Has the FTC Failed Consumer Audio Regarding Amplifier Power Claims?

[Dennis Murphy]

This is in response to a couple of statements in Speedskater's post. The most recent revisions of the Rule did not, in fact, eliminate the power bandwidth requirement, which is usually interpreted to mean 20 Hz - 20 kHz. It might seem that way given all the 1 kHz specs that are floating around, but what the original and current Rule actually requires is that manufacturers state which bandwidth applies, and give power and distortion specs over that bandwidth. A rating over 40 Hz - 15 kHz complies with the Rule. Does a rating at 1 kHz comply with the Rule? Is one frequency a "bandwidth"? It's not within the spirit of the Rule, but technically it might be. That issue has never been tested. In any event, the Rule does not explicitly allow the principal power spec to be stated at only 1 kHz. Also, the revisions did not eliminate the required distortion disclosure. Nothing was changed in that department. All I tried to do in the revisions was to get rid of the dreaded 1/3 power preconditioning requirement and make the rule applicable in a sensible way to closed systems like powered subwoofers. Finally, although I'm sure the FTC would like to see its budget doubled, it has done fairly well in the budget department. My comment about lack of resources and expertise went narrowly to enforcement of the Amplifier Rule. It's not a high priority, and given how well the Hi Fidelity industry works in general and the multitude of problems consumers face in arguably more important areas, I'm not sure it should be a high priority. But hopefully some attention can be drawn to the most blatant Rule violations Gene has helpfully pointed out.

 

[gene]

You are not wrong at all for calling out Lyngdorf on the minimal power rating disclosure on their latest integrated amp, the TDAI-3400. But note that this product was just announced within the past few weeks, and probably isn't even available for sale quite yet. The full owners manual has not yet been published. In the past, Lyngdorf has published specs "in accordance with AES-17" in the owners manual.

The TDAI-3400 appears in every way to be a refinement of the predecessor TDAI-2200, which had similar features and power ratings, but specified with THD+N at 1KHz, the same as John Atkinson's measurements at Stereophile. The owners manual for the TDAI-2200 with more inclusive power, distortion, noise, and bandwidth specs at 4/8 ohms is still available on Lyngdorf's site. Page 34.

I own the TDAI-2200 in my system "B," and I can tell you that one is a genuine muscle amp, a real cool-running beast. I bought it because the RoomPerfect automated EQ system immaculately cleaned up a very tricky semi-open 30'x14'x12' room we used to have, combined with highly compromised placement (WAF, immovable large furniture) of my Sonus Faber Cremona M speakers.

Whatever disadvantages this implementation of Class D may have, in that system in that room they were completely overwhelmed by the fine performance of the preamp/DAC/EQ.

I've seen prior class D amps from them rating power ambiguously like the example,cited in this article. If they update their specs with full disclosure of power and bandwidth with both channels driven, I'd be happy to update the article. There is no excuse to NOT have this information readily available if the product is released and shipping to consumers. I can fully measure and report an amplifiers ratings in 1 business day and I'm one person running a website with a host of other responsibilities, not a corporation with multiple engineers doing this for a living.

 

[gene]

I think the Lyngdorf, or other digital amps do need different rules/standards, or the existing ones be revised to reflect their different needs. It is not fair to subject such modern design to the ancient FTC requirements created when consumer digital amplifiers were not commonly found. There were class D amps at the time, and I am sure people argued for exceptions for those amps too, but the Lyngdorf amps are certainly much more digital than a regular so called class D amp.

I disagree, and it's partly why some manufacturer's of Class D amplifiers are getting away with this. Other than a filter to prevent test equipment from reading distortion wrong, regardless of amplifier class, the amp should still be able to swing voltage at full BW for 8 and 4 ohm loads.

There are good Class D's that can, so why let the poorer designs have a free pass to put them on equal footing by using tests that don't reveal their weaknesses?

 

[PENG]

I disagree, and it's partly why some manufacturer's of Class D amplifiers are getting away with this. Other than a filter to prevent test equipment from reading distortion wrong, regardless of amplifier class, the amp should still be able to swing voltage at full BW for 8 and 4 ohm loads.

There are good Class D's that can, so why let the poorer designs have a free pass to put them on equal footing by using tests that don't reveal their weaknesses?

