5 ms·

It's bizarre how none of these chips seem to have a digital input. All my music is digital, and despite the modern rise of vinyl, I don't think that's unusual.

by mrob 8y ago

It's bizarre how none of these chips seem to have a digital input. All my music is digital, and despite the modern rise of vinyl, I don't think that's unusual. If I want an amplifier like this then I'm forced to have a completely useless DAC/ADC pair degrading the signal quality. Does anybody know of an easily available class-D amplifier with digital input? You'd think that would be an obvious feature for a digital amplifier.

blattimwind 8y ago
> You'd think that would be an obvious feature for a digital amplifier. That's because these amplifiers are not digital. The control loop is generally analog. Though there are chips which do in fact use digital inputs and do most of the work via fixed-function DSP, but those are mostly bigger chips targeted at 5.1 or 7.1 systems.
- mrob 8y ago
  From Wikipedia: "The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits or include digital signal processing devices, the power stage deals with voltage and current as a function of non-quantized time." So what's it called if it is time quantized? The simple open-loop design depicted on the Wikipedia page could have the analog comparator + triangle wave generator replaced with a digital delta-sigma modulator (1-bit DAC). Then the switching times of the power stage would be quantized to the sample rate multiplied by the oversampling ratio. (Although it seems this open-loop model is an oversimplification, and real class-D amplifiers have feedback, so it wouldn't be that simple in practice.)
kazinator 8y ago
It's not a digital amplifier. A class-D amplifier is basically somewhat like a switched-mode power supply that varies its output voltage in response to swings in the input signal.
evancox100 8y ago
Uh, if you want to "amplify" a digital signal, just multiply all the samples by some number.
WalterBright 8y ago
All stereo components, except the amp connection to the speaker, should be ethernet. Turntable, CD player, cassette, pre-amp, everything. Then make it wifi. Just think, you could eliminate that awful rat's nest of cables. The sound quality would be better. You could locate components where-ever convenient. Each component could have a web browser interface. It'd be awesome.
- jordanthoms 8y ago
  Linn's exakt system is a little like that - the signal is sent into each speaker in digital form and then decoded and amplified there.
- jabl 8y ago
  https://en.wikipedia.org/wiki/Audio_Video_Bridging https://en.wikipedia.org/wiki/Audio_Video_Bridging
- tsukikage 8y ago
  Digital, sure. Standardized even, sure. But wifi, going through who knows what network stacks, routers, filtering, and sharing with other traffic? I'd like some guarantees on latency, please; I like my video in sync with my audio.
  - WalterBright 8y ago
    It would be on your home LAN, so presumably you know what else is using it. I stream video from my computer to a Roku box over ethernet, video consumes far more bandwidth than audio, and it works fine. Also, if you plug your audio components into its own switch, it should not get interference from the rest of your LAN.
- baq 8y ago
  Sonos, d&m heos and Yamaha's multiroom iirc do half of that and yes, latency must be tightly controlled. I imagine with sources also being 802.11 it'd be much harder to keep it in reins.
archi42 8y ago
Don't they make these ICs with I2S? Then all you need is something that digitally interfaces with your source (eg toslink, usb) and "unpacks" the PCM data and sends it out via i2s. Edit: look for example at TI TAS5756M, TAS3251 or TAS5825M.
- mrob 8y ago
  Thanks, those are the kind of chips I was looking for. And S/PDIF to I2S transceivers are also available, so they could be used with common consumer audio equipment.
  - archi42 8y ago
    TI has a nice product search. E.g.: http://www.ti.com/audio-ic/amplifiers/speaker-amplifiers/products.html?pqs=paqs&familyid=3419#p2982=Digital%20Input&p89=Class-D;Class-D%20Boosted;Smart%20Amp&p1055max=Stereo http://www.ti.com/audio-ic/amplifiers/speaker-amplifiers/pro...
squarefoot 8y ago
They don't have it because they aren't digital at all; a Class D amplifier essentially is to amplifiers what a switching power supply is to power supplies. They're still 100% analog, but they use a different driving method compared to their traditional linear counterparts to maximize performance.

by mrob 8y ago

blattimwind 8y ago

> You'd think that would be an obvious feature for a digital amplifier. That's because these amplifiers are not digital. The control loop is generally analog. Though there are chips which do in fact use digital inputs and do most of the work via fixed-function DSP, but those are mostly bigger chips targeted at 5.1 or 7.1 systems.

mrob 8y ago
From Wikipedia: "The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits or include digital signal processing devices, the power stage deals with voltage and current as a function of non-quantized time." So what's it called if it is time quantized? The simple open-loop design depicted on the Wikipedia page could have the analog comparator + triangle wave generator replaced with a digital delta-sigma modulator (1-bit DAC). Then the switching times of the power stage would be quantized to the sample rate multiplied by the oversampling ratio. (Although it seems this open-loop model is an oversimplification, and real class-D amplifiers have feedback, so it wouldn't be that simple in practice.)

kazinator 8y ago

It's not a digital amplifier. A class-D amplifier is basically somewhat like a switched-mode power supply that varies its output voltage in response to swings in the input signal.

evancox100 8y ago

Uh, if you want to "amplify" a digital signal, just multiply all the samples by some number.

WalterBright 8y ago

All stereo components, except the amp connection to the speaker, should be ethernet. Turntable, CD player, cassette, pre-amp, everything. Then make it wifi. Just think, you could eliminate that awful rat's nest of cables. The sound quality would be better. You could locate components where-ever convenient. Each component could have a web browser interface. It'd be awesome.

jordanthoms 8y ago
Linn's exakt system is a little like that - the signal is sent into each speaker in digital form and then decoded and amplified there.
jabl 8y ago
https://en.wikipedia.org/wiki/Audio_Video_Bridging https://en.wikipedia.org/wiki/Audio_Video_Bridging
tsukikage 8y ago
Digital, sure. Standardized even, sure. But wifi, going through who knows what network stacks, routers, filtering, and sharing with other traffic? I'd like some guarantees on latency, please; I like my video in sync with my audio.
- WalterBright 8y ago
  It would be on your home LAN, so presumably you know what else is using it. I stream video from my computer to a Roku box over ethernet, video consumes far more bandwidth than audio, and it works fine. Also, if you plug your audio components into its own switch, it should not get interference from the rest of your LAN.
baq 8y ago
Sonos, d&m heos and Yamaha's multiroom iirc do half of that and yes, latency must be tightly controlled. I imagine with sources also being 802.11 it'd be much harder to keep it in reins.

archi42 8y ago

Don't they make these ICs with I2S? Then all you need is something that digitally interfaces with your source (eg toslink, usb) and "unpacks" the PCM data and sends it out via i2s. Edit: look for example at TI TAS5756M, TAS3251 or TAS5825M.

mrob 8y ago
Thanks, those are the kind of chips I was looking for. And S/PDIF to I2S transceivers are also available, so they could be used with common consumer audio equipment.
- archi42 8y ago
  TI has a nice product search. E.g.: http://www.ti.com/audio-ic/amplifiers/speaker-amplifiers/products.html?pqs=paqs&familyid=3419#p2982=Digital%20Input&p89=Class-D;Class-D%20Boosted;Smart%20Amp&p1055max=Stereo http://www.ti.com/audio-ic/amplifiers/speaker-amplifiers/pro...

squarefoot 8y ago

They don't have it because they aren't digital at all; a Class D amplifier essentially is to amplifiers what a switching power supply is to power supplies. They're still 100% analog, but they use a different driving method compared to their traditional linear counterparts to maximize performance.