec for 15w ceiling speakers with a 6w volume control. Does this mean there is underutilization of the system? This is for a 100v system.
Many 'constant voltage' speakers have multiple taps, for example a nominal 15W speaker may have 15W, 7.5W, 3.75W and 1.875W taps, any of which could be used.  A 6W volume control could simply indicate that the speaker is to then be tapped using the 1.875W or 3.75W taps on its transformer.  However, if the speaker is specified to be tapped at 15W then a 6W volume control is undersized.
Logged

Devin Rice

  • Newbie
  • *
  • Offline Offline
  • Posts: 21
Re: Diagnose 70v System?
« Reply #14 on: March 15, 2012, 12:37:01 pm »

Many 'constant voltage' speakers have multiple taps, for example a nominal 15W speaker may have 15W, 7.5W, 3.75W and 1.875W taps, any of which could be used.  A 6W volume control could simply indicate that the speaker is to then be tapped using the 1.875W or 3.75W taps on its transformer.  However, if the speaker is specified to be tapped at 15W then a 6W volume control is undersized.

I have made a mistake, the ceiling speakers I am told are 6w. Tapped at 6w. Is this a common size or does it seem underpowered? The ceiling height is 11 feet.

Trust it is OK for a 6w speaker to have a 6w volume control.
Logged

Charlie Zureki

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1244
  • South Eastern Michigan (near Windsor)
Re: Diagnose 70v System?
« Reply #15 on: March 15, 2012, 03:03:18 pm »

I have made a mistake, the ceiling speakers I am told are 6w. Tapped at 6w. Is this a common size or does it seem underpowered? The ceiling height is 11 feet.

Trust it is OK for a 6w speaker to have a 6w volume control.

   Yes.     He's installing a 100v system..surely you're in Europe or the East ? 

   Hammer
Logged
Do it the right way....don't be a Dino!

Hal Bissinger/COMSYSTEC

  • Full Member
  • ***
  • Offline Offline
  • Posts: 204
    • COMSYSTEC
Re: Diagnose 70v System?
« Reply #16 on: March 15, 2012, 07:18:29 pm »

Quote
I have made a mistake, the ceiling speakers I am told are 6w. Tapped at 6w. Is this a common size or does it seem underpowered? The ceiling height is 11 feet.

I have no idea. It all depends on how big the room is and other factors.
 
-Hal
Logged

Devin Rice

  • Newbie
  • *
  • Offline Offline
  • Posts: 21
Re: Diagnose 70v System?
« Reply #17 on: March 16, 2012, 09:14:34 am »

   Yes.     He's installing a 100v system..surely you're in Europe or the East ? 

   Hammer

South Asia to be precise :)
Logged

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 8725
  • Atlanta GA
Re: Diagnose 70v System? Another car analogy---------
« Reply #18 on: March 17, 2012, 09:18:58 am »

I have had an architect spec for 15w ceiling speakers with a 6w volume control. Does this mean there is underutilization of the system? This is for a 100v system.
One of the "misunderstood" aspects of a 70V/100V etc system is the taps.  Basically they are just impedance taps (they change the impedance load that the loudspeaker presents to the amp).  Let's look at a 6 watt tap.  The only time that 6 watts is "coming" out of the loudspeaker is when the voltage on the line is 70V.  When the level is turned down, the voltage on the line is lower-therefore less power is being "dissapated" by the loudspeaker.   But the impedance load is still there-as far as the amp is concerned.

The design may be just fine with a 6 watt volume control.  Or not-hard to say without a lot more information.  The choice of the 15 watt speaker may be because of coverage pattern (they are NOT all the same), freq response, cost, physical depth, mounting weight or other factors that have to be considered in an system of this type.

Just because a loudspeaker is rated for 15 watts does not mean it has to be run that hard.  Just as with "regular" loudspeakers, it if far beter to have a more powerful loudspeaker and run it at a lower level, than to get a lessor loudspeaker and run it to the max.  Guess which one is going to sound better and last longer?

How high does the speedometer on your car go?  Do you drive it to the limit all the time?  I doubt it (unless you are racing).  So that means that you are "underutilizing your car".  Does that bother  you?  If it bothers you with loudspeakers-it should bother you with your car as well.

I hope there is a specific reason the loudspeakers-the taps involved-the size of the volume controls etc are choosen for a particular job.  That is all part of the DESIGN process
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

g'bye, Dick Rees

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 7424
  • Duluth
Re: Diagnose 70v System? Another car analogy---------
« Reply #19 on: March 17, 2012, 11:03:30 am »


How high does the speedometer on your car go?  Do you drive it to the limit all the time?  I doubt it (unless you are racing).  So that means that you are "underutilizing your car".

Bennett P excepted.....
Logged
Pay no attention to the man behind the curtain...
Pages: 1 2 [All]   Go Up
 


Page created in 0.062 seconds with 23 queries.