Help needed for my DIY DAC

[sachi]

So we get three wires.

Red is negative
black is Positive.
blue-green is earth wire ??

Am i right ?

No the earth wire goes from the earth pin to star/chassis ground of your circuit.

 

[cha_indian]

so what to do with blue -green combi wire ?

 

[sachi]

so what to do with blue -green combi wire ?

Nothing..what you are doing is wiring the two primary windings on the transformer in series. So effectively the coil length on the primary side doubled in which case if you apply 230 volts across the red and black terminals (neutral and live) then you will see the appropriate secondary voltage on the output that the transformer is rated for. If you wire it up any other way expect to short circuit the transformer winding/s and ruin your transformer or if u ended up wiring the primaries in parallel(that is for 115 volt operation) then expect your transformer to catch on fire at worst or smoke out and die at best.

 

[cha_indian]

Guys, i connected the DAC to a CDPlayer and i hear no sound!

What i did was connect only the SPDIF socket to a wire and connect the wire to the board. Although this is a Tube DAC , i did not connect the tube... Is it necessary to connect all the connectors before we use it ??

 

[cha_indian]

There is a jumper setting to select the output with a tube and without the tube setting. Apparently i have selected the direct.

 

[cha_indian]

OK...i wil connect the tube ...

The coaxial wire is below the USB.... like one upon the other... I just connected the coaxial just to test it..

 

[kaushik]

Possible dry solder on the RCA sockets ..remove the wire,scratch the socket connections,redo the soldering.

Verify the power section is working properly,check DC after regulator.

Check for solder bridges in the SPDIF chip , i see it is poorly soldered.
place a highpower bulb below pcb and see for the solder bridges. If any
remove them with de-sol wick.

Did the chip got over heated while soldering? (may be is dead by now)

 

[cha_indian]

Till now i was thinking that my DAC is dead...but now i have connected the LEDs and it is powering on !

But the bad news is that still no sound. The SPDIF socket has 4 legs to be soldered on board. Since i have soldered on a separate board, is it necessary to connect all the legs or only the leg that is of centre pin ?? Also USB is still not soldered.. i hope it works without it cos i have no plan to connect it to computer.

 

[cha_indian]

Are you sure you haven't fried it?

I have no idea man.. guys.... do i need to connect all the legs of SPDIF ???

The reason for a seperate board is because i want to integrate my EHP 606 into this if everthing goes fine . There is no place to fix the board on the rear with EHP and DAC in one box (Still lot of work is there to be done on this )

 

[kaushik]

Have you been through the SMD soldering tutorials online?
some things you need to consider :
-ESD safety
-use temperature regulated soldering iron (not controlled,that is expensive)
-fine tip soldering iron and a thin solder wire
-a cheap magnifier ,good lighting

- A low melting point (190deg c) solder - very important this will prevent the
damage during soldering
Even if you fried the chip dont worry next time you wont.
The thru hole LCR components are normally not damaged if you have placed them on the proper places .

spdif to i2S chip you can buy new one
Normally audiophile grade pcbs are very well made you can desolder and place a new chip.

 

[cha_indian]

I have soldered all the connectors to the board but still i cannot hear any sound. One good news is that USB connection with my computer is working. Win XP is recognizing the device as USB DAC and installed the drivers. Even with drivers installed, i cannot hear any output from speakers...

When i bought the DAC, i asked the seller to solder in all the chips. He soldered the following chips: DIR 9001, PCM 1798, chip on the USB daughter board. I soldered two other chips.....

1. Tube is glowing fine
2. USB indicator LED is glowing
3. I can hear small buzz from somewhere on the board...don't know it this is normal.

 

[cha_indian]

Thanks for all the replies guys.

I posed the question of no sound to the seller and she has correctly asked me to check the voltages at Opamps and SMD regs. Two of the four opamps are not getting any voltage. One SMD reg near the 7805 is outputting only 0.3V instead of 3.3 it is supposed to. Have sent the mail today and hoping to get her reply tomorrow.

 

[cha_indian]

You have to troubleshoot things one step at a time. I am not responsible for any damage - you should ideally take it to somebody in your city who's done this before. However, if you accept the risks, you can read on and see if you would like to attempt some basic troubleshooting steps.

Do you have a coaxial/optical source to test with? I'd like to know if the silence is because of the USB board and some connection issues, or the entire DAC is silent. Some tube circuits take time to power up. SMD chips are easy to short out, and re-check that you've soldered everything the right way around. check it six times.

