Budget T-Amp Shootout - Lepai vs. Indeed TA2020

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

First up is the Lepai which managed 8 watts. Note the ringing on the clipped waveform. That was common of all the Tripath amps I measured and is most likely an artifact of the switching nature of the Tripath chips.

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Next up is the Indeed 2021s which managed 9 watts.

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Next is the Indeed 2020s which measured about the same at just a hair under 9 watts.

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

I also measured a Stellar Labs amp from MCM which managed 8 watts. http://www.mcmelectronics.com/produc...0145-/50-10145

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

As a reality check I measured my Onkyo CR-325 compact receiver rated at 20W/CH into 4 ohms. It managed 22.5 watts.

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

I'll surmise that the Tripath amps I measured were ultimately limited by the PS. Looking at the data sheets for the various Tripath chips you will find that some of the chips will take more than 12V. I found that the 12V/4A brick supply that I have would drop to 11.4V with a 3A load and had plenty of ripple which doesn't help. The Indeed amps managed a little more output and I'd attribute that to the fact that they probably used higher quality parts in their output filters. They were much better built than the other amps having quality metal cases and decent input/output connectors. Bottom line is you can't expect a lot of power but they are pretty economical and I find the Stellar Labs amp I have to sound pretty good running my RS Optimus speakers hooked to my computer. I think I got it on sale for $12.

Ron

[Whitneyville1]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Ron, did you have any chance to run the Indeed amps from a heavy-duty (say 6amp+) power supply? A "retired" PC supply putting out 11.8-12 volts @greater than 6 amps dead pure DC can be found (around here) for $5 or less minus the IEC cord. They are so "stiff" a supply, the voltage is locked between 0 and 95% rated amperage output or better. Better power supplies make any amplifier sound better (from my Ham radio days). The "best" test of all of these chip amps would be to use a "12 volt" battery regulated to EXACTLY 12 volts DC, but with as much current as possible available (20 amperes at least) to take current/voltage drop out of the test results. There are "hockey puck" voltage regulators for 12 VDC that can handle 60 amps (they need to be mounted on 10mm aluminum plate and water cooled) with extremely high voltage voltage regulation accuracy. For us, a "12 volt" lead-acid freshly charged automotive battery [Optima "Yellow top"] (nominal 14.4 volts) with a string of 30 amp silicon diodes (.7 volt drop each) to bring them down below the "magic threshold voltage" of these amps, I think would be a "better" test protocol. A 20 amp lab supply would be good too, but they aren't common these days and CA-CHING!!! The major improvements in the Lepai's performance with a bigger PS and bigger, better caps indicate the importance of "instantaneous" current demand in amplifiers (I think).

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Ron, did you have any chance to run the Indeed amps from a heavy-duty (say 6amp+) power supply? A "retired" PC supply putting out 11.8-12 volts @greater than 6 amps dead pure DC can be found (around here) for $5 or less minus the IEC cord. They are so "stiff" a supply, the voltage is locked between 0 and 95% rated amperage output or better. Better power supplies make any amplifier sound better (from my Ham radio days). The "best" test of all of these chip amps would be to use a "12 volt" battery regulated to EXACTLY 12 volts DC, but with as much current as possible available (20 amperes at least) to take current/voltage drop out of the test results. There are "hockey puck" voltage regulators for 12 VDC that can handle 60 amps (they need to be mounted on 10mm aluminum plate and water cooled) with extremely high voltage voltage regulation accuracy. For us, a "12 volt" lead-acid freshly charged automotive battery [Optima "Yellow top"] (nominal 14.4 volts) with a string of 30 amp silicon diodes (.7 volt drop each) to bring them down below the "magic threshold voltage" of these amps, I think would be a "better" test protocol. A 20 amp lab supply would be good too, but they aren't common these days and CA-CHING!!! The major improvements in the Lepai's performance with a bigger PS and bigger, better caps indicate the importance of "instantaneous" current demand in amplifiers (I think).

I tested one of the amps with a regulated PS and ran it at 13V and squeezed another watt out of it. The PS was current limited at 2A and about the time the waveform started to show obvious distortion I'd hit the 2 amp limit. I also ran the Stellar Lab amp off a set of freshly charged AA batteries and lost a 1/2W. You can get a little more power out of them with more voltage but it's a marginal increase. It looks like you can take the PS voltage as the P to P output and covert to RMS voltage and predict the output.

