"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.
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