• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Multichannel Full Digital Amp (FDA) solution

ppataki

Major Contributor
Joined
Aug 7, 2019
Messages
1,216
Likes
1,356
Location
Budapest
I thought I would share my experience and learning here; hopefully it will inspire others too.
I have been fascinated by the concept of a Full Digital Amp (FDA) ever since early models started to appear; I even had a pair of active monitors using FDAs (Nubert nuPro A-300)
But I have always wanted a multichannel solution which never existed and still does not exist (besides some FDA AVRs from the past)

A few months ago I have updated my home office setup with a Sabaj A30A FDA and I was simply blown away - the sound is not comparable to anything I have heard so far (and I am not exaggerating)
So I said to myself: now it is time (again) to venture into the FDA world for multichannel for my living room setup (which is a 4.0 system using this and this)

So how could I use one A30A to drive the fronts and another one to drive the rears?

I could connect both of them to my PC via USB and use the Aggregate device feature but I am using Windows 11 and not a Mac so that option won't work

Then I tried Voicemeeter Banana which worked well, besides the clock drift issue: each and every time I measured the time delay between my front left and rear left speaker I got different values (as in totally different values)........

Finally I managed to find a solution that actually works: I needed a multichannel DDC (digital-to-digital converter) that can convert USB to multiple SPDIF outputs
The only such device I am aware of is the RME Digiface USB.

So I have ordered one and hooked up the two amps using optical fiber SPDIF cables and voila it works like a charm!

This is how it looks like:

20221201_204230.jpg


Now I do not have any clock drift issues and the sound is just as awesome as it used to be just by using these amps via USB
Needless to say, no DAC is involved in the signal chain and no analog interconnect cables are needed

I can totally recommend this solution to anybody who (like me) got hooked on the FDA concept and would like to use it in a multichannel system - or you can also use this to leverage multiple stereo DACs in a multichannel setup

Any questions/comments are welcome
 
Last edited:

somebodyelse

Major Contributor
Joined
Dec 5, 2018
Messages
3,682
Likes
2,962
There are alternatives to the Digiface although probably not that many. The MiniDSP U-DIO8 is probably most directly comparable but there are also bare boards, and some of the DSP models have multiple digital outputs. I think I've seen some other boards doing it too, but may be thinking of multichannel I2S/TDM that would need suitable outputs adding. I had hoped it might be possible with a Pi Pico, but it's only USB1.1 so bandwidth would be limited.
 

MCH

Major Contributor
Joined
Apr 10, 2021
Messages
2,581
Likes
2,197
@ppataki thank you for posting and confirming something like that works well. I thought many times about something similar.

I think I've seen some other boards doing it too, but may be thinking of multichannel I2S/TDM that would need suitable outputs adding.
i have searched in the past for a sort of cheap board or usb card with multiple spdif outs and have never found anything other than the RME and the minidsps (udio8 and nanodigi). If someone knows of any other option, i would like to know, as the three mentioned are not cheap.... is it so complex to make? seems so...
 
OP
P

ppataki

Major Contributor
Joined
Aug 7, 2019
Messages
1,216
Likes
1,356
Location
Budapest
Welcome @MarcosCh!
I hope my post will encourage people to go ahead with such a setup (it shall work flawlessly up to 8 channels in whatever configuration)
Just FYI there is one more alternative option: RayDAT - but it is even more expensive than the Digiface.... :facepalm::(

EDIT: I am not sure if the nanoDIGI would actually work since it only has one single SPDIF as an input (its USB input is for control only; no audio)
 
  • Like
Reactions: MCH

somebodyelse

Major Contributor
Joined
Dec 5, 2018
Messages
3,682
Likes
2,962
@ppataki thank you for posting and confirming something like that works well. I thought many times about something similar.


i have searched in the past for a sort of cheap board or usb card with multiple spdif outs and have never found anything other than the RME and the minidsps (udio8 and nanodigi). If someone knows of any other option, i would like to know, as the three mentioned are not cheap.... is it so complex to make? seems so...
I suspect it's what the relatively limited market of mostly pros will bear. Internals in the u-dio8 review thread show it's their USBStreamer board with a little interface board. I don't know if it's using one of the firmware images for that board or one that they reserve for the u-dio8, but both it and the MchStreamer are capable of multiple channels in sync via other combinations of interface. It's essentially the USB interface part of a multichannel audio interface, but without any of the sensitive analog stuff.

