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Grossly parallel multibit DAC adventures
Grossly parallel multibit DAC adventures
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Old 15th October 2019, 09:54 PM   #11
nautibuoy is offline nautibuoy  United Kingdom
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Originally Posted by abraxalito View Post
As I set out on the lingDAC thread, I'm not sure that a reflow approach would in fact be more efficient in time. Partly because I prefer to test the DACs first, with only power applied and partly because these chips are already desoldered and they're not mechanically consistent from part to part as fresh parts off the reel would be. They have excess solder on many pins and on the sides of the package which sometimes leads to shorts between pins. The pins are also bent out of shape in many cases so they're not all in contact with the PCB which makes me wonder if they'll be amenable to reflow.
Ah, OK. Fair enough. I didn't clock that properly before. I guess it would also ask questions about the resilience of the chips to repeated heating.

I had a look at the gerbers in a viewer - the PCBs are smaller than I imagined!
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Old 16th October 2019, 03:11 PM   #12
sgrossklass is offline sgrossklass  Germany
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AoE 3rd mentions a current input topology named a "regulated cascode", which finds use in high-bandwidth photodiode transimpedance amplifiers (up to dozens or hundreds of MHz). In this one, input voltage noise is determined by one transistor while current noise is determined by the other. Seeing your thread, maybe this would be something of use for an I/V? Transformers, while undeniably useful, are notoriously messy.
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Old 17th October 2019, 02:10 AM   #13
abraxalito is offline abraxalito  United Kingdom
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Thanks for the suggestion - in the case of active I/V I nowadays always like to have a filter between it and the DAC's output. This rather constrains I/V circuits in that they need to have a well-defined, constant input impedance (vs frequency and vs amplitude) and the lower, the better. Putting a trafo into the circuit was my solution to the conundrum of the DAC wanting a low load impedance and the I/V circuit wanting to be relatively higher input impedance.

I set out some background thinking here : How a transformer helps... | Details | Hackaday.io
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Old 18th October 2019, 03:54 AM   #14
abraxalito is offline abraxalito  United Kingdom
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In theory its possible to accommodate even more than 144 TDA1387s although I've yet to figure out a way of fitting the thicker wire on the transformer's bobbin. There has to be some way though.....
I came up with a way to get fewer turns on the transformer - add the CT later with thinner wire. Here I have 6+6 T for the primary (0.62mm) and there's enough room left for 4000T of wire for the secondary (0.05mm). This gives an impedance ratio of ~111k meaning an 11k I/V resistor on the secondary represents 0.1ohm to the DAC array. Initial listening indicates a slight improvement in LF - the price is the need for a lot more DAC chips - at least 128.
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Old 29th October 2019, 10:26 AM   #15
abraxalito is offline abraxalito  United Kingdom
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Default New set of DAC board gerbers on the way

From building up stacks of the DAC boards I found there was some very low-level hiss when listening at low digital volumes (its masked at higher volume settings). I eventually tracked this hiss down to less than perfect grounding - the groundfill is a bit too contorted to give a low enough impedance for the DACs. The remedy on the existing PCBs is to attach some 0603 0ohm links as straps to give lower ground impedance. Picture attached - I've used a couple of dozen 0 ohm links (one is 0805, all others 0603) soldered where the soldermask is scratched away with a craft knife.

A new set of PCBs with the grounding fixed will be along within a week, but if you're going to build a DAC with the gerbers I've already published you'll want to consider adding some 0 ohm straps. I didn't notice any hissing effects on a single PCB, it became apparent on a stack of 3 and gets worse with more boards added beyond that.
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Last edited by abraxalito; 29th October 2019 at 10:30 AM.
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Old 29th October 2019, 08:36 PM   #16
sajunky is offline sajunky  South Africa
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Thanks @abraxalito, looks like this project is reaching final stage. What I2S device would you recommend? I see your post here: USB->HDMI->SPDIF a waste of time?