Gene, I am a little surprised you would disagree as I wouldn't want them to get a free pass either. In fact, I share the same concerns, that the current FTC rules and other magazine test benches may not reveal their weaknesses. So again, I was not implying that they cannot handle the existing rules and standards, I was just concerned about the opposite.

Not long ago I read an article (linked below) on ee times that talked about how class D amplifiers could test well yet may sound inferior. I take it that it is just the writer's opinion, but if I remember right you have also expressed concerns of certain class D amps, one being a Pioneer's right?

https://www.eetimes.com/document.asp?doc_id=1274731

"Class D amplifiers are fundamentally different from analog amplifiers, not only in their circuitry, but more importantly in the way they operate. Yet, engineers continue to test Class D amplifiers using the same tests and test procedures that were developed generations ago specifically for analog amplifiers. Because these tests were designed for analog amplifiers and are focused on analog particulars and capabilities, it is no wonder that we have Class D amplifiers that test well in the lab, yet reproduce inferior sound under real world operation. Clearly, new tests that are specifically designed with Class D operation and behavior in mind are needed if the test results are ever going to be relevant."

I am less concerned about the more matured conventional class D amps. I was actually reacting to Nickmore's post#13 that mentioned the Lyndorf digital amp. Lyndorf claimed their amps are totally digital, short form TDA. I am not clear how exact they achieve that as I would think they still need some sort of analog output filters. That's the main reason why I thought perhaps some new or additional rules and/or test standards are needed for such "totally digital amplifiers". I am not sure if there are many other totally digital amplifiers out there yet, but if not, I think there may be, eventually.

 

[Matthew J Poes]

I disagree, and it's partly why some manufacturer's of Class D amplifiers are getting away with this. Other than a filter to prevent test equipment from reading distortion wrong, regardless of amplifier class, the amp should still be able to swing voltage at full BW for 8 and 4 ohm loads.

There are good Class D's that can, so why let the poorer designs have a free pass to put them on equal footing by using tests that don't reveal their weaknesses?

This is exactly the point of my earlier post. Class D amps need to be tested in a manner that don't hide their flaws. A filter should be used and the type and nature of that filter should be standardized. Full bandwidth is needed as well, and this pesky oscillation issue should be made obvious.

One such oscillating amplifier was tested using a filter that ultimately allowed it to hide the fact that it oscillated like this.

 

[PENG]

This is exactly the point of my earlier post. Class D amps need to be tested in a manner that don't hide their flaws. A filter should be used and the type and nature of that filter should be standardized. Full bandwidth is needed as well, and this pesky oscillation issue should be made obvious.

One such oscillating amplifier was tested using a filter that ultimately allowed it to hide the fact that it oscillated like this.

And in my earlier post, I did not mean to give class D and Lyngdorf's so called totally digital amps a break, in fact quite the opposite. I was concerned the current (but old) FTC rules and other commonly used testing and measurement methods by magazines may not reveal certain weakness of such amps. On reading my own post again, I now realize the wording "..not fair.." I used, was ambiguous/misleading, and could easily be misunderstood.

 

[Matthew J Poes]

And in my earlier post, I did not mean to give class D and Lyngdorf's so called totally digital amps a break, in fact quite the opposite. I was concerned the current (but old) FTC rules and other commonly used testing and measurement methods by magazines may not reveal certain weakness of such amps. On reading my own post again, I now realize the wording "..not fair.." I used, was ambiguous/misleading, and could easily be misunderstood.

I wasn't criticizing you, just pointing out that I think Class D amps aren't often being tested as they should.

I have concern with the filter issue because I think the lack of standardization allows companies to play with the bandwidth it is being tested under. I don't care if this is done with a subwoofer amplifier, but its a problem for amps intended as full range devices.

I think the only unfair aspect of Class D amplifier testing is that some high frequency noise present on the output is not really of consequence in practice, but makes the specs look bad. Even with an output filter on the amplifier (as is true for most Class D amplifiers), some leak through is common. The Behringer amplifier mentioned has been shown to have 6-10 volts leaking through, but this is related to its carrier signal and is at a very high frequency. It has been shown to slightly impact the shape of the sinewave even when bandwidth limited. Admittedly, in practice, a speaker will filter this, it probably won't be an issue. Still, Hypex amps don't do this.

