@jeffrey125 Thanks for the correction- I knew that once upon a time...
Digital input amp
I see a few coming on market. Previous threads were quite old.
They take a USB or other input. No DAC on the front end. Just the DSP engine to do volume, eq, etc, then whatever conversion to PCM to feed the class D output. So the only "DAC" is the output stage. This makes sense as it further reduces the functions in the chain. I have not seen objective testing or any reliable subjective testing. The ones I have seen are Infineon processer based. No idea if the output filtering or feedback implementation is up to the Purify quality. I guess the next innovation is the GaNFET output. One has a DAC to feed a sub out. Easy as any old $5 DAC will wo there.
I was browsing and came across the Sajab A30a. ( quite inexpensive) Peachtree has the old Gan-1 but coax PCM only. That would be fine if it managed buffering and clocks internally. Unfortunately my all-in-one only has USB out.
I suspect there is a lot to be learned here but it makes sense to me for the future.
Showing 5 responses by atmasphere
@tvrgeek I had the same misgivings about that bit from the marketing department. As best I can make out this amp is class T. |
@tvrgeek If this is so, then the amplifier is not also class D. Class D is a very specific class of operation. Since you apparently have a degree, then you know that class D was proposed in the 1950s and the first home implementations were sold in the 1960s. You also know the building blocks required. So pick one: if its class D then it has a DAC built into the same box to which the digital signal arrives prior to the class D circuitry and probably one the same board as the class D section. If this is false then its not a class D amplifier inside although it might employ switching technology. |
@tvrgeek What you are describing above means that the DAC is at the input of the class D amp portion of the product. Put another way, the PWM portion of the circuit is at the input of a class D amp, not its output. Digital at its fastest might be 192KHz sampling frequency. Class D amps often switch at 500KHz or higher. You can design a DAC that can produce a PWM output, but it really does have to be at the input of the class D amp in order to work. I know a lot of companies say they have a 'digital amp' but if they also say its class D then the DAC is always at the input to the class D circuitry. |
@tvrgeek To be clear, the DAC is at the input of the amp, not the output. Class D is not digital since the switching of the amp does not have meaning whereas the switching of a digital word does. So you have to convert from the latter to the former. |