RTZ SDM (DSD) DAC

[Ray P]

Very tidy SMD soldering.

Cheers Nick.

Manual application of the solder paste and parts placement (using a USB microscope),then popped into a reflow oven. Underside of the board was done the same except that I used a hot-air workstation instead of the oven.

[andrew Ivimey]

I wouldn't do it - I couldn't. Tho' I did see a YouTube video where the film maker sort of washed the tiny smt components with magic fluid and then sort of sucked up the surplus 'solder' away. It looked very impressive and I'd have thought when robots take over and eliminated human beings this is what they'd do with electronics.

[Ray P]

I'm currently listening to the first RTZ Output Filter board that I've completed, using my Noir headphone amp again. The filter board is plugged into my own RTZ DAC board mentioned in the posts above.

This filter board is part of an RTZ DAC I'm putting together for Mr. T Idler. It uses the same NE5532 opamps that were used in the prototype. The output caps are Mundorf ZNs, which are too big for the PCB so I've had to install them on the underside of the PCB and had to make the leads thinner to fit through the PCB pad holes - they're secured with adhesive foam pads to offer some strain relief and I also have a cable tie temporarily supporting the caps.

Anyway, it worked straight off the workbench and is sounding very good right from the start.

Later I'll finish assembling Dave's RTZ DAC board that will go with this filter board.

The RTZ filter board was originally designed for OPA1678 opamps but they've been unobtainable for a long time but are finally coming back into stock at Mouser and I'm hoping to receive them by the end of the month so it shouldn't be too long before I build my own filter board with the OPA opamps.

[Ray P]

Should anyone be interested in having a go at this project I have a spare set of PCBs.

There's lots of info on Marcel, the designer's thread on DIY Audio https://www.diyaudio.com/community/thre ... ac.379406/.

Tony Moore of this parish has already built his own RTZ DAC project too https://www.audio-talk.co.uk/phpBB3/vie ... php?t=8633

[Thermionic Idler]

I listened to this at Owston next to the Valve DAC - you could barely get a fag paper between them. If I had to express a preference, I actually found myself slightly more taken with the sound of the RTZ, it seemed a little more 'lively' somehow.

I will start my own thread when I get the boards back from Ray, it'll probably be quite a short one as all I have to do is design a chassis, send it off to Schaeffer, provide the power supplies, lay it out and plug some PCB's together.

I am extremely grateful to Ray for putting together these boards for me, soldering all those SMD parts was just way beyond my capabilities. I can reluctantly do SOIC-8 components in a pinch (I had to for the 'Quad' linestage as the OPA series opamps I wanted to use were not available in thru hole), but anything finer than that, forget it. And it's not only the RTZ boards, there's a Beaglebone reclocker board which needed populating to send the DSD data to the DAC (the Beaglebone being the endpoint for Roon), and that is an even more microscopic hellscape.

Thank you sir, I will buy you many beers at the next Owston.

[Cressy Snr]

I'm in awe of you guys. I couldn't hope to be able to sort any of these types of project.

[Ray P]

After a bit of troubleshooting - I had to track down a fault that was stopping one channel working - I'm listening to Mr. idlers RTZ DAC and output filter combo and very nice it is sounding too.

The fault took some tracking down and it eventually turned out to simply be a short under a UFL connector where the solder hadn't completely reflowed.

Now to move onto the really difficult part of getting an isolator/reclocker input board working - as Dave said, some of the parts are truly tiny.

[Ray P]

I'm feeling quite pleased with myself - I've now assembled three RTZ PCBs, two RTZ DAC and one RTZ output filter, and the only problem has been the UFL short so I'm pleased that the soldering of all those small ICs and transistors has been 100% successful first time (so far - I've probably just given the kiss of death to the next one).

[ed]

I'm still a bit shy of smd...I've only used my rework station once and lost interest when I found it impossible to find acetate masks. I gather the situation has changed somewhat in regard to masks...but nevertheless, even tho I bought the usb microscope the deteriation in my eyes is not helping....

any chance you could take us through your method Ray?

[Ray P]

Ed, I wouldn't attempt to do something like this with a hand soldering iron, I'm fortunate in having the loan of a reflow oven and a hot-air workstation.

Step 1: Clean the PCB
Step 2: Start with the side of the PCB with the most/smallest parts and add solder paste to all the pads. I do this by hand under a USB microscope using one of these gadgets to get a lot more control than the syringe alone https://www.vtech-smt.co.uk/jbc-dpm-a-s ... -dispenser. I use this solder paste, https://www.mouser.co.uk/ProductDetail/ ... PJPg%3D%3D - it isn't too viscous, has a fairly low melting point and keeps more or less indefinetely (a lot of solder pastes 'go off'). The trick is to apply just a tiny amount of solder paste and I use a blue nozzle on the syringe as the best compromise between precision and not needing too much pressure to push the paste out.
Step 3: Place all the parts onto the pads with fine tweezers, gently pushing the parts down onto the paste. If a part is slightly askew I adjust it with a long pointed tool.
Step 4: Place it into the reflow oven, select the right heating profile and press start.
Step 5: Remove the cooled board from the reflow oven and inspect. Fix any solder bridges with wick and an ron.

The RTZ DAC PCB also has parts on the underside of the board as well. For that I just replace step 4 with the use of my hot-air workstation - that keeps a lot of the heat from the topside. I've had no problems with parts dropping off the topside.

If I do need to had solder a part, such as a jumper resistor, I paste the pads, put the pad in place and hold it in place with a matchstick while I touch a soldering iron to the part/pad.

All of it took a lot of time for the first boards but I'm steadily getting quicker, though I don't plan to make too much of a hobby of it!

I'm sure someone will have an observation or two but what I've descibed works for me!

[Ray P]

This is the same as the reflow oven I've been using

https://www.amazon.co.uk/Infrared-Solde ... diy&sr=1-3

[Thermionic Idler]

When I soldered the SOIC-8 components onto the linestage PCB, after 'tacking down' the opposing corner legs, I discovered that I got good joints by laying a piece of thin solder across the legs and wiping the iron across the top - you'd think bridges would occur but I didn't get any.

The PCB also had chip resistors and caps at each XLR input and resistors for a 'dummy load' next to each selection relay - you can see the pads on the board design below, towards the left side of it. I just didn't have the space for through-hole components. Thankfully I was able to get JLCPCB to populate those for me as part of their manufacturing process. The parts were cheap enough for me to do it. The OPA opamps weren't so cheap, so I elected to solder those on myself!

[ed]

thanks guys
I think I'll stick to through hole if I ever do another amp. The method Ray outlined with the rework is the method I used but to make it work I reckoned I needed film stencils to avoid bridges. Nick did my first breakout for me and I had to remove a couple of bridges with wick, it was at that point I realised it's not so easy without stencils.

There is unlikely to be another amp so there will be a rework station appearing on ebay fairly soon.

[Ray P]

I have a stencil for a DSD convertor (from PCM) board I have to assemble so it will be interesting to see how much easier it makes things - it should save a lot of time compared with manually pasting the PCB pads.

[Nick]

Just checking Ed when you say film stencil do you mean the cut sheet for applying paste or the solder resist mask on a PCB.

I find having a metal paste stencil makes life many many times simpler when using a hot air gun. I would imagine using one and a oven would almost become trivial.