 

[Matthew J Poes]

I am less concerned about the more matured conventional class D amps. I was actually reacting to Nickmore's post#13 that mentioned the Lyndorf digital amp. Lyndorf claimed their amps are totally digital, short form TDA. I am not clear how exact they achieve that as I would think they still need some sort of analog output filters. That's the main reason why I thought perhaps some new or additional rules and/or test standards are needed for such "totally digital amplifiers". I am not sure if there are many other totally digital amplifiers out there yet, but if not, I think there may be, eventually.

These fully digital amplifiers often use a scheme to convert a PCM signal to a PWM signal or a delta sigma modulated signal. In this sense the amplifier is digital from input to output. However, when it goes to the speaker there is usually a filter on the output to "recover" the audio frequency. Some amplifiers, especially those using sigma delta modulation can ditch the filter and rely on the speakers natural inductance and resistance to filter the signal (that and the fact that we can't hear the carrier frequency).

I own a few filterless Class D amps, they sound ok. No obvious noise or distortion. Mine are all small (less than 20 watts) so its hard to tell often if the amp sounds bad or is just being driven to clipping. Because its filterless its also hard to measure if its clipping a little or if the deformation is noise due to the lack of a filter. I had a problem where there was an obvious sound difference between an inexpensive speaker powered through one of these and a hypex based amplifier. I took scope measurements off the amplifier output while connected to the speaker (using it as the filter and load) and found some ugly deformation that seemed to increase with level, it was squaring the wave, so I think it was clipping. However, it also wasn't a great looking sinewave to begin with (and I'm not an engineer). I was never sure what I was looking at (My scope is laptop based, so its very bandwidth limited).

 

[PENG]

These fully digital amplifiers often use a scheme to convert a PCM signal to a PWM signal or a delta sigma modulated signal. In this sense the amplifier is digital from input to output. However, when it goes to the speaker there is usually a filter on the output to "recover" the audio frequency. Some amplifiers, especially those using sigma delta modulation can ditch the filter and rely on the speakers natural inductance and resistance to filter the signal (that and the fact that we can't hear the carrier frequency).

I own a few filterless Class D amps, they sound ok. No obvious noise or distortion. Mine are all small (less than 20 watts) so its hard to tell often if the amp sounds bad or is just being driven to clipping. Because its filterless its also hard to measure if its clipping a little or if the deformation is noise due to the lack of a filter. I had a problem where there was an obvious sound difference between an inexpensive speaker powered through one of these and a hypex based amplifier. I took scope measurements off the amplifier output while connected to the speaker (using it as the filter and load) and found some ugly deformation that seemed to increase with level, it was squaring the wave, so I think it was clipping. However, it also wasn't a great looking sinewave to begin with (and I'm not an engineer). I was never sure what I was looking at (My scope is laptop based, so its very bandwidth limited).

I was wondering if the Lyngdorf TDAI amps are the types that somehow managed to do away with the output filters. There's not much technical info on their website, just marketing stuff.

 

[wire]

Nice post , I like it alot .

 

[TechHDS]

I was wondering if the Lyngdorf TDAI amps are the types that somehow managed to do away with the output filters. There's not much technical info on their website, just marketing stuff.

I wonder how "Butler" amps ya know the ones that have tubes in them can get away with 100 watts X 2 Channels into 8 Ohms with No filter after the rail. .

 

[PENG]

I wonder how "Butler" amps ya know the ones the have tubes in them can get away with 100 watts X 2 Channels into 8 Ohms with No filter after the rail. .

Thank you for mentioning such amps as I know nothing about such interesting thing. They do mention 60,000 uf per channel so I don't think you can say they have no filter after the rail but I guess the key word is "after".

They are nothing digital about them so no, I wouldn't expect output filters (just before the speakers). I probably shouldn't say anything about those amps because aside from knowing nothing, I have never even heard about them until now.

 

[TechHDS]

Thank you for mentioning such amps as I know nothing about such interesting thing. They do mention 60,000 uf per channel so I don't think you can say they have no filter after the rail but I guess the key word is "after".

They are nothing digital about them so no, I wouldn't expect output filters (just before the speakers). I probably shouldn't say anything about those amps because aside from knowing nothing, I have never even heard about them until now.