I think on the board side it must have been one of the diyinhk multichannel output xmos boards plus some I2S to spdif/toslink/aes boards.
 
  • Like
Reactions: MCH

Madslide

Member
Joined
Feb 18, 2022
Messages
30
Likes
16
Welcome @MarcosCh!
I hope my post will encourage people to go ahead with such a setup (it shall work flawlessly up to 8 channels in whatever configuration)
Just FYI there is one more alternative option: RayDAT - but it is even more expensive than the Digiface.... :facepalm::(

EDIT: I am not sure if the nanoDIGI would actually work since it only has one single SPDIF as an input (its USB input is for control only; no audio)
I completly follow you on the FDA avantages and your setup. I have an equivalent setup with two FDA (SMSL AD-18) and a Mini DSP Nano-digi and I'm very suprised that poeple prefer to have dac and standard class D amplification eaven in multi amplification systems.
You have two inputs on the nano digi. SPDIF and Toslink and I confirm that the USB B is only for programming the DSP.
Personaly I use the toslink for computer inputs and use the SPDIF with an ADC converter for the turntable.

You have now few month with the Sabaj A30A, what do you think of it ?
 
OP
P

ppataki

Major Contributor
Joined
Aug 7, 2019
Messages
1,216
Likes
1,356
Location
Budapest
You have now few month with the Sabaj A30A, what do you think of it ?

Amazing!
I have three of them, one is driving my system in my home office and two others are driving my living room 4.0 system (here and here)
I can still confirm that I have never heard anything more detailed and precise like this - I am totally blown away
Eager to wait for the next generation! (fingers crossed that it will come)
FYI @peterwen
 

peterwen

Active Member
Audio Company
Joined
Jun 5, 2019
Messages
159
Likes
309
Location
Dongguan, Guangdong, China
Amazing!
I have three of them, one is driving my system in my home office and two others are driving my living room 4.0 system (here and here)
I can still confirm that I have never heard anything more detailed and precise like this - I am totally blown away
Eager to wait for the next generation! (fingers crossed that it will come)
FYI @peterwen
On behalf of our team, thank you for your recognition.
 
OP
P

ppataki

Major Contributor
Joined
Aug 7, 2019
Messages
1,216
Likes
1,356
Location
Budapest
Interesting! We need to send one of these to Amir for review.
Check out his review on the SMSL A2 amp, basically it is the same as the Sabaj A30A

 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
What is the difference between FDA and integrated amp with DAC?

Usually integrated amp has analogue volume control

FDA is just a DAC + digital vol control + power amp in one box ?
 

notsodeadlizard

Senior Member
Joined
Feb 18, 2023
Messages
403
Likes
362
The only fact that is interesting here is the fact that the reference design for the Dutch AX5689 chip (https://www.axign.nl/products/ax5688/) with half-bridges from ST Micro (STA516BE, https://www.st.com/en/audio-ics/sta516be.html) works OK.
Because it's hard to know anything more about it, while the Dutch have only JBL PB710 Partybox on the open list of successful commercialization.
AX5689 is quite interesting IC, yes.
 
OP
P

ppataki

Major Contributor
Joined
Aug 7, 2019
Messages
1,216
Likes
1,356
Location
Budapest
What is the difference between FDA and integrated amp with DAC?

Usually integrated amp has analogue volume control

FDA is just a DAC + digital vol control + power amp in one box ?

An FDA is essentially a class D amp. The difference is that while a conventional class D amp's signal path will look like this:

analog input --> PWM conversion and amplification --> PWM to analog conversion at the output stage using a low-pass filter
(and for this to work with a digital source (computer, etc) you will need a DAC (=PCM to analog conversion) upstream in the signal chain)

the FDA's signal path will look like this:

PCM input --> PWM conversion and amplification --> PWM to analog conversion at the output stage using a low-pass filter

So there is no DAC (=PCM to analog) needed at all in the signal chain

More about it here: https://soundcheck-audio.blogspot.com/2012/08/ever-heard-about-full-digital-amps.html
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
So there is no DAC (=PCM to analog) needed at all in the signal chain

I guess if in practise Topping has an ESS DAC chip + digital vol control + really powerful power amp, all in one box, it would achieve the same thing ?

