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USB1543 DAC - Builder's Instructions

Wood Base drill pattern

Warning: The most common mistakes are to solder IC7 (the surface mount PCM2707 chip) and diodes in the wrong way. Note the white circle on the board and the circle on the chip is pin 1. If you end up with the PCM2707 chip in the wrong way, unless you take it to a pro there is no saving the chip. I recommend using a utility blade to cut the pins off the chip then remove the pins from the board with desoldering wick.

The SMD clock also uses a circle to denote pin1. The clock is sensitive to heat and shock (being dropped).

If a diode is in backwards and power is applied then there will most likely be other parts (usually voltage regulators) that will need to be replaced.

Also note that the edges of the holes are sharp and often while inserting a part the edge of the hole scrapes a very fine string of metal off the part's lead producing a very fine wire. This fine wire could end up producing a short if not removed. When I put in a part I watch for this by lifting the part back up a little to see if a fine wire was produced in the process.

Generally when stuffing a board short parts are soldered before tall parts. The reason being that when you turn the board over the parts can rest against the table surface and not fall out. Plus it is nice to keep the board light as long as possible.

If you have little or no experience with soldering then start with the small resisters. Build experience soldering and desoldering (with the included wick) a couple resistors before proceeding. Note the pads and traces on the board can be damaged by too much heat or heat for too long. The result is that the pad or trace will lift off the board. When soldering heat the pad and part at the same time by touching both with the iron's tip to both at the same time. A few times a second touch the solder to the pad and part, at some point they will be hot enough and the solder will melt and flow onto the pad and part. Hold the iron on the part and pad long enough for the solder to evenly flow over the pad and part. Sometimes you touch the solder to the tip of the iron to get the solder melting if it seems to be taking too long.

It is important to keep the iron's tip clean and conditioned to accept solder. When solder and flux sit on a hot iron a black deposit forms, this needs to wiped off before soldering. After the tip is wiped it needs to be in a state/condition that when solder is touched to the tip it will evenly flow on the tip and not bunch up. Many soldering irons come with a sponge that is kept moist and used to wipe the tip clean on. I find a DRY fluffy paper towel laying flat folded three or four times thick is much better than a moist sponge. The dry paper towel gets the tip cleaner, doesn't cool it down as much and keeps the tip in a condition to accept solder better than a moist sponge does. The paper towel also provides a visual clue as to the tip's temperature. The proper temperature is when the iron leaves a brown streak on the paper towel not a black one. Also the tip should not be catching on the paper towel. When wiping try to wipe off all the old solder before soldering the next part.

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For experienced builders familiar with SMD parts I recommend starting with IC7 the PCM2707 chip. This is the hardest part to solder. Soldering this parts takes good eyes more than anything. The way I do it is to place the chip on the board matching up the circle for correct rotation (double check the orientation). Line it up the best you can while holding it down with one finger. While holding it down solder just one of the corner pins. While keeping the solder hot on the one pin slide the chip into position. You may have to stop heating this pin while checking the placement of all the pins. Reheat the pin and slide it around until perfect. Then solder one pin from the other side of the chip. Look it over and slide it the final bit until perfectly lined up with the pads. Now solder all the pins using extra solder, creating solder bridges between most pins. Don't solder one pin at a time. Hold your iron so that you are heating and applying solder to three or more pins at a time. The idea here is that you are applying enough heat, solder and flux to make sure that all the pins have solder underneath them. Typically your soldering iron tip is only touching the board for 3 seconds at a time with you cooling the chip down with a finger or natural cooling before another bit of soldering.

Next lay the desoldering braid across a row of pins on one side of the chip, heat all of it with the side of your tip. You are trying to melt the solder through the braid, when it does the solder wicks up into the braid. When you see it soak up the solder gently pull it and the iron across the pins. When done the chip will look like there is almost no solder on it. If you look very close you will see that each pin is soldered to the pad below it. Note one side of the chip has no connections to it and is the best side to practice your technique.

Next solder the clock. Place it on the board using the circles for correct placement. Hold the chip down with one hand (finger) and place a small amount of fresh solder on the tip of the iron and quickly apply it to the area where the pad and the clock meet. Note the clock has pins on the bottom and side. Since you can't see the bottom make sure the pins on sides of the clock are soldered to the board. Once one pin is soldered you are set to solder the other pins in the normal way.

The hard parts are now done, the rest of the parts are easy to solder and if done in the following order will be hassle free. (I recommend printing this page and checking off the following items as you go)

* First we start on the bottom of the board.
R1-R4 and R6-R9 Dale 20R
R13-R14 Dale 22R1
L5-L6 small inductors get them both in the board before soldering because they are a tight fit.
F1-F2 fuses

* Top side
R15-R16 1K5
R17 1M
IC8 (TDA1543) 
R19 1K5 Riken (clip the leads) 
R18 and R20 Riken 2K7

* Opamps IC5 and IC6, insert chips but before soldering clip off the pins that are sticking above the board, clip as close to the board as possible or clip before inserting into the board. Solder from the bottom, try to keep the top of board flat and free from anything that will poke the capacitors that will be soldered above them.

