Help! Continuing to blow out my amplifier

[dk253]

Greetings,

I am continuing to blow out my "whole house" amp and neither my audio
installers nor I can figure out what the problem is. And I am tired
of paying these jokers $100 per hour to not fix the problem that they
caused in the first place! I do not know if it is a short somewhere
or the load is just too much.

The Scenario
1) I am an electrical novice... so I kind of get that speakers have
resistance and I once knew what that meant.

2) I have 9 pairs of speakers hooked to some kind of resistance device
so far back in the component cabinet that I cannot tell you what brand
it is... but I can tell you it is set to "10" at the point where it
asks "number of speaker pairs". The other choices are "8,6,4, and 2".
I have tried both 8 and 10 with the same ultimate result.

3) The speakers are eiether in ceiling speakers or outdoor speakers.
All by paradigm (I believe). I do not know what the ohm-age ratings
are.

4) Mostly there each connector on the resistance thingy has only one
pair of speakers but in the case of two of the connectors there is two
pairs of speakers hanging off each in series.

5) each set of speakers has its own in wall volume control.

6) The amplifier driving these is a Rotel RB-981.
(http://www.rotel.com/products/pdfs/rb981.pdf)
With, I believe, 2x130 Watts of power.

7) I am playing continuous music from a PC running musicmatch through
a marantz receiver that is then sending its second zone out through
the rotel. I do not believe the source is relevant... but let me know
if you want more details.

8) The Rotel lasts about 30 days and seems to be working fine then it
blows. I have tried opening it and replacing the fuses but they blow
almost immediately once it goes. It has been back to Rotel 3 times!

The Questions
This is driving me to distraction. What can I use to test each
speaker for shorts? What can I do to test the speaker switcher? What
is the math I need to do to determine whether I, in fact, have too
high of a load?

Thanks a ton for your help... I'll send a boomerang out to anyone who
gives me some good clues.

Dave

[Jerry G.]

It sounds like the amplifier is under rated and not designed for what you
want to do, and the impedance loading is not right.

For these applications there are power amplifiers specially designed to take
multiple speaker loads. Also, normally a 70 Volt speaker system is put in
with an amplifier designed to run 70 Volt speaker systems. Each speaker box
would have a 70 Volt to 8 ohm transformer driving it, that is rated at the
required wattage for its use. Normally, we have used 50 to 100 Watt rated
transformers in most installations. This gives a good headroom to avoid any
possible over saturation.

The amplifier you have was not designed for this type of application. The
impedance loading is all over the place, because of the multiple speakers
and pots. Also the total impedance is probably much too low, with a high
return loss. Your amplifier will be blowing all the time! I bet if you put
a standard pair of 8 ohm speaker boxes directly on it, with the proper
speaker wire, the amp will run for years without failure.

Look in to 70 volt audio distribution for details about how it is done, and
the proper type of equipment required. check this link for an example of
where to start http://www.milestech.com/mpt70.htm

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"dk253" > wrote in message
om...
Greetings,

I am continuing to blow out my "whole house" amp and neither my audio
installers nor I can figure out what the problem is. And I am tired
of paying these jokers $100 per hour to not fix the problem that they
caused in the first place! I do not know if it is a short somewhere
or the load is just too much.

The Scenario
1) I am an electrical novice... so I kind of get that speakers have
resistance and I once knew what that meant.

2) I have 9 pairs of speakers hooked to some kind of resistance device
so far back in the component cabinet that I cannot tell you what brand
it is... but I can tell you it is set to "10" at the point where it
asks "number of speaker pairs". The other choices are "8,6,4, and 2".
I have tried both 8 and 10 with the same ultimate result.

3) The speakers are eiether in ceiling speakers or outdoor speakers.
All by paradigm (I believe). I do not know what the ohm-age ratings
are.

4) Mostly there each connector on the resistance thingy has only one
pair of speakers but in the case of two of the connectors there is two
pairs of speakers hanging off each in series.

5) each set of speakers has its own in wall volume control.

6) The amplifier driving these is a Rotel RB-981.
(http://www.rotel.com/products/pdfs/rb981.pdf)
With, I believe, 2x130 Watts of power.

7) I am playing continuous music from a PC running musicmatch through
a marantz receiver that is then sending its second zone out through
the rotel. I do not believe the source is relevant... but let me know
if you want more details.

8) The Rotel lasts about 30 days and seems to be working fine then it
blows. I have tried opening it and replacing the fuses but they blow
almost immediately once it goes. It has been back to Rotel 3 times!

The Questions
This is driving me to distraction. What can I use to test each
speaker for shorts? What can I do to test the speaker switcher? What
is the math I need to do to determine whether I, in fact, have too
high of a load?