But in a different way

This is essentially what their DAC + headphone amps are but I can see the amplification scaling up bigly in future, for speakers
 

notsodeadlizard

Senior Member
Joined
Feb 18, 2023
Messages
403
Likes
362
What is the difference between FDA and integrated amp with DAC?

Usually integrated amp has analogue volume control

FDA is just a DAC + digital vol control + power amp in one box ?
Class D amp is a pure analog device by design.
FDA is pure digital, there is no analog domain in their design till the output of output switches, there is no even amplification in a common engineering sense, it is a direct digital converter from the PCM stream to high-frequency high-current pulses of fixed voltage. Even feedback signal from the external domain is returned to FDA with a help of ADC.
This nuance has nothing in common with the end-user's (listener's) world.
It can be considered a phenomenon in the world of production where manufacturability is critical.

There is no single perfectly right and best solution.
But FDA is interesting, this is a fact.
 

Music1969

Major Contributor
Joined
Feb 19, 2018
Messages
4,636
Likes
2,809
I remember Estelon had an active speaker years ago called LYNX which converted PCM to DSD and then amplified this DSD to drive the each driver directly

It didn't really take off and they abandoned it

I guess its all a quest for shortest analogue signal path



"
Estelon LYNX speakers are essentially a marriage of all the best technology in the field of digital audio we could imagine. The core of the audio is HQPlayer from Signalyst that works as a DSD rendering engine, converting everything to a DSD64 stream. An Integrated Roon streaming player acts as a user interface for playback from NAS or Tidal streaming service.

The final frontier of the Estelon Intelligent Audio technology is its powerdac – or the absence of it, actually. Estelon LYNX speakers have the DSD stream driving speaker elements directly. As one of the fundamental features of DSD bitstream is its capability to have analog signal reconstructed by simple analog low-pass filtering, Lynxes can get away with no signal processing at the amplification stage whatsoever.

The phase and amplitude accuracy of DSD is comparable to best analog recordings, while the
digital domain allows the lossless transport of the data. At any point, by simply re- clocking the bitstream to DSD bitrate, one will get a mesmerizingly close rendering of the original recording (if it started its life as DSD, of course). The audio data transport in Estelon LYNX takes place wirelessly, over the 2Ghz and 5Ghz Wi- Fi network while a dedicated radio chipset constantly aligns the phase and timing of the DSD clock pulses on all the speakers connected to system. In Estelon Intelligent Audio, reclocking of the DSD data is done with sub-picosecond jitter precision, while the synchronization between the channels over the air is approaching the sub-microsecond domain. This signal is then run through a precision FET driver bridge connected directly to the speaker’s analog crossover. It is difficult to imagine a shorter and more lossless signal path in the analog or digital world of audio. This approach to digital audio is the most suited to the hardcore audiophile there can be, and the sound you get this way is in some sense even closer to analog than analog itself"

 
OP
P

ppataki

Major Contributor
Joined
Aug 7, 2019
Messages
1,216
Likes
1,356
Location
Budapest
I remember Estelon had an active speaker years ago called LYNX which converted PCM to DSD and then amplified this DSD to drive the each driver directly

This is actually really interesting
As far as I know PWM and DSD signals are not that far away from each other
One could actually use Jriver for example to convert and output DSD in real-time to an FDA that could accept DSD signal and amplify it directly (if that is possible....)

1685726258739.png


This might be an even better solution
Just thinking out loud :)
 

voodooless

Grand Contributor
Forum Donor
Joined
Jun 16, 2020
Messages
10,227
Likes
17,806
Location
Netherlands
Class D amps without feedback aren't really good enough, with DSD-only output you can't have feedback working, you will need to convert to PCM to apply the feedback.
 
Top Bottom