Re: Audio Amplifier Problems


"PDI Dave" <david@xxxxxxxxxxxxx> wrote in message
news:1166859510.098648.164960@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Sounds like an overload is causing the amps to shut down. Are all of the
speakers working before it shuts down? Any chance there is a short on the
secondary side of one of the circuits?

70.7 volt systems only produce that voltage at maximum output power. How
are calculating power? Are you measuring voltage and current? Also, what
is the test signal (waveform and frequency). The meter might not be
adequate.

yeah, i does sound like an overload, except that it is inconsistent.
too inconsistent to be able to say for sure. all speakers seem to be
working fine, though with the quantities involved, i can't be sure. by
short on the secondary side, you mean on the secondary of the
transformers for the speakers?

Yes.

each speaker has its own transformer and
each is tapped at 1/2 watt.

That's good.

yes, i'm measuring voltage and current. the test signal is a speech

Speech is not the correct test signal for measuring power but is OK as a
basic check.
A 400 Hz sine wave is typical for testing audio systems.

tone. the tone seems to be around 1Khz, though i don't know the
waveform. the meter has a min-max function which i've been using to
capture peak levels. the actual voltage on the circuit is more like 50.
what kind of meter do i need? or will a meter at all even be
adequate... do i need an O-scope?

Yes, as I posted , 70.7 volts is realized only at maximum output ... so at
50 vols, the system is operating below its capability (assuming all is
normal).


what is a good dummy load? there are actually more than 100 speakers,
i'm just trying to get an idea for how to fix this and was therfore
giving an idea for 1 amp and its approximate load, i'm also learning a
lot as i go. the reality of it is more like >1000 speakers divided
across 10 amplifiers that are all separate from each other except for a
shared pre-amp input. though not all amps are causing a problem,
currently only 2 are, so the rest of it i should be able to ignore. i
think the main problem circuit is around 175 1/2 watt speakers. that
means by my calcs, i should have about 87.5 watts of speakers and
should then be well within the amps capacity. any more help is greatly
appreciated.

Is there an 8 ohm or 4 ohm output? If so, you can use a resistor of that
resistance, rated at 100 W (or somewhat less for a brief test). I use an
oscilloscope connected across the dummy load and a triangle wave test signal
at 400 Hz.


.

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