Thanks a ton for your help... I'll send a boomerang out to anyone who
gives me some good clues.

Dave

[Todd H.]

(dk253) writes:

> 8) The Rotel lasts about 30 days and seems to be working fine then it
> blows. I have tried opening it and replacing the fuses but they blow
> almost immediately once it goes. It has been back to Rotel 3 times!

Once a power transistor burns up or shorts, an overcurrent condition
in the amplifier occurs. That blows the fuse. The fuse is just doing
its job keeping your amplifier from burning down your home.

> The Questions This is driving me to distraction. What can I use to
> test each speaker for shorts?

A VOM- volt ohm meter. Such as
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=22-223

> What can I do to test the speaker switcher? What is the math I need
> to do to determine whether I, in fact, have too high of a load?

Same piece of equipment.

That meter will measure the DC resistance. The actual impedance of
the speakers is slightly higher than the CD resistance.

Sounds to me like the amplifier is working too hard and is "seeing"
too low of an impedance. I'd also be curious about the thermal and
airflow situation around that amplifier. Any amp run too hard, too
hot, and for too long will eventually fail. Semiconductor device
physics wouldn't have it any other way. ;-)

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | "4 lines suffice."

[Oceans 2K]

I agree with other posters. That ROTEL would do a wonderful job if used as
designed. It sounds like this is outside of it's realm of intended use.

It is not the amplifier...it's the way your speakers are wired (or lack of).
the ROTEL is "seeing" a low impedance overall load (sub 4 ohms).

The guys who installed didn't do a lot of thinking when designing the
system.

TC
"dk253" > wrote in message
om...
> Greetings,
>
> I am continuing to blow out my "whole house" amp and neither my audio
> installers nor I can figure out what the problem is. And I am tired
> of paying these jokers $100 per hour to not fix the problem that they
> caused in the first place! I do not know if it is a short somewhere
> or the load is just too much.
>
> The Scenario
> 1) I am an electrical novice... so I kind of get that speakers have
> resistance and I once knew what that meant.
>
> 2) I have 9 pairs of speakers hooked to some kind of resistance device
> so far back in the component cabinet that I cannot tell you what brand
> it is... but I can tell you it is set to "10" at the point where it
> asks "number of speaker pairs". The other choices are "8,6,4, and 2".
> I have tried both 8 and 10 with the same ultimate result.
>
> 3) The speakers are eiether in ceiling speakers or outdoor speakers.
> All by paradigm (I believe). I do not know what the ohm-age ratings
> are.
>
> 4) Mostly there each connector on the resistance thingy has only one
> pair of speakers but in the case of two of the connectors there is two
> pairs of speakers hanging off each in series.
>
> 5) each set of speakers has its own in wall volume control.
>
> 6) The amplifier driving these is a Rotel RB-981.
> (http://www.rotel.com/products/pdfs/rb981.pdf)
> With, I believe, 2x130 Watts of power.
>
> 7) I am playing continuous music from a PC running musicmatch through
> a marantz receiver that is then sending its second zone out through
> the rotel. I do not believe the source is relevant... but let me know
> if you want more details.
>
> 8) The Rotel lasts about 30 days and seems to be working fine then it
> blows. I have tried opening it and replacing the fuses but they blow
> almost immediately once it goes. It has been back to Rotel 3 times!
>
> The Questions
> This is driving me to distraction. What can I use to test each
> speaker for shorts? What can I do to test the speaker switcher? What
> is the math I need to do to determine whether I, in fact, have too
> high of a load?
>
> Thanks a ton for your help... I'll send a boomerang out to anyone who
> gives me some good clues.
>
> Dave
>

[Rich Andrews.]

(dk253) wrote in
om:

