Has anyone dealt with any of the various online PCB (printed circuit board) fabrication companies? I was looking at PCB123, which seems ideally suited, as I don't want to spend a lot of money on software (they give you the software for free, but the design files can only be sent to them, not exported to be used with other manufacturers--although once you place the initial order, $50 extra does get you those files).

Also with all the surface mount stuff, I'll also be looking for a place that does assembly. PCB123 does recommend a few.

I wonder who holds the record for the most 0 reply threads. I think I'm in the running. Not even a, "what you building Chris?"

Seriously, what ARE you building?

I want to try to build a simple "digital preamp", something which can take an HDMI input (PCM only), split it into 8 separate channels, and send each to a Sabre32 Reference DAC running in mono mode, then have that output to balanced, XLR jacks.

I'd be happy to get it working with only a volume control. But I found my DSP code for a Linkwitz-Riley crossover, and I think I can get it to be phase coherent (that'll stop me from defending Pioneer's global crossover--got to run some simulations first). As long as I'm including a DSP chip, if it has enough buffer memory I can do time-alignment without any big deal. Plus at that point individual channel trims are almost free.

I've been reading design guides for these new, heavily integrated chips, and they actually seem easier to design with than the old ICs I used to play with in my teens (because everything is handled for you). Other than the sheer pin-count, and the fact that everything is surface-mount these days (both of which increase the difficulty of PCB design), I don't think it'll really be that hard.

In fact, if you didn't want volume control, and single-ended (unbalanced) outputs were good enough, you could actually connect a Silicon Image HDMI receiver directly to 4, stereo Sabre32 DACs, and just power the thing up without too many extra pieces.

Nice project. How much will that run you?

The chips are actually pretty cheap (e.g. $50 each for the DACs). Looks like the PCB fab will run about $160/board for a 4-layer design.

I guess it all adds up, but less than $1000 for the full DSP version, and probably about $750 for the volume control only.

Chris, i can ask a few people, i don't know if i will be able to come up with anything for you. But i can try.

I was going to ask what you were building, but was afraid I wouldn't understand what it was....

I found someone who is custom building DA boards using the DAC I want: http://www.twistedpearaudio.com/digital/buffalo.aspx (The I2S input is the format HDMI receiver chips for output of their audio streams.)

Their I/V (current to voltage) line stage also looks really nice:
http://www.twistedpearaudio.com/linestages/ivy.aspx

So who would be interested in a receiver with only HDMI inputs, no analog, no S/PDIF; PCM only, no Dolby or DTS, but up to 24-bit/192kHz; 16 channels of balanced, XLR outputs, no RCA?

It'll use a home-brew algorithms to turn up to a 7.1 channels into, rear, heights, wides, etc., along with multiple independent sub outs. In any combination you want. Say Charles wants to run 16 EP800s and nothing else, fine. Want Left, Right, Center, Left Surround, Right Surround, Left Rear, Right Rear, Left Wide, Right Wide, Left Height, Right Height, 4 Subs, and a ButtKicker, it'll do that too.

I've just about finished the DAC board schematic, it looks good. Picked top quality parts. You know the stereo output on the Oppo Special Edition? I'm using one of those DACs in mono, differential mode for each channel. Along with a pair of opamps designed to handle ultrasound imaging, or even radar. Giving it a dynamic range of 135 dB, with -120 dB of THD, virtually noise-free (especially into a balanced input). The problem is the DAC board itself already has a $500 bill of materials. That's not really bad for 16 channels, but that doesn't include the DSP board (I'm not sure how much horsepower I'll need yet for all these channels @192kHz), the power supply(ies), or the HDMI interface.

I'm trying to avoid having to license code from the big boys, because for a small run of electronics that'll be a huge percentage of the cost. I am afraid I'll run afoul of patents, even if I figure out the channel processing on my own.

Anyway, that's an update. I'll probably have all the DAC parts narrowed down soon (need to find an I2C repeater which will allow me to address multiple slaves which would normally all answer on the same address). I probably won't do much of the PCB layout myself. I found a company who will look over designs, give implementation ideas, design the PCB, and send it to manufacture. I have to pay them for the work, but that's the same as hiring someone at a company to do this job, but I only have to pay them once.

EDIT: Found the solution to the I2C problem: http://ics.nxp.com/products/i2chubs/
"Addressing selected devices if there are multiple devices in the system with the same I2C address"