Hi;

Does anyone know for sure the power rating of the Luxman M117 ? I saw it from
Google as 200WPC RMS @ 8 ohms, 400@4 and 700@2. While it looks like the amp can
handle 2 ohms (three pairs 2SC2922 and its comp), my observation is different.

I fixed one today. With an amp like this I run a full power clipping check
under load. The load I use is resistive. If I did more audio I might setup a
complex dummy load/power soak, but I usually do RPTVs. In a discreet component
amp, the VERY least is the full power check under load.

Anyway, I used the clipping level on the scope to calculate. It was 54 volt
peak, that is 108 V P-P. At 54 V peak my calculations yield about 182 WPC at
clipping. By this I mean a sine wave will fit there within the rails.

The method used:

(54*.707)^2/8
and with SMAD, you divide last.

So where did I go wrong, RMS means RMS voltage right ? If you square it first
you get a bigger number in the end, but to my knowledge that would not be the
correct number.

I didn't check the line voltage at the time, but realistically:

1. Our shop used to have a machine shop in the back, it used to be an auto
parts store, so the wiring is probably more than adequate.

2. The last time I was in any question about it my Fluke (TRMS) reported the
line at 125VAC.

3. If it's actually rated 400@4 how could there not be any more inherent losses
in the power supply. An amp that does 700 into 2 ohms would have to have some
clipping headroom on an FTC rating at 8, or am I wrong ? (actually not FTC, but
what Stereo Review and such used to test)

In this can of worms we are not talking about a box under your dash that says
200W that has a 4 amp fuse. This is a discreet power amp from Luxman, very
expensive and possibly even THX licensed. (I didn't look into it)

I remember the old way, they gave continuous, and clipping and dynamic headroom
in dBs. Actually 3 dB of clipping headroom meant it had alot more power than it
said, but may have crossed over a line in THD or IM that was unacceptable.
Dynamic headroom referred to the time after a relatively queiscent period there
would be a very loud sound, before the main filters discharged a bit. It was
measured with a burst.

I know you'll never hear the difference between 182 and 200 WPC, but if the
numbers are to mean anything they need to be accurate.

Quick question about that amp, I got .002V on average across the emitter
resistors (cold). This is on the unblown channel, I set the exblown channel to
that, but it seems quite low to me. Of course there are three sets in paralell.
I'd guess Luxman would have you use a watt or current meter on the AC line and
adjust for a certain increase. Setting it to within a hundredth of a volt it'll
be fine, but what if it both channels were blown or it was a monoblock ?

In that case I do have a foolproof method using a scope to set the bias on any
audio amp. I will not delve into that now because if I did I'd have to remove
the "(short)" from the subject line. Thing that gets me is that I almost ALWAYS
see an amp spec out higher on the scope than the rating in power, as long as
it's rated right, in RMS. What gives here Luxman ?

JURB

I think I would have just used the Fluke on an AC range. Scope readings are
rather approximate. Run the amp right up to clipping, as viewed on the
scope, measure with the Fluke. At the least your reading will have an
accurate numerical value.

(Boy, you can tell I don't have a newer scope with readout, can't you?)


Mark Z.


"JURB6006" wrote in message
...
Hi;

Does anyone know for sure the power rating of the Luxman M117 ? I saw it
from
Google as 200WPC RMS @ 8 ohms, 400@4 and 700@2. While it looks like the
amp can
handle 2 ohms (three pairs 2SC2922 and its comp), my observation is
different.

I fixed one today. With an amp like this I run a full power clipping check
under load. The load I use is resistive. If I did more audio I might setup
a
complex dummy load/power soak, but I usually do RPTVs. In a discreet
component
amp, the VERY least is the full power check under load.

Anyway, I used the clipping level on the scope to calculate. It was 54
volt
peak, that is 108 V P-P. At 54 V peak my calculations yield about 182 WPC
at
clipping. By this I mean a sine wave will fit there within the rails.

The method used:

(54*.707)^2/8
and with SMAD, you divide last.

