paging system problem

[[email protected]]

I'm working on a 70 volt system that has a great deal of speakers.
There was a 35 watt amplifier that was tripping out on page. I thought
that given the large amount of speakers perhaps the 35 watt amplifier
was a bit light so I replaced it with a Bogen 70 watt unit.
Bogen gives resistance notations on their output taps. The 70 volt tap
is printed 10.3 ohms. I'm assuming that regardless of how you tap the
speakers, the load should not be greater than that.
The newly installed 70 watt unit does not trip out on page now but if
you try to get any kind of decent level out of it it becomes very
distorted.
There are three speaker trunk lines coming down to this amplifier. I
disconnected them and they read 20, 16, and 5.5 ohms respectively. If
I run the amplifier with just the 16 ohm trunk the portion of the
building that is on this line, (about 10 or 12 speakers) sounds good.
If I parallel the 16 and 20 ohm lines I can still make it work if I
don't push it too hard. However if I add the 5.5 ohm line, (most of
the remainder of the building) to the mix the amplifier can't handle
it. It becomes very distorted. In fact it was little surprise to note
that the amplifier will not drive just this 5.5 ohm line by itself
either.
We looked at some of the speakers on this 5.5 ohm line and most are
tapped a 2 watts while some are tapped a 4 watts.
I took a typical 70 volt line to voice transformer and looked at the
primary. The specs are as follows:
Tap (W) Resistance (ohms)
---- ------------
4.0 115
2.0 170
1.0 250
..50 450
..25 700
To employ multiple speakers in the following scenario I would
calculate RT. From the above transformer readings using ohms law it
seems that I can employ a maximum of 16 speakers tapped at 2 watts for
a total resistance of 10.625 ohms. Thats only asking a 70 watt
amplifier to produce a maximum of 32 watts.
Now I would have thought that I could use a 70 watt amplifier, tap my
speakers any way I would like to, not to exceed 56 watts and have a
system with a 20 percent safety margin regardless of what the total
parallel resistance works out to be. Is this correct or am I missing
something?
With old wiring, lines teed in everywhere, and improperly insulated
splices through out the building this place is a nightmare. However it
is a nursing home and I'm due to leave on vacation 10 days, so I've
got to get this fixed this upcoming week. So any suggestions or advice
would be most sincerely appreciated. Lenny Stein, Barlen Electronics.

 

[Ken Weitzel]

I'm working on a 70 volt system that has a great deal of speakers.
There was a 35 watt amplifier that was tripping out on page. I thought
that given the large amount of speakers perhaps the 35 watt amplifier
was a bit light so I replaced it with a Bogen 70 watt unit.
Bogen gives resistance notations on their output taps. The 70 volt tap
is printed 10.3 ohms. I'm assuming that regardless of how you tap the
speakers, the load should not be greater than that.
The newly installed 70 watt unit does not trip out on page now but if
you try to get any kind of decent level out of it it becomes very
distorted.
There are three speaker trunk lines coming down to this amplifier. I
disconnected them and they read 20, 16, and 5.5 ohms respectively. If
I run the amplifier with just the 16 ohm trunk the portion of the
building that is on this line, (about 10 or 12 speakers) sounds good.
If I parallel the 16 and 20 ohm lines I can still make it work if I
don't push it too hard. However if I add the 5.5 ohm line, (most of
the remainder of the building) to the mix the amplifier can't handle
it. It becomes very distorted. In fact it was little surprise to note
that the amplifier will not drive just this 5.5 ohm line by itself
either.
We looked at some of the speakers on this 5.5 ohm line and most are
tapped a 2 watts while some are tapped a 4 watts.
I took a typical 70 volt line to voice transformer and looked at the
primary. The specs are as follows:
Tap (W) Resistance (ohms)
---- ------------
4.0 115
2.0 170
1.0 250
.50 450
.25 700
To employ multiple speakers in the following scenario I would
calculate RT. From the above transformer readings using ohms law it
seems that I can employ a maximum of 16 speakers tapped at 2 watts for
a total resistance of 10.625 ohms. Thats only asking a 70 watt
amplifier to produce a maximum of 32 watts.
Now I would have thought that I could use a 70 watt amplifier, tap my
speakers any way I would like to, not to exceed 56 watts and have a
system with a 20 percent safety margin regardless of what the total
parallel resistance works out to be. Is this correct or am I missing
something?
With old wiring, lines teed in everywhere, and improperly insulated
splices through out the building this place is a nightmare. However it
is a nursing home and I'm due to leave on vacation 10 days, so I've
got to get this fixed this upcoming week. So any suggestions or advice
would be most sincerely appreciated. Lenny Stein, Barlen Electronics.

