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tda1387 dac pcb "front end"
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Old 12th January 2019, 09:55 AM   #451
abraxalito is offline abraxalito  United Kingdom
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The 'base' (actually gate) voltage of 2.5V for J327 will work just as well for J56. A quick look at the DS shows the maximum Vth for both is -1V @1mA. Good luck with the soldering if you take the leap for J56 - remember to order the MFV package - the other one is even more of a nightmare to solder.
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Old 31st January 2019, 03:48 PM   #452
pcgab is offline pcgab  United States
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tda1387 dac pcb "front end"
Looks like Mouser has the 327's back in stock:

SSM3J327R,LF Toshiba | Mouser
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Old 31st January 2019, 05:46 PM   #453
twocents is offline twocents  South Africa
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tda1387 dac pcb "front end"
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Looks like Mouser has the 327's back in stock:
Fantastic news. Thank you for the heads-up pcgab! Ironically I received most of my components today from Mouser via a local agent, including the replacement J56's.
they are super tiny. I can probably TRY to solder them using a friend's microscope but the main problem is the solder pads on the pcb are too spaced out for those tiny legs. I think I will rather order the J327's and wait a little longer.
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Old 31st January 2019, 11:51 PM   #454
abraxalito is offline abraxalito  United Kingdom
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What I do with the J56s is solder one (or perhaps two) legs onto the pads. Then bridge the second (and/or third) pin with a 0ohm 0603 resistor to the PCB. Depending on layout the resistor could be to the gate terminal in which case can be the gate stopper R (I use 330R to 470R).
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Old 28th February 2019, 06:44 PM   #455
twocents is offline twocents  South Africa
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tda1387 dac pcb "front end"
Much too quiet around here.

Matt, on the HAT DAC v1.6 BOM there are alternatives (MELF) for R4, R9. When to use the alternatives or shall I stick with the originals? I ordered both (2k7 and 1k1).

Started with stuffing my board, only to discover I slipped up ordering R12 and R13.
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Old 2nd March 2019, 02:17 AM   #456
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
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Much too quiet around here.
Indeed, though I'm much to blame on that front. Another big hobby of mine (guitar playing) just came out of a too-long hiatus. No room left in the "real life" part of the time budget to take for guitar, and the "hobby" slice isn't too big to begin with, and now it's heavily biased towards getting my playing back to a non-embarassing state. I'm thinking my next diyAudio project(s) will likely be for guitar, either effect pedals or tube amps. But I'll still check in here, for sure, so not going away!


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Matt, on the HAT DAC v1.6 BOM there are alternatives (MELF) for R4, R9. When to use the alternatives or shall I stick with the originals? I ordered both (2k7 and 1k1).
Those are the I/V resistors. You probably want to use decent tolerance or hand-match the values, just so the left and right channels are balanced. But after that, it's more about taste, or more specifically, output power and impedance matching.

MELF resistors generally have ultra high tolerance, but they aren't necessary unless you're going for more of a "premium" build. (Well, those megabuck metal foil resistors would be the ultra-premium parts.)

The actual resistance value can also be adjusted to taste: the higher the value, the higher the output. Likewise, the lower the value, the lower the output. IIRC, 3.5k is the highest you can go given the tda1387's voltage compliance (at datasheet 5v supply anyway; if you overvolt the chip like Abraxalito likes to do, you can squeeze a bit more juice out of it).

I personally tend to use the lower values (around 1k) just because I have very modest power needs, and the lower values are simply a practical matter of giving me a more usable volume range (since I'm not using a pre-amp or active buffer).


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Started with stuffing my board, only to discover I slipped up ordering R12 and R13.
It's not a real project until it can't be finished due to missing one boring part that you thought you had on hand or forgot to order! At least that's what I tell myself, since it seems to happen on, oh, 90% of my projects!

Enjoy the build, let me know if you have any more questions! If you go too long without a response, feel free to PM me, that will trigger an email.
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Old 2nd March 2019, 07:00 PM   #457
stellarelephant is online now stellarelephant  United States
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I just received some v1.6 hat boards from Matt. Looking forward to building one up soon.
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Old 3rd March 2019, 12:53 PM   #458
twocents is offline twocents  South Africa
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tda1387 dac pcb "front end"
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I personally tend to use the lower values (around 1k) just because I have very modest power needs, and the lower values are simply a practical matter of giving me a more usable volume range (since I'm not using a pre-amp or active buffer).
Ok, thanks – I will try the original values first. I will be feeding a Aksa Lender preamp.

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The actual resistance value can also be adjusted to taste: the higher the value, the higher the output. Likewise, the lower the value, the lower the output. IIRC, 3.5k is the highest you can go given the tda1387's voltage compliance (at datasheet 5v supply anyway; if you overvolt the chip like Abraxalito likes to do, you can squeeze a bit more juice out of it).
Interesting. What are the advantages of overvolting the TDA1387 – i.e. squeezing more juice out of it – are there SQ benefits? And what voltage would the limit be?

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It's not a real project until it can't be finished due to missing one boring part that you thought you had on hand or forgot to order! At least that's what I tell myself, since it seems to happen on, oh, 90% of my projects!
Yes, I feel/experience the same. Apart from two resistors I also short some hardware stuff – things you “think” are in your parts bin, like on/off switches, output sockets, etc. Only to find you’ve used the last ones on the previous project.

Great to see you are also coming on board Stellar.
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Old 3rd March 2019, 01:09 PM   #459
abraxalito is offline abraxalito  United Kingdom
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I don't call a 6V supply for the TDA1387 'overvolting' myself, its right up against the absolute maximum but not beyond it. The advantage for me is it gives the possibility to go up to 4.5V on the DAC's output pins giving more flexibility for the I/V circuitry. The 20% extra current comes in handy too. I wouldn't say it sounds better though. Some other DIYers have gone beyond 6V...
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Old 3rd March 2019, 03:28 PM   #460
stellarelephant is online now stellarelephant  United States
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I have worked hard to make my RPi a quality I2S streamer, and auditioned many different DAC hats along the way. For a while I thought my favorite DAC might be the Audiophonics 1387 board. Nope. Once I got these simple DIY speakers set up for optimal imaging in my new listening room yesterday, there was no contest. Matt's RPi DAC v1.2 just beats everything else I have tried for realism. I would describe it as a sense of perfect focus. Approved by my 2-year-old son, too. I need to get in gear and build v1.6!
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