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lingDAC - cost effective RBCD multibit DAC design
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Old 18th July 2019, 12:38 PM   #451
laserscrape is offline laserscrape
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The LED was blown actually but seemed to still work, after replacing nothing changed aside from it being illuminated. There is 4.3V after the LED.
I forgot to mention I am using BC327 instead 807, I thought this was through hole equivalent of 807 but it has higher gain bandwidth product, shouldnt matter right?
Also bought ''16'' variant of the transistor with hFE from 100-250 by mistake when the ''40'' 250-600 variant is specified in V2 BOM, again dont think this should matter.
This is the Ling I/V from the link in the first post, not the V2 version, so only 1 LED.

You were offering sets of kits at one point, not sure if that offer is still open, but I guess you weren't intending to gain anything from that, only to make it easier and cheaper for others to build them?
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Old 18th July 2019, 12:53 PM   #452
abraxalito is offline abraxalito  United Kingdom
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With a 6V supply there should be about 4V on the LED if its an amber/yellow one (around 2V) - 4.3V sounds a bit too high as then the DAC's output pin is held too high. The DAC chip itself needs to run at 6V - check that its output pin isn't higher than 4.6V.


The transistors you're using seem fine.


I still have a few kits left of the original PhiDAC design. My aim of selling kits has been to encourage DIYers to build DACs themselves and make them as presents to give to others around them. This way word gets spread and also enjoyable sound is shared more widely. Once I've worked out all the fine details of the new parallel DAC design I may well do kits again to get that more widely shared.
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Old 18th July 2019, 01:29 PM   #453
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There is 4.8V on the DAC output.


I would be interested in a PhiDAC kit, and parallel kit if you decide to do it.
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Old 18th July 2019, 01:41 PM   #454
abraxalito is offline abraxalito  United Kingdom
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4.8V is outside the compliance range of the DAC, it really needs to be lower. R15 (62R) can be raised in value to get this voltage down to 4.5V - try changing it to 330R.

If you'd just like a single PhiDAC kit then try contacting those who bought packs of 10 kits to see if they've got a spare one to sell. If you're not in a hurry though I'd wait for the parallel DAC kit (I plan to call it 'DeNa DAC') to show up. Its BOM cost is going to be significantly higher than PhiDAC (for a start it'll have two PCBs at least) but for a DAC it'll still be very cheap.
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Old 18th July 2019, 02:12 PM   #455
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yeah, that got it down to 4.5V. Seems to be working ok AFAICT, only there isnt the expected 3.9V on the output of the I/V.

I'll wait then, looking forward to hearing what a proper attempt at paralleling can do.
In theory, would this offer very low noise floor, rivalling that of the modern Sabre DACs?
Really the Sabre DACs need to operate in mono mode with all 8 outputs in parallel to achieve their advertised figures.
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Old 18th July 2019, 02:28 PM   #456
abraxalito is offline abraxalito  United Kingdom
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The 3.9V figure I mentioned was because I made the assumption you were building the v2 lingDAC. For the v1 lingDAC it will be lower - I reckon it should be about 2.3V. The v1 lingDAC used more than one DAC chip (four I think) so if you're only using one that's another reason for a difference.

No, the noise floor won't get anywhere near that for the latest ESS chips. In theory the noise goes down by 3dB for doubling of the number of chips but eventually the noise gets limited by the fact of only accepting 16bits - if the recording's correctly dithered this sets the lower limit around -93dB. Driving an array of paralleled DACs can get to better than 16bit performance but it'll need an MCU to direct the different I2S streams to the various DACs - that'll probably come on a later generation 'DeNa DAC'
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Old 18th July 2019, 03:29 PM   #457
laserscrape is offline laserscrape
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Had to recheck that, it turns out it is the V2 i/v, the one linked in the first post.

This was labeled as V2 (...'2V') and looked more complex which threw me off, obviously it predates the real V2.


I have seen the DAC array mentioned before, not sure anyone has actually attempted it?
Might be because of how rare/expensive most of NOS chips have become.
At that stage seperate L+R channel data would be an ''easy'' addition to the design.
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Old 22nd July 2019, 08:56 PM   #458
matt_garman is offline matt_garman  United States
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lingDAC - cost effective RBCD multibit DAC design
Quote:
Originally Posted by laserscrape View Post
I would be interested in a PhiDAC kit, and parallel kit if you decide to do it.
I have five PhiDAC kits available! The kit is free, you just pay for shipping.

I believe I mentioned above that I was out of kits. That was the case. However, someone originally contacted me for five kits, to further re-distribute in his country. But it's been a month since I've heard from him, and I never received his shipping details. So I'm putting the kits back up for grabs.
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Old 23rd July 2019, 10:00 PM   #459
hollowman is offline hollowman  United States
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Default Counter-proposal

Quote:
Originally Posted by matt_garman View Post
I have five PhiDAC kits available! The kit is free, you just pay for shipping.
How about braxy cover ALL costs and add a couple of bucks on top for the COURTESY of a favorable review?
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Old 25th July 2019, 02:13 AM   #460
abraxalito is offline abraxalito  United Kingdom
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Default Paralled DAC progress...

The PCBs came in at the beginning of the week and I've been hunched over my soldering iron for a few hours building some up. Initially I decided to build a stack of 4 boards but that turned out to be way too ambitious to do in one leap, without prior testing of the individual PCBs. When I first powered up the 4 board stack it sounded terrible - noisy. Which means some of the DAC chips had failed, so I had to take it apart again to see which. Lesson learned - some leaps are just too great to make!

I was curious to find out if it was something I'm doing in the circuit which was causing chips to fail or if they were suspect even before I plugged them in. As I haven't figured out a way to test a chip out of circuit yet I decided to put them down on the PCB but only solder the two power pins - mainly to simplify extraction if they're proven to fail. With power on, pin7 is the experience-proven way to check if they're OK - the voltage on this pin is supposed to be 1/6th of the supply voltage (so 1V when 6V is used to power them). It turns out that it varies a little bit. maybe 10mV either way but is fairly predictable on a working DAC. But non-working DACs give voltages far away from this - from a few hundred mV up to 5V or so.

So far, having soldered in 216 DAC chips I've found about 9 to have failed. What's odd is that I can't remember prior to this having found a single dud out of the tube, though I've blown up more than one in-circuit. Something of a mystery.
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Last edited by abraxalito; 25th July 2019 at 02:40 AM.
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