2. amps-preamps
  3. 159074-115924

Same watts at 8 and 4 ohms?

I'm in the market for an integrated amp and trying to sort through tech specs. My understanding of the tech aspects of hi-fi gear is limited. Looking for some clarity in regard to watts-per-channel specs.

It is my understanding that wpc at 4 ohms is typically 1.5x -2x the wpc at 8 ohms.

But I'm seeing a number of respectable mid-fi integrateds with the same wpc for both 8 and 4 ohms. The NAD 388 is one and I think this is true for several of the Cambridge Audio units at a similar price point ($1500-$2000).

The NAD features make a point of saying " 4-ohm stable for use with a wide range of speakers". 

Would appreciate any insight to what these specs mean and what 4 ohm stable really means to me. My speakers are 4 ohm speakers.

Thanks,

George
n80

Showing 3 responses by erik_squires

erik_squires
16,649 posts
 
Hi @dsper
My main speakers are Thiel CS5’s and we have talked on other threads about how they are a difficult load as they dip close to 2 ohms and 82 dbl sensitivity. There has also been associated discussion about how more power can mean more noise.

In this regards, Pass’ point that the signal to noise in the first watt matters more than the 200th watt, and that high power amps skew their S/N ratings if measured only at full power is true. However it is not universally true that a bigger amp will have more noise at 1 watt.

Just looked at the CS5 impedance curve. Wow.

https://www.stereophile.com/content/thiel-cs5-loudspeaker-measurements-0
You definitely want a beefy solid state amp. It doesn’t have to have a lot of power, but doubling power from 8 to 4 to 2 Ohms will be recommended or the speaker will sound like the impedance curve.

One brand you may not have thought of is Sander’s Sound. Their ESL and Magtech amps are the best there is when it comes to this particular feature.


Best,
E
erik_squires
16,649 posts
 
The distortion vs. output profile is a little more complicated than explained earlier. Please see figures 5 and 7 for what a very well behaved linear amp’s output usually looks like vs. output power.


https://www.stereophile.com/content/luxman-l-509x-integrated-amplifier-measurements


The limiting factor is often notch or crossover distortion, which is constant and occurs near zero output. As the output rises this distortion becomes a smaller proportion. Of course, eventually the amplifier will clip and distortion is dominated by the top of the waveform being flattened as the voltage at the output reaches the voltage of the power rails.
Of course I am a Luxman fanboy but this curve is very common.
erik_squires
16,649 posts
 
Hi George,

Take a look at any speaker review on Stereophile and they will plot the speaker impedance.

This impedance is never a flat line at 4 or 8 Ohms and in fact take quite complicated shapes.

The lower the impedance, the more current the amp has to produce to maintain a stable output, otherwise it starts to drop.  If you think of a wall wart, 12V, 2 Amps.  If you try to draw more than 2 amps, it no longer produces 12 V but instead the voltage sags until it overheats.  Amps do the same thing.

An ideal amp maintains the voltage output regardless of speaker impedance, which is synonymous with saying it doubles the wattage as the impedance is cut in half.

You may not need an ideal amp or like how it sounds matched to your speakers though, so keep this in mind.  The C 388 uses a hybrid Class D designed by Bruno Putzeys (or nCore?) which is a pretty sweet little thing. It puts a linear amp in the middle of the Class D.  I have another NAD integrated with it and I like the sound a lot.  It's not as fun to listen to as my Luxman, but nothing wrong with it either. 
More to discover