Ron

[Whitneyville1]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

I understand the voltage limitations, but the current draw (if it is virtually unlimited) I think is far underestimated in these chip amps. Watts in X power factor for the amp => RMS watts output. A pure class A amp may have a power factor of .10 or even less. You put 100 watts into them and you might get 10 watts output (or less). These "T-class" amps are quite efficient, To flatten the FR, they give-up a little pure power. If you can't boost the voltage, I can't help but wonder if more amperage would help.

[bkeane1259]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Ron, this is a most excellent analysis!! :applause:

Thanks so much for taking the time to run the tests/measurements and for sharing the findings with everyone. It's good to see the REAL specs for these amps, especially since they are so popular. Crappy, unreliable, manufacturer specs really confuse people all the time.

Just to be clear though.....for the t-amp measurements, you did both channels driven. So for the Lepai TA2020, when you say 8 watts, that means 8 watts RMS both channels driven, A.K.A. 4 watts per channel RMS? After reading this a few times, that's my only question.

Again, great job man!!

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Just to be clear though.....for the t-amp measurements, you did both channels driven. So for the Lepai TA2020, when you say 8 watts, that means 8 watts RMS both channels driven, A.K.A. 4 watts per channel RMS? After reading this a few times, that's my only question.

When I say both channels driven I mean that both channels had the same signal and load applied to both channels while the measurements were made. That means that in the example you gave the Lapai is capable of 8 watts RMS from each channel with a 4 ohm load. I don't have two 8 ohm load resistors but I did measure one of the amps with 1 channel running into 8 ohms and measured the same voltage which would be half the power.

Ron

[Ron_E]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

I understand the voltage limitations, but the current draw (if it is virtually unlimited) I think is far underestimated in these chip amps. Watts in X power factor for the amp => RMS watts output. A pure class A amp may have a power factor of .10 or even less. You put 100 watts into them and you might get 10 watts output (or less). These "T-class" amps are quite efficient, To flatten the FR, they give-up a little pure power. If you can't boost the voltage, I can't help but wonder if more amperage would help.

More current would help up to a point. With a perfect amp you only have I=V/R to work with and the current draw (which is limited by the load) would be far less then the 5 amp supply I was testing with.

These amps gain their efficiency because they're switching amps and the output transistors are mostly all the way on or all the way off all the time. In either state there's little power dissipated in the transistor. If it's on there very little resistance in the transistor and if it's off there's no current flowing through it. Class A amplifiers have the output transistors biased half way on all the time so there's lots of power dissipated all the time even with no signal.

Ron

[bkeane1259]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

When I say both channels driven I mean that both channels had the same signal and load applied to both channels while the measurements were made. That means that in the example you gave the Lapai is capable of 8 watts RMS from each channel with a 4 ohm load. I don't have two 8 ohm load resistors but I did measure one of the amps with 1 channel running into 8 ohms and measured the same voltage which would be half the power.

Ron

Excellent, so our beloved Lepai TA2020 is capable of 8 watts/channel RMS @ 4ohms and 4 watts/channel RMS @ 8ohms. Sweet. With a pair of high sensitivity or even moderate sensitivity speakers (say 91db), that will be lots of volume. Even driving my Speedsters (nominal 5ohm-ish and about 82db) all of the above T-amps can produce room-filling sound in small/moderate sized rooms.

They are all great value amps for sure.

[JRT]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Brian was kind enough to loan me his collection of amps so I could take some power measurements.

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Ron, I think you will find interesting the Tripath application notes at this link from the Internet Archive for background info. See especially application notes 4, 5, and 6, which are related to measurements. I suspect that the clipping characteristics described in application note 6, very different from the clipping characteristics of a class AB amplifier, may point to why these Tripath class D amplifiers may be worthwhile. Similarly, this link gets you to a lot of the Tripath data sheets and evaluation board documentation. Enjoy.



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[prighello]

Re: Budget T-Amp Shootout - Lepai vs. Indeed TA2020

Great info! Thank you all for taking the time. It just blows my mind that my little SMSL TA2020 is only putting out 8 or 9 watts and still fills a room with sound. I'm using it to run some OS TMs which are not highly sensitive but yet it has no problem playing beyond comfortable hearing levels. Makes me rethink the whole watts thing and how much you actually need.