Sierra-1 with F5 amp

[bk_856er]

Thinking of building a (Nelson Pass) FirstWatt F5 power amp to use with my Sierra-1 NRT.

Anyone have any experience with this combo? I expect it to be fabulous.

The standard F5 is rated at 25W/channel, but it can also be built to make twice that amount

Is 25W sufficient for the Sierra-1 NRT?

BK

[choirbass]

According to the specifications, a minimum of 45 watts is recommended.

[Dark Ranger]

Hi bk,

The short version is that I agree with choirbass and suggest you consider a more powerful amplifier.

That said, technically one can use any amplifier as long as one knows what they're doing. Under certain conditions, your Sierra-1 NrTs would be absolutely fine with the 25-watt amplifier. One of the caveats is the following:

Using the F5, I would strongly recommend you do not exceed low to moderate volume levels with this combination. Here are some rough numbers to demonstrate the general capability of this combo.

F5 output - resulting dB level at 1 meter
1 watt......- 87 dB
2 watts....- 90 dB
4 watts....- 93 dB
8 watts....- 96 dB
16 watts..- 99 dB
25 watts..- 100.50 dB

Add another 3 dB to each entry since you have a pair of loudspeakers. In addition, final output may be slightly less due to various limitations (nothing provides 100% efficiency in our entropic world). In addition, SPL falls off by 6 dB for every doubling of distance (or increases by 6 dB by halving distance) according to the inverse square law. For example, SPL of 95 dB at 1 meter becomes 89 dB at 2 meters, and 83 dB at 4 meters.

So if someone sitting 4 meters away from the loudspeakers wants 90 dB at the listening position, a 25 watt amplifier just barely cuts the mustard. And that's without even bringing up dynamics and transients! Unless your music is extremely compressed, it will have dynamics that peak above the average SPL. In many cases, these peaks can run 12-21 dB above average, requiring an enormous amount of power (over 10 times the power at 12 dB and over 100 times the power at 21 dB)!

It's a bit more complicated that what I've written, but that's the quick and dirty version. So unless you are going to listen at low to medium volumes or listen in a near-field setup, I would strongly consider more powerful amplification.

Hope this helps. :)

[bk_856er]

Thanks, guys. Very helpful indeed and the table is a good way to look at.

I was aware of the Sierra specs, but was hoping to get a reality check from real-world experience with the FirstWatt amps and their non-exaggerated specifications.

Sounds like I should either aim for one of the "enhanced" F5 variants, or a different design altogether with more base power and class A/B operation. I don't listen at loud levels, but some healthy headroom is almost always a good thing.

BK