So, next up is a headphone amplifier (AmpTwo) and a bluetooth interface (BlueOne - if you couldn't guess).
Headphone amplifier is pretty basic, I can get dual stereo out of one of the audio connectors of the ADAU1966 DAC, might as well make the headphone amp a dual stereo design. Component placement is 90% there, need to route the PCB, so I am sure the component placement will shortly end up as 100% incomplete again!
The next thing I would like to play with is aptX bluetooth. Now the only module I can currently find that is easy to use, and I have used before, is the Blue Creations BC127-aptX module. However these are not cheap to buy, stupidly expensive in fact. I will see if I can spin up a small (maybe 5x5) PCB to hold one of these as it would be nice to play with some wireless audio. And if it's not viable/too expensive, I can always design something else in the future.
Another set of (untested) design files are up on GitHub, this time for a 4 channel class D amplifier. I have chosen ST chips to play with (TDA7498 or TDA7492 series).
Designed to plug into the output of the ADAU1966 DAC PCB.
Decided I wanted some snazzier names for projects, so have just gone with something basic, so the ADAU1966 dac will become DACOne, if I make an AK4490 DAC which I have been planning this would be DACTwo and so on. Not the most exciting thing in the universe but it seems functional
Have PCBs on order for AmpOne and CoreOne, say they are "in production" at the moment. Did try and get some free samples of parts from ST but they declined which I thought was a bit mean...
So some new design files are up on GitHub. I have only just ordered these today so they are untested at the moment. I am sure there are plenty of errors I will find!
This will hopefully become a very useful microcontroller and DSP combination board. It is designed with SPDIF, I2S, USB, Ethernet, I2C, SPI interfaces, Not sure on the USB/Ethernet as the PCBs are not impedance controlled, although I have designed them to meet the impedance needed for USB and Ethernet traces.
Assuming the PCBs work and talk with the XMOS dev tools there will be a lot of software work to do. Interesting times ahead....
Well that's what my Rotel amp is doing out of one of the six channels. Having stripped it down the power switch fell off it's PCB, and the channel crackling was the one closest to the power switch. Here's hoping that's an easy fix, although I think a good general service is in order having gone to all this effort so far.
Why is this relevant? Well it will power my home built speakers which are now up and running (or were up and running until the amp gave up). The current active crossovers are a couple of 2x4 MiniDSP units. Now these are nice units, easy and simple to use and the Analog Devices chips inside always sound good anyway, but I feel the system is lacking a box full of OHDSP boards in their place.
The box is almost ready, just waiting for these ADC boards that have been on hold for a while. A Farnell order is due with many parts for many projects so I will finally get the resistors I am missing, and I will finally have somewhere I can work on these more sensibly than before. Now I just need to sort through the mess of "neatly" packed electronics I did when I moved...
Stay tuned for more to come!
for anyone who is following this, or stumbled on this site and wondering what is going on, well you are not alone, I can't work it out sometimes either!
Some intolerable neighbours (3 sets in fact, after a few years of trouble free renting so I am sure it's not me) have forced a house move. This is not a bad thing, I now have quite a bit of space, which means I can set up a decent work area to work on this project.
My homebuilt speakers are almost back together and looking rather smart, just hoping a system of my OHDSP boards can make them sound alright!
These two incidents (speakers and moving) are coindicing very well, as I can now use my speakers with the digital crossover box I threw together. However I am still short of 10Kohm MELF resistors to finish the balanced ADC as I did not get around to placing a farnell order I had put together, but this will not stop me!
Nothing can stop me now!
Still working on this slowly at the moment, other things have had to take priority. Only a temporary set back though.
Have been building up the balanced input ADC boards I received when I found I have run out of 10k MELF0204 resistors, I also do not need to order anything else at the moment, which makes a £3 order from farnell a little pointless (and the shipping would cost more!)
I am working on some new ideas now. Looking to make the "boards" more obvious and user friendly with documentation (and simple things like catchy names, hardware tweaks to interfaces/layouts and so on). Working on a new micro-controller board, packed with features, which could be quite flexible/powerful. Would like to get a better website up as well, as we head into autumn/winter the darker evenings will end up being the time for this.
My Frankenstein clone is alive! Well, okay, I admit that is not true, but the picture on the homepage, and the full picture in the last blog post show a half finished box with some of my boards in partly wired. Well it is now 75% complete, awaiting a populated balanced ADC board (in place of the single ended one), but it works from a SPDIF source. All 8 outputs play music (set as four stereo outputs).
Bit dark to take pictures but just imagine the last picture with a few more boring wires added.
Edit: Oh yes, I am also looking at spinning up an XMOS 200 based DSP/control board, should sit nicely along with the ADAU1452. Would give the option for some DSP/usb streaming without the need for the ADAU1452 board. Looks like there would be some initial limitations (such as the xmos I2S code only supporting 48k in TDM mode, and my rusty programming skills), but the potential for a lot of features could be big.
Just a little update, project is on a go-slow for the next couple of months whilst I deal with some none project related things. Hoping to order PCBs for new revisions sometime in August or September. Might change the DSP board for small vias on the ADAU145x and buy my self a toaster oven and fit it with a controller to do reflow on this just to make life easy.
I have been building up my speaker crossovers, well the first version using hardware I have designed:
Work in progress but the boards work. All 3 DSP boards where I hand soldered the LFCSP chip seem fine. No idea on long term reliability yet but hoping to use the above box to do some testing for this (i.e. just leaving it on a lot).
So I released new board revisions over the past few days, I have done my best initial check on these but I have not yet ordered them to build up. Even if I had ordered them I would still correct any mistakes in new revisions so the files might as well be public.
I am also working on a differential version of the PCM4202 ADC board, I did have a revision 1.0 design but I am not happy with it and so decided to rework this. It should be a more versatile solution than the single ended version and have a better PCB layout.
I also came across Orange Pi SBCs which look very neat with the AllWinner H3 SoC onboard all of them. Early 2015 I had started designing an ADAU1452 Raspberry Pi hat type board, unfinished designs still available at github.com/pwzj/ohdsp.
I stopped working on this as the Pi only support I2S in stereo with no TDM, limiting what I wanted to do with it. The AllWinner H3 SoC datasheet specifies support for all the normal I2S/left and right justified/TDM modes on the audio data lines and so this may work for my original idea. I am very tempted to either spin an ADAU1452 DSP board to interface with this, or make an adapter board to hook into my current DSP design. This all depends on software/driver support for TDM mode, and I need to do a lot more research.
An electronics engineer and a long term electronics hobbyist. I like tinkering with stuff and making things.