High power vs high Current

[swraman]

Hi,

I just placed an order for a receiver for a basic 2-ch stereo system as my tv speakers are horrible and hard to understand sometimes.

I was going to buy the Sony STR-DH100: http://www.newegg.com/Product/Product.aspx?Item=N82E16882105281

but then I saw that the reviews for the Onkyo TX-8255 were better, and it was only $10 more. So I bought it. http://www.newegg.com/Product/Product.aspx?Item=N82E16882120128

The Sony was 100W/channel, but acording to reviews of the Onkyo it outpreforms many other brands' (someone even listed Sony as one) 100W/ch receivers in both quality and loudness. I see that the THD is slightly less on the Onkyo, and it passes a much larger frequency range, so aside from the power rating it seems to be a better product than the Sony.

So whats the deal? I read somewhere that a high current receiver (as the Onkyo) is more capable of delivering a more power than receivers who'se RMS powers are rated higher. Is there any truth to this? Is the power rating on the Sony just deceptive; ie. is it the power rating at a certain frequency output, while the 50W rating on the Onkyo is the average across all audible frequencies?

Thanks, Im fairly new to audio, but I have a technical background and would appreciate a technical answer.

thanks

 

[sholling]

I'm an Onkyo fan but without getting into specifics about these two products I can tell you that there are many ways to rate receiver power. You could pick a single easy to drive frequency, say 1khz and rate your product as 100wpc at 1khz with only one channel driven. You'd do that if your power supply wasn't big enough to pass a 100wpc at 1khz all channels drive, much able to drive both channels from 20-20,000hz.

Or you might rate your receiver at 100wpc from 20-20,000hz all channels driven if it has the power on tap to back it up.

Moving from stereo receivers to 7.1 channel receivers you see both the 1khz rating and the more useful 20-20,000hz ratings. Some take that and apply it to a (a very few) 1 channel driven rating, many others a 2 channels driven rating, others all channels driven.

In this case I think you made the right decision.

 

[PENG]

Thanks, Im fairly new to audio, but I have a technical background and would appreciate a technical answer.

thanks

Since you asked for a technical answer, please realize that "RMS power" is some sort of a misnomer. "RMS" voltage and "RMS" current are well defined but for what we are talking about here, we should consider "Average Power", not the meaningless "RMS power".

The term "high current" is not even loosely defined, it is more of an expression/adjective that gets thrown around. That being said, some people probably consider high current capable amp/receiver as one that is able to increase it's output when the load impedance dips from 8 ohms to say 4 ohms or even 2 ohms, while high power could simply mean anything over 300WPC, but it could also mean as little as 200WPC or as much as 500WPC or higher.

High power amplifiers (not tubes) generally are high current (again, not defined) capable whereas the reverse may not be true. For example, a $5000 30WPC Luxman class A integrated amp could claim "high current" as it can double down to 60W for sure, but 60W is hardly high power by most people's standards.

Now, let's compare the published specs of the 8255 and DH100:

Onkyo 8255

All channels: 50 watts minimum continuous power
per channel, 8 ohm loads, 2 channels
driven from 20 Hz to 20 kHz, with a
maximum total harmonic distortion of
0.08 %
Rated Output Power (IEC) (European and Australian)
2 ch × 90 W at 4 ohms, 1 kHz, 1 ch driven

Sony DH100

With 8 ohm loads, both channel driven, from 20-20,000 Hz; rated 90 watts per channel minimum RMS powr, with no more than 0.09% total harmonic distortion from 250 milliwatts to rated output.

Based on the published specs, even if the Sony is current limited to it's 8 ohm power output rating, it would still half down (as opposed to double down) to 45W for the FR of 20-20,000 Hz, very close to the Onkyo's published rating into 8 ohm loads. So I would guess that the output power of the two are comparable.

 

[sholling]

BTW a slightly better choice might have been the more powerful Onkyo TX8555.

 

[swraman]

Thanks, that cleared up some of the myths/facts Ive doubted in my head for a long time.

 

[3db]

Hi,

I just placed an order for a receiver for a basic 2-ch stereo system as my tv speakers are horrible and hard to understand sometimes.

I was going to buy the Sony STR-DH100: http://www.newegg.com/Product/Product.aspx?Item=N82E16882105281

but then I saw that the reviews for the Onkyo TX-8255 were better, and it was only $10 more. So I bought it. http://www.newegg.com/Product/Product.aspx?Item=N82E16882120128

The Sony was 100W/channel, but acording to reviews of the Onkyo it outpreforms many other brands' (someone even listed Sony as one) 100W/ch receivers in both quality and loudness. I see that the THD is slightly less on the Onkyo, and it passes a much larger frequency range, so aside from the power rating it seems to be a better product than the Sony.

So whats the deal? I read somewhere that a high current receiver (as the Onkyo) is more capable of delivering a more power than receivers who'se RMS powers are rated higher. Is there any truth to this? Is the power rating on the Sony just deceptive; ie. is it the power rating at a certain frequency output, while the 50W rating on the Onkyo is the average across all audible frequencies?

Thanks, Im fairly new to audio, but I have a technical background and would appreciate a technical answer.

thanks

High current models usually imply high power in that the power supply has enough reserves to sustain the current through the speakers and maintain the voltage across the speaker's terminal through all of its channels at full audio spectrum, 20Hz-20KHz. That to me means high power. The other catch is that its relative...a 500w high current ampliier is more high power than say a 60 watt high current amplfier. However, the Sony's of this world cannot sustain this kind of load and either distort the signal because of clipping.