Hi Lenny...

I suspect that you're confusing resistance with impedance...

The dc resistance that you're reading on your speaker lines is just
the resistance of the wiring to those speakers (transformers),
because after all it is a transformer, so the dc resistance should
be virtually zero ohms, right?

The math is indeed simple, divide your 70 watts by the total of all
of the tap wattages - add a little margin - and if it fits you should
be OK.

If that works out, then afraid you're gonna have to check each and
every transformer primary individually - perhaps by sub'ing - or maybe
just disconnecting the primary looking for a large change in
level - until you find one that's gone shorted, or until you find shoddy
workmanship at a transformer or a splice that's a dead short.

Wear your oldest clothes, cause you're gonna be crawling around in
an awful lot of really dirty dusty crawl spaces. Did it myself 20
years ago in a hospital, and wouldn't like to do it again.

Take care.

Ken

 

[Arfa Daily]

Hi Lenny...

I suspect that you're confusing resistance with impedance...

The dc resistance that you're reading on your speaker lines is just
the resistance of the wiring to those speakers (transformers),
because after all it is a transformer, so the dc resistance should
be virtually zero ohms, right?

The math is indeed simple, divide your 70 watts by the total of all
of the tap wattages - add a little margin - and if it fits you should
be OK.

If that works out, then afraid you're gonna have to check each and
every transformer primary individually - perhaps by sub'ing - or maybe
just disconnecting the primary looking for a large change in
level - until you find one that's gone shorted, or until you find shoddy
workmanship at a transformer or a splice that's a dead short.

Wear your oldest clothes, cause you're gonna be crawling around in
an awful lot of really dirty dusty crawl spaces. Did it myself 20
years ago in a hospital, and wouldn't like to do it again.

Take care.

Ken

Has either amp got a slaving input ? If so, run the low resistance leg with
a lot of speakers on it, off one of them on its own. You could also try
calling the manufacturers of the new amp just to make sure that you are
interpreting the specs correctly. Also, if all of the speaker / transformer
combinations are pretty much the same, you could try disconnecting a couple
of examples on each leg and measuring their primaries, then counting up how
many individual stations there are on each leg, and just working out the
math to see if the readings you are getting back at the amp are about right
for that number of primaries in parallel. That way you would know if you
have a bad one for sure, but in any case, if you did, from what I can
remember, it having been some years since I was last involved in this stuff,
a bad station usually produces low output, whilst all of the others continue
to function.

The primary of a 70v line transformer should not have a resistance of close
to zero. One that I just looked up, for instance, was a 100v line type for 2
watts into 8 ohms, and its quoted primary resistance (not impedance) was 320
ohms. I would expect 70v line trannies to be broadly similar. That would
lead me to believe, as the primaries of these TXs are quoted by resistance
and not impedance, that the figure of ~10 ohms on the back of the amp, is a
DC load resistance figure. With a primary resistance figure of 320 ohms,
that would allow for 30 of these TXs in parallel, to get down to your 10
ohms, and with each one 'stealing' 2 watts off the line for its speaker,
that would take about 70 watts off the amplifier.

Now I know that's very rough 'back of a cigarette packet' math that I'm
talking there, with no TX efficiency or line losses factored in, and that
we're mixing 70v and 100v systems in the discussion, but that sounds like a
pretty typical installation to me. I wonder if your low resistance "pretty
much the rest of the building" leg at ~ 5 ohms, has around 50 - 60 speakers
on it ? If it does, then it's probably about right. If not, then you need to
do the primary disconnect and measure that I said above.

Just as a matter of interest, did the original system *ever* work right, or
has it just gone faulty ? If the original amp was only 35 watts, sounds like
it was under-rated for the job, or has become so as a result of more and
more stations being added over the years.

