Inexpensive mini-amplifiers: Discussion of power ratings and distortion

[GGroch]

About the seemingly greatly exaggerated power specs on most Chinese class D amps. Texas Instruments provides detailed specs on each of their amp chips. But, it seems they also condone giving amp manufacturer's a lot of leeway on how they describe this power in advertising.

See this TI report on Amps and Advertised Power ratings.

On page 4 they conclude:
The need for attractive marketing strategies requires TI customers to devise creative ways to use power rating for advertisements.
This paper assists TI customers in determining the suitable power rating to be used in the advertisement of their products. TI supports customers internationally and understands that each region of the world requires different marketing strategies. While the power rating for the US market is dictated by the FTC, other countries may not be restricted to such requirements. In those cases, TI customers are open to choose the acceptable power rating for advertisement. As mentioned in the introduction, PMPO generally is not well-defined and accepted as an audio performance measurement. It is used mostly for advertisements.

The report was written in 2005. The FTC has not enforced power rating standards in the U.S. for more than 10 years...so that restriction seems quaint now.

 

[Sal1950]

The need for attractive marketing strategies requires TI customers to devise creative ways to use power rating for advertisements.

Now that right there is funny!
I'm sort of amazed that TI puts it in writing that it's OK to fudge the ratings claims. LOL

 

[GGroch]

Yes that surprised me... I was also taken back by what sounds like blatant ethnocentrism..... "We do not do it here, but its alright for the rest of you to prevaricate since it's your culture"

In the U.S., our current climate of truthiness suggests that we were just behind the curve.

 

[RayDunzl]

I can't seem to find the word "prevaricate" in the referenced document.

 

[GGroch]

I can't seem to find the word "prevaricate"

I believe "PMPO Power" is an acronym equivalent to prevaricate in most languages. The TI whitepaper spends about a quarter of its text saying both that PMPO has no technical meaning, while also describing how it can be calculated from TI's stats for advertising purposes.

Back in the day we used to cal thel PMPO stat "WLS power" Meaning When LIghtning Strikes.

 

[JohnBooty]

Yes that surprised me... I was also taken back by what sounds like blatant ethnocentrism..... "We do not do it here, but its alright for the rest of you to prevaricate since it's your culture"

In the U.S., our current climate of truthiness suggests that we were just behind the curve.

Haha. Amen to your observation about the current climate.

I like the FTC's strict rating method because of its strictness, but it's not exactly more "honest" than other power rating methods. It is almost laughably unrealistic.

The FTC requires that the amplifier be pre-conditioned at one-eighth of rated total power output (for a multiple-output system, all channels are on) for one hour using a sine wave at a frequency of 1,000 Hz.

The power spectrum measurement is then collected with two channels at maximum rated power over the audio frequency range of 20 Hz to 20,000 Hz, in ambient still air of not less than 25°C, for the a duration of not less than 5 minutes.

Essentially, pink noise. Volume cranked to max. Five minutes! It's like testing a car by mashing the brake and gas pedals to the floor for five minutes while doing random things to the clutch. It's kind of valuable in a "well, if it can survive this, it can survive anything" sense but it's also sort of detached from reality.

I might say that other countries' more relaxed standards were actually more honest in the sense that they reflected reality better. Although at least the FTC's rating scheme let you know that the amp probably wouldn't set itself on fire no matter what you threw at it.

 

[tktran303]

Topping is quite transparent in terms of its products’ measured performance:

http://www.tpdz.net/products_detail/productId=33.html


Translating this to Armir AP style dashboard measurements

Input level= 217mV
Output• 5W; 8 ohms
Frequency=1KHz
THD+N= 0.03
SINAD = 70dB

Power before clipping: 30W into 8 ohms

 

[Westsounds]

I just tried a class D from Amazon as I could try on a return basis, its a Fosi TDA98e, its the first 98e I tried, and it was selling quite a bit cheaper than the SMSL 98e but still having great reviews. I haven't given it much time yet (do these things benefit from a good burn in period by the way? ) but from the start, my verdict was the amplifier isn't bad but lacks a lot in midrange body and solid drive. Detail is quite nice though and nice and delicate sounding just a bit soft and lacking a bit of presence in its delivery. Hiss is very low for what I read can be a noisy design. Its only really audible if you turn the amplifier quite loud when there is nothing playing, but most amplifiers would have some audible noise if you did that. Thankfully there is no pop or bump when you turn it on though. There is quite a bit of scratchiness on the volume pot though but things with these size volume pots are a bit prone to being not very good I expect, and the quality control would be low on these I imagine. Think some contact cleaner may help here.

This was the amp

https://www.amazon.co.uk/gp/product/B077GWVHHN/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

My next step is maybe try another from China, the return thing will be out of the question and its pot luck what quality you get. I wouldnt mind trying one of those TPA's which seem to have good reviews. May be a TPA3251 or PDA3255? But there is a thread on here some where that doesnt give those much encouragement.



But Ive been recommend a Allo Volt + D as well, but it's almost 3x the cost and less powerful.