Why all amps and receivers aren't the same.

Seth=L · 09-26-2006, 12:11 AM

I don't know if this is relevant, or if this thread will even stay open, but I am going to give this a shot anyway.

So you might ask yourself, what difference is there between my Kenwood 600 watt receiver and his H/K 225 watt receiver. The difference is truth in ratings. The FCC doesn't regulate these things closely enough, maybe they don't have the resources anymore, who knows. So many audio manufacturers bloat their power ratings with a little cunning, or they just straight up lie. Some of you may have seen the white van scams before, those guys are straight up lying. Not much of their specs are real, they quite literally pull numbers, numbers that look good, out of thin air.

Many factors can be looked at when considering a new receiver or amplifier. One of the most popular is reading user reviews or maybe specifications. Just know that what you read isn't nearly as usefull as listening to something for yourself. People have different listening needs. An individual likes to listen to heavy metal probably won't have a very usefull review for someone who listens to classical and jazz. Not to say reviews are bad, they deffinitely are usefull to find reliability and maybe erganomics.

Things to be aware of when looking at amplifier or receiver amplifier performance specs:

The wattage: I will show you a bad example of a power rating.
110 watts RMS per channel 6 ohms (1khz at 0.7 THD)

Then a good one:

95 watts RMS per channel, all channels driven 8 ohms (20hz-20khz at 0.06 THD)

The problems with the first rating are:
The (1khz), this is the frequency that they tested the amplifier's power, This single frequency is not a difficult one to produce. A more accurate rating will tell that it is able to provide that amount of power at any given frequency between 20hz (being the lowest and most demanding frequency to reproduce) and 20khz (the highest average frequency audible to humans).

Another thing to look at is the load impedance. Some of these specs aren't offered in great detail for many manufacturers. They should have the wattage ratings for each impedance(resistance to electron flow), measured in ohms. If the ratings for the 8 ohms vs. the 4ohms are higher then make sure your speakers don't have lower ohms before buying many budget brands, lower ohms means more resistance.

Another important factor is continuous output and all channels driven. These manufacturers are very carefull in how they word things. If the specs say something like this [100 watts per channel RMS] that could mean that the receiver is theoretically capable of delivering 100 watts RMS on just one channel, were the RMS of all the channels together may be in the neigborhood of 20 watts RMS. A rating like this [100 watts RMS, all 5 channels driven] would indicate the amp is capable of delivering 100 watts of power RMS to each channel at the same time.

One very simple way to evaluate most receivers and amps without listening to them to find what they are really packing is size of parts (weight), power consumption, and some internal #'s. Not all these methods will always work. Manufacturers have found many ways to make things more eco-friendly. Digital amplifiers operate very efficiently. They run cooler than analog amps, and weigh much less. They have their short comings and upsides as well. Some have boomy bass and reticent highs.

Large power supplies (transformers), large capacitors (round can shaped objects) and hefty discrete output stages (transistors) are all characteristics of a quality amp. If the caps are the size of a spool of thread, the transformer the size of a rubix cube, and a couple large transistors might get moderate performance in a receiver. Though a transformer that weighs 10 pounds, and caps as big as pill bottles, and lots of transistors on a nice heatsink might indicate a more powerfull amplifier

Anyone feel free to add your opinions, and correct possible mistakes. I really hope that this can help someone in the quest to buy a receiver or amplifier.

FeisalK · 09-26-2006, 01:54 AM

There's a few articles at Audioholics about this

The All Channels Driven (ACD) Amplifier Test
Product Managing Receiver Platforms & Power Ratings
The All Channels Driven Amplifier Test Controversy

Arthur S · 09-26-2006, 08:06 AM

Seth

I have a Kenwood reciever, which one do you have? Or were you just using that as an example?

Thanks

Seth=L · 09-26-2006, 09:11 AM

Quote:

Originally Posted by Arthur S

Or were you just using that as an example?