Arfa

 

[[email protected]]

Has either amp got a slaving input ? If so, run the low resistance leg with
a lot of speakers on it, off one of them on its own. You could also try
calling the manufacturers of the new amp just to make sure that you are
interpreting the specs correctly. Also, if all of the speaker / transformer
combinations are pretty much the same, you could try disconnecting a couple
of examples on each leg and measuring their primaries, then counting up how
many individual stations there are on each leg, and just working out the
math to see if the readings you are getting back at the amp are about right
for that number of primaries in parallel. That way you would know if you
have a bad one for sure, but in any case, if you did, from what I can
remember, it having been some years since I was last involved in this stuff,
a bad station usually produces low output, whilst all of the others continue
to function.

The primary of a 70v line transformer should not have a resistance of close
to zero. One that I just looked up, for instance, was a 100v line type for 2
watts into 8 ohms, and its quoted primary resistance (not impedance) was 320
ohms. I would expect 70v line trannies to be broadly similar. That would
lead me to believe, as the primaries of these TXs are quoted by resistance
and not impedance, that the figure of ~10 ohms on the back of the amp, is a
DC load resistance figure. With a primary resistance figure of 320 ohms,
that would allow for 30 of these TXs in parallel, to get down to your 10
ohms, and with each one 'stealing' 2 watts off the line for its speaker,
that would take about 70 watts off the amplifier.

Now I know that's very rough 'back of a cigarette packet' math that I'm
talking there, with no TX efficiency or line losses factored in, and that
we're mixing 70v and 100v systems in the discussion, but that sounds like a
pretty typical installation to me. I wonder if your low resistance "pretty
much the rest of the building" leg at ~ 5 ohms, has around 50 - 60 speakers
on it ? If it does, then it's probably about right. If not, then you need to
do the primary disconnect and measure that I said above.

Just as a matter of interest, did the original system *ever* work right, or
has it just gone faulty ? If the original amp was only 35 watts, sounds like
it was under-rated for the job, or has become so as a result of more and
more stations being added over the years.

Arfa- Hide quoted text -

- Show quoted text -

It did work at one point. They couldhave added things. They say they
didn't but who knows. I'm going to look at it again on Monday. Thanks
to everyone for all the advice. i really appreciate it. Lenny.

 

[hr(bob) [email protected]]

It did work at one point. They couldhave added things. They say they
didn't but who knows. I'm going to look at it again on Monday. Thanks
to everyone for all the advice. i really appreciate it. Lenny.- Hide quoted text -

- Show quoted text -

Since the one leg won't work by itself, I would look for a short
somewhere on that leg. Probably break it at midpoint, and see what
happens, or maybe run a new wire pair to the midpoint and then try
feeding each half to see what happens., With a long run, and a short
at at unknown location, it will be a problem, but I bet a short is
what the problem is.

H. R. (Bob) Hofmann

 

[Michael A. Terrell]

It did work at one point. They couldhave added things. They say they
didn't but who knows. I'm going to look at it again on Monday. Thanks
to everyone for all the advice. i really appreciate it. Lenny.

That doesn't mean that some employee didn't tamper with it because it
was too loud, or not loud enough where they worked. The so called
'maintenance man where I worked kept screwing around, till the system
was useless. I started at the amp, on the leg with the most problems,
finding lots of miswired speakers. The volume was low, so the idiot
changed the taps from .625 W to 5 W on speaker after speaker, making the
problems worse. I was almost to the end of that line when i hit the
production floor. Someone had moved a speaker, and extended the wire.
They had shorted out the trunk line. When I pulled the tape off to take
a look, the volume went way up, and one speaker cabinet caught on fire.
Some idiot had removed the line transformer and connected the trunk line
across the 20 ohm fader control. It went up in flames, and set the voice
coil on fire.

