[13mh13]

Hi!
A question about the BDA-1 that uses dual CS4398 dac chips ....

Does the BDA-1 use one CS4398  per channel , or are the CS4398 chips paralleled? By "parallel", I mean both CS4398 chips are stacked. Nothing wrong with parallel -- many high-end players and dacs (Luxman, Accuphase, etc) have done this to improve S/N or DR.

Thanks!

[James Tanner]

Hi - one per channel

james

[13mh13]

Hi - one per channel

james

Hmm... the CS4398 does not have a dual-differential mode option (unlike other DACs ,such as popular WM8740) . So either it is stacked or Bryston is using only one of the two provided channel outputs (e.g., AOUTA- ,
 AOUTA+ ) It's like using using two stereo amps for "dual mono". You feed the preamp L to one  stereo amp and preamp R to the other  stereo amp.  So ...  one of the  stereo amp channels is left dangling and never used. This can be done but it's rare.
Also, the BDA-1 is the only digital device (CD player or d/a processor) that uses 2xCS4398
See https://www.dutchaudioclassics.nl/the_complete_d_a_dac_converter_list/
 ... and CTR+ F for "CS4398". Every other device on this fairly comprehensive list uses only one CS4398.

Now if anyone with schematics or the service manual can confirm, I may be able to help a service customer out.

[13mh13]

Actually, there is one more possibility for the dual CS-4398 use: one for std outs; the other for balanced outs. Can a Bryston insider confirm that ?

[R. Daneel]

Hi!

Are you sure the CS4398 doesn’t have a single channel mode? Several years ago I was looking at its datasheet and remember this was an option configurable through its firmware. The dynamic range was specified as 120dB (it was a top-spec chip at the time) and 123dB in a single channel mode. Perhaps it was a misprint in the datasheet but I doubt it.

There would be no point in using a dual-channel (stereo) chip and using just one channel for, let’s say, the left channel and then another chip for the right channel. You’d be using twice as many chips as needed! 😊

If you look at a photo of the D/A-analogue section, it is laid out very elegantly, even beautifully, and it does look like a differential circuit.

But I don’t know, I am not an electronic design engineer. It’s an interesting question to be sure!

Cheers,
Antun

[James Tanner]

I will ask Engineering

[James Tanner]

Hi James, one CS4398 per channel in mono mode.

[13mh13]

Are you sure the CS4398 doesn’t have a single channel mode? Several years ago I was looking at its datasheet and remember this was an option configurable through its firmware.

The ability for a dac chip to be used as a single-channel (mono) or dual-channel (stereo) is a very deliberate and UN-obfuscated feature. See the datasheets of other dac chips that offer this (WM8740, PCM1794, etc).
The CS4398's datasheet is here:
https://www.cirrus.com/products/cs4398/
You can search the DS with search term "mono". I've looked thru it multiple times. The default stereo outputs are differential. There is no provision for a "mono" mode (software or hardware) that I could find.
I still have no clue as to what's going on inside my client's BDA-1 !!!

[13mh13]

FYI, the modification project my client is considering is to dual-parallel the CS-4398. What I noted earlier. This is what Arcam did in their FMJ CD33 cd player from 2004 with another, similar delta-sigma DAC chip (WM8740). Arcam used four of them; two parallel (stacked) and then each of those stacked pair in mono mode. So, two stereo DAC chips for R; and two  stereo DAC chips for L.
Arcam also obfuscates much of their topology  by unobtanium service manuals and schematics. Which is the exact opposite situation of major players like Philips and Sony.
See:
https://www.hifiengine.com/manual_library/bryston/bda-1.shtml


Below are photos found in Google images searches of the BDA-1 PCB. Tracing the handiwork should be .... ahem .. fun!

[13mh13]

I did find some PCB shots of the similar BCD-1 cd player (2008) that uses no SRC and a single CS4398. Notice the similarity of the output stage. BOTH the dac and the cdp feature balanced (din) and std. (rca) outs.