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Class-T (Tripath-based) amplifier boards
thesurfingalien
post Dec 11 2011, 15:28
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Hi All,

Does anyone here have experience with Tripath-based (Class-T) amplifier boards, especially the ones that use the TA3020? I am quite interested in these because of price, power, efficiency and good specs.

It is my understanding that the design of the PCB and part placement are very important for proper performance, but some products available on the Internet are regarded as not too well designed.

Although a "dangerous" question I want to ask if I can expect a sonic performance equal to that of regular Class A/B amps. After all, the digital class is a different technology that might (not might not) be perfected (yet). From the specifications in general I really do no see why that would be the case.

Especially a recommendation for a specific supplier of these boards would be highly appreciated! I prefer assembled boards since I do not trust my soldering skills well enough to do a good job on SMD-parts (a lot of DIY-kits have these).


The idea is to build a digitally filtered 3-way active loudspeaker, but I would like to test this with my existing 2-way loudspeakers first.

For digital filtering I plan to use Thuneau Loudspeaker Frequency Allocator (http://www.thuneau.com/allocator.htm)


Any info / remarks / suggestions are welcome!

Regard & thanks,
Peter




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Light-Fire
post Dec 11 2011, 19:14
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QUOTE (thesurfingalien @ Dec 11 2011, 10:28) *
...After all, the digital class is a different technology that might (not might not) be perfected (yet)...


Just a little terminology correction here. There is no such a thing as "digital amplifier". Class D and T are switched but analogue amplifiers. By definition it is impossible to built a digital amplifier.
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thesurfingalien
post Dec 11 2011, 19:39
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QUOTE (Light-Fire @ Dec 11 2011, 16:14) *
QUOTE (thesurfingalien @ Dec 11 2011, 10:28) *
...After all, the digital class is a different technology that might (not might not) be perfected (yet)...


Just a little terminology correction here. There is no such a thing as "digital amplifier". Class D and T are switched but analogue amplifiers. By definition it is impossible to built a digital amplifier.


I believe this is just the common name for it. I am aware this is an incorrect term, but I suppose it will do smile.gif

Any suggestions perhaps?

Thanks,
Peter
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kraut
post Dec 11 2011, 21:20
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QUOTE
Any suggestions perhaps


what about sma (switch mode amp)

QUOTE
Hi All,

Does anyone here have experience with Tripath-based (Class-T) amplifier boards, especially the ones that use the TA3020? I am quite interested in these because of price, power, efficiency and good specs.

No idea about the tripath.
I drive my kef 104-2 with hypex AS2 100 amps, one per speaker. They are fed directly with 48kHz signal from my server via spdif.
They replaced bryston 4B st , 4B amps - I have no regrets.
I could not hear a sonic difference.

This post has been edited by kraut: Dec 11 2011, 21:25
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DVDdoug
post Dec 11 2011, 21:47
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I don't know about these particular chips, but certainly it's possible to build a good quality "digital" amp. Reputable manufacturers like Crown make class D amps. And, the selected chip is only one factor. A bad dsiign can give bad results, and with a good design, there may be some "tricks" to get improvement over the basic chip specs.

I'm somewhat skeptical about the power claims for these small amplifier boards. Hopefully, they don't stretch the distortion, noise & frequency response specs too much.

Make sure your power supply has enough power (Watts) to drive the amps... You can't get 100W out of an amp unless you put more than 100W in. And, you need enough voltage into the speaker to get the needed/calculated power. Do you know the various power calculation formulas?

QUOTE
The idea is to build a digitally filtered 3-way active loudspeaker, but I would like to test this with my existing 2-way loudspeakers first.
Just one suggestion - Put "safety" capacitors in series with the midrange & tweeter in case something goes wrong. High-power bass (or accidentical DC) into a tweeter will burn it out. Just use large-enough capacitors so that it doesn't interfer with your active crossover frequency, and small enough to block "dangerous" lower frequencies.

This post has been edited by DVDdoug: Dec 11 2011, 21:48
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kraut
post Dec 11 2011, 22:16
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QUOTE
The idea is to build a digitally filtered 3-way active loudspeaker


the hypex has build in dsp, where you can set the crossover slope and the q-factor, feeding the filtered hi and low pass signal to the amps.
This permits any crossover permutation that you like. I have mine set up to feed a combined signal to a single subwoofer.
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thesurfingalien
post Dec 12 2011, 01:16
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@kraut & DVDoug,

Thanks for the input and advise!