> Greetings,
>
> I am continuing to blow out my "whole house" amp and neither my audio
> installers nor I can figure out what the problem is. And I am tired
> of paying these jokers $100 per hour to not fix the problem that they
> caused in the first place! I do not know if it is a short somewhere
> or the load is just too much.
>
> The Scenario
> 1) I am an electrical novice... so I kind of get that speakers have
> resistance and I once knew what that meant.
>
> 2) I have 9 pairs of speakers hooked to some kind of resistance device
> so far back in the component cabinet that I cannot tell you what brand
> it is... but I can tell you it is set to "10" at the point where it
> asks "number of speaker pairs". The other choices are "8,6,4, and 2".
> I have tried both 8 and 10 with the same ultimate result.
>
> 3) The speakers are eiether in ceiling speakers or outdoor speakers.
> All by paradigm (I believe). I do not know what the ohm-age ratings
> are.
>
> 4) Mostly there each connector on the resistance thingy has only one
> pair of speakers but in the case of two of the connectors there is two
> pairs of speakers hanging off each in series.
>
> 5) each set of speakers has its own in wall volume control.
>
> 6) The amplifier driving these is a Rotel RB-981.
> (http://www.rotel.com/products/pdfs/rb981.pdf)
> With, I believe, 2x130 Watts of power.
>
> 7) I am playing continuous music from a PC running musicmatch through
> a marantz receiver that is then sending its second zone out through
> the rotel. I do not believe the source is relevant... but let me know
> if you want more details.
>
> 8) The Rotel lasts about 30 days and seems to be working fine then it
> blows. I have tried opening it and replacing the fuses but they blow
> almost immediately once it goes. It has been back to Rotel 3 times!
>
> The Questions
> This is driving me to distraction. What can I use to test each
> speaker for shorts? What can I do to test the speaker switcher? What
> is the math I need to do to determine whether I, in fact, have too
> high of a load?
>
> Thanks a ton for your help... I'll send a boomerang out to anyone who
> gives me some good clues.
>
> Dave
>

Dave,

Electricians are not audio engineers.

Based on my experience I am going to say that the speakers are not wired
correctly for the amp. 9 pairs of speakers is a fair number and would
guess that they are located at various places throughout your home. I
would also guess that they are directly or indirectly wired in parallel.
If all of they are in use at one time, and their nominal impedance is 4
ohms, then the load to the amp is something less than 1/2 ohm. Very few
amplifiers can handle a load like that. You have two choices. Replace
the amp with one that can handle that low a load or wire the speakers in a
series/parallel configuration so that the amp sees an impedance that it is
designed for. As to which solution is right for you requires a bit more
data.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

[Tim Padrick]

The other posters seem to have missed your mention of "some kind of
resistance device". This is likely a multi-tapped transformer that is
designed to maintain the proper load on the amp when driving multiple pairs
of speakers, such as
http://www.nilesaudio.com/products/hp_impedance_matching.html. It should
work fine.

Make sure that they did not use shielded cable from the amp or the box, or
from the box to any of the speakers. The capacitance of such cable would
cause the impedance to become very low at high frequencies, which will make
some amps unstable, overheat, or blow.

The box may be overly capacitive. Try locating the box farther from the
amp, and use longer cables between the amp and box. The inductance of the
cable may then isolate the amp from the box's capacitance enough to keep it
stable and working.

If the "jokers" did the install and supplied the gear, it's their
responsibility to make it work - free. If they don't, I'd tell them to take
it away and refund your money. If they don't, take them to small claims
court. (If you already had the amp and speakers, it's still their
responsibility to make sure that what they add and install will function
with the equipment that you supplied.)


"dk253" > wrote in message
om...
> Greetings,
>
> I am continuing to blow out my "whole house" amp and neither my audio
> installers nor I can figure out what the problem is. And I am tired
> of paying these jokers $100 per hour to not fix the problem that they
> caused in the first place! I do not know if it is a short somewhere
> or the load is just too much.
>
> The Scenario
> 1) I am an electrical novice... so I kind of get that speakers have
> resistance and I once knew what that meant.
>
> 2) I have 9 pairs of speakers hooked to some kind of resistance device
> so far back in the component cabinet that I cannot tell you what brand
> it is... but I can tell you it is set to "10" at the point where it
> asks "number of speaker pairs". The other choices are "8,6,4, and 2".
> I have tried both 8 and 10 with the same ultimate result.
>
> 3) The speakers are eiether in ceiling speakers or outdoor speakers.
> All by paradigm (I believe). I do not know what the ohm-age ratings
> are.
>
> 4) Mostly there each connector on the resistance thingy has only one
> pair of speakers but in the case of two of the connectors there is two
> pairs of speakers hanging off each in series.
>
> 5) each set of speakers has its own in wall volume control.
>
> 6) The amplifier driving these is a Rotel RB-981.
> (http://www.rotel.com/products/pdfs/rb981.pdf)
> With, I believe, 2x130 Watts of power.
>
> 7) I am playing continuous music from a PC running musicmatch through
> a marantz receiver that is then sending its second zone out through
> the rotel. I do not believe the source is relevant... but let me know
> if you want more details.
>
> 8) The Rotel lasts about 30 days and seems to be working fine then it
> blows. I have tried opening it and replacing the fuses but they blow
> almost immediately once it goes. It has been back to Rotel 3 times!
>
> The Questions
> This is driving me to distraction. What can I use to test each
> speaker for shorts? What can I do to test the speaker switcher? What
> is the math I need to do to determine whether I, in fact, have too
> high of a load?
>
> Thanks a ton for your help... I'll send a boomerang out to anyone who
> gives me some good clues.
>
> Dave
>

[Arny Krueger]

"dk253" > wrote in message
om

> 8) The Rotel lasts about 30 days and seems to be working fine then it
> blows. I have tried opening it and replacing the fuses but they blow
> almost immediately once it goes. It has been back to Rotel 3 times!
>
> The Questions
> This is driving me to distraction. What can I use to test each
> speaker for shorts? What can I do to test the speaker switcher? What
> is the math I need to do to determine whether I, in fact, have too
> high of a load?


