[NotImportant]

On Feb 14, 3:51*pm, "Karl Uppiano" wrote:
"NotImportant" wrote in message

...



On Feb 12, 2:30 am, "Peter Larsen" wrote:
NotImportant wrote:
On Feb 10, 11:47 pm, "Peter Larsen" wrote:
NotImportant wrote:

If I use a timer to do the switch over
do you think it is safe, for the amplifier and the tweeters, to use a
contactor without first having a way to lower the volume first ? *How
would the volume be lowered automatically before the switch over ?

As I see this what you suggest is more stuff that could fail, imo you
would
reduce the mean time between failures rather than increase it.

* Hi Peter,

* * * I may still want to parallel the amp output and switch over at
regular interval. My concern is the spike that would be created upon
sudden shutting off of the amp. Would it help if I have a resistor
shunt to ground - let's say 100 Ohm ?

* * * *The power in the tweeters could then be channelled to ground
before the new amp come on. *The power loss in the resistor is very
minimal but it would help prevent dangerous spikes.

* *Your opinion is much appreciated. Thanks.

PMJI, but I really don't think you need to be concerned about spikes. They
shouldn't occur, but even if they do, why would spikes be any worse than the
intended signal? And piezo tweeters are not fragile.

I also wonder why you feel you need two amplifiers, except for backup in
case one failed. In that case, you could simply turn off the dead one and
swap in the good one. For as frequently as you should need to do it, quick
disconnect speaker jacks would work just fine. Solid state audio amplifiers
are generally very reliable, and as long as the load and the signal remain
within the amplifier's rated capabilities, the amplifier could run for many
years without any attention whatsoever.

Case in point, I worked at a radio station that used a cheap Radio Shack 30
watt solid state PA amplifier to feed the station's off-the-air program
audio to dozens of 25-volt ceiling speakers all around the facility. The
audio was not amplifier-friendly: compressed, with a very low
peak-to-average ratio, and at night there was a strong 10 KHz whistle from
adjacent channels. The amplifier ran at nearly full output, 24x7, for the
six years that I worked there, with never any down time whatsoever (except
for unplanned power failures). It sat high on a shelf in a hot furnace room
the whole time. It was running on my first day working there, and it was
running on my last day working there. I blew the dust off of it a few times.
The heat sinks were always too hot to touch. Part of its longevity
undoubtedly was due to the fact that it had no moving parts. There was no
fan to gum up and stop, or to draw dust through the works.

Which occurs to me... PA amplifiers with 25-volt outputs are typically the
way to drive multiple speaker arrays. The speakers usually bridge the
transmission line at various points along the way, using matching
transformers, but I think you could probably bridge piezo tweeters directly.
You would need actual performance data on the tweeters to determine how many
you could put on the line, and how many watts the amplifier would need.


Thanks for the input.

My view was that when you are driving 100s of watts into a load
and suddenly turning it off will result in a huge spike if these
energy has no way to go. I was thinking of connecting a 100 Ohm / 10
Watt or 10 Ohm/10 watt to ground at the amplifier output so that when
the amplifier is switched off the energy has a path to ground before
the next amplifier is turnd on.

But I think your advice is well noted and I will follow this.

Thanks again.

[Karl Uppiano[_2_]]

"NotImportant" wrote in message
...
On Feb 14, 3:51 pm, "Karl Uppiano" wrote:
"NotImportant" wrote in message

...



On Feb 12, 2:30 am, "Peter Larsen" wrote:
NotImportant wrote:
On Feb 10, 11:47 pm, "Peter Larsen" wrote:
NotImportant wrote:

If I use a timer to do the switch over
do you think it is safe, for the amplifier and the tweeters, to use
a
contactor without first having a way to lower the volume first ?
How
would the volume be lowered automatically before the switch over ?

As I see this what you suggest is more stuff that could fail, imo you
would
reduce the mean time between failures rather than increase it.

Hi Peter,

I may still want to parallel the amp output and switch over at
regular interval. My concern is the spike that would be created upon
sudden shutting off of the amp. Would it help if I have a resistor
shunt to ground - let's say 100 Ohm ?

The power in the tweeters could then be channelled to ground
before the new amp come on. The power loss in the resistor is very
minimal but it would help prevent dangerous spikes.

Your opinion is much appreciated. Thanks.

PMJI, but I really don't think you need to be concerned about spikes.
They
shouldn't occur, but even if they do, why would spikes be any worse than
the
intended signal? And piezo tweeters are not fragile.

I also wonder why you feel you need two amplifiers, except for backup in
case one failed. In that case, you could simply turn off the dead one and
swap in the good one. For as frequently as you should need to do it,
quick
disconnect speaker jacks would work just fine. Solid state audio
amplifiers
are generally very reliable, and as long as the load and the signal
remain
within the amplifier's rated capabilities, the amplifier could run for
many
years without any attention whatsoever.

Case in point, I worked at a radio station that used a cheap Radio Shack
30
watt solid state PA amplifier to feed the station's off-the-air program
audio to dozens of 25-volt ceiling speakers all around the facility. The
audio was not amplifier-friendly: compressed, with a very low
peak-to-average ratio, and at night there was a strong 10 KHz whistle
from
adjacent channels. The amplifier ran at nearly full output, 24x7, for the
six years that I worked there, with never any down time whatsoever
(except
for unplanned power failures). It sat high on a shelf in a hot furnace
room
the whole time. It was running on my first day working there, and it was
running on my last day working there. I blew the dust off of it a few
times.
The heat sinks were always too hot to touch. Part of its longevity
undoubtedly was due to the fact that it had no moving parts. There was no
fan to gum up and stop, or to draw dust through the works.

