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Old 31st May 2002, 03:02 AM   #1
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Default DIY True Digital Amps

I posted this to Solid-State but this might be a better place to put it... Sorry about the cross post

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Hi all, I have been looking at starting a new amplification project for some time and I finally have the time now. I have previously built 2 Tripath amps, one for me and another much improved one for a friend. I love the sound once all the tweaks are in but the fact that it does not feature a digital input is limiting as I am experimenting with microprocessor based digital crossovers and want to build an all digital active speaker.

Does anyone have any experience with true digital amps (TacT Millennium etc) in a DIY capacity? There seem to be a few chips out there such as the Pulsus PS9604 (http://www.pulsustech.com/products.htm) which seems to operate at the resolution I am looking for (24 bit >= 96kHz) but I cant really find much about it. Mainstream manufacturers (http://www.puredigitalaudio.org/dig...shtml#Resources) also seem to have products but most seem to be geared to integrated systems with emphasis on cost and gimmicky DSP instead of hi quality audio. Any suggestions or starting points?

Rahul
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Old 31st May 2002, 08:48 AM   #2
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Hello,

I have not build any true digital amp but I have been looking att TAS 5012 and TAS 5015 from Texas (www.ti.com). I think there was a thread about this subject at this forum some time ago.

Regards
Carl
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Old 1st June 2002, 03:04 AM   #3
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Thanks for the note Carl, the 5015 seems to be exactly what I was looking for. Has anyone tried this chip out? Any subjective/objective evaluations or circuits? The last bit of activity on these chips was a while ago...

Rahul
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Old 1st June 2002, 09:16 AM   #4
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Default Problem with the 5015

The TI TAS5015 is a problem for DIY'ers since TI won't sell it to anyone without a contract (at about $10K). You also need a variable power supply to act as "volume control". TI has developed that too, but if you search, most SMPS are designed for fixed output voltage, and not audio quality.

Having said that, the eval board available from TI for lesser parts seems to be usable with nominal modification for the higher end chips -- notably balanced line shorting null resistors can be removed, input scheme can be converted -- pinout is very similar to the lesser devices.

There is considereable intellectual property avaiable at TI which would be nice to evaluate, particularly the power supply (and possibly the H-bridge setup and analog filter design).

Others report great service from TI. My experience was abysmal. They not only refrained from answering (Has my company signed the TAS5015 agreement), but also specifically told me that my part selection was inappropriate and that I should use the cheap and cheerful parts before asking me to submit an evaluation of this service level which I did . Based on this, I expect that TI is only interested in volume partners on the TAS5015. I find it strange that no manufacturers but TacT have come up with a commercial design and can only speculate what the reason is given that the part is more than a year old.

Petter
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Old 2nd June 2002, 05:49 PM   #5
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We're doing some work for a parts broker house, I might be able to find that TI part brokered - do you want me to try? What's the full manufacturer's part number, TAS5015? Any specific packaging we need?

These guys are pretty sharp but they aren't engineers, I'll need the EXACT part number. if I can get some, I'll see if I can get 10-20
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Old 2nd June 2002, 08:54 PM   #6
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I believe the part is TAS5015PFB. Its a 48 Plastic Flat Pack and they dont supply samples . Would happily buy them off anyone that can send a few my way. I cant really find any other parts that do true digital amplification at 24 bits and 192khz. Does anyone have any idea what Sharp use in there prototypes? (Custom FPGA?)

Rahul
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Old 2nd June 2002, 11:34 PM   #7
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What is needed is the following:

TAS5100EVB (which is $500) -- this board should be convertable into 5015 use. Ideal delivery from this package is the gerber files so one can use that as a building block, but this is not really necessary if using a real home-made H-bridge, in which case i recommend the IRF devices developed for MHz switching of the Cirrus digital system.

Part number mentioned above is correct -- the 5100EVB has the 5010 which is in the same package and with a similar pinout.

So, I guess that in practice it is just the 5015's which are of interest. I have looked at it and it may need more housekeeping functions than I am willing to go with at this juncture + I don't like working on SMT stuff. Having said that it would not be an impossible task to create a digital amp using this chip! The main diff between this and the 5010 is the lack of internal PLL, as well as balanced outputs + need for setting volume from power supply.

An alternative solution would be to do something with an FPGA, but that would likely be a bigger task than using the 5015.

As much as I would like to venture into this territory, I don't have the bandwidth at present, especially without access to the TI design papers on power supply. Still it would be nice to see what info resourceful members might dig up

Device cost should be $25 per unit (1000 pieces). I would be very interested in what pricing can be found when brokered in small quantities, but I doubt they are avaiable (just re-read some articles that I scouted off Google) -- period.

Petter
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Old 4th June 2002, 01:22 AM   #8
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If the TAS5010 or TAS5012 are acceptable, they are available for small quantity orders from http://www.digikey.com as well as sampling from ti.

If not, you can order the TAS5015 in quantity greater than 20 ($45 each) from http://www.insight.na.memec.com... Not sure if that's the actual availability, though, because they say to ask.

Will
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Old 6th June 2002, 07:36 PM   #9
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That chip has a maximum bit rate. Having a limit on bit rate can degrade the sound quality a little bit. The circuit needs some buffering, so the bit rate isn't off. Digital components trying to record or play sound have to equal several super computers to play a 16 bit sound. However, a hefty filter to remove the digital artifacts from the sound needs to be used.

About a year ago I found an amplifier class that isn't retricted by bit rates and power supplies. The class of this amplifier is called J. This amplifier is from JAM. With this amplifier you can use a 5 volt power supply to power a 20 watt speaker at 8 ohms. It doesn't need a filter like some digital amplifiers.

I don't work for them or have license to use their amplifers.

http://www.jam-tech.com
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Old 6th June 2002, 08:26 PM   #10
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Looks interesting but very little information on the site. As i understand it, Jam have a sparse logic gate based implementation that they licence. Coupled with their 'E bridge' circuit on the output, this gives you digital amplification.... So does anyone know of any company that has something for the market using this 'Class J' implementation?

Rahul
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