preamp vs. preamp

Archived from groups: rec.audio.high-end (More info?)

Russ Button wrote:

> There seems to be a vocal contingent here in rec.audio.hi-end that
> claims there is little audible difference between power amplifiers.
> One regular here pointed us at an old Stereo Review article which made
> a case for suggesting that a Pioneer receiver power amp section
> sounded almost identical to a Mark Levinson amp costing about
> 10 times as much. Certainly there are a number of people here
> who feel that an inexpensive pro grade power amp is as good a
> sounding power amp as you can find, at any price.
>
> This same contingent also seems to say that there is little audible difference
> between SACD and redbook CD.
>
> So this brings me to ask this question with regards to preamplifiers.
> Do you of the group I describe above, also feel there is little audible
> difference between solid state preamps? Pyle and Gemini both have
> new preamps, with phono sections, that sell for about $100 new or
> less. What about an Adcom preamp? Carver or Parasound? And let's
> not forget our more hi-end guys like Linn, Krell, Mark Levinson,
> McIntosh, C-J, Audio Research, or whoever.
>
> If there are real differences one can expect to be heard in preamps,
> then why?
>
> Russ

First of all, phono preamps can sound quite different. I have seen phono
preamps with almost 1 dB of error in the audio band, and I would think
that those would sound different than another one with 0.1 dB of error.
In addition, since a lot of MM cartridges need to work into a
well-specified input impedance, you can get different responses if the
preamps have different MM input impedances.

It is much easier to design a line-level preamp than a power amp, so in
theory line-level preamps should sound the same. In practice, there is
one significant cause of why preamps can sound different: L/R Level
matching. In most preamps, that is a function of the volume control
potentiometer/attenuator. One can get substantial L/R tracking errors
from poorly made pots/attenuators. Preamps utilizing digital attenuators
are actually much better in this respect.

Just like power amps and CD players, preamps have to be compared at the
same output level, so level matching is necessary. There are also
preamps with intentional errors so they would sound different. And some
poorly designed preamps can have excessive sensitivity to picking up
line noises.

Archived from groups: rec.audio.high-end (More info?)

Russ Button wrote:
> Chung wrote:
>>
>> First of all, phono preamps can sound quite different. I have seen phono
>> preamps with almost 1 dB of error in the audio band, and I would think
>> that those would sound different than another one with 0.1 dB of error.
>> In addition, since a lot of MM cartridges need to work into a
>> well-specified input impedance, you can get different responses if the
>> preamps have different MM input impedances.
>
> I used to own a Holman preamp. It was interesting in that it had
> switchable levels of capacitance on the phono inputs. All in all, I
> always thought it was a pretty good piece of gear. It had an
> enormous amount of functionality as well. Tom Holman always
> struck me as a thoughtful engineer.
>
>> It is much easier to design a line-level preamp than a power amp, so in
>> theory line-level preamps should sound the same. In practice, there is
>> one significant cause of why preamps can sound different: L/R Level
>> matching.
>
> What do you think of the Chinese made pro items such as the
> Gemini or Pyle preamps you see for less than $100 now?
>
> Gemini
> http://www.jr.com/JRProductPage.pr [...] ct=3719099
>
> Pyle
> http://www.digitallyunique.com/pyp-1.html
>
> Although Behringer doesn't make a comparable unit, do you
> feel that either Gemini or Pyle offer equipment at the same
> level of quality as Behringer?
>

I have not listened to any of these. I would be concerned about (a) the
kind of pots and switches they use, and (b) the type of opamps they use.
Poor pots and switches will become noisy over time, or the pots may have
channel mismatches. On some of the really cheap stuff, they use opamps
that are sub-par in terms of bandwidth, noise, distortion and slew
rates. Also check and make sure that there is no excessive noise and
line pick-ups. These units do not appear to have phono inputs.

> These are very inexpensive pieces of Chinese made gear.
> Can their line level sections be expected to perform as well
> as more commercially oriented equipment from manufacturers
> such as Rotel, B&K, Parasound, or the more hi-end lines such
> as Linn, Krell, Rowland Research, C-J, Audio Research, etc?
>

I think the consumer level stuff from Sony, Rotel, etc. will be the
sonic equivalent of the high-end solid-state models. Or simply use a
receiver as a preamp. With tubed units, you have to be careful, since
there may be some intentional coloration introduced.

On the really cheap stuff, I worry about the things I mentioned earlier,
especially the quality of the pots and switches.

> When you spend more on a preamp, what is it that you're
> paying for?

Low noise, great volume control, features, reliability, and user
interfaces. Maybe a good phono stage. Never underestimate the importance
of the remote control!

>
> Russ

Archived from groups: rec.audio.high-end (More info?)

Uptown Audio wrote:

> Noise is the largest factor in making a quality preamp. Very low noise
> active preamps are quite expensive.

You can get noise to be < 96 dB or so easily, for a line stage. Not
expensive at all. There are several opamps that work very well for
line-level preamps. 96 dB is better than what CD's can offer.

Phono preamps are harder tp design, but then vinyl has so much surface
noise that the preamp actually contributes little when a vinyl record is
being played.


> You might compare the brands you
> mention sonically, you can ignore the spec sheets on the budget stuff
> as that is only useful as toilet paper (it isn't very good for that
> either!...). If you haven't made some listening comparisons, you have
> no idea what the differences are. I have owned tons of preamps and can
> confirm a wide range of soncs.
> Passive "preamps" (an oxymoron) are noiseless, yet have other issues
> in practical use.

Passive preamps are definitely NOT noiseless. Resistors are a large
source of noise. You can end up with more noise than an active preamp,
if the *input noise current* of the following stage (typically the power
amp) is high.


> Some people can live with them and they can vary in
> price from really cheap single input boxes to really expensive, more
> useful types. These can be used with line level inputs only.
> -Bill
> www.uptownaudio.com
> Roanoke VA
> (540) 343-1250
>
>

Archived from groups: rec.audio.high-end (More info?)

RobertLang wrote:
> Mr. Chung wrote,
>
> "Passive preamps are definitely NOT noiseless. Resistors are a large
> source of noise. You can end up with more noise than an active preamp,
> if the *input noise current* of the following stage (typically the power
> amp) is high."
>
> Agreed. However, a well designed passive line stage (such as those from
> Placette) that is well matched to cables and amplifier is virtually
> without noise in my experience.

Sure, if you have a really quiet power amp input stage. OTOH, I have
heard active preamps that are virtually noiseless, too. Remember that
the passive amp does not provide any gain, so you have to make sure it's
an apples-to-apples comparison.

> At full unity gain (probably 8-10 db
> beyond what would ever be employed when listening to music) noise is only
> faintly audible when the ear is right near the speaker.

The biggest noise contribution from a passive preamp occurs when the
volume is at the -6dB position, when the source is connected. That
presents the highest source impedance to the power amp. If you do not
connect any source, then the highest noise occurs at minimum attenuation.


Of course, at
> normal volume settings this is far below the music floor, and noise is
> completely inaudible, even during the most quite passages.
>
> And as an aside, contrary to some popular misconceptions, with my passive
> line stage I am able to reproduce a level of bass slam that subjectively
> matches the best I have heard including that of an active pre amp based
> system that featured the Wilson Audio Watchdog subwoofer.
>

Any problem with passive preamp is likely to occur at high frequencies,
due to the high source impedance interacting with the cable and power
amp input capacitance. At low frequencies there is problem only if the
coupling capacitor at the input of the power amp is too small for the job.

> Robert C. Lang