Tranparent Pre-Amps?

Is there such a thing as a totally transparent preamp? I've tried maybe 10 different pre-amps and nearly all of them added something to the sound compared to bypassing the preamp and going direct to the amp. Sometimes the difference is startling and disheartening. I have a hard time accepting the veiling that my preamps often add.

I find Mark Levinson No 38s & No 380s very transparent.
I stick to ML forever as Pre Amp in my set-up.

I did not hear any PreAmp transparent like these.

However, I don't like their Power Amps as much.

"dolph"

The older PS Audio pre-amps, like my 5.6, allow you to bypass the balance control and gain stage (called "straightwire"), leaving you with a passive source selector and volume control. The Adcom GFP-750 also has such a feature.

I do most of my listening in "straightwire", except when I am listening to my B&W DM602 S3s. I find that the character of the PS Audio 5.6's gain stage makes up for some of the shortcomings I perceive in the these speakers.

I find Mark Levinson No 38s & No 380s very transparent.
I stick to ML forever as Pre Amp in my set-up.

I did not hear any PreAmp transparent like these.

However, I don't like their Power Amps as much.

"dolph"

Thanks for the tip Dolph. I'm going to have to slink into the high-end audio store near me and check out the ML's. Not sure I can afford one so maybe the salesman won't catch on...

Straightwire, that's the term I was looking for! I've heard similar praise for the Adcom straightline or straightwire preamps. They are relatively inexpensive so that may be a better option for me. I'm thinking a simple RCA selector might do. Then I can use one of my receivers with pre-out for when I'm in the mood for vinyl or FM. There has to be a better answer than this...

This post has been edited by socal sam on December 01, 2008 09:24 pm

Creek, QED, and a few other builders make passive pre-amps, which sounds like what you may be searching for.

Basically a volume knob and selector and no additional gain.



Sam, I have found that not all amps are a good match for a passive. Some work better with a powered pre.

rroobbcc,

I hate to derail the thread, but what did you find the B&W shortcomings were?

Not really a derail, as it is relevant to the discussion of a passive pre-amp. I find the top-end of the B&W DM602 S3 to be a bit muted, lacking a crispness that I love from my 9 Kappas. For example, I find that little bit of extra "shimmer" from cymbals to be missing from the DM602 S3s when compared to the 9 Kappas. Being a 2-way bookshelf design the DM602 obviously gives up a little bit in the low-end. I do find they go suprisingly deep, but lack a bit of low-end control and dynamics.

I find the gain stage of the PS Audio 5.6 pre-amp to be a bit bright, which actually works well with the muted top-end of the DM602 S3s to produce a smooth and detailed high-end. The gain stage also seems to support improved dynamics, which allows the DM602 S3s to deliver the music with a bit more low-end impact. The original series Adcom GFA-555 amplifier (not the II) also works well here as it has good bass control and "slam", and its tendency toward a bit of harshness in the top-end also works well with the muted tweeter of the B&Ws.

I guess what I am really talking about here is matching the qualities of various components to achieve the best possible sound. So while absolute transparency is a primary objective, sometimes you can use the character of one component to balance out the character of another.

HTH,

Rob

I bought a couple years ago used but in excellent condition a very good preamp from Musical Fidelity. The Musical Fidelity the Preamp (3ax) from the '80's with passive and active outputs. The cd stage is good but the phono stage is just awesome.
MF recently resurrected the old A1 and B1 and also the old preamp but keeping the retro '80's style:

http://www.musicalfidelity.com/reviews/pdf...p_hifiworld.pdf

Imo, the pre-amp is one of the most important links in an audio chain just because is inside of the pre amp that lies the capacity to amplify every input tension. And if we consider that the gain input value can varied from source to source ( 1 volt from a digital source and 100 to 200mV from a MC cartridge), and also that a pre-amp has two step amplifications, one before the volume control and another after it, more easily we can understand how the delicate equilibrium between these two step gains should be, and this "simple" audio fact can have for sure great impact and dictate the many differences between sound on some audio systems and how import is the role of a good pre-amp in any hi-fi chain.

Passive Pre Amps, selector boxes and seperate potetiometers are neutral to the point of their buid quality and internal wiring...............BUT they have no gain.

Very few power amps live happily everafter with passive preamps.

I will only recommend this as a kind of emergency echonomical based solution.

I find that a stand alone coal- or similar potentiometer is having more influence on the sound than ML 38s/380s with their remote controlled digitally operated 2 X >1100 step analog pass through progressive matrix attenuator with 0,1 dB readout for volume regulation.

"dolph"

Actually, the term "passive preamp" is slightly misleading and even contradictory. The word preamp or preamplifier is not supposed to be a passive device, as a passive device may not provide amplification. So a better term than passive preamp would be passive volume control, because no active electronics and therefore no power supply is required.

Today, many signal sources such as cd players have sufficient output level to drive most power amplifiers directly. It means that no additional amplification is required, so for level purposes there is no need for a preamplifier. With a high quality passive volume control in between, the signal from the source may be fed directly to the power amplifier. The non-linearities, noise and distortion from the preamplifier are avoided. IMO, Even the most expensive preamplifiers add coloration - sound signature... - and distortion to the sound.