As far as rated power, yes, it might be a little exaggerated (depending on design & voltage about 300W per channel). I would say some 50 - 100 W per channel, depending on load, is realistic with low THD. That is way more than I will ever use...

I plan to use a 1000 VA power-supply, but I am sort of struggling with the fact that the voltage here (I live in Brasil) has some serious drops. It should average 127V (115V minimal, 135V maximum), but sometimes it drops to 90V. If I am correct, T-amps usually require a minimum voltage for proper operation, and the voltage fluctuations here might get troublesome at some point. The Naim amp I am using now can not deal with this very well.

I thought of using a higher-than-necessary voltage torroid, and using a voltage regulator circuit to stabilize the voltage. Unfortunately, I am not very knowledgeable in that area, so I am not sure if that is a possibility altogether.

About the filtering... The reason for using Thuneau software is also that it allows phase correction on individual units, which I believe (at least in theory) to be beneficial sonically. Never have heard a phase-correct loudspeaker though, so it could be wishful thinking :-) But as far as I can tell, the software is designed really well, allowing high-order filters of different types. Another reason is that I can use my E-MU 1820 as multi-channel DAC. It measures quite well (RMAA), and should do just fine in this setup.


Any other thoughts are welcome!

Regards,
Peter




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honestguv
post Dec 12 2011, 16:59
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This is a few years old but may be helpful:

www.genelec.com/documents/publications/aes112th.pdf

I get the impression that pro monitors tend towards using class D for woofers and class A/B for tweeters which would seem to fit with the pros and cons of the two types of amplifiers.

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DVDdoug
post Dec 12 2011, 23:22
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QUOTE
thought of using a higher-than-necessary voltage torroid, and using a voltage regulator circuit to stabilize the voltage.
Good idea. A regulated power supply is standard on a power amp... It's actually standard on any audio circuit. In addition to regulating the voltage, it knocks-out any AC power-line hum (power supply ripple) that's not filtered-out by the capacitors.

You can buy open-frame power supplies (example), but you might end-up spending as much money on power supplies as you are spending on the amps... sad.gif

There are three kinds of regulated supplies:

- The simplest is a linear power supply. This is a transformer, full-wave rectifier, and filter capacitors, followed by a linear regulator. For low-power applications, there are simple-inexpensive 3-terminal (in-out-ground) fixed regulator chips such as the LM7815. I'm not sure what's available for higher-power applications. You'd have to do some research.

This is the least efficient design. Current flows straight through the regulator, and there is a variable voltage-drop across the regulator. If you run 20V into at 15V regulator and "pull" one amp, you have 5V @ 1 amp (5 Watts of power/heat) dissipated by the regulator. The regulator chip (or transistor) can get hot and you often need a heatsink.


- Next is a switching regulator. This is the same transformer, rectifier, and capacitor, but followed by a switching regulator. Again, there are switching-regulator chips, but a few more parts are required (including an inductor). These are more efficient (like your switching amplifier). Due to the efficiency (and power conversion), if you increase the voltage on the input side of the regulator, less current will flow-in. You can actually get more current-out than flows-in! (With lower voltage on the output side, of course). If the regulator were 100% efficient, power-in (Vin x Iin) would equal power out (Vout x Iout).

- The third type of supply is the full switching supply. The AC power is rectified and fed-into a high-frequency oscillator. The higher frequency means you can get-away with a smaller transformer and smaller filter capacitors. (Like the other designs negative feedback holds the output voltage constant.) These are very efficient and they often run on any AC voltage between 90VAC and 250VAC, so the same power supply can be used worldwide. But, these are complicated... probably as complicated as the amplifier, and I wouldn't want to build one. (The link above is a switching power supply.)
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googlebot
post Dec 13 2011, 17:00
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QUOTE (Light-Fire @ Dec 11 2011, 19:14) *
Just a little terminology correction here. There is no such a thing as "digital amplifier". Class D and T are switched but analogue amplifiers. By definition it is impossible to built a digital amplifier.


Just because Wikipedia says so, this doesn't have to be correct.

A Class D or digital amplifier is comparable to an 1 bit ADC. It generates a symbol stream of 0s and 1s out of an analog input signal. The clock rate is encoded trivially and implicitly into the bitstream. An ADC with S/PDIF output doesn't basically do anything else. The clock rate is also encoded implicitly and just as prone to jitter as a 'digital amplifier'.

