Re: LCD refresh rates - don't understand

In article <313030303737303648B4D7E284@xxxxxxxxxxxxxxxx>, Johnny B Good
<jcs.computers***@xxxxxxxxxxxxxxxx> wrote:
The message <VA.000004ca.0334d587@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
from Roderick Stewart <rjfs@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
contains these words:

In article <313030303737303648B4517211@xxxxxxxxxxxxxxxx>, Johnny B
Good wrote:
The voltage available from the PSU during quieter passages could
quite easily rise 50% or more above that during RMS test signal
conditions for maximum undistorted power from all channels. This
would allow double the rms power for a few tens of milliseconds or
double that again for the 'Peak Power' on the crest of the waveform.

50% regulation? That sounds like what I'd call a truly *** power
supply. Even I could design a better one than that.

Well, believe it or not, that's quite typical of even the more
expensive 100 watt rms per channel Hi-Fi amps (although the pre-driver
stages will normally enjoy the benefit of a regulated lower voltage
supply).

As with your comments in another thread on miltipath and Capture Ratio you
seem to be making a sweeping assertion here. I can't say that my
experience agrees with your assertion. 50% strikes me as being a bit on
the high side for the kind of power amps I'd call 'hifi'. Perhaps you
can give references to a few review measurements to support your
claim?

I can agree that some amps might show a 50% higher rail when off load
than when driven to the rated continuous power. But that isn't the
same as estabilishing this is "typical" for hifi amps in general.

If you make sweeping claims about what is "typical" you may need to
be able to provide evidence that this *is* typical based on measurements
of a number of amplifiers.


I was also able to add clip limit LED indicators[1] to show the onset
of clipping before it became audibly obvious. These indicators also
doubled up to show when a shorting fault had occurred by permanently
glowing and an accompanying loss of sound, removal of the fault
condition would automatically reset the electronic circuit breaker used
to provide said overload protection[2].

Sound like you did something like I also did back in c1980. In my case I
used a sensor that detected any unusually high in-loop differentials and
triggered a monostable. That way even very brief clips or saturations would
light the LED for long enough to be clearly visible.

In the end, the amplifier I produced could deliver 100 watts rms per
channel into 8 ohm loads or 200 watt rms per channel into 4 ohm loads...
simultaneously, i.e. a total rms power output of 400 watts

In my case it was >200 Wpc continuous sinewave 8 Ohms and >400 into 4.



[2] My philosophy regarding overload protection (whether it be short cct
faults or 'awkward' speaker impedance problems) is that it should be an
all or nothing shutdown mechanism rather than the namby pamby drive
limiting 'protection' so oft employed by a lot of the idiot commercial
designers of home hi-fi equipment.

Mine was to have no active protection. Just ensure adequate ratings for the
devices and rely on fuses for sustained gross mistreatment. Worked fine
even when did things to try and blow up the result. Just need fuses that
seem a bit cautious for the power ratings. So I guess mine was "all or
nothing" as well. :-)

Given the indicator and the lack of active protection the user can
then expect the o/p to be a scaled up version of the i/p if they
can hear the music and the indicator isn't lit. Gives peace of mind
to worriers... :-)


I might add that such clip indications don't demand the use of a
regulated PSU,


Indeed. No real reason why they should if they are sensing the amp
behaviour, not blindly comparing with something else.


Slainte,

Jim

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