However I would prefer modern low jitter device with asynchronous USB transfer like this one with XU-208, three premium oscilators and CPLD chip, see the post by @obscurus. He tested it working with PhiDAC, it seems compatible. If you order one for testing, it will be on my account and risk. I need at least three. If stops working, it doesn't affect payment. lingDAC - cost effective RBCD multibit DAC design

EDIT: It doesn't say about availability of drivers. This one has the same PID/VID as Amanero device: WEILIANG AUDIO Combo384 USB to I2S digital interface refer to Amanero 384kHz/32bit DSD512|amanero usb|usb to i2s|breeze audio - AliExpress - 11.11_Double 11_Singles Day

Last edited by sajunky; 29th October 2019 at 08:49 PM.
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Old 29th October 2019, 09:15 PM   #17
Markw4 is offline Markw4  United States
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Originally Posted by sajunky View Post
EDIT: It doesn't say about availability of drivers. This one has the same PID/VID as Amanero device...
IIRC, the Chinese Amanero clones work with Amanero Windows drivers, but the firmware is an old version that doesn't support ASIO or DSD. Trying to burn newer Amanero firmware will brick it. Thus, it is no better or worse than the Chinese XMOS boards. Also despite what the picture shows, many of those boards are now shipping with black plastic non-crystal clock oscillator modules. Such clocks have more jitter than appropriately selected crystal clocks.

The best USB board I have tried (out of several, including some with plug-in clock modules) is JLSounds I2SoverUSB. Sorry, it does cost more than a Chinese clone. However, it can be transferred to a new dac and used for multiple dac projects over a long period of time. Jitter is very low and it is configurable for various dac chips: I2SoverUSB - I2S over USB Audio
http://jlsounds.com/uploads/I2SoverUSB%20v.III.pdf

Last edited by Markw4; 29th October 2019 at 09:18 PM.
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Old 29th October 2019, 10:32 PM   #18
nautibuoy is offline nautibuoy  United Kingdom
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Originally Posted by Markw4 View Post
The best USB board I have tried (out of several, including some with plug-in clock modules) is JLSounds I2SoverUSB. Sorry, it does cost more than a Chinese clone. However, it can be transferred to a new dac and used for multiple dac projects over a long period of time. Jitter is very low and it is configurable for various dac chips: I2SoverUSB - I2S over USB Audio
http://jlsounds.com/uploads/I2SoverUSB%20v.III.pdf
I second that recommendation. The JLSounds board, which I use, have proven to be excellent and completely reliable. IMO they're superior to the Amanero (especially the version 3 which matches the Amanero data rates) because they have onboard isolation and reclocking. Their other stuff is good too.

I wouldn't use a Chinese Amanero clone - too many bad tales about them, apart from which they represent IPR theft.

Last edited by nautibuoy; 29th October 2019 at 10:40 PM.
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Old 30th October 2019, 12:35 AM   #19
canvas is offline canvas  Taiwan
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Also despite what the picture shows, many of those boards are now shipping with black plastic non-crystal clock oscillator modules. Such clocks have more jitter than appropriately selected crystal clocks.
I believe these are XOs from SiTime, like SiT8208 series.
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Old 30th October 2019, 02:56 AM   #20
abraxalito is offline abraxalito  United Kingdom
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Thanks @abraxalito, looks like this project is reaching final stage. What I2S device would you recommend? I see your post here: USB->HDMI->SPDIF a waste of time?
At this stage I don't have any particular recommendations to make - the guy in that link wanted an interface for his Nexus tablet and I have experience getting Android phones working with those simple, cheap first generation USB chips.

The I2S (and S/PDIF) source I use from my PC is based on CMedia CM6631A. Its async but has an annoying feature that after the PC has hibernated, the S/PDIF output stops working and it needs to be power cycled to function again.

CM6631A???? USB?I2S/SPDIF?????32/24Bit 192K??DAC-???

(Note this one is an updated model, mine is a bit long in the tooth now).
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