* 3.3 Volt regulators IC10 and IC11, first straighten the legs then pull back the middle one a little.(tip: solder one pin then flip over the board and make sure the part looks straight before soldering the other pins)

* All the rest of the voltage regulators
IC1 and IC2 are 78L18
IC3 and IC4 are 79L18
IC9 is 8008

* C22 is Oscon
C23 and C25 is 10uf
C24 is WIMA (note all but C24 caps have a negative and positive pin, the short leg is negative, see the plus sign by each cap for proper placement.)
 
* 16 diodes D1 to D16, Tip: put in all the diodes and have them all slanting one way, put a long piece of tape over them, flip the board over and pull the tape a little to straighten them all at once. Solder the same one pin on all diodes. Hold the board so that you can go over all the diodes one at a time while pushing down on each diode and making sure it is straight while reheating the soldered pin. Now solder the second pin of all the diodes.

* Big inductors L1 to L4, try to get them all in the same direction.

* C5,6,7,8 and C21 Note: The BG N caps sound best with the short leg/pin to positive +, these are BG N :)
insert all caps, flip over the board and solder one leg, flip over and reheat each leg while pushing down on cap, get all caps straight then solder the second leg on all caps. Keep the cut off leads for use as jumpers.

* C12, this cap is non-polar but sounds best with short leg to negative. Keep the cut off leads for use as jumpers.

* C1-C4 and C10 Panasonic caps with short lead to negative
C9 and C11 Nichicon caps with short lead to negative

* All the jumpers, 10 or 12 of them depending if using 115 or 230 volt mains. Use the cut off leads from previous steps

* Volume control (tip: do one pin, push down on part and reheat pin to make sure it is straight, then solder other pins)

* USB connector

* IEC power receptacles

* Transformers (note one is 8 volts and one is 15 volts)

* Even though we are not finished; now is a good time to see if the USB interface is working or not. Double and triple check everything. Check that all the diodes and caps are in the right way. Have some one check over your work if this is your first time soldering.

Connect the DAC to the computer with a USB cable. Apply power to the DAC and if it works the computer will display a message that reads "New Hardware Found". Or open device manager and expand the Universal Serial Bus controllers section and watch for an entry named " USB Composite Device". If you get "unknown USB device" then you have circuit problems. If the clock is not running you will get this error. If error then check voltages in and out of voltage regulators. If you have a scope then check for a clock signal and so on.

* Connect the Preamp to the DAC's output with wires under the board. Remove 5 mm of insulation from one end of the blue and orange pair of wires from the kit. Notice the blue wire has more twists than the orange. Untwist the blue to match the orange, then untwist them both a bit more. The orange wire is the right channel and blue the left. Wire the DAC's Right output to the preamp's B-IN input and wire the DAC's Left output to the preamp's A-IN input. Wire B-OUT to the back RCA jack, wire A-OUT to the front RCA jack. (note the actual RCA connectors are not solder to the board yet)

* Break in the RCA jacks before soldering them to the board, Plug and unplug them a few times, twisting as you plug and unplug. Better now than after soldered to the board.

* Remove the white plastic spacers on the RCA jacks. Tighten up the nut with the tab lined up with the notch on its center pin, see picture and read the next item for more details.

* Solder the RCA jacks onto the board like so.. Take the solid copper wire, pull off the insulation, stick one end of the copper wire into the back end of the jack and make a sharp 90 degree bend in the wire. Position the red jack in the back position, solder the copper wire to the center pin of the jack, solder the tab to the board, solder the copper wire to the board. Do the same for the black RCA jack. Tip, if you plug RCA connectors into the jacks it makes them longer and easier to soldered them straight. If not straight then reheat the solder tab and slide it around until perfect.

* Fill all the vias (small holes in the board) with solder.

* Mount your board onto the wood base with a screw in each corner.

* Plug it in and enjoy the music.

The music the DAC  produces at this point is pretty amazing but it now goes through a break-in period. Over the next 8 hours the sound quality will degrade. It may be hard to put your finger on what has changed but the following day listening to the DAC will not be as much fun. The following week the DAC may be close to where it was the first night. After a month it will be 90% broken-in. Try to keep it plugged in and running 24/7, at least keep it plugged into the mains 24/7. If left unplugged for a month at a time the DAC may require a short break-in period again.

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If you find these instructions are unclear or have errors then please email your comments to "brent [at] diyAudioSystem.com"
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