Ideas for a bluetooth controlled preamp / headphone amp combo (PGA2311)

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Hi, I have an idea for a miniature preamp in a configuration I haven't quite seen before aside from some headphone amps. I have some experience with the NRF52840 bluetooth chips, they are really good for building remote controlled devices, and I'd like to try using it to control a small desktop preamp that can do double duty as a headset/headphone amp.

The goals of the preamp would be:

  • parts cost under $50
  • low noise, clean sound
  • power supply from a USB 2A 5V wall wart (same as raspberry pi 3)
  • small size (similar to a FiiO portable headphone amp)
  • no source selection (1 source, 1 output)
  • headset jacks instead of RCA's (for size and headset support)
  • pass through microphone line level signal
  • 4-segment clock-style display (or maybe an OLED)
  • ultra-minimalist design, no buttons or switches (100% Bluetooth controlled)
  • use a Bluetooth remote for volume, mute, power, balance

Inspiration:

Basically I want a smaller, more minimalist, all bluetooth version of the Schiit Saga S with maybe better performance.

I wasn't sure if I'd be able to pull this off until I started studying some other diy PGA2311 projects, particularly this one:


This looks fairly easy to build, and can probably be miniaturized, but from what I understand it should have some additional low-noise power supply and filters/buffers.

There are few other PGA2311 projects on this forum that I want to borrow ideas from, like like this one from user @kulamario. He posted an Eagle file I can start with for my analog section:


Parts:
- PGA2311PA (or smd version PGA2311UA/1K)
- LT3045 for the analog +5V
- MAX1044 for the -5V inverter
- NRF52840 feather board for the MCU, 3.3V regulator, and USB 5V jack
- simple 4 digit display like this one

See the attached image for the basic plan.

My main questions that I could use some help answering:

- will this design be suitable for both driving headphones and powered speakers or a power amp, all off a 2A wall wart?

- will this give adequate low-noise sound quality for "most" people?

- any reason to go with RCA jacks's instead of 3.5mm headset jacks?

- any better/newer digital potentiometers I should be looking at? (eg. CS3318)

- are there more efficient / cheaper alternatives to LT3045 that I should look at?

- is daisy chaining a LT3045 to a MAX1044 a good or bad idea?

- is @kulamario's PGA2311 Eagle design a good place to start?

This is my first audio project so I'd appreciate any tips or suggestions before I get in over my head. I haven't really started anything yet other than reading up and buying some of the parts I plan to use.
 

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After a bit of reading, it looks like PGA2311 isn't going to be sufficient for a headphone amplifier.

Do I need an amp for my project using a PGA2311

So if I want to do a headphone out I'd need to add some additional circuitry, and someone there recommended AD8656 as an option. I updated the plan image a bit but will probably only tackle the headphone part after I got the rest working.
 

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Use a $10 Sanwu BT module. Power that with 5v from a cell phone charger. Use 3.5mm output to feed TPA6120A headphone amp module. Now you can drive just about any headphone. It needs a basic $10 10VA 15v toroidal trafo from Antek.

http://www.ti.com/lit/ds/symlink/tpa6120a2.pdf

TPA6120A Headphone Amplifier ALPS Tone Tuning for 32 ohm to 600 ohm Headset 8751762610793 | eBay

It’s tough to beat specs on that without a lot of work.

Sanwu BT:
SANWU Wireless bluetooth Audio Receiver Digital Amplifier Board With Remote Cont | eBay
 
Actually I wasn't even going to add Bluetooth "audio" support, but only to use the Bluetooth MCU (NRF52) to remote control all features of the preamp. There won't even be a volume knob on the box itself because I have a bluetooth optical rotary encoder I can connect to the box to perform all the volume and other controls. So unfortunately I can't use any headphone or preamp kit that has a pot built into it. I'll probably have to print my own boards.

I'm still really struggling with figuring out the power supply. I have zero experience with toroidal power supplies and was hoping I could get by with just a 5V usb cell phone charger.

I read in another forum that someone mentioned using this 5V dual rail power supply to power his PGA2311:

https://www.digikey.ca/products/en?keywords=NMA0505SC

It's a bit more expensive than I was hoping but if it'll work then I might not need a toroidal?
 
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That $12 Sanwu module above is 5v USB and can actually power headphones to a certain extent all by itself. I thought you were looking for a pretty powerful headphone amp which is why I suggested TPA6120 but that needs +/-v supply. You can get +/-v DC-DC converter from 5v. But they will need some post filtering and can sound good.

Look for Murata DC-DC converter (get at least 150mA) and look for 5v input and +/-15v output or +/-12v outout. Add a 22uH and 2.2uF film cap filter on the output.
 
