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DDX 320 - Improvement Proposals

DDX 320 - Improvement Proposals

Yubing wanted me to give some advise on teh DDX320:



Nice. And you're welcome to give any advice too for our boards. Have a nice day.:)



Here it comes:



I tried also at:





http://www.diyaudio.com/forums/vendors-bazaar/172050-another-project-all-digital-ddx-amplifier-31.html





Without much suceess.





I do think that you got some design flaws/weaknesses in your Rev 1. batch.



Of course there's the main noise issue, we're all aware of.



It's maybe related to a flaw of the input stage and an improper reset scheme. It might disappear if some of below gets solved.





1. Powers supply / regulation of digital parts -- just one 3.3V reg for everything (clock, cs8416 analog and digital asf.) !!

Look up modern DAC designs. The key is the quality of power supply and regulation, as well as proper decoupling.

There's a lot of space for improvement on your board. It's very basic.

Hint: Twisted pear audio introduced nice 3.3V sockets on their DACs. This way you can hook up your own external regulators

or you you just use the TP stock regs.

2. I havn't seen much of noise supression measures on the board.

3. Output stage interferences (ELCO sits between coils!) I removed relais and put better coils (Wuerth) underneath the board with good results.

4. CS8416 200ps Jitter performance not state of the art ( there are better chips (50ps) out there)

5. No SPDIF input pulsetransformer ( It's very important to choose the best - they all come with a different sound signature)

6. Input stage to CS8416 should be made differential (There are many good examples on the net!)

7. BNC connector as a choice would be the better choice compared to RCA

8. There seem to be a flaw in the reseting scheme of the CS8416 when switching 44.1 96 sample rates - sometimes the

output relais is activated sometimes nothing happens. You should have a look at the whole reseting scheme of the CS8416 in particular.

I don't think it is properly initialised at all times.

9. Pretty high overall noise floor ( seems partly to be related to the upsampling and/or CS8416 reset) -- Maybe try to avoid upsampling

My offline upsampled 16/44.1 -->> 24/96 material sounds much metter with less noise then the CS8416 realtime 24/96 upsampling.

10. Try to avoid all unnecassary LED signaling. A simple switch for Toslink to SPDIF would do.

There's IMO no need to have LEDs for volume control. Keep it simple.

12. Please introduce I2S header. I'd love to feed the amp with an USB - I2S interface. There are many devices available.

People out there would love it I guess.

13. Make it possible that all ouput relais can be removed. ( I do think removing my 3rd relais caused a breakdown of my first

board, though I'm not sure about it.)

14. Introduce a firmware upgrade option.



Note: My TAS 5706 based amp doesn't have any noise issues. It also runs with CS8416. But without upsampling, and without external clock.



Looks like a long list.



However: I do think the amp got great potential. I hope that you can make use of some of above comments in Rev 2. of that amp.



Let me know - what you think ??? -- We can take it also offline -- Just drop me a mail.



Cheers
Just to mention it. Some things I observed:

1.
If I switch from 44.1/16 to 24/96 there'll be a reset (you can hear it from the relays being activated)

If I switch from 24/96 to 44.1/16 there won't be a reset.

Could be an indication tht something is wrong on your resetting scheme.

2.

The main noise issue has maybe also seomething to do with it, since it requires power on/off resets to get the noise away.
Obviously power/off on won't seems to cause a defined reset on the chips. That might explain the random bahaviour of noise yes/no.

3.

I guess you don't turn the CS8416 during off during standby. Since the SPDIF LED stays locked.

Maybe it would be a good idea to run a system reset incl CS8416 when leaving standby mode.


What's needed than.

My guess:

If the sample rate and maybe bitdepth and the system state changes the system requires a defined RESET on all chips.

Maybe even if playback is started there's a need for a reset prior to it.



Cheers
Hi, thanks a lot for your feedback. Apologize we haven't responded to the diyaudio thread. There are holidays in China now, we'll respond as soon as possible.
Hi folks.

Any news?

Just to mention it.

When listening to the strange noise flaw. I got the feeling that some left channel content makes it into the right channel (as a distorted noise). Something must go pretty wrong in your setup.