You never know what you'll find. I had the same problem in a high
school. The intercom worked fine, except to two speakers. but the all
call was low and distorted. Someone had removed the transformer form one
of the speakers, and that upset the entire system. The other speaker
had an open pair back to the office, and the building had been wired
with very early shielded pair cable, with no outer jacket. It was old
and so hard that over half the building would have had to be rewired to
fix the problem.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

Since the one leg won't work by itself, I would look for a short
somewhere on that leg. Probably break it at midpoint, and see what
happens, or maybe run a new wire pair to the midpoint and then try
feeding each half to see what happens., With a long run, and a short
at at unknown location, it will be a problem, but I bet a short is
what the problem is.

When I was installing new systems, I tried to put no more than five
speakers on each run. A 'Bud minibox' with a row of toggle switches
mounted near the amp, with a small monitor speaker and fader control
allowed isolating trouble to a bad zone in a few minutes, then you could
troubleshoot the bad zone while the rest of the system was in use. If
you go this route, you need a layout of the building to mark each zone,
and the speaker locations, for future reference. I always did that step
when giving a bid.

http://www.budind.com/view.php?part=sc-mb shows the aluminum boxes I
used.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

When I was installing new systems, I tried to put no more than five
speakers on each run. A 'Bud minibox' with a row of toggle switches
mounted near the amp, with a small monitor speaker and fader control
allowed isolating trouble to a bad zone in a few minutes, then you could
troubleshoot the bad zone while the rest of the system was in use. If
you go this route, you need a layout of the building to mark each zone,
and the speaker locations, for future reference. I always did that step
when giving a bid.

http://www.budind.com/view.php?part=sc-mbshows the aluminum boxes I
used.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Thats a really good idea for the future. The guy who installed this
nightmare did something like that. There is a home made relay box on
the wall near the amp. I'm guessing that at one time they did some
kind of zone paging however no one remembers ever doing this or where
the control point for this ever was.In theory then there should be
only one wire feeding the amp from this box, I mean thats what I would
have done but who knows what other people could have added or done
over the years. Sometimes we can get lucky by pulling relays thereby
opening the line at various points and finding the bad area but not so
this time. I think I'm going to go in at various points in the line
with my ESR meter and look for what I'm guessing, (hoping) is a dead
short somewhere. Hopefully I can jump in somewhere and work my way
toward the lowest resistance. It's going to be hot and messy and I'm
really not looking forward to this one week before my vacation starts
but I just know that I will feel so much better if we can get this
cluster &&&& behind us and then I can sip my margaritas on the beach
without thinking about it. Lenny..

 

[Ken Weitzel]

Thats a really good idea for the future. The guy who installed this
nightmare did something like that. There is a home made relay box on
the wall near the amp. I'm guessing that at one time they did some
kind of zone paging however no one remembers ever doing this or where
the control point for this ever was.In theory then there should be
only one wire feeding the amp from this box, I mean thats what I would
have done but who knows what other people could have added or done
over the years. Sometimes we can get lucky by pulling relays thereby
opening the line at various points and finding the bad area but not so
this time. I think I'm going to go in at various points in the line
with my ESR meter and look for what I'm guessing, (hoping) is a dead
short somewhere. Hopefully I can jump in somewhere and work my way
toward the lowest resistance. It's going to be hot and messy and I'm
really not looking forward to this one week before my vacation starts
but I just know that I will feel so much better if we can get this
cluster &&&& behind us and then I can sip my margaritas on the beach
without thinking about it. Lenny..

Hmmmm.... cool drinks on the beach... lovely ladies in bikini's...

Now I have one more suggestion, if I may...

In the interests of efficiency, I propose that you put off fixing
this problem until after your vacation. And that you should invite
all of us along to discuss the repair, thereby turning it into a
business meeting with all the attendant tax advantages. I think
that after a couple of weeks of cool drinks, lovely ladies, and sunny
beach we'll have come up with a consensus, and you can get back to
work.

All in favor?

Take care.

Ken

 

[Bob Urz]

Thats a really good idea for the future. The guy who installed this
nightmare did something like that. There is a home made relay box on
the wall near the amp. I'm guessing that at one time they did some
kind of zone paging however no one remembers ever doing this or where
the control point for this ever was.In theory then there should be
only one wire feeding the amp from this box, I mean thats what I would
have done but who knows what other people could have added or done
over the years. Sometimes we can get lucky by pulling relays thereby
opening the line at various points and finding the bad area but not so
this time. I think I'm going to go in at various points in the line
with my ESR meter and look for what I'm guessing, (hoping) is a dead
short somewhere. Hopefully I can jump in somewhere and work my way
toward the lowest resistance. It's going to be hot and messy and I'm
really not looking forward to this one week before my vacation starts
but I just know that I will feel so much better if we can get this
cluster &&&& behind us and then I can sip my margaritas on the beach
without thinking about it. Lenny..