On the receiving side it is easier to reconstruct the 'intended' clock rate to some extend from a S/PDIF stream, due to some encoding features. With a little effort you could also extract the clock rate from a digital amp's output, it's just easier if the output is encoded as S/PDIF protocol.

This post has been edited by googlebot: Dec 13 2011, 17:06
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thesurfingalien
post Dec 14 2011, 09:13
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QUOTE (DVDdoug @ Dec 12 2011, 20:22) *
QUOTE
thought of using a higher-than-necessary voltage torroid, and using a voltage regulator circuit to stabilize the voltage.
Good idea. A regulated power supply is standard on a power amp... It's actually standard on any audio circuit. In addition to regulating the voltage, it knocks-out any AC power-line hum (power supply ripple) that's not filtered-out by the capacitors.



I have been looking (with interest) at switched PSU's too. Especially the Mean Well brand seems to be respectable. This one, for example...

I know it's rather expensive, but for a 1KVA torroid + parts I probably pay more.

Perhaps it is something I should overcome, and I have no real base for it either, but it has been my understanding that for audio purposes torroid-based PSU's were always preferred. However, in some articles on the Internet I read that switching PSU's actually are a better match for class D & T amps and some even claim they (subjectively) sound better. I have the feeling that this has more to do with the idea of (in a way) similar technology for both PSU and amp.

What I like about switching amps is the efficiency and the fact that they, as you mentioned, go from 90-250 volts. Especially in Brasil, where there is not only unstable voltage, but different states have different voltages.

Peter
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Nessuno
post Dec 14 2011, 10:38
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QUOTE (googlebot @ Dec 13 2011, 17:00) *
QUOTE (Light-Fire @ Dec 11 2011, 19:14) *
Just a little terminology correction here. There is no such a thing as "digital amplifier". Class D and T are switched but analogue amplifiers. By definition it is impossible to built a digital amplifier.


Just because Wikipedia says so, this doesn't have to be correct.



True, but let's put it terminologically simple: a "digital" amplifier is called multiplier. wink.gif


QUOTE
A Class D or digital amplifier is comparable to an 1 bit ADC. It generates a symbol stream of 0s and 1s out of an analog input signal.


Thus it does not operate on a digital domain only and strictu sensu I will not call it a "digital" device.


--------------------
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googlebot
post Dec 14 2011, 18:31
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QUOTE (Nessuno @ Dec 14 2011, 10:38) *
Thus it does not operate on a digital domain only and strictu sensu I will not call it a "digital" device.


By that logic an analog-to-digital-converter with S/PDIF output would be no "digital" device either. Feel free to add to http://en.wikipedia.org/wiki/Analog-to-digital_converter, that ADCs should not be called digital.

This post has been edited by googlebot: Dec 14 2011, 18:32
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stephan_g
post Dec 17 2011, 21:16
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ADCs and DACs are, in fact, "mixed-signal" devices, and that's the most that even a digital-input-only Class-D amp will ever qualify for. A basic Class-D amp with analog input is no more "digital" than a switch-mode power supply. It could have a 3-level PWM, +1, 0 and -1.

BTW, I'm leery of digital-input-only Class-D. The concept may sound quite appealing at first, but it's virtually impossible to apply feedback in it. That in turns means power supply rejection is abysmal, as any variation of supply rails will amplitude modulate the output, giving rise to intermodulation distortion. Even in "analog" Class-D amps, the amount of feedback is relatively limited, so you'll typically find them with inherently regulated switch-mode supplies.

Hypex modules enjoy a good reputation; Bruno Putzeys really knows what he's doing. If you can find a good SMPS (kit) that matches these...

As a DIYer, I'd probably put up with the increase power and cooling demands of a conventional AB amp and go for ease of application instead. I'm actually a little surprised that the Naim would have trouble. Normally power amp supplies aren't particularly critical, especially if the amp is heavily current sourced as it's typical for ICs (like the common LM3886 and relatives). What may be happening either is that the lower regulated supplies are dropping out of regulation once mains voltage gets too low, or an overactive protection circuit considers supplies too low. When using a linear supply, things must not run out of spec or overheat at maximum mains voltage, but at the same time there must still be a high-enough input voltage to the regulators at minimum mains voltage. Dissipation resistors in front of regulators may be useful.
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