Preamp & DAC project

[QRikard]

Hi

First i think it's proper for a short introduction of me and the reason for this project. I'm studying for a masters in electrical engineering, most of the courses has been towards the analog domain, none towards digital hardware. Before now that is, this is for a project course and the goal of the course is to make a system with both digital and analog electronics and some programming.

My suggestion was to build a preamp with a DAC included, the plan is to have both a analog input (no AD conversion), a spdif input and a single stereo output, maybe a headphone output if time allows. The plan is to keep things simple without compromising to much in quality.

The project will get some funding from the school and the rest from my pocket. So the component cost should not be to high, around 150$ give or take. My current system is not worth mentioning but it will be upgraded if/when i get some cash, thats where and when the preamp comes in...

The final PCB will be ordered from china so multilayer is possible. When it comes to soldering the equipment at school is good, SMD is preferred. But i would like to avoid things like ballpoint packages if possible, as long as the components have legs i should manage


Requirements:
uC for controlling various buttons and functions, it should also be able to do some signal processing. An idea for a future project to measure a speaker and make software compensation and filtering. The plan was to use the uC for decoding the spdif signal as well.
I don't have any real experience with uCs so one with pre-made drivers and large forum support is preferable (planning on C programming). I'm taking a course with AVR butterfly atm. but i have been looking towards blackfin as well for the uClinux support. The volume and other settings should be kept if the power is lost so a non-volatile memory is required.

Remote control for volume control, source selection and similar.

Analog and spdif input, single analog output. Volume control for both the digital and analog signal.

The supply will probably be a toroid transformer and then separate regulators for the different parts.


What i need help with now is mostly the component selection. There is a huge amount of information on this forum alone, i have gone trough some but far from all.

uC:
Here i need lots of help since i don't know where to start

DAC:
CS4398 and AD1853 seems to be popular and fairly easy to implement which is preferable. Are there any more similar chips that should be considered?

Opamp:
Maybe OPA132UA? I have read a few of the post in the opamp thread by Andrea: and this came up early and its both cheap and available
http://www.diyaudio.com/forums/showthread.php?t=154106

Volume control:
The teacher suggested PGA2310, this will make it easy to control the volume with remote control but some solution for the analog turn wheel is needed instead.

Modular design:
Yes please. If it is possible without to much extra work the plan is to make the design modular to simplify for future projects. Or if someone else would like to play with the design.


I hope someone has the time to read all of this and leave some constructive comments.
Best regards // Rikard

[Mooly]

For a good PIC based remote volume (motorised pot) and comprehensise programming options this is excellent,
FPRC5RX - DIY learning IR decoder

You can't beat a good ALPS pot for quality IMO as against an electronic option.
Source switching... my prefered option is discrete FET's as close to the inputs as possible... possibly with a buffer stage before.

[analog_sa]

Originally Posted by QRikard

The plan was to use the uC for decoding the spdif signal as well.

[Mooly]

It's quite an ambitious project... as a lot of things come into play. I am thinking physical layout, grounding etc... all have to be done right for it to be a top performer.

My programming skills aren't up too much I'm afraid Wouldn't know where to begin trying to decode SPDIF from scratch.

A modular approach is good though ... have done that before now.

[skumi]

Instead, the OPA132 is OPA2132 should keep doing? Personally, with 2132, which, OPA134 or OPA2134 I literally could not look, feel a big difference.

Or like MUSILAND SVDAC05 AND MD10
OP275 and matching the CS4398 seems to be doing fine with it.

I think this sounds fine, but the CS4398, RMAA when DYMAMIC RANGE, SNR measurements have not personally come to ingratiate WOLFSON, or TI D / A CONVERTER that will be used.

But CIRRUS LOGIC D / A converters are positive, negative differential consideration to the operation of the circuit impedance matched to the reference circuit has a data sheet. As part as the value of the specification to obtain and to have made a good enough measure of CS4398 are confident the results will come.

[xTr3Me]

hi QRikard ,

this sounds quite interesting. from my experience i can tell:

the pga2310 is quite good for preamps, the cs4398 can sound excellent (my gigaworks has it)

concerning the pga u might have a look at this page: krishu.de » LSQR2: Digital gesteuerter analoger Vorverstärker 2.0
it is german but maybe you can make some use out of the boardlayouts/pictures

i dont know if this is a help since i cant "develope" such things myself, i only build what i can get and then see if its good or not :P

[jstang]

I built a dual mono block amp and pre-amp while in school... still have them 25+ years later.....

jk

[QRikard]

Mooly:
Thanks for the link, will go trough that mote in detail later. I have a hard time to decide about the pot, personally i was planing to go for a normal rotary potentiometer. But then the remote control came along which makes things more complicated, so im intrested in all options available.

I have done a few PCBs before, sure none of this magnitude and complexity. But I'm actually looking forward to this part, i think its fun to lay the puzzle even if it will take a lot of time since im a perfectionist when it comes to these things. If required i can get help from my teachers because they have more practical and theoretical experience in this area.

We will see about the spdif, i have been looking at the CS8416 which could work as a backup solution. But from my understanding the spdif signal is fairly simple to decode, one main problem seems to be timing.

xTr3Me:
CS4398 has the upper hand at the moment, i will have to look into this further to get impedance matching and a good opamp.
My german is terrible or worse :P but google translate made things a lot easier. The schematics are good, will probably take a closer look tonight.

My main fear of this project is the programming and uC interface, this is also one of the main reasons for this project.

[QRikard]

skumi:
I have taken a look at OPA132 and OPA134, to me they look really similar so which one is recommended? The OPA134 is slightly cheaper but not much, and i might use the dual package depending on layout but that will be decided later.

The SVDAC05 and MD10 looks really nice, the more projects i find the more popular the CS4398 seems to be. Is there any advantage of using OP275 compared to OPA132/4?

jstang:
I have also recently made a dual mono block class AB amp (2*40W). Its not 100% complete yet, some soldering, measurements and report writing left. It sounds pretty good, but there is a soft whistle in the higher frequency range (only heard when i placed my ear near the speaker element).
This was during a test in the lab right beside all the other electronic equipment so that might have something to do with it.


If any one have any tips for the uC and other peripherals that would be highly appreciated.
A good solution for a volume control would also be great, motorized pot sounds best so far. What im afraid of with this solution is the final sound quality, but i need a solution that can be controlled with a turn knob and remote control.

Thanks for all the tips so far // Rikard

[xTr3Me]

CS4398 has the upper hand at the moment, i will have to look into this further to get impedance matching and a good opamp.

Maybe you should try some line trannies first. they sound better than opamps to me and also to a lot of other people in this thread: gigaworks dac

that might be interesting, i dont want to tell you what to do but that might be an idea

greetings,
chris