What you need if your working on distributed sounds systems on a regular
basis is a impedance meter like a TOA ZM-104.

It will tell you the AC load to the amp in ohms as well as put a 1000 HZ
tone on the line so you can audibly hear if the speakers are working or not.

Bob

 

[Arfa Daily]

Thats a really good idea for the future. The guy who installed this
nightmare did something like that. There is a home made relay box on
the wall near the amp. I'm guessing that at one time they did some
kind of zone paging however no one remembers ever doing this or where
the control point for this ever was.In theory then there should be
only one wire feeding the amp from this box, I mean thats what I would
have done but who knows what other people could have added or done
over the years. Sometimes we can get lucky by pulling relays thereby
opening the line at various points and finding the bad area but not so
this time. I think I'm going to go in at various points in the line
with my ESR meter and look for what I'm guessing, (hoping) is a dead
short somewhere. Hopefully I can jump in somewhere and work my way
toward the lowest resistance. It's going to be hot and messy and I'm
really not looking forward to this one week before my vacation starts
but I just know that I will feel so much better if we can get this
cluster &&&& behind us and then I can sip my margaritas on the beach
without thinking about it. Lenny..

I don't know as an ESR meter is going to help you too much. The fact that
these usually run at a number of tens of kHz to make their measurement, may
well lead to some pretty misleading readings in a system full of so much
lumped and distributed L and C. Better to use the low ohms range of a
'standard' multimeter, I think.

Arfa

 

[[email protected]]

I don't know as an ESR meter is going to help you too much. The fact that
these usually run at a number of tens of kHz to make their measurement, may
well lead to some pretty misleading readings in a system full of so much
lumped and distributed L and C. Better to use the low ohms range of a
'standard' multimeter, I think.

Arfa- Hide quoted text -

- Show quoted text -

That makes a lot of sense. I'll bring the DVM. Thanks, Lenny

 

[Michael A. Terrell]

I don't know as an ESR meter is going to help you too much. The fact that
these usually run at a number of tens of kHz to make their measurement, may
well lead to some pretty misleading readings in a system full of so much
lumped and distributed L and C. Better to use the low ohms range of a
'standard' multimeter, I think.

Arfa

Actually, the ESR meter will show a short better than an ohm meter,
The inductance in the transformer primaries at 100 KHz will present a
high impedance to the meter. The capacitance between parallel
conductors can cause some problems, but you are well under a wavelength
in any normal sound system. 100 KHz would have a wavelength of 3
kilometers. Any system that large would have to be broken into
transformer isolated zones, and use multiple amplifiers.

If you can find both ends of a run and check both ends you can decide
which end is closer to the problem. Another thing to watch out for is a
trunk line shorted to the building's ground somewhere. This happens
when the wire is run across drop tile ceilings and the insulation is
damaged by the metal suspension grid. Another cause is using bare steel
wire to hang bundles of cable, and some idiot twisting the steel wire so
tight that it cut into the bundle of wires.

If you use DPDT toggle switches with center off in the box I
described, you can create a "Test buss" to connect your meter, or even a
second amp for troubleshooting. I like to use a terminal block to
terminate all wiring at the amp, so changes can be made quickly. When
possible, I used surplus 66 series telephone blocks and staked the
wires. The bridging clips work as well as the switches, but are not as
easy to use.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[msg]

I used surplus 66 series telephone blocks and staked the
wires. The bridging clips work as well as the switches, but are not as
easy to use.

The few building sound systems upon which I have worked all used
telecom punch blocks; perhaps it was because the sound system was
also integrated into the music-on-hold features of the pbx.

Regards,

Michael

 

[Michael A. Terrell]

The few building sound systems upon which I have worked all used
telecom punch blocks; perhaps it was because the sound system was
also integrated into the music-on-hold features of the pbx.

