NotImportant
February 16th 09, 01:33 PM
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.
> "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.