"Steven Sullivan" <ssully@[EMAIL PROTECTED]
> wrote in message
news:ft11o30311@[EMAIL PROTECTED]
> Harry Lavo <hlavo@[EMAIL PROTECTED]
> wrote:
>> "Serge Auckland" <sergeauckland@[EMAIL PROTECTED]
> wrote in message
>> news:fsuj6801lg7@[EMAIL PROTECTED]
>> > "Harry Lavo" <hlavo@[EMAIL PROTECTED]
> wrote in message
>> > news:fsroub01t7k@[EMAIL PROTECTED]
>> >> "Serge Auckland" <sergeauckland@[EMAIL PROTECTED]
> wrote in message
>> >> news:fsp1hd02u4a@[EMAIL PROTECTED]
>> >>
>> >>>snip<
>> >>
>> >>>
>> >>> The issue of all amplifiers sounding the same is one of thresholds
of
>> >>> hearing. All modern electronics, unless specifically designed to be
>> >>> so,
>> >>> will
>> >>> have an essentially flat frequency response, low distortion in all
>> >>> its
>> >>> forms
>> >>> and low noise. As these are well below the threshold of audibility,
>> >>> it
>> >>> follows that all electronics will sound the same once level matched
>> >>> and
>> >>> used
>> >>> within their design parameters. This will apply even more to
pre-amps
>> >>> which
>> >>> by their very nature have an easier task than power amps.
>> >>>
>> >>> The sole proviso to the above is the RIAA equalisation and
cartridge
>> >>> loading
>> >>> that some pre-amps still provide if they have phono inputs. The
RIAA
>> >>> accuracy will determine the overall phono frequency response, and
the
>> >>> cartridge loading will determine how the cartridge performs.
>> >>> Consequently,
>> >>> I
>> >>> would expect that if there are any differences when levels are
>> >>> accurately
>> >>> matched and under suitably blind conditions, then it is most likely
>> >>> due
>> >>> to
>> >>> the RIAA eq or cartridge.
>> >>>
>> >>
>> >> Don't forget the interface.....output impedances of preamps can vary
>> >> widely
>> >> with frequency response and vary greatly from model to model. This
>> >> makes
>> >> matching up with the input impedances of power amps iffy in some
>> >> cases.
>> >> I
>> >> have Onkyo preamps, for example, that work fine with most power amps
>> >> but
>> >> roll off noticeably when mated with Outlaw monoblocks. Yet the
>> >> preamps
>> >> rated output impedance (at 1000 ohms) is the standard "100 ohms" and
>> >> the
>> >> input impedance of the amps is the standard "10k ohms".
>> >>
>> >
>> > If there is roll-off with the Outlaw monoblocks, then there are
several
>> > possibilities:-
>> >
>> > 1) The roll-off is a subjective impression which is not there when
>> > measured.
>> > By the way, I assume you meant (at 1000 Hz) not 1000 ohms.
>> >
>> > 2) You are using a very long length of cable between your preamp and
>> > Outlaw
>> > power amp ;-) With an output impedance of 100 ohms into 10k, there
>> > should
>> > be
>> > no roll off in the audio band unless the capacitance is pretty high.
I
>> > calculate a 3dB drop at 20kHz needs a capacitance of 79nF. With
typical
>> > 100-150pF/metre capacitance, that's 527-790 metres of cable!
>> >
>> > 3) The output impedance of the preamp is not 100 ohms, but a great
deal
>> > higher.
>> >
>> > 4) The input of the Outlaw power amp has a very high capacitance.
>> > Normally
>> > it would be a few pF, but if Outlaw for whatever reason put, for
>> > example,
>> > 100nF, then there would indeed be a noticeable roll-off even with
short
>> > cables.
>> >
>> > If 1) above is not the case, then there's ALWAYS a measurable reason
>> > for
>> > any
>> > effect.
>
>> It's either 3 or 4. Cables are short, and the monoblocks sound fine
with
>> my
>> ARC and Audionics preamps.
>
>> It may be a combination of both. The Onkyo preamps are their AV models
>> from
>> the early 90's (I tried three with remote as a poor man's multichannel
>> amp...works well except for the rolloff). I doubt that they use a
>> buffered
>> output, and suspect that impedance rises with frequency.
>
>> The outlaw monoblocks are a hybrid class A/AB up to 60 watts, then a
>> digital
>> amp above that. Their stated input impedance is a bit low at 10k at
>> 1000hz
>> (yep!) and may drop further at high frequencies.
>
>> Nonetheless, I think while most preamp/amp mismatches are more subtle
>> than
>> mine, some variance can sometimes be found which can influence system
>> matching. That was my point.
>
> I'm not seeing strong evidence for 'rolloff' here. Possibility
> #1 has by no means been discounted.
Measurement, no. But in a system I know and has always sounded "one way"
with much other equipment, and suddenly it is dull and lifeless when these
preamps are inserted....careful listening was used to determine that I
wasn't just imagining it involving lots of swapping (yes, Steven, I am
objective enough that the thought occurred to me....I often start where
you
leave off). There is a HF rolloff that is pretty severe and sonically
very
degrading. And it is a design parameter, not a flaw...since it exists no
matter which of the three preamps are used with the Outlaws, and it
doesn't
exist with any one of three other power amps or with other preamps used
with
the same power amps. And it is infinitely repeatable.
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