J
JURB6006
- Jan 1, 1970
- 0
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
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
