Digital Control of Attenuation – Repository for DIY

[jpk73]

Yes, the muses chip will only see "dirt" on the same SPI if the display does some stuff while the muses is not doing anything... BTW I am trying to understand how the internal isolation inside the muses works. The SPI lines and the +5V with it's GND is isolated from the rest, so external isolation does not seem to be necessary unless you feed the +5V from the analog +15V supply and share GND. If I understand the datasheet correctly the muses chip has a lot of separate power inputs:

At the clean side of the islolator we could have as many as 5 separate 0V lines for digital, analog and signal return (like in a mono DAC chip). Power decoupling could look like this:

We could feed the muses from 7 voltage regulators or use the 7805 to get +5V.

So the question is: how much isolation and separate power rails are needed if sound quality is paramount?

 

[derekr]

Yes, I tend to agree re not needing the isolator if you are using a separate 5VDC rail for the Muses digital supply. Definitely need it if taking the digital 5VDC from the +15V analog rail. In my case I found a dual-rail 5VDC supply (7805) which I hadn't remembered I had so opted to use that. And having two rails to play with said 'Why not use the isolator as you have a spare rail'. So one rail for the 'dirty' side - for the ESP32, ADuM 1300 VDD1 and various other necessities of my particular implementation - and the second rail for the clean side of the isolator.

Interesting approach to separating the 15V supplies. My take is that the "D_V" pins aren't shown on the datasheet as actually connected to the isolated digital logic section so should be fine being supplied by the analog 15V as shown by the datasheet. They may not actually be seeing any sort of 'digital' signal internally. Can't see Muses stopping short of suggesting separate rails if those pins posed any threat to the analog section. But that's just my non-EE take .

Typo on the pin 16 input voltages on the Adum and Muses?

In my implementation I'm not using the gain on the Muses so opted to ground all the pins between 1 and 16 (except for 6, 11 and 16 obviously) to the GND on the Iron Pre - which has an NTC to chassis ground.

Like the filtering, especially on the digital 5V! If I didn't already have my Muses boards I'd steal it!!!

 

[Skylar88]

OK, I updated the code and made it possible to freely specify all pins in the soft-SPI version (Skylar88, you might want to add a link to the first post).

Done.