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-   -   Anyone interested in a digital amplifier project? (http://www.diyaudio.com/forums/class-d/7754-anyone-interested-digital-amplifier-project.html)

Rookie 18th November 2002 11:57 AM

Anyone interested in a digital amplifier project?
 
I've read reviews of TacT Millennium digital amplifier and got
interested in this new aplification method (actually there's no
amplification at all).I've searched the internet for ready DIY digital
amplifier projects, and couldn't find not one.There was few threads on this topic here, but none of them ended with some project.

Recently, I've got TAS5015 samples from TI.It is TI's best PCM/PWM modulator specified for high-end digital amplification.It wasn't available through TI's sample program until recently.

I haven't enough knowledge and experience to design such a complicated project on my own, but I'm sure there are many experienced DIYers who could do this.

It would be really nice to have an amplifier similar to TacT Millennium which is by many reviewers maybe the best amplifier in the world.

Anyone interested?

halojoy 18th November 2002 12:23 PM

What is a Digital Amplifier
 
Or what can it be?
There is a lot of very high quality knowledge
in this "Digital" and "Solide State" and "Pass" forums.

So if enough interest is around
this would be a piece of cake
to make a very GREAT digital Amplifier.

For me to become interested,
such an amplifier would have to have so many advantages over Analog Amplifier
that it would justify the complexity and costs involved in the project.

I seldome do things, only because they are "the highest fashion".
Who would like to belong to the In-Crowd? :cool:
when you can be a Happy-Outsider! ;)

An amplifier is not yet like a CD-player or a TV-set.
If business agrees on new CD-standards to make my old player useless
or the broadcasting comapnies changes the nature of signals used for TV, to make my old TV-set useless, I would have to buy new gear.

When EVERYONE have bought a standard CD-player, the sells go down for Sony, Pioneer and the rest of the Audio Industry.
What can they do?
Who sets the standard?
Why have Sony bought the music-producing Companies and the Copyright to the recordings?
I only ask. :bawling:

peranders 18th November 2002 01:24 PM

Re: Anyone interested in a digital amplifier project?
 
Quote:

Originally posted by Rookie
I've read reviews of TacT Millennium digital amplifier and got
interested in this new aplification method (actually there's no
amplification at all).I've searched the internet for ready DIY digital
amplifier projects, and couldn't find not one.There was few threads on this topic here, but none of them ended with some project.

Recently, I've got TAS5015 samples from TI.It is TI's best PCM/PWM modulator specified for high-end digital amplification.It wasn't available through TI's sample program until recently.

I haven't enough knowledge and experience to design such a complicated project on my own, but I'm sure there are many experienced DIYers who could do this.

It would be really nice to have an amplifier similar to TacT Millennium which is by many reviewers maybe the best amplifier in the world.

Never checked IcePower?

peranders 18th November 2002 01:26 PM

Re: What is a Digital Amplifier
 
Quote:

Originally posted by halojoy
Or what can it be?
There is a lot of very high quality knowledge
in this "Digital" and "Solide State" and "Pass" forums.

So if enough interest is around
this would be a piece of cake
to make a very GREAT digital Amplifier.

For me to become interested,
such an amplifier would have to have so many advantages over Analog Amplifier
that it would justify the complexity and costs involved in the project.

I seldome do things, only because they are "the highest fashion".
Who would like to belong to the In-Crowd? :cool:
when you can be a Happy-Outsider! ;)

An amplifier is not yet like a CD-player or a TV-set.
If business agrees on new CD-standards to make my old player useless
or the broadcasting comapnies changes the nature of signals used for TV, to make my old TV-set useless, I would have to buy new gear.

When EVERYONE have bought a standard CD-player, the sells go down for Sony, Pioneer and the rest of the Audio Industry.
What can they do?
Who sets the standard?
Why have Sony bought the music-producing Companies and the Copyright to the recordings?
I only ask. :bawling:

....where is the fun gone?....:confused:

Rookie 18th November 2002 01:49 PM

Re: Re: Anyone interested in a digital amplifier project?
 
Quote:

Originally posted by peranders


Never checked IcePower?

Thanks for the link.

MWP 18th November 2002 03:06 PM

I also just recieved a couple of TAS5015s.

Ill probably look into making an amp with it at a later date.
Not sure when though.... got to make a few DAC units first.

Brian Brown 18th November 2002 05:41 PM

Equibit Experiment
 
For those not familiar, TI's digital amps are basically class D PWM amplifier output stages.

Conventional Class D amps start with an analog signal and then modulate it into PWM by a comparator that's also being fed a triangle wave running at the carrier frequency (usually at 100KHz to 1MHz). Most Class D amps require feedback for stability, and this imposes some pretty serious gain-bandwidth limitations. This is why present-day use is primarily on subwoofers (bandwidth can be limited), car audio (higher distortion of outputs is tolerated by the market), or headphones (gain is limited).

