Help understanding receiver specs

[iramegdal]

Years ago I was aware of unscrupulous manufacturers who overstated the output of the amplifier sections of receivers. They rated them at what was peak or instantaneous power, or some such term, I believe.
Then I remember the concept of continuous or RMS power coming into play, and presumably resolving the problem. I thought that the FTC got involved as well. As I remember it the result was that WPC would be described as X WPC, into 8 ohms, from 20Hz to 20kHz with 0.1 THD, both channels driven.
Recently I was looking at an Onkyo TX-8150 that was well received by What Hi-Fi. It is a European model only with a DAB tuner. It is rated at 135 WPC (IEC) one channel driven into 6 Ohms, at 1kHz with 1 per cent THD. What kid of hinky rating is this?
The purpose of this inquiry was to compare the TX-8150 with the identical looking TX-8140, available in the US. It is rated using FTC rather than ITC. Slightly less WPC, less THD and no DAB, of course. Is there any way of comparing to tell whether these are essentially identical units, but-for the DAB?

 

[Pyrrho]

FTC rules only apply in the U.S. Products made in other countries and marketed for other countries do not have to follow laws in the U.S. regarding ratings.

As for whether the units are essentially the same or not, that would require an examination of the circuitry involved (which would be easiest by consulting with service manuals). But you might be able to get some idea about this by looking at the owner's manuals for the U.S. product and the European model and compare, as each may contain multiple different ratings regarding this matter. For the U.S., the FTC requires continuous RMS ratings, but they do not prohibit listing other types of ratings as well in the manual; it is common for companies to have multiple different types of ratings in the owner's manual on the specifications page.

 

[Blue Shadow]

Years ago I was aware of unscrupulous manufacturers who overstated the output of the amplifier sections of receivers...

I thought that the FTC got involved as well. As I remember it the result was that WPC would be described as X WPC, into 8 ohms, from 20Hz to 20kHz with 0.1 THD, both channels driven.

Before November 4, 1974 power specs in the US were generally done per the IHF (Institute of High Fidelity) and the added power of both channels gave a unit of say 110 watts. Boiling this down to a later FTC rating and one might get 20 watts per channel. See the attached Pioneer specs for the SX-626 a unit that was available before the promulgation of the FTC ruling.

The FTC ruling required pre-conditioning at 1/3 power (max heat build up in a typical amp) for an hour, then testing at full frequency into a specified load and measuring the total harmonic distortion, THD. This test was for 2 channel units, not the later Home Theater units which can advertise some big power and sound weak compared to a vintage unit.
The rule required the
WPC @ XΩ, for a specified frequency range with a maximum of Y% THD. for example,
100 wpc into 4 Ohms from 20-20kHz with less than 0.03% THD.
Watts per channel must be specified, any frequency spectrum can be specified, both channels must be running during the test (notice how power drops when both channels are driven in the Pioneer example), the speaker load (impedance in Ohms) must be specified as well as the THD. This must be in larger print than any other measurement method. Frequency range of some small early receivers were sometimes mentioned as 40-20kHz which allowed a higher number since the bass was the big power hog. Sansui did this with the 331 and others. You were allowed to specify at more than one load, such as both 4 and 8 Ω, but did not need to and the lack of a rating at a different load was not an indication of an inability to drive that load. The instruction manual or back panel of the unit would talk to the ability to drive different loads.

There weren't too many crooks listing the many different specs, that came with car audio an IPP, instantaneous peak power at cranked up input voltage (over 14V for a 12V auto system) and such but the multitude of numbers in the Pioneer spec were typical for home gear. Some companies only supplying a couple numbers made it difficult for Joe Stereo Buyer to compare and the Feds put a stop to the confusion using the new method which is NOT how we listen. We don't listen at steady state watts per channel, music is variable watts, generally.

A tech will bench test an amp and the number is always higher, sometimes way higher... No preconditioning, only one channel, only one frequency (usually close to 1000Hz) into the techs standard load usually to clipping. This I call a bench number and checking around everything does 15-30% more with a bench number than an FTC number.

 

[Grenadeslio]

To add to the confusion, from what I gather AVR's are not held to this standard so their specs should be taken with a grain of salt.

 

[SoCal Sam]

...Recently I was looking at an Onkyo TX-8150 that was well received by What Hi-Fi. It is a European model only with a DAB tuner. It is rated at 135 WPC (IEC) one channel driven into 6 Ohms, at 1kHz with 1 per cent THD. What kid of hinky rating is this?
The purpose of this inquiry was to compare the TX-8150 with the identical looking TX-8140, available in the US. It is rated using FTC rather than ITC. Slightly less WPC, less THD and no DAB, of course. Is there any way of comparing to tell whether these are essentially identical units, but-for the DAB?

Massaging is done to advertise a higher WPC. If the amp has headroom and most do, lower impedance tends to inflate WPC. 1 kHz is the easiest frequency to drive so more watts are delivered. Again, WPC is inflated. THD can also be used to massage WPC. The higher the THD, the greater the wattage that can be quoted. Most reputable makers market low THD so to attain this, they measured at a lower output. My guess is the Onkyo TX-8150 similar to the U.S. model which is 80 WPC, FTC.

 

[catrafter]

I remember reading testing results that indicated a well known 130 Watt 5 channel amplifier could only deliver 26 Watts with all channels driven.
If you compare the 1974 FTC documents on power amplifier testing to the latest documents it appears that this is allowed.



From the FTC power amp test ruling, 2010:
Sony commented
further that ‘‘to maintain the same power
ratings if it were necessary to drive all
channels simultaneously during testing,
virtually all manufacturers would have
to change the sound platform of their
amplifiers and receivers to be able to
sustain such output,’’ which ‘‘would
drive up the costs of production
considerably, [and] in turn drive up the
ultimate cost to consumers.’’
The Commission has received no
contrary evidence indicating that all
channels of a multi-channel home
theater system frequently would be
driven to maximum power
simultaneously during typical playback
conditions in home use. Absent such
evidence, the Rule should not be
amended.

Tom


P.S. If someone has a better copy of the 1974 FTC document please let me know, all I have is the old jpeg posted above.
T.