Example, many of the lower end Kenwood, Sony, Pioneer, even Yamaha, Denon and Onkyo do this sometimes, they use some very misleading power ratings. It is less common for H/K or Outlaw to boast power they don't realistically have.

Seth=L · 09-26-2006, 09:17 AM

Quote:

Originally Posted by FeisalK

There's a few articles at Audioholics about this

The All Channels Driven (ACD) Amplifier Test
Product Managing Receiver Platforms & Power Ratings
The All Channels Driven Amplifier Test Controversy

Those are very good articles. I would recomend anyone looking for a new amp or receiver read those articles. Thank you, FeisalK.

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Seth=L · 09-26-2006, 09:47 AM

For music listeners, true RMS power is important. If one listens to heavy metal at very high volume, then they would likely want some true rated power. With home theater we may not need that continuous power.

An example of how skewed the ratings are. I have a Carver AV-505 5 channel amplifier. It is rated at 80 watts RMS per channel all channels driven 8 ohms from 20hz-20khz at 0.08THD. The amp weighs 42 pounds. It has an oversized power supply, modular design, and caps the size of small aerasol cans. I had a Onkyo TX-DS787 THX Select receiver rated at 100 watts RMS 8 ohms (20hz-20khz at no more than 0.08THD). It weighed 36.6 pounds.

Now I am not saying the Onkyo TX-DS787 is a bad receiver, I am just saying it's power ratings are less than true. Note the Onkyo has a six channel amp versus the 5 channel Carver, so not only is the power divided amongst more channels in the Onkyo, it has numerous other factors weighing against it's truth in power. Input power is 440 watts, where as the Carver can draw up to 900 watts. The Onkyo weighs almost 10 pounds short of the Carver, which the Carver is exclusively an amplifier. The Power supply is smaller in the Onkyo,as are the Capacitors, and the output stages.

While 80 watts doesn't seem like much, it really is on the Carver. It makes the THX certified Onkyo's 100 watts, tuck it's tail between it's legs and run home to it's mommy. I also had at one time a Kenwood power amp that was rated at 150 watts rms, the Carver still smokes even that.

Funny thing is, you can get Carver amplifiers for so cheap now, because the company doesn't really exist anymore, Bob has moved on to bigger and better things since Carver.

FeisalK · 09-26-2006, 09:57 AM

I think the most important thing about those articles is that the 100W per channel is a marketer's concoction; audiophiles the world over live with tube amps that put out 10 or 20 watts per channel; one of the best sounding amps I've heard in recent times was a Tripath powered Charlize putting out only 10W at 4Ω. Power is overrated (pun intended) sometimes

and besides, is there such a thing as true RMS watts?

also, I read recently on TI that they only need to test for 1/8th peak power draw to be certified for a power consumption rating; so if an amp can draw 100W per channel peak, it can be rated as 12.5W per channel active power consumption; it does make sense in a way because there is never a program (music or movies) that will draw 100W in all channels all the time.

All this averaging out helps the marketing people stretch the power output rating

Arthur S · 09-26-2006, 10:45 AM

Seth

I have both a Kenwood receiver that test benched at 92 watts X 6 with all channels driven simultaneously, and a 70 pound Citation 7.1, rated at 425 watts X 2. Power draw on the Citation is 2500 watts max. The difference in sound quality is minimal.

JeremyErwin · 09-26-2006, 11:01 AM

Want to maximize the power rating? Specify a 6-ohm load or less. My Onkyo TX-SR502 has a 3-ohm rating.

Dynamic Power: 160 W, 3 Ohm. (The more rational claim is 75W, 8 Ohm, 20Hz--20kHz).

However, despite the claims about WRAT, and High Current, Low Impedence loads, another section of the manual warns against connecting low impedence speakers.

Maybe the dynamic power is meant for those "8-ohm speakers" that actually bottom out at...

...consults manual...

3.0 ohm.

They sound pretty good to me...