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Old 4th November 2008, 05:31 AM   #1
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Default Fully digital amplifier.

Hi,

I was wondering if anybody ever come across a fully digital amplifier kit or fully built. Kit would be good. My definition would no conversion from the digital signal to the analog first. Tripath used to have a few chips that could do this, but never found any kits who used it.

Oon
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Old 4th November 2008, 06:01 AM   #2
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An example would be this chip from Tripath....

http://doc.chipfind.ru/tripath/tcd6000.htm
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Old 4th November 2008, 07:42 AM   #3
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I will see if I can find any TCD6000. I know a person who has the schematic and gerber files for the eval board. It will probably take a day or two for the supplier to get back to me on their availability.

The only other full digital power amps I know of are the TI PurePath products. I don't think there are any kits available. There are ready made consumer products that use these though.
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Old 4th November 2008, 08:58 AM   #4
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I already received a response from the supplier (very fast service, nice people). I was quoted $7.35 each for 100pcs. I can order any quantity, even one piece, but the price will be higher.

I'm not sure which powerstage the eval board uses, but they would need to be ordered as well if you wanted to build one.
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Old 5th November 2008, 12:49 AM   #5
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That's interesting. Would be interested in joining you in that, I think the powerstage uses a dedicated chip as well, and they come as a pair. I have a feeling Panasonic uses it for their car stereo previously, the high end ones. Do you know if any home theatre unit uses the tripath series...

How is the sound quality of the TI purepath products? Which are the products using it....?

Oon
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Old 5th November 2008, 02:17 AM   #6
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Quote:
Originally posted by oon_the_kid
Which are the products using it....?
Oon
The other two fully digital amplifier series that I know of are the ST DDX chips (developed by Apogee) and Cirrus. Sony has a full digital design, but as far as I know it isn't available to the DIY community. The ST DDX chips are used in many products, including: Harman Kardon DPR 1001, Hitachi HTD-K1XX, JVC TH-SX, Zenith DA3520 and others. Don't know who is using the Cirrus products, if anyone. There are quite a few receivers using the TI purepath products--the Panasonic SA-XR series is probably the highest volume product. The DRUID paper has some good background information: DRUID Paper

One of the design challenges with the Purepath chips is that you need a well regulated supply, because there is no feedback to compensate for power supply variations. Cirrus has feedback into the output stage modulator, and the ST chips have an integrated A/D to monitor the power supply and provide rejection. TI is starting to add output stage feedback to increase the PSRR, but so far this feature is only available in their low-power output stages.

The Tripath chip also uses output stage feedback, but it is a product that is no longer in production. Cirrus bought their IP, but so far we haven't seen the results of that acquisition in the 6-8 channel chips. You may want to reconsider designing with a "dead-end" chip.

There aren't any kits for these amps, but the circuits aren't overly complex, and there are many PCB layouts and parts lists in the data sheets for making your own boards. You will need to be able to solder SMD devices, but that is easier than you might expect with good-quality hand equipment.

However, once you are fully digital you might as well add in a digital processor for active crossovers or EQ, and that's where things get more difficult, due to the software design. An easy way to make crossovers and provide EQ is to use the biquads that are in the ST or TI chips. That's a challenge I've been working on...
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Old 5th November 2008, 04:44 AM   #7
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Quote:
Originally posted by oon_the_kid
That's interesting. Would be interested in joining you in that, I think the powerstage uses a dedicated chip as well, and they come as a pair. I have a feeling Panasonic uses it for their car stereo previously, the high end ones. Do you know if any home theatre unit uses the tripath series..
The Tripath chip interested me because I have a PC setup with three digital outputs that is used as a 3-way active XO/DSP. It would be nice to have a single 6-channel amp that does the D/A conversion as well. Right now I'm using three separate DACs and three power amps.

Unfortunately the person who I thought had the gerber files for the PCB only had PDFs of the board layers along with the schematics. I have these files if anyone is interested.

Sorry, I don't have the knowledge or experience to design a board from scratch based on the TCD6000.

I don't think the IC was ever implemented in any products. It came out right around the time their business started going down hill.
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Old 7th November 2008, 12:24 AM   #8
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Oh well, it was worth a shot. I thought a fully digital amplifier is the way to go for the next step. My own personal philosophy in audio design is a minimalist approach between the signal source and output to preserve signal integrity.

Conversion from digital to analog, divide everything by 10 at the volume control, then converting it back to digital pulses seem like a pretty stupid thing to do. However it would also defeat the purpose if volume control is accomplished by down scaling the digital signal...

I did a circuit by using the inverting amp of the input of the tripath as part of the I to V circuitry. I will post it up in another thread. But directly converting to output PWM seems like a much better solution to do....

I will put up another thread to see anybody has used or know off any amp which uses the TCD6000 chip.....

Oon
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Old 7th November 2008, 01:50 AM   #9
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Quote:
Originally posted by oon_the_kid
Oh well, it was worth a shot. I thought a fully digital amplifier is the way to go for the next step...
You can buy one of the Spherex Xbox 5.1 systems right now on eBay for $130 or less. It uses the Apogee DDX8001 controller chip, along with 6 H-bridges that will give you about 50W per channel. It's a fully digital path: SPDIF input, digital signal processing and very good quality digital amps, with a decent power supply.

I've been working on mods for this amp, and I'm very much impressed at the engineering behind the Apogee chips. These are very smartly designed devices that are easy to use and far more capable than anything else at the time when they were released in 2002. ST makes the chips, and Apogee sold the amplifier technology to Sigmatel. ST has new versions of the DDX8001 (STA309), so the design is still active. ST claims to have shipped over 5 million of the DDX devices. That's a lot of devices, but overall this technology probably didn't achieve the commercial success that it deserves.
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Old 8th November 2008, 07:39 AM   #10
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Fully digital?
Tripath uses pulse density modulation with feedback, draw your own conclusions from that.
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