A family member yesterday hooked up my old but favored NAD 3240PE amp
and crossed the bare speaker cable ends at the binding posts, creating
a dead short on one channel. I fixed this (and installed connectors)
when I got home. Both L and R sound fine now, but with a solid state
amp I would be surprised if the amp had not been damaged.

How likely is damage?

What would be the best ways to determine whether the amp is damaged?

If it sounds fine to my ears, should I forget it?

Tks

J. Newell

I'd worry about something else. Sounds like no damage at all. Some amps
have built in protection circuitry.





in article , JNewell at
wrote on 8/11/04 7:42 AM:

A family member yesterday hooked up my old but favored NAD 3240PE amp
and crossed the bare speaker cable ends at the binding posts, creating
a dead short on one channel. I fixed this (and installed connectors)
when I got home. Both L and R sound fine now, but with a solid state
amp I would be surprised if the amp had not been damaged.

How likely is damage?

What would be the best ways to determine whether the amp is damaged?

If it sounds fine to my ears, should I forget it?

Tks

J. Newell

"Jon Yaeger" wrote in message


I'd worry about something else. Sounds like no damage at all. Some
amps have built in protection circuitry.

Actually, just about all of them, particularly those built after 1970.

In article ,
JNewell wrote:

A family member yesterday hooked up my old but favored NAD 3240PE amp
and crossed the bare speaker cable ends at the binding posts, creating
a dead short on one channel. I fixed this (and installed connectors)
when I got home. Both L and R sound fine now, but with a solid state
amp I would be surprised if the amp had not been damaged.

How likely is damage?

If an amp doesn't include protective circuitry in its output stage, a
dead short circuit would almost certainly blow out the output
transistors in a puff of blue smoke within a fraction of a second
after the amp was turned on with an audio signal present.

The fact that this didn't occur, and that the amp still plays OK,
suggests to me that there's some form of overcurrent detector/limiter
in the output stage and drivers. Such a circuit would react
instantaneously (quite a lot faster than a fuse) and limit the
output-transistor dissipation to a value less than the transistor's
safety limit.

What would be the best ways to determine whether the amp is damaged?

One way is to hook it up to a suitably-sized 8-ohm dummy load, start
playing a signal of gradually increasing amplitude, crank it up slowly
from "silent" to "full power", and monitor the waveform on an
oscilloscope. If it'll deliver all power levels (for many amps, 1/3
of full rated power is just about the most stressful in terms of heat
dissipation), and the waveform doesn't show nasty anomalies, then it's
OK. Don't run this test for too long, as it may overheat the output
stage or the dummy load.

Odds are, though, that if it sounds OK on music at your usual
listening level (or a bit higher), then it hasn't suffered damage.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On 11 Aug 2004 04:42:13 -0700, (JNewell) wrote:

A family member yesterday hooked up my old but favored NAD 3240PE amp
and crossed the bare speaker cable ends at the binding posts, creating
a dead short on one channel. I fixed this (and installed connectors)
when I got home. Both L and R sound fine now, but with a solid state
amp I would be surprised if the amp had not been damaged.

How likely is damage?

What would be the best ways to determine whether the amp is damaged?

If it sounds fine to my ears, should I forget it?

If it was damaged, you'd have found out about it very quickly.

Shorted speaker connections are not uncommon. It's standard to have
some protection built in to the amp.

"JNewell" wrote in message
om...
A family member yesterday hooked up my old but favored NAD 3240PE amp
and crossed the bare speaker cable ends at the binding posts, creating
a dead short on one channel. I fixed this (and installed connectors)
when I got home. Both L and R sound fine now, but with a solid state
amp I would be surprised if the amp had not been damaged.

How likely is damage?

**Not too likely (With that particular model). Earlier NAD models employed
fuses for protection. Fuses may fail AFTER output device failure.


What would be the best ways to determine whether the amp is damaged?

**Listen to it. Any damage will likely be catastrophic and easy to detect.


If it sounds fine to my ears, should I forget it?

**Yep.

Funnily enough, a short circuit is not the worst treatment you can dish out
to a modern SS amplifier. A low impedance load, is likely to cause far more
difficulty, as output devices may be driven past their SOA limits. Back in
the 1970s, I was service manager for Marantz (Australia). In every Marantz
service manual, there was a procedure, where a switch was to be fitted
across the dummy loads, shorting the outputs. This test was the suggested
procedure for all output stage repairs. As long as the job has been done
correctly, it is a non-event. A (say) 2 Ohm load, for a few minutes,
however, is a whole different story. In fact, the only Marantz amp which
could reliably survive such treatment was the Marantz model 500 (ca.1973),
which was fitted with true SOA protection systems, incorporating Voltage AND
current limiting).


--
Trevor Wilson
www.rageaudio.com.au

Trevor Wilson wrote:

In fact, the only Marantz amp which
could reliably survive such treatment was the Marantz model 500 (ca.1973),
which was fitted with true SOA protection systems, incorporating Voltage AND
current limiting).

Don't tell Phil Allison !



Graham

"Pooh Bear" wrote in message
...


Trevor Wilson wrote:

In fact, the only Marantz amp which
could reliably survive such treatment was the Marantz model 500
(ca.1973),
which was fitted with true SOA protection systems, incorporating Voltage
AND
current limiting).

Don't tell Phil Allison !

**He already knows.


--
Trevor Wilson
www.rageaudio.com.au