Stuck as a Duck on the Doede Dac!

[Lucas_G]

Dear Dac builders,

I had completed the Doede TDA 1543 DAC a while ago.

http://www.dddac.de/ma_dac21.htm

However, It does not what it is supposed to do.

It is quiet when no digital SPDIFF signal comes in, but as soon as I feed it with some digital data, it starts making a high frequency noise, in which you can faintly hear some parts of the music in the background. The louder the digital signal, the louder the fuzzy noise...

I have tried everything I could in the past week.
I also asked Doede some questions, but he prefers not to go into detail - which is his good right, of course. He never promised anybody to give support on his design....

Now, I am very much hoping that someone else can give advice.

All measurements with my multimeter seem to be ok.
I get 5.04 Volts on VBD and VBA1.
With VBAdjust on 1.25 kOhm I get 7.5 Volt at VBA2.

Here is the scheme:
http://www.dddac.de/pics/dddac1543/pcb1543.gif

I have two questions:

1. In some older schemes, Doede mentions 10 nF caps at the SPDIFF In and Ground. On later schemes he uses 100 nF caps (so that is what I used). Could it be that the use of 100 nf instead of 10 nF is responsible for the fuzz?

2. I did solder all the chips straight in the pcb (except for the Tent clock). I used a 20 Watt soldering iron, and I worked quickly... Is the CS8412 extremely sensitive to heat?

Any suggestions extremely appreciated!!!!

Regards,

Lucas

[Taco]

The CS8412 is not very sensitive to heat, the surface mount version CS8414 survived my punishment with a 25W solderingiron.

The change from 10nF to 100nF isn't your problem I think. But how many TDA1543 you're using?

-I would suggest to try things first without the extra clock. So connecting the CS8412 directly to your DAC's.

-Also what is your spdiff connection, optical or electrical?

-is the output of pin 26 of the CS8412 steady? (data line)

[Peter Daniel]

I observed similar behaviour yesterday in my DAC, when the ground connection from external clock to the DAC board was missing. After connecting ground it was fine.

[Duck-Twacy]

But I haven't even started yet?

[peranders]

Originally posted by Lucas_G
2. I did solder all the chips straight in the pcb (except for the Tent clock). I used a 20 Watt soldering iron, and I worked quickly... Is the CS8412 extremely sensitive to heat?

Heat sensitive? More than usually for an IC? Don't think so. It's plain silicone. 250 deg C for 10 seconds in owen is OK.

I would not very heat sensitive

[Lucas_G]

Originally posted by Taco
The CS8412 is not very sensitive to heat, the surface mount version CS8414 survived my punishment with a 25W solderingiron.

The change from 10nF to 100nF isn't your problem I think. But how many TDA1543 you're using?

-I would suggest to try things first without the extra clock. So connecting the CS8412 directly to your DAC's.

-Also what is your spdiff connection, optical or electrical?

-is the output of pin 26 of the CS8412 steady? (data line)

Hi Taco,

I am using 8 dacs in a tower. I could adjust the voltage to 8.5 V and the output CD to 3.5, just like Doede recommends...

I tried both ways. I have a switch with which I can toggle all three switches at once: either all three closed or open.

I use an electrical SPDIFF. The inner pole connected to the SPDIFF in pin. The outer pole connected to the D-gound, next to the 12 Volt plus in for the Digital domain. I also fitted a 75 Ohm resistor between these two poles.

How can I know whether the ouput of pin 26 of the CD8412 is steady? Can I meusure it?

Thanks!

Lucas.

[Taco]

If you measure a stable voltage without great fluctuations then it's oke.

But like Peter said it could also be a ground problem. Have you measured if all the components that should be connected to ground have a low resistance? Are the digital and analog ground connected together?

And have you bypassed the clock, to eliminate that possibility?

[Cobra2]

Your DAC-chips are overheating, use a fan and / or reduce voltage to 7+...

Arne K

[finneybear]

I think it's overheating, too. Also, check the way you built the DAC tower. Did you stick copper foil to the top of each dac and ground them all together?

I have Doede's board, too. Still have not started the work yet. Am thinking a good way to build the tower. Probably I will make my own PCB. Piggyback two 1543 together as a set then mount them on both sides of the PCB. Two sets on top, two sets on the bottom.

[Lucas_G]

Originally posted by finneybear
I think it's overheating, too. Also, check the way you built the DAC tower. Did you stick copper foil to the top of each dac and ground them all together?

I have Doede's board, too. Still have not started the work yet. Am thinking a good way to build the tower. Probably I will make my own PCB. Piggyback two 1543 together as a set then mount them on both sides of the PCB. Two sets on top, two sets on the bottom.

I took small pieces of aluminium (6 mm wide, 10 mm long, 2 mm thick) which I glued on top of each 1543. This gave me a tower of appr. 7 cm lenght. On the sides I glued two strips of 10 mm width and 10 cm lenght.

Actually it does cool quite well. I stick two larger heatsinks on the sidebars for extra cooling. Then the temp stays well below 40 degrees Celsius.

If it were a matter of heat, it should perform well during the first minutes, shouldn't it?

I am now also contemplating to make my own pcb (a kind of veroboard) with p2p wiring. Your idea of 4 times 2 tda's appeals to me...

Also, I would never again solder the chips straight on the PCB; When there are problems (such as I have now) one keeps asking himself whether the chips themseves are still ok...

Regards,

Lucas.