Comments for my PCM2702 DAC layout? - Page 15

Holy S**T!!!! just received the parts from Digi-key, those are sooooo small, especially the DAC chip "legs".

I could really use any hint you can give me before getting in populating the board (when they arrive from TomB).

You can do it. You need magnification (more if you're my age, less if you're young with the eyes I used to have). I use a dissecting scope nowadays. Even if you can see what you're doing to solder, good magnification is really helpful to review your work.

There are also some good tutorials on line.

Tangent has a video on SMD soldering here: Tangent Tutorials

The Bantam instructions also offer some good advice.

There are some other approaches with videos -- search on YouTube but take some of the more imaginative approaches with a grain of salt, or flux or whatever...

Magnification is always a good idea even with 20/20 eyesight, with such small components, no need to force your eyes, that will only hurt you latter.

I have a lamp with magnification, great tool, even with something not so small, it helps!

I already went thru all tangeant video and text tutorials before starting my first CMoy, I read Bantam instructions and I just haven't tought of magnification but it was obvious.

I think I just need to gather my courage and make sure I'm not on an overdose of sugar, cafeine or something of the kind to help to have steady hands...

Good thought. I try to do the same thing - make sure you have everything organized, distractions minimized, and wait until you feel comfortable, rested, and calm. It seems to help me a lot on soldering that PCM chip.

Remember, flux is the secret sauce.

I remember trying to de-bridge the pcm on my alien dac without flux for bout half an hour, and it was a nightmare.

With flux, it took me about 1-2 minutes to get the pcm's on all three of my Bantam dacs.

I don't have any "secret sauce" because I haven't needed any up to now. Should I go get some right away or I should see if I can work it out without any flux of some kind? I do have wick with flux in it, I tought it would be enough...

Get the flux first, just buy a cheap flux pen. It's indispensable with SMD, and I'd consider it a necessity, especially if you're inexperienced. Wick may be enough, but lots of flux makes life easier, and easy is good.

Agree 100% - X10, even. Excellent point as usual, error401!

I like to solder while drinking something strong

I'm not kidding about the above statement

Get the little bottle of flux, a dispenser bottle (it has the skinny metal tube sticking out of the top), and the giant size bottle of alcohol to clean it all up. While I probably use a lot of flux compared to other DIYers here, I still don't really use a lot. As a result though, I also use a HUGE amount of alcohol. I'm spoiled from working in electronics manufacturing for many years, so I got a dispenser bottle for that as well (I bought this one 35704 ) You might also want a brush like this one 577-2020

Yes I know buying tools costs more then the projects, but you can use them forever. Can you get by without them? Probably, but I built my skillset using them, so I need them


EDIT:
I forgot to ask my questions :P I came to this thread because I built a Bantam last night, but it isn't performing well.

First off, I made it a cable DAC. I ordered the board, case, cable, and Panasonic FM cap from the website. I didn't use RCAs though, I wired on a mini phono since that's what my amps have as inputs. All parts not from Bazaar came from Mouser.

I got it all soldered up fine. The only difficulty were the 4 test pins on the IC. Those pads aren't as well tinned or something, because I couldn't get a good joint there. After I looked at the schematic and realized those 4 pins (2 pairs on each side at the end away from the polarity mark) weren't used, I moved on. Everything went OK. As I alluded to above, I used to work in SMT assembly for many years. I mostly ran the pick & place machines, but I did plenty of hand soldering and rework. So I was comfortable with the components.

When I hooked it up, Windows XP installed it fine. Fired up Foobar and I got it to make sound feeding a cmoy with some cheap earbuds. Once I knew it was functional, I started listening. Immediately I could tell the right channel was louder. It sounds like the balance control is shifted to the right. I'll go over all the solder joints again, but it was late last night, so I didn't do that right then. I didn't use 2 wires for the ground to the output. It looked like both of the attachment points we connected, so I didn't think it would matter. Could this have anything to do with the imbalance? I still think it has to do with a solder connection somewhere. I suspect it's the phone plug. Is was a style I had never used before. I thought I had good connections, but maybe not. I'll try reflowing the joints there first then reflow everything inside the DAC.

When I hooked it up to my Millet Hybrid Starving Student, it had a horrible hum. I'm pretty confident I can fix the balance problem, but the hum has me concerned. Any ideas what it might be?

thanks all for your advices, I will get flux as soon as I can (might be in more than a week) and wait for the appropriate moment to build everything (have parts for 2) and will then see how to stuff one of those with my uncased Mini³

Actually, they're attached to the ground plane, so it takes a much hotter touch of the iron to get the solder to stick properly there. I've found if those are the last pins soldered, usually the iron and the surrounding area is hot enough to make this a bit easier. Hum most definitely can indicate a ground connection problem. Plus, a hum plus channel imbalance can easily be caused by incorrect wiring to an output plug.

One way to confirm is if you have correct voltage at the output of the DAC. If you can measure the DC voltage to ground of OL and OR just prior to the output caps, that should tell you whether there's an imbalance/problem with the DAC chip. It's a little bit awkward, but probably safer than putting a probe to one of the DAC pins while it's power - flip the board over and see if you can carefully place one probe on the first coupling cap lead (closest to the PCM chip output) and the second probe on OG. Do this for Left and Right channels. You should be able to measure about ~2.3 to 2.4VDC for each channel. If so, then the issue is most likely with how you wired the jack/plug. If not, then there's a problem with the DAC chip.

So do they need to be soldered? I used the solder wick to take most of the solder out of that area since they were bridging pretty bad. I got nice joints on all the other pins, but I couldn't get those 4 to work well. In the schematic they don't seem to be connected to anything, so I didn't think it would matter.

I'll check those values. I didn't get any time last night to troubleshoot the issues I'm having with the DAC. My meter works fine, but my brother borrowed it and somehow managed to break the pointy tips off my probes They still work, but they are kinda "stubby" now hehe. I need to get new ones or files these back down to a point. Hopefully the points you're suggesting I test are big enough. I have trouble with measuring tiny contacts. I couldn't probe the DAC chip's legs, but I have the attachments with little wire hooks that I could grab the legs with. Enough of that little sidenote :P

I realize that hum is usually a grounding issue, so that's an area I was going to look into. The problem is the worst with my MHSS amp. It sounds great with a signal from the line out of an iPod, but it was absolutely unlistenable with this DAC It's not a little bit of hum, it's LOUD. I'm not saying that it's the DAC for sure. It certainly could be partially the amp's problem, and I suspect it is. I just completed the amp this week also, so I may give my wiring another going over.

Thanks for the help Tom

Not suggesting that this is the problem, cause I've been known to be wrong, but are the heatsinks in your MHSS greased?

I had the same problem with my first Bantam. It sounded like a loud glitch and the music was quieter than it was supposed to be. I resoldered the chip and it was gone. I hope it will help.