audio-talk

Well, I should add another big thumbs up for JLCPCB - the boards arrived this morning from China and the quality looks just as good as any other project PCB that I've worked on in the past.

Need to update this thread - just haven't had the time in the last week or so.

The new power management PCB has now been populated and installed into the AMB linestage along with the Silentswitcher. This component is now operating 'off-grid', unaffected by what might be going on in the mains.

To give some perspective on how quiet the Silentswitcher is, the regulated supply that used to power the linestage boards had a noise spec of less than 10uV. The Silentswitcher is specced to 0.2uV.

It wasn't very long ago that I would have heard the words 'switched-mode' and just NOPED my way right out of there. I even had a plan to build a linear supply for my music server at one point. The recommendation from Joachim Gerhard (of Paradise phono stage fame) prompted me to take a fresh look at it, and I realised that getting mains out of the chassis could in fact be a Good Thing.

Can I hear a difference? If there is, it's very subtle, I need to do some more listening, but I think there is a little less 'haze' - a bit like taking your glasses off and cleaning them. The linestage is a differential circuit so I'm not sure in reality how sensitive it is to tiny changes in power supply noise at the microvolt level. The key thing is that the infrastructure is in place for the upcoming DAC and phono stage. I suspect the phono in particular, with its use of RIAA inductors and step-up iron, will benefit from not having any mains near it.

Anyway, the all-essential pics. Before, taken a few years ago during the original build:



And after. This was taken 'powered on', note the meter illumination bulbs are lit, and power has been disconnected from the battery charging boards (just to hedge against any RF crap they might spew out). The two 3.7V lithium packs are connected in series to the SilentSwitcher and the XLR output socket that will supply the DAC and phono, but charged in parallel from the two charging boards at power-down. This way you can basically forget about the batteries, the whole thing takes care of itself automatically.



I also updated the software again to fix a couple of user interface things that were annoying me, and also to change the DAC source switch pin (see new yellow wire coming from the Arduino board) to go high on USB (server) select rather than SP/DIF. The reasoning behind this will become clear when I get to the DAC build...

Lovely work as usual.

Nice piece of work, I hope that Alps blue is not in he signal path?

Nick wrote: ↑Mon Oct 25, 2021 8:39 am Nice piece of work, I hope that Alps blue is not in he signal path?

Thanks. Nope, it's definitely not in the signal path, it's a control interface to the Arduino processor, a bit like a modern car's 'drive by wire' throttle. It acts like a motorised volume control, but what actually controls the volume is that array of relays and resistors you can see in the upper right of the picture.

Thats good.

Bloody shoddy if you ask me!

Very....


...nice indeed!

But what does it sound like?

Ray P wrote: ↑Tue Oct 26, 2021 6:52 pm Bloody shoddy if you ask me!

^^^Agreed.

But at the same time ...

jack wrote: ↑Tue Oct 26, 2021 8:43 pm Very....


...nice indeed!

But what does it sound like?

Pretty similar to before, I think. I wasn't expecting it to make a significant difference to the linestage itself. The exercise here was more around providing a power source for the DAC and phonostage builds.

I realised that if I converted the linestage to use a SilentSwitcher as well, it would release enough space in the chassis for the necessary batteries, and I would be able to piggyback automated charging onto the existing LCDuino functionality.

It also removes all mains transformers from the vicinity of the LR Phono, which has both step-ups and RIAA inductors, and saves quite a bit of space - the DAC and phono stage will each now fit in a half-width chassis.

So now that's all done, I'm turning my attention to the DAC.

For this, I have to tie together several PCB's:

- Silentswitcher - to provide separate digital and analogue power supplies
- A DIR9001 SP/DIF to I2S module which I got off Banggood (for AV)
- JLSounds I2S over USB module (for the music server)
- Twisted Pear OTTO-II Digital Switching module
- and the Twisted Pear Opus DAC itself.

Being able to have one-off PCB's made affordably by the likes of JLPCB is quite a game-changer. I thought I was going to have a nightmare trying to mount and wire all these together by hand, but I think I'm going to put everything on a sort of backplane PCB, where these can all slot in via headers. This way I can also make sure everything is connected together correctly via the KiCad schematic.

I figured that this morning I would start with the I2SoverUSB module headers. I've never built a DAC before, so it's a bit tricky getting my head around this stuff and the documentation is a bit daunting. I may well need to call for help, if that's the case I'll post something on the Beginners section.

I'ved the JLSounds board a few times Dave, and built a few DACs so more than happy to help out, just shout.

Ray

Ray P wrote: ↑Sat Oct 30, 2021 6:35 pm I'ved the JLSounds board a few times Dave, and built a few DACs so more than happy to help out, just shout.

Ray

Thanks Ray, the good thing about doing a backplane PCB is that I'll be able to share the schematic for it, so you and others will be able to spot my schoolboy errors!

The documentation for the Opus is not exactly... comprehensive (for example there's no mention of the controller block connector, I have no idea how that fits in although I can guess what MUTE does). And non-existent for the Otto, although to be fair the Otto's functionality is quite simple.

Did you check out these Dave?

http://www.twistedpearaudio.com/docs/di ... manual.pdf

http://www.twistedpearaudio.com/docs/di ... manual.pdf

http://www.twistedpearaudio.com/docs/di ... ematic.pdf

And don't forget there's a whole thread on the Opus at DIY Audio

https://www.diyaudio.com/forums/twisted ... d-dac.html

I did take a look at the manuals, but not the schematic! Looking at the connectivity, I should be able to work out what the controller block connections do from the Wolfson data sheet. That thread is useful too, thanks.