The headphone section is looking a bit too complicated for me right now, I think maybe I'll revisit that after I get the PGA2311 section fully working and sounding good.

I updated my plan image with a Murata +5-5V supply connected to a 2.5A usb wall wart.

Would I use the 22uH inductor and 2.2uF film cap filter on each of the +5V and -5V outputs of the Murata, before connecting them to the PGA2311?

I already got the MCU and cathode display all hooked up and working. Those cathode segment displays look much better in person than on the photo.
 

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Would I use the 22uH inductor and 2.2uF film cap filter on each of the +5V and -5V outputs of the Murata, before connecting them to the PGA2311?

Yes - it helps to get the noise and ripple of the DC-DC down to about 10mV per the spec sheet. If the PGA has a good PSRR that should be fine. Don’t forget to lots of bypass caps. 10uF and 100nF X7R next to Vcc and Vee pins.
 
@xrk971, I really appreciate the help.

There are over 4000 22uH inductors and over 3700 2.2uF film capacitors on Digikey with a huge variety of values. What a nightmare. Do you happen to know a good manufacturer numbers to choose?

I already have some Nichicon capacitors that I was planning to use for the PGA.
 
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You will have to figure it out with specs. Look at your required current and resistance at DC, and the then go by mounting options (SMT vs through hole) and size. Wurth or Coilcraft or Vishay or TDK are all good. Then price of course. For cap a Wima 2.2uF MKS 50v radial 10% is a good bet. It’s not that critical to get it exactly right. You probably need at least 100mA for the headphone although I would bet it’s a lot less.
 
I'm gonna pick up both of those inductors and just try them out. There are just so many of them to choose from I'll have to do some trial and error and see if I can determine which one results in a lower noise floor.

Bourns 22uH - 78F220J-RC

Bourns 22uH - 9230-52-RC

I see there are some really fancy ones too like this.

Digikey also has those 2.2uH caps you mentioned.

Wima 2.2uH - MKS4F042205G00KSSD

I also have a few different resistors to try out. The PGA spec sheet says to use "Ceramic or metal film" for the 0.1uF, and "tantalum or aluminum electrolytic" for the 10uF but I've heard mixed things about tantalum in audio equipment.

Vishay Ceramic 0.1UF - A104K15X7RF5TAA

Nichicon Aluminum Electrolytic 0.1UF - UFG1H0R1MDM

Nichicon Aluminum Electrolytic 10UF - UFW2A100MED1TD

I've decided to add source selection to my design, so I managed to find some 5V relays that have a 1A current rating. I'm just hoping the 2.5A 5V power supply has enough juice to activate them.

Omron 5V 1A - G6K-2P DC5
 
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Despite its hideous appearance my breadboard design actually works! And it sounds really good so far. I don't have golden ears, mind you, but I'm just thrilled with the sound and the performance. No obvious hiss or distortion (will do more testing once I have it soldered up and not so dangerous), and the PGA2311 puts out enough power to power my (easy to drive) V-Moda M100's. The Bluetooth control over the PGA is amazingly fast, I was worried I'd have to rate-limit the Serial data but seems like I won't have to. And with the zero crossing pin pulled high I don't hear any clicks or pops when changing volume, even very quickly.

I ended up deciding to add 6 buttons to what will be the front panel (power, mute, and 4 dedicated buttons for source/output selection), and for the back panel I'll have 2 sets of inputs and outputs - one RCA and 3.5mm headset jack in, and one RCA and 3.5mm headset jack outputs. So the 4 source buttons would be Input 1, Input 2, Output 1, and Output 2. I can do all that with just 2 DPDT Omron signal relays. But the breadboard got messy because the NRF52 bluetooth chips is at 3.3V, and nearly everything else is at 5V. So I had to level shift, and use mosfets for nearly everything. I'm going to be adding some more stuff too, like a mute relay, and then try to add that TPA6120 headphone amp as well. I just hope the power supply has enough juice to power the TPA chip well enough.

These are the key parts relating to the PGA2311 that I'm using at the moment:

Power Supply:
Inductor 22uH Bourns 78F220J-RC
Ceramic Capacitor 2.2uF Murata RDER71E104K0K1H03B
Dual Rail +/- 5V Murata NMA0505SC

PGA caps:
Aluminum Capacitor 10uH Nichicon UFW2A100MED1TD
Ceramic Capacitor 0.1uH Vishay BC A104K15X7RF5TAA
and some cheap carbon film 100 ohm series resistors on the inputs and ouputs

Sounds good so far. But I need to now to solder everything up onto permaboards, and do some listening tests and see if I can detect which caps and resistors sound best.
 

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