"Butler" amps are both SS, Tubes and Only After the 'Rail' output stage. Not before Pre-Amp output. I mean after all it All comes out "Analog" between the output and the input of your speaker's or speaker, unless just your using a PA system for announcements with just one speaker. Pyle or Crown that use just a switching power supply. in " Some" key word, But I never said "Butler" amps didn't use a " filter" all I stated was 'I "Wonder" key word how Butler can "spec"
100 X 2 into 8 Ohms". . Genes, Thread is about manufacturers posting outrageous inflated specs getting away with ramming it down consumers throats and the FTC or the audio industry laughs all the way to the bank on unsuspecting consumers. Correct me if I'm wrong but isn't this Threads about, protecting the consumer?

 

[Jason Trosclair]

That's why you should simply purchase NAD products. If anything, they don't provide themselves with enough credit as their amps outperform their own power ratings (at least in my testing and experience).

But yeah, its sad that most manufacturers lie and cannot be trusted with their claims.

 

[PENG]

That's why you should simply purchase NAD products. If anything, they don't provide themselves with enough credit as their amps outperform their own power ratings (at least in my testing and experience).

But yeah, its sad that most manufacturers lie and cannot be trusted with their claims.

In most publicly available bench test results I have seen, NAD AVRs didn't do better, and often worse, than D&M's in 2, 5, 7 outputs at 0.1% THD, 8 and 4 ohms. They are also keen on the dynamic power rating thing, that is sort of controversial. I do like their integrated amps, and have a little C326 Bee for my desktop, but imo there isn't anything special about their power ratings as such.

 

[TechHDS]

That's why you should simply purchase NAD products. If anything, they don't provide themselves with enough credit as their amps outperform their own power ratings (at least in my testing and experience).

But yeah, its sad that most manufacturers lie and cannot be trusted with their claims.

Why just NAD? Outlaw Amps, on a continuous basis outperforms their specs posted with their products. Harman/Kardon 3490 two channel rated at 120 X 2. with a dynamic headroom of 35 watts is considered one of the best value Two channel with a Optical and Coaxial input to boot on the market. For a home audio unit that's not a AVR .

 

[PENG]

Why just NAD? Outlaw Amps, on a continuous basis outperforms their specs posted with their products. Harman/Kardon 3490 two channel rated at 120 X 2. with a dynamic headroom of 35 watts is considered one of the best value Two channel with a Optical and Coaxial input to boot on the market. For a home audio unit that's not a AVR .

I wish Harman would make an AV version of that receiver, do away with the radio tuner, but add HDMI and Asynchronous USB for external DAC, and build in a good REQ feature such as Dirac (preferred), or at least Audyssey XT32 with Sub EQ HT. I am sure there is a market for a 2 channel AVR for Audioholics.

 

[M Code]

I wish Harman would make an AV version of that receiver, do away with the radio tuner, but add HDMI and Asynchronous USB for external DAC, and build in a good REQ feature such as Dirac (preferred), or at least Audyssey XT32 with Sub EQ HT. I am sure there is a market for a 2 channel AVR for Audioholics.

Interesting product idea...
But will never happen under Samsung leadership..
Samsung is only interested in the high profit $ for 12V OE infotainment systems. We ran many new product development projects for HK & JBL including the 3490..
But now their only interest in consumer audio is either BT speakers, headphones or licensing their DSP in laptop computers. They had a great opportunity to go after a bigger share of the audio/hi-fi biz but passed when they deleted their talented USA audio development team and shifted all projects to Shenzhen China.
Perhaps with the procurement of Arcam they to re-enter the consumer audio biz but for now they will stay only in the high end brand markets of Mark Levinson, JBL Synthesis, Lexicon and Revel mainly to support the respective brand images used in their highly profitable automotive OE biz..

Just my $0.02..

 

[panteragstk]

I wish Harman would make an AV version of that receiver, do away with the radio tuner, but add HDMI and Asynchronous USB for external DAC, and build in a good REQ feature such as Dirac (preferred), or at least Audyssey XT32 with Sub EQ HT. I am sure there is a market for a 2 channel AVR for Audioholics.

I'd buy this. Two different rooms where something like this would be very handy.

 

[gene]

I wish Harman would make an AV version of that receiver, do away with the radio tuner, but add HDMI and Asynchronous USB for external DAC, and build in a good REQ feature such as Dirac (preferred), or at least Audyssey XT32 with Sub EQ HT. I am sure there is a market for a 2 channel AVR for Audioholics.

Harman/Kardon hasn't made a decent receiver in a very long time, especially multi-ch. It's not their core business.