TI's digital amps use a technology called Equibit that was developed by Tocatta Industries and was first commercially offered by TacT.

Equibit is a direct digital modulation technique that converts a standard digital audio PCM data stream into PWM.

Before Equibit, there was a limitation to achieving a direct PCM to PWM conversion: for sixteen bit audio data (not to even mention 24bit), the variation in duty cycle of the PWM wave would have required a carrier frequency up in the GHz range. This isn't practical for today's output devices to handle.

Equibit gets around the carrier frequency limitation by skewing the relative turn-on and turn-off timing of the upper and lower transistors of the output H bridge. This allows much finer resolution than could be achieved by the duty cycle varying at multiples of the carrier cycle alone. (Equibit typically runs at a 384KHz carrier).

Equibit modulation runs completely open loop, with no feedback. This avoids the bandwidth problems of most Class D, but it makes the quality of the power supply very important.
In a way, an Equibit amplifier could be compared to a high power DAC. To continue the analogy, the amp's power supply could be compared to a DAC's voltage reference.

Advantages of Equibit:
Efficiency comparable to conventional Class D (80% to 95%).
Preserves audio in digital format until the last possible moment.
Because there are no low level analog signals, there is also no amplification of low level noise.
PWM has no zero-crossing distortion (Class A is the only other type that can make this claim).
Exceptionally high damping factor. If the crossover is done digitally, with a separate amp for each driver, any back EMF is shunted directly to the power supply.

I'm just about finished with my first digital amp board layout. I'm starting with the TAS5012 modlulator chip combined with a TAS 5110DAD integrated output chip (50W into 6 Ohms). This is TI's highest performance combination that doesn't use a discrete output section. I figured that it would be the easiest way to get some direct hands-on experience with this technology. I'm also basically copying the layout of their 5100EVM board to use as a starting point.

I believe the quality of the power supply is the fundamental issue that will determine the quality of the overall amp. At least in the audio band, the PSRR is essentially non-existant. What is less clear to me is how critical ultra-sonic noise will be. I'm laying out my board in a way that I can experiement with a lot of different power supply topologies (everything from linear regulators and off-line switchers to a stack of gel-cells). I anticipate quite a few months of power supply experimentation once I get the first prototype up and running. I also want to experiment with varying the supply level for volume control (to preserve dynamic range) vs simple digital attenuation (it seems to me that 24bit data with 72bit processing should be pretty good by itself).

The TAS5015 chip looks like it will be pretty tricky to use. It requires the designer to discretely build all of the protection circuitry around the output stage.

The Panasonic SA-XR10 (AV receiver) is the first commercial product that I've seen to use a TI Equibit chip. I haven't heard one, but I did buy the service manual which has the schematic. It's using a single switching supply for all five channels. Depending on how good the supplies bandwidth is, I've wondered if it has any cross-talk issues (at least it has a good separation spec with a 1KHz test tone, but it'd be interesting to 'listen' to the supply with another amp coupled to its rails by some caps while real music is going through it (one of my preferred methods for evaluating supplies)).

There's a new chip, the TAS5182 (not sampling yet), that still accomodates a discrete output section (up to 100W), while providing all of the protection and sensing functions needed. It may not quite match the TAS5015's potential, but I think ease of use will make the TAS5182 the chip of choice for most designers interested in high performance.

Anyway, I think that Equibit is one of the most promising things to come along in digital audio. TacT appears to have done some great stuff with it on the high end (I haven't heard a TacT amp myself). We'll have to see how good it can be on a more practical cost level.

Regards,
Brian.:cubist:

Tube_Dude 19th November 2002 06:31 PM

Panasonic SA-XR10
 
Hei Brian...

I have one of this beautys and the sound is simply amazing...it come to mind the Karajan sentence (Anything else is gazlight)..

I have changed the output terminals to good ones and changed the imput AC receptacule to a good one too....and i'm very pleased with yhe results.

I'm using the coaxial output of my CD because is the one with better sonics...when i use the analogic output the usual intermodulation that we are used to , come back!

At the end of the day my feelings are mixed...happy with the vast improvement in sound...unhappy because my 30 years hobbye are a little menaced...

It will be very happy if you can send me a coppy of the schematic
(my twekers blood...will never die).i think that i can make the XR10 even better!:D

Regards

Jorge Santos

Franklin 19th November 2002 08:12 PM

Hello Rookie,

You could also check this link:

http://www.tripath.com.

Tirpath also has several modules which are complete amps and only need a few additional components.

Franklin

Rookie 20th November 2002 06:10 PM

I've heard about Tripath but as i know it has only analog output. I would like to have a true digital amplifier to avoid unnecessary DA conversion and stay completely in digital domain.


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