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tda1387 dac pcb "front end"
tda1387 dac pcb "front end"
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Old 12th October 2017, 04:13 PM   #1
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
Default tda1387 dac pcb "front end"

Based on this tda1387x8 thread, I developed a bit of an affinity for the sound of the old tda1387 DAC chip. The topic of the linked thread was a standalone DAC that had eight of those chips paralleled; it also had optical or coaxial SPDIF input (and optional USB input), single-ended output, and a basic op-amp IV circuit. Some fairly simple mods (detailed in the wiki) made it go from just OK to quite engaging and enjoyable (at least to my ears).

Taking all the lessons learned from modding that DAC, and some of my personal goals, I wanted to create a basic "front end" DAC with these chips. Attached are images of what I came up with, with the following features/goals in mind:
  • I2S input: use an SBC, SPDIF receiver, XMOS, etc.
  • User-supplied power supply: be as cheap/simple or fancy as you want.
  • Adding capacitance to pin7 of the tda1387 chip was one of the biggest gains in sound quality improvement (particularly bass); this board has room for 2x 8mm pin7 caps per tda1387 chip.
  • Solder pads on the bottom of the board for up to four 10mm caps for the tda1387 chip's VDD supply (pin5); this allows tda1387 chips to be "stacked", boosting current output (e.g. this could be made into a headphone amp).
  • Uses a logic inverter chip (74HC86) to optionally invert the I2s DATA signal to half the tda1387 chips. This allows for balanced output. Note this is optional, a jumper setting allows the user to select single-ended output mode (i.e. don't invert the data).
  • Has jumper pins for user-selectable simple passive I/V, or direct current-output for a custom I/V scheme.

I think this is pretty flexible: you could get up and running quickly with only one tda1387 chip and passive IV; or you could go crazy and max out all the caps, stack multiple tda1387 chips, and implement the fanciest IV scheme you can imagine. Or anything in-between!

Also, the package and pinout for the tda1543 is the same as the tda1387. I see no reason why this board couldn't be used for the tda1543 as well. Edit: this is incorrect, the package sizes for tda1543 and tda1387 are different.

Note: I only just now rendered the gerber files, and looking at the bottom of the board, I see the big pin5 cap footprints interfere with the little pin5 SMD caps. Should be easy enough to fix.

Happy to hear any comments, critiques, suggestions.
Attached Images
File Type: jpg schem-20171011.jpg (468.6 KB, 82 views)
File Type: png board-20171011.png (163.4 KB, 78 views)
File Type: jpg pcb_front-20171012.jpg (285.1 KB, 76 views)
File Type: jpg pcb_back-20171012.jpg (150.8 KB, 73 views)

Last edited by matt_garman; 13th October 2017 at 10:14 PM.
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Old 13th October 2017, 01:22 AM   #2
abraxalito is offline abraxalito  United Kingdom
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Hope this isn't too much of a 'fly in the ointment' but the SMT package of TDA1543 is rather different (SO16 wide) from that of TDA1387 (SO8). As a result I reckon it would be very tricky to try to fit them here. The pin orderings and positions are the same though, not that that's too much consolation.
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Old 13th October 2017, 10:12 PM   #3
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
Quote:
Originally Posted by abraxalito View Post
Hope this isn't too much of a 'fly in the ointment' but the SMT package of TDA1543 is rather different (SO16 wide) from that of TDA1387 (SO8). As a result I reckon it would be very tricky to try to fit them here. The pin orderings and positions are the same though, not that that's too much consolation.
D'oh, I just saw that the pinouts were the same, and didn't realize that the package size was different. No matter though, tda1543 compatibility wasn't an explicit design goal---I just (wrongly) assumed it was a useful side-effect.

Although I suppose an enterprising individual could get creative with little jumper wires and the soldering iron and make it work. That person ain't me!
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Old 14th October 2017, 02:29 AM   #4
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
In hindsight, perhaps designing this for tda1543 from the start would have been the smarter move. It would be much easier to fit the tda1387 into the tda1543 footprint, rather than the other way around. All think about doing that, as I'm working on learning KiCAD (in place of Eagle), and that would be a good exercise. Available time will be the main factor though.

At any rate, here's the latest and greatest. Passes all automatic checks, and I don't see any obvious errors. Thinking of submitting to the fab house.
Attached Images
File Type: jpg schem-20171013.jpg (468.6 KB, 25 views)
File Type: png board-20171013.png (166.2 KB, 7 views)
File Type: png tda1387_gerber_front-20171013.png (525.4 KB, 7 views)
File Type: png tda1387_gerber_back-20171013.png (356.0 KB, 7 views)
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Old 14th October 2017, 02:35 AM   #5
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
FYI, here are some useful diyAudio links on the tda1387 chip, for anyone who might be interested:

TDA1387 x8 DAC: let's check its design, mod it -or not-, play music -or not! -

TDA1387 X8 NOS DAC (Wiki)

TDA1387 continuous calibration dac

Improving passive I/V for Pi dac 8 x TDA1387
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