common ground output ampliers
dangling entity
not? How can you tell if yours is or isn't?
Serge Auckland
1) Dual mono with floating earth. This means that there is no audio path
between the ground side of the two stereo channels.
2) Bridged output amplifiers. This is where each loudspeaker terminal is
connected effectively to a separate power amplifier, these two operating in
anti-phase. It is a useful technique for getting more output volts from a
limited supply voltage, and is most used in in-car power amps. It's also a
good way of getting more power for home use by turning a stereo power
amplifier into a bridged-mono amp. It can theoretically provide twice the
power, but each "side" sees half the load impedance, so has to provide twice
the current.
The best way of telling is by reading the manual. Bridged amplifiers usually
tell you not to ground either output terminal, nor to join the two black
terminals together for any reason. If you have a dual-mono amplifier, one
non-conclusive test is to measure if you have a DC path between the two
black loudspeaker terminals. If there isn't then its a good chance that the
amp is dual mono, floating ground, but it could be bridged.
Serge
"dangling entity" <randy...@mac.com> wrote in message
news:a8set...@enews1.newsguy.com...
dangling entity
Is it possible to have only partially burned out an amp. That is, I
hooked it up wrong (like a dumba$$- smacks palm to forehead), saw
smoke, but shut it off in time before it stopped working outright.
(Possibly, I inadvertently grounded the hot terminal on one amplifier
channel. Beats me why the autoprotect circuit didn't engage, if that
is the case. I heard a constant, rapid popping sound on that speaker
channel as this was occuring, and then j-u-s-t started to see smoke
wiffing from what looked like the preamp board location- didn't seem
to be the output devices that were smoking as they are definitely
further back in the chassis.) Upon starting it up again, both
channels appear to be operating normally with no apparent discrepancy
in channel balance to my casual observation. Both channels seem to be
playing cleanly- no distortion. I haven't tried any high power tests.
I ran an informal internal test and pumped some pink noise into the
system and took a line level reading on my RTA (fed by a tape monitor
output). Both channels seem to be operating full range at the same
amplitude.
So what gives? I know I saw the smoke- even smelled it. However my
amp still is operational. Anybody care to guess where I will lose
out? Full power compromised on one channel, lifespan of one channel
drastically reduced, or no damage at all (yeah, right- how could this
be if I saw smoke, ehh?)? Anybody ever heard of an amp surviving a
smoking incident, or am I just extremely lucky?
dangling entity
Is there also a case where the amp may claim to be "dual mono" (a
"two amp block configuration", for instance), but essentially works
like any other common ground amplifier? Would it be safe to say that
any mass consumer type of amp would be a common ground amplifier?
So what is the benefit of a dual mono scheme? Is it basically that
if one channel happens to be loaded heavily (high power transient
signal), the voltage and current capability of the other channel
won't be affected?
Serge Auckland
less correctly.
Smoke from an amplifier is usually (but not always) caused by an overheating
resistor. The two most common resistors to overheat are the output
transistor emitter resistors, or a power-supply dropper resistor. There are
lots of other possibilities, but in my experience, these are the most
common. If these overheat, the cement coating burns. When cooled down, the
resistors may have changed their value, but if they are emitter resistors,
the amp will continue to work OK, but it is possible, depending on the
circuit used, that any overcurrent protection on the output may not be fully
effective any more. If it's a power supply resistor that's cooked, again, a
modest change in value won't affect operation too much.
However, these components have been stressed, so their life will in all
probability be shortened, and the overcurrent will have stressed other
components, which again may lead to early failure.
My advice is to replace any components that looked cooked, but not to worry
about it too much. Yes, the amplifier may fail prematurely, but equally, it
may go on for years.
BTW, output devices will seldom smoke, if they are metal can devices, they
will just fail. If they are plastic cased, they could smoke, but are much
more likely to fail before the whole case gets so hot it smokes. Transistors
fail very fast, unlike valves that can be heated dull red and still work,
trannies blow instantly if abused excessively. I had an amp once whose
outputs would regularly blow to protect the fuse!
Serge
"dangling entity" <randy...@mac.com> wrote in message
news:a8tp8m$pkj$1...@bourbaki.localdomain...
BEAR
Get your amplifier repaired now, before it gives up completely and
smokes the internal parts and your speakers.
You probably overheated a resistor which is now holding on for dear
life (so to speak). The amp may or may not be operating properly.
At least open the cover and look with a bright light, the power OFF
and UNPLUGGED for any obvious burnt, cracked or smoked parts.
Then take it to be repaired.
_-_-bear
--
_-_-bearlabs
http://www.bearlabsUSA.com
- Silver Lightning Interconnects -
Serge Auckland
Most "decent" consumer amps are indeed common ground, but the cheapest may
use an IC power amp module, some of which are bridged. The only real way to
tell is to get hold of a circuit diagram.
Dual mono gives better stereo separation as there can be no interactions
between the two channels through a common power supply. It also allows each
channel to give its maximum power regardless of what the other channel is
doing.
Is there any specific reason for the interest in common ground, or just
academic interest?
Serge
"dangling entity" <randy...@mac.com> wrote in message
news:a8v3k...@enews1.newsguy.com...
dangling entity
mention of a "dual-mono-ish" feature. How many of them are actually
dual mono (unless you paid 2 or 3k for them).
Serge Auckland
from two completely separate amps, even down to the mains cord, just sharing
a common box, to separate power supplies coming from separate secondary
windings on a common transformer, to a common power supply, with the power
amps just as separate boards. Isn't marketing wonderful?
Serge
"dangling entity" <randy...@mac.com> wrote in message
news:a94e2...@enews1.newsguy.com...
dangling entity
Turns out, I was fully correct in connecting the subwoofer to the amp
using the speaker level input method. All of my polarities were true-
red-to-red, black-to-black. However, the left positive output on my
amp does not seem to behave like the hot terminal, and the left
negative output does not seem to behave like the grounded terminal.
So when I hooked up the subwoofer with the leads from my amp reversed
(which the subwoofer manual explicitly warns not to do), everything
worked fine! (???) The right amp channel, however, works exactly how
you expect it to.
So then you might suspect my amp got wired up wrong internally on the
left output channel. However, I'm not sure this is the case either.
If the polarity is reversed between my left and right channel, I would
have noticed cancellation between my main speakers by now, wouldn't I?
I tried hooking up my mains both ways today just to make sure,
though. The polarity doesn't seem to be reversed, as the fullest
sound and centered stereo image seems to occur when you hook the
speakers up normally (though oddly, the difference wasn't really that
pronounced when I tried them in reverse phase).
I tried the subwoofer on the right channel of my amp, as well.
Everything works fine, when you hook it up exactly how you are
supposed to (red-to-red, black-to-black). So I don't think it is a
case where the sub inputs are improperly labeled or hooked-up
internally. So the only thing I can think of is that the left channel
of my amp is hot on the black terminal and grounded on the red
terminal, yet the signal remains in proper polarity with the right
channel. So can anybody think at all why my amp could possibly be
setup like this??? Is it an accident, is it deliberate by design?
What?
Serge Auckland
an amplifier that ran one channel inverted from the other, and then reversed
the colour coding on the 'speaker terminals. The manufacturer's reasoning
was that this balanced the power supply better and allowed easy bridging by
simply paralleling the inputs!
Can't remember much more, but it could possibly explain what you found.
Serge
"dangling entity" <randy...@mac.com> wrote in message
news:a9djm6$2dq$1...@bourbaki.localdomain...