Should Class D (Tripath/TDA etc.) Chips be called High Fidelity ?

[Hiten]

Hello everyone,
What I gather is Class D (Tripath/TDA etc.) chips works by converting input audio signal into digital pulse width representation (low frequency=wide pulse, high frequency=short pulse). This representation is amplified and converted back to analogue form to drive the speakers. So Should they be called high fidelity? Not asking from the listening point of view which can be subjective. Since Digital chips (Tripath, TDA etc.) are much highly compared to costly hifi amps, am asking out of curiosity. I am not a technical person so kindly use simple language .
Thanks

 

[kanwar]

Hello everyone,
What I gather is Class D (Tripath/TDA etc.) chips works by converting input audio signal into digital pulse width representation (low frequency=wide pulse, high frequency=short pulse). This representation is amplified and converted back to analogue form to drive the speakers. So Should they be called high fidelity? Not asking from the listening point of view which can be subjective. Since Digital chips (Tripath, TDA etc.) are much highly compared to costly hifi amps, am asking out of curiosity. I am not a technical person so kindly use simple language .
Thanks

Tripath mainly uses Pulse density modulation which is alternate to delta sigma modulation. This is just a technique, we cannot simply state that this technique is HI-FI just because this technique is different from linear processing of analog signals. Theoretically on paper its perfect but its implementation on real world practical situation has some pitfalls which fall in technical domain, so i won't discuss them here.

The hype created by Class-D Chip manufacturers is the main reason why the objectivism surfaces here and there.


Kanwar

 

[Hiten]

Thanks Kanwar. So only 'major' advantages of this technique would be efficiency and compact design. Right ?? or are there any other things ?
Regds.

 

[kanwar]

Thanks Kanwar. So only 'major' advantages of this technique would be efficiency and compact design. Right ?? or are there any other things ?
Regds.

No, there is one more main feature in Class-D which is absence of cross over distortion and much less to non-existent phase error/delay in audio domain. In that way the output signal is more perfect representation of input signal because the device parameters don't effect the sound in direct manner as they do in linear amps where component choice play major role in establishing the transparency of the music output. In class-D there are other things which effect the sound quality but in much less manner in comparison to linear amps.

Due to advancements in semiconductor technology, its possible to build much better switching amplifiers which can take over linear counterparts very easily.


Kanwar

 

[avidyarthy]

There is something on 'feedback circuitry' on the Tripath amps too, which makes them sound so clean. If you could throw some light on it ....

No wonder the D class and the Tripaths have caused this much of a flutter in the audio industry. 'Such' fabulous performance at 'such' affordable costs with 'such' high efficiency (low power, no heat) and addressing space constraints!

 

[thatguy]

Isn't NAD M2 a Class D amplifier? Or Onkyo A-9555? Both highly recommended by Stereophile. What has being or not being a class D got to do with the hi-fi label. If it amplifies the signal faithfully, it is hi-fi.

The real question should be: is Tripath TA2020, which costs $3, a hi-fi amplifier?

 

[keith_correa]

The real question should be: is Tripath TA2020, which costs $3, a hi-fi amplifier?

Where can one buy a $3 amplifier that uses the TA2020 chipset?

 

[avidyarthy]

The real question should be: is Tripath TA2020, which costs $3, a hi-fi amplifier?

.... ummm, it is a hi-fi chip ..

 

[no1lives4ever]

Does it really matter what technology goes into making an amp? If it sounds good, then it is good. If it does not, then

even the best technology in it will not make it sound good. Audition the amp with your rig and see if it is any good. If it is, then use it, or else move on and audition something else.

Class D and similar switching amps have been around for some time. If manufacturers can provide them in their high end products, then they must be good enough for HiFi use.

Where can one buy a $3 amplifier that uses the TA2020 chipset?

How do you expect to buy an amp for the same price as one of it's components? This chip requires additional components, to function as a amp that you can connect to your audio rig.

@Kanwar, I have read that Class D amps can be used with digital signals w/o using a DAC to do the analog to digital conversion. How does this work? Is this available with any commercial products?

-- no1lives4ever

 

[avidyarthy]

I am thinking of getting myself a 'Temple Audio Bantam Gold' .... it is said to produce even better music than the Tripath 2020 based amps.

The Bantams use a different D class chip ... 25 W as compared to @ 15 W output .... costs @ 180 pounds ex-UK. Any comments on these?

 

[thatguy]

.... ummm, it is a hi-fi chip ..

Where can one buy a $3 amplifier that uses the TA2020 chipset?

Since you guys decided to pick on my choice of words ...

Quote from the *chip's* data sheet (http://www.kafka.elektroda.eu/pdf/tripath/TA2020.pdf):

The TA2020-020 is a power (high current) amplifier that operates at relatively high switching frequencies. The outputs of the amplifier switch between the supply voltage and ground at high speeds while driving high currents. This high-frequency digital signal is passed through an LC low-pass filter to recover the amplified audio signal. Since the amplifier must drive the inductive LC output filter and speaker loads, the amplifier outputs can be pulled above the supply voltage and below ground by the energy in the output inductance ...

<snip>

IEEE Spectrum Magazine's mention of TA2020 (http://spectrum.ieee.org/semiconductors/processors/25-microchips-that-shook-the-world/0):

Tripath Technology TA2020 AudioAmplifier (1998)

... Like most class-D amps, the 2020 was very power efficient; it didnt require a heat sink and could use a compact package. Tripaths low-end, 15-watt version of the TA2020 sold for US $3 and was used in boom boxes and ministereos. ...