Cheers
Hi folks.

Any news?

Just to mention it.

When listening to the strange noise flaw. I got the feeling that some left channel content makes it into the right channel (as a distorted noise). Something must go pretty wrong in your setup.

Cheers

Thanks again for all your input and suggestions, really appreciate that. we are looking into it, but I can't promise any timeframe.
Yes, that channel seperation issue was one of the things I noticed and which makes it easy to hear when the amp is in "noise mode".
Thanks again for all your input and suggestions, really appreciate that. we are looking into it, but I can't promise any timeframe.
Yes, that channel seperation issue was one of the things I noticed and which makes it easy to hear when the amp is in "noise mode".

I'd still guess it's a reset scheme resp. reset timing issue.

You should have a look at the TI chips and application notes. I do think the TI chips are the better ones.
24db volume control over VCC on the power chip. IMO much better.

I'd love to see you guys coming up with a simple I2S NO-FRILL module. Just controller and amp. No resampling no SPDIF.

Cheers
Hi guys.

Any progress?

What do you think about a simple I2S version of that amp? Just take the CS8416 and the clock out.



There are many USB to I2S or SPDIF to I2S modules out there.


I think people would love it.


You could add your own SPDIF-I2S or USB-I2S interface later on. I think a modular approach would just be fine.


I'm almost sure that your noise problem would also be gone on the I2S version only.


Let me know if it would be helpful to go after a group-buy for such a device?? What would be the minimum batch size to
get you start working on the subject??


It might also be very helpful if you could tell me how to feed I2S to the amp. I figured out the soldering joints. But I guess I'd have to remove the CS 8416 and the permanent clock to make it work. I'm also not sure if your controller
would accept a missing CS 8416?!?!?

Giving me any directions would be great!!



Cheers
Hi guys.

What do you think about a simple I2S version of that amp? Just take the CS8416 and the clock out.







There are many USB to I2S or SPDIF to I2S modules out there.





I think people would love it.





You could add your own SPDIF-I2S or USB-I2S interface later on. I think a modular approach would just be fine.





I'm almost sure that your noise problem would also be gone on the I2S version only.



Cheers



I totally agree with this.

Also would be great removing the mcu and the external user interface, and adding a sheet with a sort of i2c instruction list.

So we can easily rewrite our personal user interface (standard interface Sucks) and also access to the dsp options of the chip.
Hi, guys.
An I2S version sounds as good idea but we have to know the input sample rate and oversampling rate, and then we need to TELL the ddx chip by MCU(only that will make ddx chip works). Also removing cs8416 is not ok, the mcu will stop and the board will not working then.
But some ideas from you will help me for the new design, so thanks~~
Yubing
Hi, guys.

An I2S version sounds as good idea but we have to know the input sample rate and oversampling rate, and then we need to TELL the ddx chip by MCU(only that will make ddx chip works). Also removing cs8416 is not ok, the mcu will stop and the board will not working then.

But some ideas from you will help me for the new design, so thanks~~

Yubing



Have a look at the TI purepath chips. Probably much easier to handle.

The power chips are pin compatible for different power demands. And volume control is probably much better.



You can also implement very easily multichannel amps.
Hi Hifimediy.

Any progress on the subject?? Can we expect a new board sooner or later?

THX
Hi there.

Let's continue with some proposals:

1. Different PIC configurations.

It would be nice to have an amp with swappable PICs allowing different firmware settings. (see Twisted Pear Buffallo)

I'd really like to see a two channel model with all internal DSP ( EQs/Volumecontrol etc on neutral)
You can sell such a PIC at a little extra. I would order both or more to compare..


2. The HifiMe 4398 DAC comes with a much better input stage (WM8804-50ps jitter ) compared to the DDX320.
I guess you could easily use that one for the amp. You might also solve the noise issue with this.


Last. Perhaps you could tell us if you consider to revise the DDX320??

THX
Hi, soundcheck.
Many thanks to your focus and suggestions. I made something new these days and hope we can success.
20
Looks promsing.



Put me on the list of beta testers. ;) You know my e-mail.



Thx.
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