looking for a partner to help with pcb design/layout on an audio-related DIY - Page 1
Forum section: electronics / projects

author: linux-works
author_rank: Super Contributor
timestamp: May 15, 2014, 02:30:25 pm
content: I've had a prototype working for well over a year now (its an audio project; preamp, switch, controller) but I only have a single hand wired proto on perf board and I'd like to have a board laid out and an initial run made for a group-buy. I'm looking at this more of a DIY buildable project and its not meant as a profit-oriented project; so targeted at folks who might want to build and 'own' (change, upgrade, etc) their own stereo systems, a component at a time.while I can do pcb layout, its not my strong point and I'd rather concentrate on other aspects of the project (firmware being the closest to my heart and skill set).what I'm looking for is someone to partner with who has designed and shipped either audio boards or RF boards. 4 layers would be more than sufficient and it would involve an onboard controller as well as onboard psu parts and the attenuator (8ch volume control chip) as well.I can give more details (and photos of what I have right now) but if you would like to work on such a project, PM me and we can discuss the details.a short term goal is to produce some demo boards, sell them (for cost) during the beta-test period and ultimately revise any changes to the final board. I plan to release the source code as well as schematic to the public; its not clear if gerbers would be released or not, but everything else would be.this is a front shot of the one proof-of-concept build I did, about a year or 2 ago. its been working and running my home audio system all that time; and so the circuit and design have proven themselves and I'd like to take it to the 'green pcb' level instead of hand wired perf boards inside.thanks in advance.

author: linux-works
author_rank: Super Contributor
timestamp: May 18, 2014, 02:03:25 am
content: here's some of the back-story, with photos, to help explain what this project is about.for audio systems that use active crossovers, you need a way to vary the volume in multiple channels simultaneously. there are not a lot of choices in the market (and very few for DIY) that offer a good quality multi-gang 'volume control' system and even fewer are open source on hardware and software/firmware. I went about designing and prototyping some building blocks to help get this idea implemented.first, a photo of a whole working system:and a general flow diagram (an early version):the photo shows 4 boxes; from top to bottom:- behringer dcx-2496 digital crossover- DIY 24/192 dual DAC- the preamp/volume control (this box, that I am discussing in this post)- a multichannel amplifierthe unique part of this configuration is that for the most part, the input is digital audio (spdif) as it comes out of a pc or a dvd/cd/bd player. the source (player) sends digital audio to the crossover (or to an spdif switch, first; the lower/left hand area of the diagram) and that may go to an EQ (also digital in and digital out) or it may go direct to the crossover. the signal can be up to 96k sample rate and if lower, the crossover upsamples to 96k for internal math. you can configure up to 3 filters typically used for highpass, bandpass and lowpass (tweeter, midbass and subwoofer).on the diagram shown, the crossover outputs 3 sets of stereo line-outs in analog format, but what can also happen is that the dcx2496 can be modified to output spdif and go into outboard DACs. that's what I'm doing and that's what one of the black 1U boxes is about; its 2 stereo dacs inside that chassis and it takes 2 of the crossover spdif outs and converts to analog.now that we're analog, we feed into a multichannel volume control. that's what this box is about and it uses the cirrus cs3318 8ch volume control chip. here is what my protoboard (nicely working, too, btw) looks like:the smd chip is mounted on a chip carrier but on the real board (the one I want help in getting designed) the chip will mount to the surface, directly. on that board is an arduino (328) chip and that's used to interface the device-specific protocol (cirrus) to something a bit easier for users to talk to - an ascii protocol that you send via the built in serial uart on the arduino. there is an opto-coupler (bottom/left) that isolates the cpu from the SPI bus and I'm using SPI to talk to the cirrus chip since its easy to use, is unidirectional and I can use the opto buffers for total isolation.the idc connectors carry L/R signals and one edge is inputs while the other is outputs. the idea is that the user can 'punch down' any input or output ('port') to any rear jack and build up any config that makes sense for him. here's a chassis view of an early build:and a later build:on the later build, I was experimenting with some input buffering (left mostly-empty board area) and post buffering (right hand area with 4 small muting relays and 8pin DIP sockets). I can discuss the need for pre and post buffering later on. on the far right/lower is the analog psu; that was a simple version but I have since gone with some TI chips instead which are much lower noise:on that same lower/right area is a set of TI eval boards that provide the dual 8v needed for the cirrus chip. this regulator chip is nearly noise-free and I would like to embed those chips on the same small board the cirrus would live on.that's some background on this project. before this solid-state multi-channel volume control project was started, I worked on a relay based attenuator and that used an lcd controller that I designed called the LCDuino:and that runs my main UI firmware that shows the volume, accepts learned IR commands from a sony (etc) handheld remote, can use rotary encoders or motor pots or buttons for front panel controls and also has a back-end web strategy for phone/tablet style remote control:and a very primitive (only a proof-of-concept) web interface:this requires a small linux pc to be serially coupled to the preamp; such as a raspberry pi or beaglebone.the LCDuino code (called volu-master) started off controlling relay attenuator modules, such as these, called the delta1 and delta2 (r2r relay atten and in/out analog selector):and so, that brings us from the first version of the volume control/preamp design (the relay stuff) up to the present where I'm now concentrating more on the 8channel analog volume control via the cirrus solid state chip (no noisy relays clacking as you vary the volume knob).the design works, the code works and the user interface is all working. what's left is to migrate the cs3318 board from perf-board to a real circuit-board.for the person who is willing to join the project and help get this board designed, I will make sure they end up with a working prototype (at the very least) for their efforts. if boards are made and sold, we would share what we make. the goal is to create a design that DIYers can easily build and get world class analog performance along with (hopefully) world-class feature set, all in a box that they can fix, modify and extend without any closed-source parts (hw or sw) getting in the way.