I will repeat; TA2020 is an amplifier and it (used to) cost $3. Google cache still has the price listings:



Uploaded with ImageShack.us

 

[keith_correa]

Quote from the *chip's* data sheet (http://www.kafka.elektroda.eu/pdf/tripath/TA2020.pdf):

Since you are quoting this - I prefer to call it "amplifier driver" or "amplifier IC" as mentioned in parts of that very datasheet.
But all this is mere verbiage. I misunderstood - you were saying $3 is for the "amplifier"/chip and I thought it was for an "amplifier" using this chip. Allll izzzzz welllll

 

[kanwar]

@Kanwar, I have read that Class D amps can be used with digital signals w/o using a DAC to do the analog to digital conversion. How does this work? Is this available with any commercial products?

-- no1lives4ever

Yeah, There are some Class-D amps which directly accept digital input in Pulse Coded Modulation format [spdif]also, they have inbuilt PCM to PWM converter and they don't need any DAC in that case. They do the same work as any other DAC does but also gives power to drive speakers so they are sometimes known as power DACs. There are many commercial products which offer such feature. PowerDAC

There is something on 'feedback circuitry' on the Tripath amps too, which makes them sound so clean. If you could throw some light on it ....

Yeah, there patented feedback circuitry which is based on Delta Sigma Modulation scheme, its old technique in switching electronics which is new for analog designers though. Nothing new so far.

Cheers,
Kanwar

 

[Hiten]

Dear Friends,
As I have clearly said in my first post. This is not about any particular chip or how good they sound, rather technical aspects with reference to fidelity.

Few more questions
~ a general question...Do all class D chips roll off high frequency ?
~ Is there any hybrid concept which uses best of digital chips and linear amplification ? That would be really interesting.
~ Is it true that digital chip amplifiers due to fast switching are more prone to EMI interference compared to SS amps?
~ when converting input signal do they compress data ?
regards

 

[kanwar]

Dear Friends,
As I have clearly said in my first post. This is not about any particular chip or how good they sound, rather technical aspects with reference to fidelity.

Few more questions
~ a general question...Do all class D chips roll off high frequency ?
~ Is there any hybrid concept which uses best of digital chips and linear amplification ? That would be really interesting.
~ Is it true that digital chip amplifiers due to fast switching are more prone to EMI interference compared to SS amps?
~ when converting input signal do they compress data ?
regards

First of all Class-D is not DIGITAL in any way, it just converts an analogue signal into Pulse width Modulation and then the output inductor averages the pulses to shape them into analogue signal at output.
Only POWERDAC's which have direct PCM to PWM conversion could be called as digital amps to some extent.

1 Roll off at HF is caused by 2nd order filter on the output of class-D amp which comprises of L in series and C in shunt with output. It is designer dependent and of course topology dependent criterion, whether the Roll off has to be greater or smaller and with specified bandwidth.

2 Google for BASH chips and one more Class-TD which uses linear amp + Class-D power rails which maximizes efficiency but still maintains linear way of amplification of signal.

3 Yes Fast switching generates EMI, but if proper care is taken while developing and engineering the PCB layout with Solid Ground Planes, one can very easily get away with any sort of EMI and hence its not a problem, just depends on the skill set of designer.

4 In Class-D compression of input signal doesn't takes place.


Cheers,
Kanwar

 

[sound1]

@Kanwar, I have read that Class D amps can be used with digital signals w/o using a DAC to do the analog to digital conversion. How does this work? Is this available with any commercial products?

-- no1lives4ever

Interesting read...
The Truth About Digital (Class D) Amplifiers &mdash; Reviews and News from Audioholics [audioholics.com]

 

[Hiten]

Only POWERDAC's which have direct PCM to PWM conversion could be called as digital amps to some extent.

Sorry for late posting. my PC was down with virus. Thanks kanwar. Searched the net, powerdac looks good (Wadia 151 and MSBtech) but are costly. No kits or modules on ebay. I think this must be latest development.
Regards

 

[kanwar]

Sorry for late posting. my PC was down with virus. Thanks kanwar. Searched the net, powerdac looks good (Wadia 151 and MSBtech) but are costly. No kits or modules on ebay. I think this must be latest development.
Regards

Powerdacs require regulated supplies in them, otherwise their performance suffer drasticly because of absence of analog feedback which can compensate for changes in power supply voltage and other parameters. A class-D without feedback has ZERO PSRR[power supply rejection ratio] which means its gain would vary with power supply rails.

Kanwar

 

[Hiten]

whether the Roll off has to be greater or smaller and with specified bandwidth.

So there is HF roll off, unless amp design has wide bandwidth and designer has taken care that roll off is as small as possible. (Which I guess is not easy).
Is that the reason I see BASH chips are primarily used in subwoofers
Any other powerdac chips ??
thanks

 

[kanwar]

So there is HF roll off, unless amp design has wide bandwidth and designer has taken care that roll off is as small as possible. (Which I guess is not easy).
Is that the reason I see BASH chips are primarily used in subwoofers
Any other powerdac chips ??
thanks

It depends on the need of HF limit , to what extent you want HF response, should it be 20khz or 100khz flat. Wider bandwidth requires high switching frequency and which need proper engineering of the stuff you are designing.

BASH chips are poor one, they tried to exploit the class-TD topology but haven't been able to make it full range thats why limited to subwoofer use.

For power Dac chips you can glance at this link:

http://focus.ti.com/lit/ds/symlink/tas5715.pdf

Speaker Amplifier and Modulator - Mid/High-Power Amplifier - TAS5715 - TI.com



Kanwar