Pre and Power Amplifiers: One adds the flavour, the other adds the punch?

Pre is dealing with a relatively low-level signal and provides most amplification and does the Gain control, as well as any source-switching, input and output buffering. It seems these things can be done 'adequately' relatively easily, but to do them really well without injecting all sorts of rubbish is more difficult.
Why it makes such a big difference is easy to hear but difficult to believe unless you have the demo and hear it, so abstract discussions will go in a circle and come up with answers that everyone wants.

Over many years of owning different HiFi systems I've always found getting the best Pre gives the best reward in performance. I tried otherwise and even removing the Pre and it leads to a thin gutless sound with no soul so want not a good experience other than I learned from it.

In the replay chain I place Source and Pre very close with power Amp next and Speakers an important last. They are important in that you have to have a pair you like or the system will not work for you and you will be continually changing them. But in financial outlay terms they are not the highest priority to get right IMO.

DB.

As I understand in the simplest terms it as an interface that matches the input to the correct impedance and sensitivity. In doing this  it reduces the loading on source component as well. As-side from all of this - as the device is near the source it has a big impact on sonic character ..... as it is driving the main power amp. So it can imbue a sonic foot print maybe forward in nature or indeed the reverse. Every amp has its own sonic signature. It has been noted by Paul McGowan and Arny Nudel that a really good preamp  ..... can make somehow things sound downright better. In that sense I don't think anybody really knows why.... it just can. I think it is best to view Naim preamps and amps as a unified system - and judge the quality from there.

I think Richieroo is right in that it's best to consider Naim pre-amps and power amps as two parts of a unified system.  

As Alba mentions above, the pre-amp is important within the system hierarchy, the overriding rule of which is that no component can improve the quality of its incoming signal;  the best any individual component can do is deal faithfully with its input without loss of musical information.  Thus a simple hierarchy is established, led by the source material and replay device which then defines the absolute quality of the music signal.  The pre-amp and power come next, and in that order.

I'd love to channel JV and give you chapter and verse on the thinking behind Naim's preamp designs (there are a number of interviews out there that give you more insight here), however it's perhaps best instead to look at what Naim said in the old dealer handbook:

NAIM PREAMPLIFIER DESIGN CRITERIA

An audio preamplifier has a whole series of complex and vital tasks to perform. Input circuitry must accept the entire output of the chosen source without being overloaded, frequency response and level of input signals must be normalised. The signal then needs further conditioning to ensure that the power amplifier is never driven outside its correct operating parameters.

All of our preamplifiers have a frequency response to within +/-1dB between 20Hz and 20kHz and offer perfect stability under all working conditions. There are no switched filters, loudness or tone controls, due partly to their outstanding transient capability. Further, such controls can never improve the quality of the original signal and their inclusion results in lost information.

Our phono circuit has a linear first stage with relatively low gain, after which RIAA equalisation is split into two parts. Complete theoretical and practical stability is attained in this way, with a much wider open loop bandwidth than usual. Exceptional overload capability is thus maintained over the whole audio bandwidth.

The magnetic fields radiated by transformers can interfere with sensitive circuits, so our preamps all use separate power supplies to ensure optimum performance. These can be either those fitted to certain of our power amplifiers or, for enhanced performance, by the FLAT-CAP, HI-CAP or SUPERCAP.

From my experience pre-amps are ***** difficult to get right.  Although I could design and build a very good power-amp, I never managed to get pre-amp design quite right.

Richard is absolutely right that in the Naim world the pre-amp and power-amp are two parts of a unified whole.  In order to work well with a passive "pre-amp" a power-amp has to be specifically designed for that.  Naim power-amps are specifically designed to interface to the voltage, output impedance and bandwidth and complement general sonic character of Naim pre-amps.

The point about "no component can improve the quality of its incoming signal" is also absolutely true, each component adds it's own limitations and colourations to the signal, what you hear at the end is the sum of all these defects and any defects arising from the effect of one component on another.
(For instance if you have high quality revealing speakers that happen to be a difficult load for an amp and drive them using an inadequate power-amp, the speakers will badly affect how the the power-amp operates; so not only will the 'better' speakers show up the inherent limitations of the power-amp, the 'better' speakers will actually degrade it's performance still further!)

My experiences of updating first my NAP 110 to a 250 and then shortly afterwards my NAC 42-5 to a 72 really upended my expectations. (I did the upgrade in the "wrong" order because I had to wait for pre-amp, but my dealer had the power amp in stock).

I was expecting the bigger better power amp to make my system go louder and sound more powerful and punchy, and I was expecting the preamp to provide more detail and refinement.

In fact, the power amp upgrade reduced the noise floor and brought greater refinement and control but did not provide the higher volume and greater punch that I was expecting. That said, I was more than delighted with the improvements it did bring. However, it was the preamp that gave me the greater power and punch I was looking for, probably because it was letting more of the original signal through. Upgrading the 72 to a 52 brought even more power and punch.

Paul Davies posted:

.. However, it was the preamp that gave me the greater power and punch I was looking for, probably because it was letting more of the original signal through.

I've always had exactly this experience. The Pre gives the Bass weight and sets the stable reference frame within which the music happens.
The better the Pre the wider the stable space for the music to just work as it should. As you improve the Pre the music becomes more effortlessly dynamic and free of restrictions is how I hear it.

DB.

The 552 is like a large bay window which lets lots of light through and the 155XS is the shutter that controls what to do with the light.

The 152XS is like a velux window which lets in some light and the 500 is the shutter that controls what to do with the light.

In the latter example, the 500 does not have much light to control in the beginning so even at its brightest, the velux window is dim compared to the bay window.

In a nut shell, rubbish in, rubbish out. So, no matter how good your power amp or speakers, they'll never produce any missing info that your pre or source 'cocked up'. As others have said, a good demo will prove the point. Rich 

before buying a great preamp, I would buy a great source first.

Rich 1 posted:

In a nut shell, rubbish in, rubbish out. So, no matter how good your power amp or speakers, they'll never produce any missing info that your pre or source 'cocked up'. As others have said, a good demo will prove the point. Rich 

Similarly the speakers will never produce any missing info that your pre, source or power-amp 'cocked up'.

All the bits are equally important in their own way.

I was knocked out with improvement from NAC 82 to 52 which I had anticipated but I was very surprised to find that the improvement from 1 x 250 to 2 x 135 transcended being merely a power thing - much more definition and musicality; obviously a function of the greater control over the speakers but still a pleasant surprise