Assuming you have checked everything seven times...

Obviously the board has power, so you need to work out if there is any analog output at all, and where it terminates.

The first step is to check if the PCM1798 has a valid analog signal at the output. Disconnect the tube with the DAC switched off. It is not necessary to reset the jumpers just yet.

Keep the amp volume very, very low. I would not venture past two clicks from the zero position. Amplifier should be in power off position at this time. Power up your sources. Preferably have two sources playing, one connected to optical/coax and the other to USB. Keep them powered up.

Now, disconnect the 'live' output wire from the output RCAs at the board. This will give you an RCA socket with two wires, one connected to ground and the other hanging in free air. Don't worry about the other channel just yet.

Trace the output path from the PCM1798 (look at the datasheet - there will be four such pins - L+, L-, R+ and R-). Solder the hanging wire from our previous step to one of the outputs (does not matter which, but don't solder on the chip itself, trace it to the next available pad and solder it there...) and power up the DAC. At this time, put your two sources in 'Play' mode, and after two minutes, power up the amp.

If there is still no output - the output here may be very faint and distorted, but it does not matter - your DAC chip is fried, or may be missing some critical setting, usually jumpers are used in standalone mode to 'program' the DACs. Look at the datasheets. There are three blank jumpers in front of one of the chips. They may be used for mode control and user settings. Look at the chip documentation and the papers that come with your DAC.

The PCM 27xx has an analog output, test that next - but you will also have to connect the ground wire to it as the analog ground may not be shared between the two boards. The PCM27xx is not doing analog duty in this application, some creativity may be required to hear whether it will work (I strongly suspect it will be working).

Good luck. Eventually the best course of action is to work with the seller as they know what it takes to get it working. Post on the Head-Fi site (or wherever you saw the references) and post for follow-up help - people who've built this earlier will know of familiar pitfalls. Doing more by remote will be very very difficult for me, as I can't diagnose something sitting so far away.

Cranky, i just got email from the seller asking me to check all the ICs on the board. The damn things are so small that i can hardly see the legs..... Since the ICs are soldered by the company itself, i am sure they might have done a good job of that. I just came back after visiting many cellphone repair shops and all them refused to check the board. I wonder why they are so scared to even consider checking it.

Since you have done quite a few DIY project, I am sure you might be able to diagnose the problem. If you are OK with it, shall i send it to you for checking?

 

[cha_indian]

I inquired at DTDC cargo and it takes only about 100 rupees. Why would sales tax come in picture ?? It would be great if you can suggest any courier company. How about our plain old India Post EMS ??

 

[quad]

If you are not getting o/p out of the 3.3V reg, either
the 3.3V line is shorted somewhere or that reg chip is
fried. Check very carefully if two adjacent pins
are shorted somewhere - very easy for this to
happen when soldering SMD devices.

 

[cha_indian]

I inquired at DTDC again and now they refused to take in electronic items.... Is is illegal to send electronics within our country ?? I get all my stuff from Hong Kong without any hassles and now i have to run around for sending within my country

 

[kaushik]

Trakkon courier is one option they ship all pc peripherials from techenclave seller..

but GATi is cheapest it was 13 Rs per kg , but there is a min value.Remember to mark it fragile ..

 

[cha_indian]

Guys, i am happy to inform you all that my DAC is working :yahoo:

I talked to Cranky and after taking his advice i checked for all the solder joins and found 3 shorts on chips. It took less than a hour to set this right. I would like to thank Cranky and all the fellow hifiers for the help.

Immediately i find that the DAC is producing quite deep bass. Earlier the bass was bit 'mid rangy'. Now it seem bass is quite low and deep. I will switch it on for one week and see how it sounds.

 

[sachi]

nice going..i have an idea how you felt when you were able to first listen to the DAC come to life.

and nice job Cranky!:clapping:

 

[cha_indian]

I guess your brother fixed things right up for you Really good to have a short-circuit proof regulator (most are, not all though).

Just for information, was the bad soldering done by you, or was it on the chips the seller soldered?

Hi Cranky,

Yes, you are right! My brother removed the shorts and all the three shorts were caused by the ICs soldered by the seller.

Even though i am getting nice sound, still there is no voltage at two opamps which i indicated earlier. the seller is saying that there might still soldering problems somewhere....so still there is work needed to be done.