But when a CD player with sufficient output to feed the power amps is actually depending on the internal, and often volume controlled, preamplification in the CD, then the question is not about comparing a "passive preamp" and an active preamp but to compare the active preamp with the preamp build into the CD with sufficient signal level.

I would suggest, in this case, to choose the CD without build in preamp and then have the very widely choise of active preamps.

"dolph"

I understand and respect your opinion but i have a different approach about this issue.
The rule-of-thumb for digital high performance says that we must minimize analog processing by keeping the signal in the digital domain for as far along the audio chain as possible.

So, the primary disadvantage of a preamp-based system is the sonic losses that inevitably occur with complex analog circuitry. Better preamps can reduce the sonic degradation, but even the finest designs available cannot eliminate the losses of analog circuitry. In addition, the cost of this type of system can be very high. The better the preamp, the less degradation, but the greater the cost. A preamp of sufficient quality can cost as much or more than the digital playback equipment.
Also, less-sophisticated digital equipment designs, can create high frequency noise that contaminates the analog signal, causing audible degradation.

Nothing is perfect and passive preamps do offer great circuit simplicity compared to conventional analog preamps and they cost less than good quality conventional preamps as well. However, with no output buffer to drive the cable and power amplifier, performance is variable depending on cable type, volume level, amplifier impedance, and the quality of the CD player’s output buffer.

Even though, if care is taken in dealing with these issues it is not a problem in most Hi-Fi systems.
My choice goes to “passive preamp”.

Gentlemen: Awesome and very informative discussion. My main system is primarly CD so your points are on the mark. OK, it seems that some sort of amplification of the source is needed before input to the amp. While I am not up on the science behind your positions, it seems that both approaches can be achieved relatively easily. Dolph suggests passive CD to active preamp, which the Sony TA-E77ESD is capable. IIRC, it has an on-board DAC for digital only input. Clint's approach can work. Some CDP's like the Sony CDP-X77ES and the 707ES have separate transformers for digital and analog signal paths which presumeably results in lower noise floor. I think either will work and this is the direction I will take. I'm leaning towards the preamp route as it is remote controllable AND has a phono amp.

This post has been edited by socal sam on December 02, 2008 06:46 pm

Most line level components have MORE THAN ENOUGH output to drive typical power amps.

Here are some examples of the output capability of various components...
CD Players
Adcom GCD-575: 2.5V
Adcom GCD-750 (unbalanced): 3V
Carver TL-3220: 2V
McIntosh MCD500: 2V
Classe CDP-102: 2V
Marantz CD5001: 2V
Sony CDP-X777ES: 2V
DACs
Adcom GDA-600: 2.234V
Nakamichi Dragon DAC: 2V
Cassette Deck:
Sony TC-K850ES: 0.44V <--- not very strong pre-amp will be necessary

And here is the level of input required to achieve full power output for a variety of power amplifiers...

McIntosh MC252: 1.6V
Adcom GFA-5802: 1.7V
Adcom GFA-555II: 1.75V
Classe CA-2200: 1.4V
Classe CA-M400: 2V <--- this is borderline for some line-level components to drive
Accuphase P-360: 1.59V
Acurus A205: 1.2V

So you can see that the output level of many line-level components is plenty to drive most power amplifiers to their full power. There are however some exceptions, such as the Classe CA-M400, which would just barely reach full power with most components (of course not many really need the full 400W this amp puts out). When amps are bridged they often also require a greater input signal level to achieve the full bridged power output. For example the Accuphase P-360 requires a 2.76V input signal to achieve full output power when bridged.

Some of the components mentioned above also include a variable output, in addition to their normal fixed level output. Many of these components, e.g. the Adcom GCD-575 and many Sony components, drive their variable output via the headphone section. This adds an additional stage of amplification AFTER the line level output stage, but does allow for slightly greater output levels for some components. In this case there is some validity to the point made by Dolph that the quality of the variable output (i.e. the components headphone stage) would be compared to the output stage of a pre-amp when determining which was of better quality. The pre-amp has the advantage of a more purpose built gain stage, but brings the penalty of the source switching mechanisms and an additional set of interconnect cables. Here are a few components which include a variable output...
Adcom GCD-575: 4.5V
McIntosh MCD500: 4.0V
Sony CDP-X777ES: 2V

The final list is a list of pre-amps. As you can see the gain stage of a pre-amp can deliver a signal level as high as 10V, which far more than necessary to drive the inputs of even bridged power amps to the level need to achieve max output power.
Adcom GFP-555: 10V
Carver CT-seven: 8V
McIntosh C220: 8V
Classe SSP-300: 8V
Accuphase C-280L: 10V

So the summary is...

1. that the output level of most components is usually sufficient to provide most power amps with a signal that will allow the power amp to achieve maximum output power. In these cases a simple passive pre-amp can provide for source selction and volume control without the need for another gain stage (a pre-amp), and its coloration, in the signal path.

2. Many components that have a variable output drive this output by an additional gain stage within the component (often the headphone output). While driving a power amp directly with this variable output you are greatly simplifying the signal path (no source selector and less cables), but you are dependent on the quality of the gain stage of this variable output (I actually think the Adcom GCD-575's variable output is really good).

Just my $.03

Rob