Return-to-zero shift register FIRDAC

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pgour

Member
Joined 2003
I used hot air and a lot of gel flux.
The transistor flipped with a little help of tweezers and re-soldered correctly at the same time.
The output relays are armed.
I'll post the new voltage measurements tomorrow.
Also I'll continue the test procedure hoping for some sound on the outputs.
Thanks for helping.
 
NickKUK

NickKUK

Member
Joined 2019
MarcelvdG said:
Chip Quik was the brand name of the special low-temperature solder meant for desoldering. Mind you, they also have other products, including solder meant for soldering heat-sensitive components.
Click to expand...

Yes, they have quite a range - including Bismuth (although joints can become brittle). I used TS391SNL - a lead free Sn96.5/Ag3/Cu0.5 blend with T4 sized solder balls and pretty much a water soluble wipe clean flux. I would still have a fume extractor running.
 
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Cestrian

Member
Joined 2005
I have to say I was looking at this as an incremental research project but now I'm at the point of "throw it into a box and call it done"! (it's that good and much better than expected) Which in my case is where I spend loads of time, effort and money making it permanent and looking good. I do have a "box" to throw it into... was a previous project that is based on Schaeffer panels and wine bottle stoppers. :) I will post photos tomorrow.
 
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pgour

Member
Joined 2003
Well, it works, without any major fault from my building skills.
After some fiddling with the USB interface, I have beautiful sound coming out from both channels.
Soon to be converted to Ethernet input after finishing the DSDit II board, (another challenge for me definitely).
I am excited with the sound of it, DSD Valve DAC will have a hard time comparing with it, for sure, but I leave that for later.
A small issue I face is that the Right channel's output is phase inverted and I cannot see why.
Did anybody had a similar issue?
Great respect to the designer and a thank you to the organiser of the GB.
-Periklis

DAC3-pgour I2SUSB.jpg
 
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pgour

Member
Joined 2003
The input is DSD-R, L, BCK signal, from I2SoverUSB v.III card from JLsounds, same behavior with I2SoverUSB v.II, (both XMOS chip equipped).
I have not any Amanero available to check with.
Please note that only one channel's phase is inverted. (I have concluded that it is the Right channel but I'll investigate it further tonight).
Anyway I have connected the wires reversed pin2<->pin3 on the XLR socket and OutpN to the RCA center pin on the Right channel for now.
This way the problem is bypassed for now, the absolute phase remains to be checked but it is more important to find why this happens.


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pgour

Member
Joined 2003
If with your question about the input you mean where the signal inverts, I can't see any point of possible inversion and this is the reason I am asking. But you are right, I should disassemble the DAC PCB from the Filter PCB and trace the signal, before this I am asking for some guidance for suspect points, if any. Thanks for answering.
 
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atohmdiy

Member
Joined 2019
MarcelvdG said:
Do you use hot air or a classical soldering iron? Desoldering with hot air and tweezers is straightforward once you have figured out how much you have to heat up the dual transistor and its surroundings.

It's not so straightforward with a soldering iron, but there is some trick with special low-temperature solder. I never used it, but @acg did on the valve DAC thread. If I remember well, he managed to desolder 80 pin SMD connectors with it.

As these dual transistors have only six pins, maybe you can heat all pins up simultaneously with a soldering iron and some improvized metal heat spreader. I don't know, I never tried.
Click to expand...

Well i can definitively confirm you can heat up with one soldering iron and some flux by quickly moving the iron each side. I manage to screw up my build by putting a lot of these 6 pin IC in the wrong side. I desolder some of them with two irons too. It's fine now, but i hope i don't damage anything.

Except that i nearly finish my build, i am waiting for the last parts. In the X-Altra phono preamp i am also building, there is a discussion about this website : https://www.lcsc.com

They have some in stock some parts i am waiting for, including the opa1678.

I make some progress with my interface board, but before finishing it i want to make a comparison of the fpga modulator and the dsd'it ak4137 board i am also building.
 
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pgour

Member
Joined 2003
I am struggling with another issue which I cannot solve, so asking again for some help.
I have 2.5dbV difference between the channels. The channel with the lower output has also a small amount of 2nd harmonic, the other is clean down to -100db.
Input signal: 1000Hz, -3dbFs
Output 1: -5,75dbV
Output 2: -3.24dbV
I have traced the signal back to U12,U5 with similar results
 
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pgour

Member
Joined 2003
I have indeed checked everything, for connectivity, short circuit and the values.
But you know, sometimes it is in front of your eyes but you can't see it.
As for the distortion classification even or odd I am not quite sure because during the last tests I am using a handheld Neutrik Minilyzer which has not the proper screen resolution. Still, I can hook it at the output and get some instant measurements easily.
Some days back I used ARTA but I have done so many tries back and forth tracing the error that I am not sure any more.
I have to do it again.
From memory I can say that it is 2nd harmonic and since it is a balanced circuit that could not happen, so I predict that the fault channel is that with the small distortion and the lower output.
-Periklis
 
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