2. amps-preamps
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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 5 responses by cakyol

cakyol's avatar
cakyol
940 posts
 
invalid, georgehifi,

This is the spec page from D’Agostino Relentless welding machine.

https://dandagostino.com/products/relentless-monoblock.php

Please show/indicate to me where the ’incorrect’ or ’misleading’ information is.
cakyol's avatar
cakyol
940 posts
 
invalid,

Here are some amps (more like welding machines) that can do double the power:

D'agostino Relentless.
Pass labs, almost all their amps.
Boulder 3050 monoblock,

and there are more......
cakyol's avatar
cakyol
940 posts
 
Ideally, a power amp should be able to deliver twice as much power at half the impedance. The way it can achieve this is if:

1) Its power supply can meet the demand (probably the most important criteria).
2) Its output stage/heatsinks are designed to dissipate the demands of the extra power.
3) It is still stable with the higher load (less impedance).

So, if it is NOT able to do it, most likely one or more of the above is suspect. Most of the time, it is the power supply inadequacies (item 1 above).

cakyol's avatar
cakyol
940 posts
 
atmasphere,

You are right in saying that the internal impedance of an amplifier must be way less than the speaker impedance, in order to deliver power indirectly proportional to the speaker impedance. I took that as a given, since that is the case with most amps these days. However, if the supply line starts collapsing under the extra load, it will never be able to deliver the extra power, no matter what other parameters are tweaked.
cakyol's avatar
cakyol
940 posts
 
invalid,

Of course you can get more power.  It is ludicrous to think otherwise.  An amp is like (bit of an exaggeration to get the point across) your mains amplifying a 60 Hz signal.  If you connect a 120 ohm load to mains, you will get 120 watts, if you connect a 60 ohm load, you will get 240 watts, if you connect a 30 ohm load, you will get 480 watts, etc, until you blow your fuse.

AS LONG AS YOUR MAINS DOES NOT COLLAPSE AND YOU DO NOT EXCEED YOUR CURRENT LIMIT, you WILL get more power.  It is virtually the same in amps.  It is like supplying a 60 hz continuous signal.  As long as the power supply can supply the needed current, it will keep on supplying more power.  The limitation with amps is the heatsink/output stage design (transistor current limits), the maximum internal impedance and its stability at different frequencies.  The ideal amp (again, an asymptotic exaggeration) will even handle a short cirtcuit across its speaker where the current will be limited by only the internal impedance of the output stage.  This obviously will blow the transistors but you get my point.

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