I must have missed it if you mentioned this before. What revisions do you have in mind? I recently spent some time testing your first generation hat against Allo Boss and Piano 2.1. I actually stripped my stack down to the basics for the test, so no isolator or recllocker, and just a single good linear power supply. Your DAC won hands-down. In fact, I was rather shocked at how two-dimensional the Allo units sounded in comparison, since they are popular products and generally well-liked. Anyway, I am looking forward to seeing what you do next.
Hi stellarelephant! Which linear PSU did you use in your test? And was that one supply for both the RPI and the DAC, or separate PSUs? That's pretty flattering to say you like my simplistic tda1387 over the Allo Boss and Piano! I don't have a Piano, but I do have a Boss. I've always had similar feelings, but just assumed that was my "baby bias" at play!
The next revision (v1.6) to the single-ended RPI HAT DAC deals with power to the I/V transistor. Previously I used a TL431, which is adjustable, and allowed some choice in transistor selection. Now instead I'm using a MAX6071 precision voltage reference. This outputs a fixed 2.5v, so choice of I/V transistor is now limited. I specified the Toshiba SSM3J327R.
I conceived of this back in September, got the boards made, but that J327 MOSFET has been out of stock forever. Another friendly forum member found some and ordered a bulk batch, and gave me some. So now I have the parts, but I haven't had a moment to actually make sure it works (holidays, work stuff, kids' activities, etc). What little diyAudio time I've had has been giving to building Paul Carmody's Isetta for my wife, and even that's not finished!
The next revision (v1.6) to the single-ended RPI HAT DAC deals with power to the I/V transistor. Previously I used a TL431, which is adjustable, and allowed some choice in transistor selection. Now instead I'm using a MAX6071 precision voltage reference. This outputs a fixed 2.5v, so choice of I/V transistor is now limited. I specified the Toshiba SSM3J327R.
I conceived of this back in September, got the boards made, but that J327 MOSFET has been out of stock forever. Another friendly forum member found some and ordered a bulk batch, and gave me some. So now I have the parts, but I haven't had a moment to actually make sure it works (holidays, work stuff, kids' activities, etc). What little diyAudio time I've had has been giving to building Paul Carmody's Isetta for my wife, and even that's not finished!
I am currently using a single PSU to power both RPi and DAC. It is Greg Stewart's "budget wonder" creation, using two of his modified 12V Jameco supplies and one of these The Wire dual quad LT3042 regulator boards, which has two 1A rails set up in parallel for 2A capability. It gets a little hot (I need to add heat sinks) but it seems to handle the load OK. Speaking of which, do you know the current draw of the original single-ended hat? I assume it is in the 100-200mA range.
Thanks for an explanation of your updates on the DAC.
I have a Carmody Sprite...the Isetta you are building looks like a bass monster boombox! I wish my wife would ask me to build her some speakers...
Thanks for an explanation of your updates on the DAC.
I have a Carmody Sprite...the Isetta you are building looks like a bass monster boombox! I wish my wife would ask me to build her some speakers...
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To be clear, she didn't really ask me to build her the speaker. She wanted to buy one of those bluetooth speakers. As a dedicated diyAudio enthusiast, how could I stand by while my family spends money on and listens to an off-the-shelf speaker, that I assume either sounds awful and/or costs too much (or both)? So I politely asked (she might use the word insisted) if I could DIY a wireless speaker for her instead of spending money on something I just knew would be dubious.
She wanted to buy one of those bluetooth speakers. As a dedicated diyAudio enthusiast, how could I stand by while my family spends money on and listens to an off-the-shelf speaker, that I assume either sounds awful and/or costs too much (or both)? So I politely asked (she might use the word insisted) if I could DIY a wireless speaker for her instead of spending money on something I just knew would be dubious. To be clear, she didn't really ask me to build her the speaker.
That's precisely what I would have done!
In fact, I'm considering building one for my youngest daughter, essentially for the same reasons.
Cheers,
Gable
It probably passed unnoticed at the end of a thread page, but in post #380 I added a list of DAC design/gerber files shared in this thread, if you think it can be of any value to add in the first post, in newest to oldest order.
I was also asking if you know of for Z-out and VRMS formulas so I can calculate those depending on the designs above using different number of chips.
Lastly, and very off-topic, I'd love to know where you guys get your boards fab'ed. I'm also considering DIY etching.
Thank you!
I was also asking if you know of for Z-out and VRMS formulas so I can calculate those depending on the designs above using different number of chips.
Lastly, and very off-topic, I'd love to know where you guys get your boards fab'ed. I'm also considering DIY etching.
Thank you!
I'm considering doing this conversion myself after I decide for one of your boards(probably the 8x v2), depending on the calculations mentioned above. I will contribute back here with the modified boards if you're interested.
The idea I have is to have tracks for both sizes, but I would personally use the DIP8 socket and a SO8 to DIP8 adaptor.
The maximum output voltage swing (peak to peak) is first and foremost determined by the DAC supply voltage - for 5V supply its 3.5V and for 6V (the max recommended) its 4.5V. These translate into RMS as 1.2V and 1.6V respectively.
For 5V the peak to peak DAC current is 1mA, for 6V its 1.2mA. If you parallel DACs you simply multiply this current by the number of DACs in the stack. Given the peak to peak output voltage you want (always <= the max's above) you divide the peak to peak output voltage by the current you have and this gives you your resistor value.
A worked example - you're running 5V supply with 4 DACs. You want the max output voltage swing (3.5V p-p) and your p-p current is 4mA. Your I/V resistor is therefore 3.5/4 in kohm or 0.875. Choose the next lowest E24 value which is 820R.
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I have used OSHPark. Not the cheapest, but easy upload and quick service, plus purple boards sure do look cool.
Edit: Nevermind! Just noticed that you are in Europe!
@Matt
@Matt Not sure I "have to ask for permission" but I'm willing to contribute back to the community the conversion of the v2 board into DIP8, if you're interested. It'll serve me as well to learn how to use Kicad.
Thank you, I will have a look
Yeah, they're quite expensive TBH, but thank you for the link.
+1
I've had very good experiences with Elecrow, they're easy to use, priced right and the quality has been great.
Cheers,
Gable
Shipping to Barcelona costs me around $25. I'd rather get them from China or etch the boards myself. But thank you again!
You definitely don't need to ask for permission!
Not to discourage you, but it may be a bit tricky, mostly because having an eight-chip row of tda1387s is nearly 10cm wide. You definitely won't be able to fit eight of the much bigger tda1543 chips within 10cm. Why is 10cm important? Because, at least with Elecrow, that is the max size for their "cheap" class of PCBs. If you go over 10cm, the price jumps up really quickly. Obviously, other fab houses may have a different pricing schedule.
Also, FWIW, I've found Elecrow's shipping costs (to the USA) to vary quite a bit. I always order 10 boards from them (because it's the same cost as five), and I've paid shipping as low as $5 and as high as $15.
OHHHH you're right! (of course) Fitting 8x DIP8 of 1cm means I'd have max 1.25 per each, so a distance of 1mm between each socket and zero margin on the board edge. Not realistic... unless I go the DIY etch route and use bigger, custom size boards. I was nearly decided to go that route anyway because of shipping costs.
Another option would be to simplify and use 4x SE or 2x2x Balanced.
I hope I wasn't too pushy
I missed that one! (since the other day I was scanning the whole thread in search of zip files). Is it too much abuse asking for Gerber/Kicad files for this board? I think it's the one having most potential from yours, and it's even already tested.