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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
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
3,003 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.
bombaywalla's avatar
bombaywalla
1,958 posts
 
Abhi,
from my experience it is not correct to think that just because a speaker is of high(er) efficiency that a low(er) power amplifier will do the job.
I have a Tannoy studio monitor that is 94dB SPL/W/m & I use it with a 120W/ch class-AB amp with very good effect. This studio monitor is, well..........., used in studios where the power amplifiers are of 100s of watts & often even 1000s of watts. The max wattage handling capacity of my speakers is 350W/speaker even tho' it's rated a 94dB SPL/W/m. To me this in itself is a huge hint from Tannoy to me that my speaker will do very well with a high power amp despite its high efficiency.
A higher power amp with a Tannoy will give you more control over the music & a lot more dynamic headroom. You music will sound alive as there will be plenty of wattage on-tap for dynamics.
I would try to find an excellent 100W/ch power amp for this Turnberry SE speaker. Maybe Pass' own offerings or some well regarded 100W tube amp.....

I tend to agree with Chayro - NAIM gear seems to sounds its very best with associated NAIM components. The magic falls off the cliff once you put a NAIM component with some other brand. IMHO. YMMV. Have you heard NAIM gear mixed-matched with other non-NAIM gear? If yes, did it have the same magic as with all-NAIM gear?

atmasphere's avatar
atmasphere
11,913 posts
 
Just a FWIW: 93 db is not considered high efficiency. It is a moderate efficiency. You are transitioning from moderate to high efficiency about 97 or 98 db.

If the room is small enough or lively enough, I would go with the F5 in a heartbeat- it is one of the best transistor amps made and by that I mean best-sounding. But if you keep running it out of gas it will be frustrating in the long run. Any chance to do an audition?
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