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25 watts Class A or 70 watts Class A/B ?

I understand these days there are many good examples of both Class A and Class A/B amps. To the point that a well designed Class A/B can beat a similar pedigree Class A amp. However my question is in particular related to these two amps:

1. First Watt F5 (Pass Labs)
2. Naim NAP 300

The speaker to be driven is a Tannoy dual concentric Turnberry SE. It is a 93 db sensitive 8 ohm load and in general considered to go well with both high powered and low powered amps.

F5 is a highly purist class A 25 watts design with a robust power supply. It is a push-pull design so it can generally drive difficult loads better than typical single ended first watt models (F3, F4 etc). I have heard the F5 on an Altec horn system and I loved its pure and direct sound.

Naim amps in general has always appealed to me, again because of their very direct presentation. Music has a certain excitement and bounce through them. The NAP 300 is one of their top models and I am sure it will be a very refined amp.

However I will only buy one. Both these amps must be having few fundamental differences in the way they present music considering they are coming from very different designers. Even the topology is different here.

The first question here is, can a 25 watts F5 drive the Tannoys well ? My room size is 200 sqft and I listen to music at reasonably medium to loud levels. I dont play very loud though. I listen to all kinds of music from Mozart to Metallica.

Qualitatively, sound per sound, how do these two amps compare ?
pani
pani OP
1,219 posts
 
Pani,
I would think the 25 watt First Watt amplifier is a very good match with your speakers.I doubt that you'd be disappointed given your listening preferences.
Charles,

Yes Charles, considering that at the moment I use a Wavac 300B amp which I love to the core, except for its 10 watts power rating, I guess the F5 would be a more suitable transition for me. On the other hand, some have suggested that I go with one of the big McIntosh amps, like the MC452. With 450 watts on tap, probably it will be a experience in itself. But then Wavac - First Watt - Naim - McIntosh seems to be too wide a palate. I have to narrow it down.
pbnaudio's avatar
pbnaudio
1,613 posts
 
Of the two you mention I'd choose the PASS F5 any day.

Good Listening

Peter
charles1dad's avatar
charles1dad
10,250 posts
 
Pani,
As we both know, listening to all the choices is the only way to get a
definitive answer (easier said than done).Depending on the type of sound
you're after I can understand the 450 watt amplifier recommendation. From
your list the First Watt is the most appealing choice by a considerable
margin.Pure class A simple circuit design created by an audio icon. The
McIntosh and First Watt move in very different directions philosophically
and in execution. It seems they would attract quite different listeners and
cater to contrasting priorities.
Charles,
almarg's avatar
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almarg
9,670 posts
 
While I have no doubt that in many setups the F5 would provide great sound (within its power range), the facts that it has a very wide specified 3db bandwidth of 1 MHz, a high input impedance of 100K, and uses feedback, raise some caution flags in my mind.

You've probably already seen it, but just to be sure I'll quote this paragraph from the manual:
A caveat is in order here – this is a very wide band amplifier with a high input impedance. In order to prevent the output voltage from bleeding back to the input at very high frequencies (thus making a fine power oscillator), keep the input and output cables separate, and don’t externally connect the speaker ground to the input ground. Good ground shielding on the input cables is important, and caution is called for in using Litz and other specially low inductance / high capacitance cables. I have not seen a specific example of a problem, but historically it is to be expected when an amplifier’s bandwidth exceeds 200 KHz. If the amp makes funny noises, runs extra hot, or blows fuses, this might be an indicator of such an issue.
Also, I would be particularly cautious if the F5 would have to be placed close to a component containing significant amounts of digital circuitry, or if there is reason to suspect that you may be in a high RFI area (e.g., nearby radio stations), or if there is reason to suspect that your AC power is particularly noisy (e.g., nearby industrial plants).

Also, keeping speaker cables as short as possible would seem to be desirable, both to minimize capacitance and to minimize RFI pickup that may be injected into the amp's feedback loop.

Not sure how critical any of this is, but these kinds of things strike me as being potential sonic issues (or worse) with any very wide band high input impedance amp that uses feedback.

Regards,
-- Al
chayro
2,985 posts
 
While others might disagree, Naim amps function best with Naim preamps. The 300 is a wonderful amplifier, but I don't know if you'll be getting the best out of it without at least a Naim 282 preamp or better. IMO, Class A, Class B or whatever doesn't really mean anything in and of itself. The design has to be taken as a whole and judged on sonics, not specs.
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