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Old 3rd December 2010, 09:42 AM   #1
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Default Is there a Class-D amplifier chip that does it's own D/A on chip?

I am really interested to see if there is a Class-D amp that keeps everything in the digital domain right before analog conversion and power output.

I ask because with the common setup of a discrete DAC, then a Tripath amp, the sound goes from digital to analog two times. With an on-chip D/A, it seems like there could be a good increase in sound quality by eliminating the second D/A conversion.

Do you know of any chips capable of this?

Thanks
-Ted
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Old 3rd December 2010, 10:07 AM   #2
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MiniDSP uses one on there amp.I can't tell you which one though.

Steve
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Old 3rd December 2010, 01:10 PM   #3
nmiljac is offline nmiljac  Germany
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Texas Instruments has amplifiers with I2S input.

Stereo amplifiers ranging 20-25 Wpc.

Have a look at their site.
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Old 3rd December 2010, 01:34 PM   #4
Pano is offline Pano  United States
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Apogee did. Now made by ST. Nice amps.
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Old 3rd December 2010, 01:39 PM   #5
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Both MiniDSP and the TI amps has DACs before the class-D amplifier output stage so they don't qualify.

What you're really searching for is a PCM to PWM modulator. TI makes at least one such modulator under the PurePath name.

Last edited by Saturnus; 3rd December 2010 at 01:42 PM.
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Old 3rd December 2010, 01:42 PM   #6
Pano is offline Pano  United States
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I'm pretty sure the Apogee DDX stuff was all PCM to PWM.
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Old 3rd December 2010, 02:31 PM   #7
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Quote:
Originally Posted by panomaniac View Post
I'm pretty sure the Apogee DDX stuff was all PCM to PWM.
I think so too. TACT audio, Steinway-Lyngdorff, and others have also made "pure" digital systems. Where "pure" is hyphernated since it's still not completely digital but the DA conversion happens either in the amplifier output filter or directly in the loudspeaker voice coil (for non-filtered digital output stages).

But the core remains, it's a PCM-PWM modulator he's searching for to drive digital output stages directly from a digital input signal without any analogue conversion steps.
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Old 3rd December 2010, 02:53 PM   #8
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Yes - the Apogee DDX and the TI Equibit/PurePath are the only implementations I'm aware of. Supposedly Tripath had a digital-input system in the works but I'm not sure whether that was direct PCM->PWM or whether it was just their standard modulator with a conventional DAC grafted on the front.

I have had various incarnations of the TI Equibit system for a while in the form of the Panny receivers and generally like it. Since it's open-loop the power supply quality is critical so you've basically just done an engineering trade-off. With a top-notch supply (not sure that any of the Panasonic implementations qualify in stock form) I think it can be very good, particularly if you could go digital active and drive each driver directly with an output filter tuned appropriately (I never went that far). Tuning the output filter is a bit tricky, but the Equibit EVM I have includes on-chip biquads so the digital active part is pretty viable.
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Old 3rd December 2010, 03:05 PM   #9
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Nad have an amplifier with digital input that uses direct delta sigma modulation with error correcting feedback on the output stage via pulse shaping the next pulse and global feedback:
NAD Electronics :: M2 Direct Digital Amplifier
as far as I can tell the clever bit is mostly the programing of its FPGA.
basicly my deam amp but priced acordingly!
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Old 11th December 2010, 01:29 AM   #10
minidsp is offline minidsp  Hong Kong
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Quote:
Originally Posted by Saturnus View Post
Both MiniDSP and the TI amps has DACs before the class-D amplifier output stage so they don't qualify.

What you're really searching for is a PCM to PWM modulator. TI makes at least one such modulator under the PurePath name.
FYI,
maybe just to clarify what carstereogeek said is that MiniDSP - miniAMPminiAMP (from the miniDSP product range) is indeed what I guess you could call a "Pure digital" amplifier since it's driven from an I2S input and actually uses the TI series of purepath IC. Just wanted to prevent confusion. :-)

Hope this helps,
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