On Tue, 1 Apr 2008 19:08:40 -0700, Harry Lavo wrote
(in article <fsupr802s6@[EMAIL PROTECTED]
>):
> "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.
By digital, do you mean "class D"? So, this amp changes from class A and
A/B
above 60 Watts to class D? I'd love to see how they accomplish THAT!
>
> 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.
Well, I think that it would have to be SOME roll-off for anyone to
actually
hear any attenuation above about 10KHz.
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