Regards,

Michael

A lot of the systems I serviced were installed before 1950, when the
WE was still using molded bakelite blocks with solid brass hardware.
Back them, they didn't sell to anyone outside their trade.

I modified some of the school intercom systems to 50 pin 'Amphenol
blue ribbon' plugs, so each bank of 25 switches plugged into the wall. A
pair of mating nine pin Molex plugs allowed you to remove and exchange a
panel by removing four screw, and three plugs. Then you could use
solder wick on the switch lugs to clean off the old solder, clip all
eight buss wires on one side of the switch, and pull out the bad
switch. It made repairs that normally took hours something that took
under 15 minutes.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Bob Urz]

That makes a lot of sense. I'll bring the DVM. Thanks, Lenny

Like it tried to tell you before, a DVM or regular ohm meter is of
limited use on 70 volt systems. If your doing school or business
distributed sound systems, get a audio impedance meter. It uses a 1000
hertz or so tone and translates that into a ohms on the line reading.
With this, you can determine the actual amp load in watts and see if a
line is actually shorted. A DVM will just show the resistance of the
line transformers primary and is of limited use.


Toa makes one. MCM electronics did have one. Goldline sells one too.

Bob

 

[Arfa Daily]

Actually, the ESR meter will show a short better than an ohm meter,
The inductance in the transformer primaries at 100 KHz will present a
high impedance to the meter. The capacitance between parallel
conductors can cause some problems, but you are well under a wavelength
in any normal sound system. 100 KHz would have a wavelength of 3
kilometers. Any system that large would have to be broken into
transformer isolated zones, and use multiple amplifiers.

Your theory is sound Michael, but I have been mislead in the past looking
for low resistances on a 'dynamic' system using my ESR meter. Just as an
experiment, I just tried measuring a roll of power cable that I had here,
using my Bob Parker / Dick Smith ESR meter. There is about 80m of cable on
the reel. I measured the open circuit capacitance, and came up with 11pf. I
then shorted the far end, and measured the inductance, as it was on a roll.
This came up at 0.032uH. So neither figure is particularly huge. However,
when I measured the cable with a low ohms range on a standard digital
multimeter, far-end short still in place, I got a figure of about 1 ohm.
When I repeated with the ESR meter, I got 55 ohms. I know that this isn't
really a 'fair' test with the cable being on a roll and so on, but I think
that it does illustrate that the readings you get on an ESR meter when you
are not right on top of the short, may not be what you are expecting. Just
as a matter of interest, the 'test' voltage from the Bob Parker appears to
be pulses of about 10uS duration, occuring every 5mS or so.

Arfa

 

[[email protected]]

Your theory is sound Michael, but I have been mislead in the past looking
for low resistances on a 'dynamic' system using my ESR meter. Just as an
experiment, I just tried measuring a roll of power cable that I had here,
using my Bob Parker / Dick Smith ESR meter. There is about 80m of cable on
the reel. I measured the open circuit capacitance, and came up with 11pf. I
then shorted the far end, and measured the inductance, as it was on a roll.
This came up at 0.032uH. So neither figure is particularly huge. However,
when I measured the cable with a low ohms range on a standard digital
multimeter, far-end short still in place, I got a figure of about 1 ohm.
When I repeated with the ESR meter, I got 55 ohms. I know that this isn't
really a 'fair' test with the cable being on a roll and so on, but I think
that it does illustrate that the readings you get on an ESR meter when you
are not right on top of the short, may not be what you are expecting. Just
as a matter of interest, the 'test' voltage from the Bob Parker appears to
be pulses of about 10uS duration, occuring every 5mS or so.