The Rotel is obviously a POS. A well-designed power amp will either work or
shut itself down without damage, under almost any conceivable situation.
Surf EBay and pick up a QSC USA 850 or 900, they usually close for about
$200 (apparently the cost of just 2 hours of incompetent labor). IME the QSC
will either blow away whatever is causing the problem, or it will just run
indefinitely.

[bg]

When your service guy comes in, tell him to measure the Z or wattage
consumption of the string of speakers. Those numbers have to agree with the
rotel's specifications. If the guy is worth 100 per hour he should be
equipped to do so and should already know what numbers he was shooting for
in the first place. This procedure won't fix the system problem but it will
tell you if the sound guy is a quack. This isn't rocket science. Even Radio
Shack would have the answere!
bg


dk253 wrote in message ...
>Greetings,
>
>I am continuing to blow out my "whole house" amp and neither my audio
>big snip ---------

[UnionPac2001]

wrote:

<snip>


>This isn't rocket science. Even Radio
>Shack would have the answere!
>bg

I think you're dreaming! : )
Radio Shack has NEVER had ANY answers (at least not informed, intelligent, or
correct ones).

Jeff

[dk253]

Thanks to everyone who responded! Very helpful.

1) I purchaed on ebay (as suggested) a QSC 850 amp for $195

2) I checked the wiring and distance and all seems ok

3) the "resistance thingy" is a russound 12 speaker set distribution
panel. but I may have it set wrong. I think my amp is 4 ohm but I am
not sure what the speakers are set to. I have to take one out of the
cieling to find out.

I do not know how to test with the ohmeter. Some more help here would
be great. How would you test with the ohmmeter to see if speakers are
4 ohm or 8 ohm?

Thanks

Dave


(dk253) wrote in message >...
> Greetings,
>
> I am continuing to blow out my "whole house" amp and neither my audio
> installers nor I can figure out what the problem is. And I am tired
> of paying these jokers $100 per hour to not fix the problem that they
> caused in the first place! I do not know if it is a short somewhere
> or the load is just too much.
>
> The Scenario
> 1) I am an electrical novice... so I kind of get that speakers have
> resistance and I once knew what that meant.
>
> 2) I have 9 pairs of speakers hooked to some kind of resistance device
> so far back in the component cabinet that I cannot tell you what brand
> it is... but I can tell you it is set to "10" at the point where it
> asks "number of speaker pairs". The other choices are "8,6,4, and 2".
> I have tried both 8 and 10 with the same ultimate result.
>
> 3) The speakers are eiether in ceiling speakers or outdoor speakers.
> All by paradigm (I believe). I do not know what the ohm-age ratings
> are.
>
> 4) Mostly there each connector on the resistance thingy has only one
> pair of speakers but in the case of two of the connectors there is two
> pairs of speakers hanging off each in series.
>
> 5) each set of speakers has its own in wall volume control.
>
> 6) The amplifier driving these is a Rotel RB-981.
> (http://www.rotel.com/products/pdfs/rb981.pdf)
> With, I believe, 2x130 Watts of power.
>
> 7) I am playing continuous music from a PC running musicmatch through
> a marantz receiver that is then sending its second zone out through
> the rotel. I do not believe the source is relevant... but let me know
> if you want more details.
>
> 8) The Rotel lasts about 30 days and seems to be working fine then it
> blows. I have tried opening it and replacing the fuses but they blow
> almost immediately once it goes. It has been back to Rotel 3 times!
>
> The Questions
> This is driving me to distraction. What can I use to test each
> speaker for shorts? What can I do to test the speaker switcher? What
> is the math I need to do to determine whether I, in fact, have too
> high of a load?
>
> Thanks a ton for your help... I'll send a boomerang out to anyone who
> gives me some good clues.
>
> Dave
>

[Arny Krueger]

"dk253" > wrote in message
m


> I do not know how to test with the ohmmeter. Some more help here would
> be great. How would you test with the ohmmeter to see if speakers are
> 4 ohm or 8 ohm?

Connect the ohm meter across the terminals of the speakers(s) you want to
test. The reading on the ohm meter is very close to the speaker's nominal
impedance. Yup, that simple! It should be between 1 ohm and 20 ohms. If
it's less than 4 ohms, it's too low.