So where did I go wrong, RMS means RMS voltage right ? If you square it
first
you get a bigger number in the end, but to my knowledge that would not be
the
correct number.

I didn't check the line voltage at the time, but realistically:

1. Our shop used to have a machine shop in the back, it used to be an auto
parts store, so the wiring is probably more than adequate.

2. The last time I was in any question about it my Fluke (TRMS) reported
the
line at 125VAC.

3. If it's actually rated 400@4 how could there not be any more inherent
losses
in the power supply. An amp that does 700 into 2 ohms would have to have
some
clipping headroom on an FTC rating at 8, or am I wrong ? (actually not
FTC, but
what Stereo Review and such used to test)

In this can of worms we are not talking about a box under your dash that
says
200W that has a 4 amp fuse. This is a discreet power amp from Luxman, very
expensive and possibly even THX licensed. (I didn't look into it)

I remember the old way, they gave continuous, and clipping and dynamic
headroom
in dBs. Actually 3 dB of clipping headroom meant it had alot more power
than it
said, but may have crossed over a line in THD or IM that was unacceptable.
Dynamic headroom referred to the time after a relatively queiscent period
there
would be a very loud sound, before the main filters discharged a bit. It
was
measured with a burst.

I know you'll never hear the difference between 182 and 200 WPC, but if
the
numbers are to mean anything they need to be accurate.

Quick question about that amp, I got .002V on average across the emitter
resistors (cold). This is on the unblown channel, I set the exblown
channel to
that, but it seems quite low to me. Of course there are three sets in
paralell.
I'd guess Luxman would have you use a watt or current meter on the AC line
and
adjust for a certain increase. Setting it to within a hundredth of a volt
it'll
be fine, but what if it both channels were blown or it was a monoblock ?

In that case I do have a foolproof method using a scope to set the bias on
any
audio amp. I will not delve into that now because if I did I'd have to
remove
the "(short)" from the subject line. Thing that gets me is that I almost
ALWAYS
see an amp spec out higher on the scope than the rating in power, as long
as
it's rated right, in RMS. What gives here Luxman ?

JURB

Greetings to all fellow techs. from Longueuil,Quebec!

Your calculations are right.I think that Luxman rounded up their
power rating to 200W. Looks nicer....

Anyway I would like to learn how to properly adjust the bias level on
any amplifier by using a scope.This would be a very useful tip.

Thanks for the info.

Jacques


--

Jacques Carrier [Electronics Tech.]
Collège Édouard-Montpetit
Electronics Dept. (TGE)
945 chemin de Chambly
Longueuil (Québec)
CANADA J4H 3M6

Phone: 450-679-2631 EXT:5860 #
Fax : 450-679-5570 Box: 004
Email:
Phone (home) : 450-651-5253

Anyway I would like to learn how to properly adjust the bias level on
any amplifier by using a scope.This would be a very useful tip.

I will post it in a different thread, perhaps tonight if I can do it before my
crowd of Friday night rowdies shows up.

JURB

(Jacques Carrier) wrote in message . com...
Greetings to all fellow techs. from Longueuil,Quebec!

Your calculations are right.I think that Luxman rounded up their
power rating to 200W. Looks nicer....

Anyway I would like to learn how to properly adjust the bias level on
any amplifier by using a scope.This would be a very useful tip.

Thanks for the info.

Jacques


--

Jacques Carrier [Electronics Tech.]
Collège Édouard-Montpetit
Electronics Dept. (TGE)
945 chemin de Chambly
Longueuil (Québec)
CANADA J4H 3M6

Phone: 450-679-2631 EXT:5860 #
Fax : 450-679-5570 Box: 004
Email:
Phone (home) : 450-651-5253

Most high power amps I've seen over the years do not have regulated
power supplies and are very sensitive to the AC line voltage. A change
from 110 to 125 volts will cause power capability to go up by 1.29
((125/110)^2). Note that the gain will not change vs supply voltage,
just max level at clipping. How is your line voltage, particularly
under load ?

GG