Arfa- Hide quoted text -

- Show quoted text -

Well we made the dreaded service call today to try to resolve this
problem. We brought a DVM, an ESR meter, and a used 100W amp which I
checked on the bench last night. I confirmed that it produced a clean
90W RMS into an 8 ohm load. We were loaded for bear.
We decided to forego all the troubleshooting and just connect up the
replacement amp to all three trunks in parallel and see what happens.
The total DC resistance of 20, 16, and 5.5 ohms in parallel without
calculating it must have been down below 3 ohms. I remembered that we
are dealing with impedance. I just never thought that the resistive
component could be that low. to our surprise the system worked
perfectly! I brought both amps, their original 35W amp as well as the
60W unit that I installed last week back to the shop for evaluation. I
determined that their original 35W amp produced 21W into 8 ohms before
clipping. My 70W amp could not even squeeze out 1 measly watt! Their
amp became weak and something happened to mine at some point that I
was not aware of. It seems that after all this effort I'm embarrased
to say that there was apparently nothing wrong with the distribution
system. It was normal component failure after all. I never suspected
my replacement, which was on the shelf marked "good" to be no good.
But confirming power output on the 100W amp last night was the ticket.
But anyway now I'm really ready for that vacation. Thanks to everyone
who took part in this discussion. It was very helpful and enjoyable
and I really appreciated it. Lenny Stein, Barlen Electronics.

 

[Bob Urz]

Well we made the dreaded service call today to try to resolve this
problem. We brought a DVM, an ESR meter, and a used 100W amp which I
checked on the bench last night. I confirmed that it produced a clean
90W RMS into an 8 ohm load. We were loaded for bear.
We decided to forego all the troubleshooting and just connect up the
replacement amp to all three trunks in parallel and see what happens.
The total DC resistance of 20, 16, and 5.5 ohms in parallel without
calculating it must have been down below 3 ohms. I remembered that we
are dealing with impedance. I just never thought that the resistive
component could be that low. to our surprise the system worked
perfectly! I brought both amps, their original 35W amp as well as the
60W unit that I installed last week back to the shop for evaluation. I
determined that their original 35W amp produced 21W into 8 ohms before
clipping. My 70W amp could not even squeeze out 1 measly watt! Their
amp became weak and something happened to mine at some point that I
was not aware of. It seems that after all this effort I'm embarrased
to say that there was apparently nothing wrong with the distribution
system. It was normal component failure after all. I never suspected
my replacement, which was on the shelf marked "good" to be no good.
But confirming power output on the 100W amp last night was the ticket.
But anyway now I'm really ready for that vacation. Thanks to everyone
who took part in this discussion. It was very helpful and enjoyable
and I really appreciated it. Lenny Stein, Barlen Electronics.

The thing you have to remember about some distributed systems is they
can be in a dynamic environment. Especially in a factory or such
with temperature extremes or vibration. One day they can be fine,
the next day the line could be shorted. A shorted line could overheat
the amp and cause a component failure.

The nice thing about a audio z meter is you can read the load and there
is a chart to tell you how many watts that load is into 25/70 volt line.
There is on digital unit that will tell you the wattage load directly



Bob

 

[Arfa Daily]

Well we made the dreaded service call today to try to resolve this
problem. We brought a DVM, an ESR meter, and a used 100W amp which I
checked on the bench last night. I confirmed that it produced a clean
90W RMS into an 8 ohm load. We were loaded for bear.
We decided to forego all the troubleshooting and just connect up the
replacement amp to all three trunks in parallel and see what happens.
The total DC resistance of 20, 16, and 5.5 ohms in parallel without
calculating it must have been down below 3 ohms. I remembered that we
are dealing with impedance. I just never thought that the resistive
component could be that low. to our surprise the system worked
perfectly! I brought both amps, their original 35W amp as well as the
60W unit that I installed last week back to the shop for evaluation. I
determined that their original 35W amp produced 21W into 8 ohms before
clipping. My 70W amp could not even squeeze out 1 measly watt! Their
amp became weak and something happened to mine at some point that I
was not aware of. It seems that after all this effort I'm embarrased
to say that there was apparently nothing wrong with the distribution
system. It was normal component failure after all. I never suspected
my replacement, which was on the shelf marked "good" to be no good.
But confirming power output on the 100W amp last night was the ticket.
But anyway now I'm really ready for that vacation. Thanks to everyone
who took part in this discussion. It was very helpful and enjoyable
and I really appreciated it. Lenny Stein, Barlen Electronics.

Good that you seem to have gotten to the bottom of it. There's nothing worse
than having a job like that hanging over you, is there, particularly when
you have some event like a vacation coming up ? Have a good 'un !

Arfa