Which occurs to me... PA amplifiers with 25-volt outputs are typically
the
way to drive multiple speaker arrays. The speakers usually bridge the
transmission line at various points along the way, using matching
transformers, but I think you could probably bridge piezo tweeters
directly.
You would need actual performance data on the tweeters to determine how
many
you could put on the line, and how many watts the amplifier would need.


Thanks for the input.

My view was that when you are driving 100s of watts into a load
and suddenly turning it off will result in a huge spike if these
energy has no way to go. I was thinking of connecting a 100 Ohm / 10
Watt or 10 Ohm/10 watt to ground at the amplifier output so that when
the amplifier is switched off the energy has a path to ground before
the next amplifier is turnd on.

The energy goes where all the energy goes... it dissipates as audio and as
heat. Turning off the amplifier is no different than if the audio stops
suddenly (because the orchestra stops playing, or you hit stop on the CD
player). It isn't as if you have 100 watts circulating around in the system
with nowhere to go. It is exiting the speakers as fast as the amplifier
generates it. There is simply no need to try to "absorb" it. It simply
wastes power that would otherwise go to create sound, and makes the
amplifier work harder. It will actually reduce overall reliability.

[NotImportant]

On Feb 17, 10:56*am, "Karl Uppiano" wrote:
"NotImportant" wrote in message

...



On Feb 14, 3:51 pm, "Karl Uppiano" wrote:
"NotImportant" wrote in message

....

On Feb 12, 2:30 am, "Peter Larsen" wrote:
NotImportant wrote:
On Feb 10, 11:47 pm, "Peter Larsen" wrote:
NotImportant wrote:

If I use a timer to do the switch over
do you think it is safe, for the amplifier and the tweeters, to use
a
contactor without first having a way to lower the volume first ?
How
would the volume be lowered automatically before the switch over ?

As I see this what you suggest is more stuff that could fail, imo you
would
reduce the mean time between failures rather than increase it.

* Hi Peter,

* * * I may still want to parallel the amp output and switch over at
regular interval. My concern is the spike that would be created upon
sudden shutting off of the amp. Would it help if I have a resistor
shunt to ground - let's say 100 Ohm ?

* * * *The power in the tweeters could then be channelled to ground
before the new amp come on. *The power loss in the resistor is very
minimal but it would help prevent dangerous spikes.

* *Your opinion is much appreciated. Thanks.

PMJI, but I really don't think you need to be concerned about spikes.
They
shouldn't occur, but even if they do, why would spikes be any worse than
the
intended signal? And piezo tweeters are not fragile.

I also wonder why you feel you need two amplifiers, except for backup in
case one failed. In that case, you could simply turn off the dead one and
swap in the good one. For as frequently as you should need to do it,
quick
disconnect speaker jacks would work just fine. Solid state audio
amplifiers
are generally very reliable, and as long as the load and the signal
remain
within the amplifier's rated capabilities, the amplifier could run for
many
years without any attention whatsoever.

Case in point, I worked at a radio station that used a cheap Radio Shack
30
watt solid state PA amplifier to feed the station's off-the-air program
audio to dozens of 25-volt ceiling speakers all around the facility. The
audio was not amplifier-friendly: compressed, with a very low
peak-to-average ratio, and at night there was a strong 10 KHz whistle
from
adjacent channels. The amplifier ran at nearly full output, 24x7, for the
six years that I worked there, with never any down time whatsoever
(except
for unplanned power failures). It sat high on a shelf in a hot furnace
room
the whole time. It was running on my first day working there, and it was
running on my last day working there. I blew the dust off of it a few
times.
The heat sinks were always too hot to touch. Part of its longevity
undoubtedly was due to the fact that it had no moving parts. There was no
fan to gum up and stop, or to draw dust through the works.

Which occurs to me... PA amplifiers with 25-volt outputs are typically
the
way to drive multiple speaker arrays. The speakers usually bridge the
transmission line at various points along the way, using matching
transformers, but I think you could probably bridge piezo tweeters
directly.
You would need actual performance data on the tweeters to determine how
many
you could put on the line, and how many watts the amplifier would need..

* Thanks for the input.

* *My view was that when you are driving 100s of watts into a load
and suddenly turning it off will result in a huge spike if these
energy has no way to go. *I was thinking of connecting a 100 Ohm / 10
Watt or 10 Ohm/10 watt to ground at the amplifier output so that when
the amplifier is switched off the energy has a path to ground before
the next amplifier is turnd on.

The energy goes where all the energy goes... it dissipates as audio and as
heat. Turning off the amplifier is no different than if the audio stops
suddenly (because the orchestra stops playing, or you hit stop on the CD
player). It isn't as if you have 100 watts circulating around in the system
with nowhere to go. It is exiting the speakers as fast as the amplifier
generates it. There is simply no need to try to "absorb" it. It simply
wastes power that would otherwise go to create sound, and makes the
amplifier work harder. It will actually reduce overall reliability.


Point noted. Thank you.