CS4397 dac

[Bodran]

Andre,
It's not for computer I am testing in my main system. I can use the balance control there. But I want to find and fix the source of the problem. That is my experiment. To see if I can do this, with little help of course.

[Rare Bird]

Andre,
It's not for computer I am testing in my main system. I can use the balance control there. But I want to find and fix the source of the problem. That is my experiment. To see if I can do this, with little help of course.

Leo's yer man

http://theartofsound.net/forum/showthread.php?t=315

[leo]

Need some basic help. First let me state that my background is in mechanical engineering rather than electrical but I do like a challenge.
So far I’m using this dac stock with the supplied power supply. I was happy that it worked at all after I hooked it up. First problem I noticed was it is louder in one channel and I have to use the balance control on my preamp (lucky I even have one). So I have been looking here for a solution.
Could the different values of R8, 9, 14 & 17 cause this?
Later on I read about that someone had a bad voltage regulator, I figured that is easy to check so I did and the +5 volts is +5.1v the +12v is +11.81 but the -12v is -16.44v. Looks like a problem on the -12v to me but is it causing the channel imbalance? I measured at the first power supply connector relative to the AG pin.
Regards.

It could be caused by a few things, example incorrect or drifted value resistor in the output stage, fb resistor etc, one channel of the dac chip output maybe faulty or maybe loaded down too much.
Also check the soldering especially around the dac chip

Is the input voltage to the left and right channel op-amp the same? (inverted and non inverted input not the supply)
The voltage regs feeds both channels so if one was faulty it would affect both channels

[robertor]

dismantled all the previous mods and installed for another time some new some old twek nothing changed.
if can help anyone where is the led i measure 3,4-3,5v with the optical input and 1,3-1,35v when there is the jump on coax input.
but nothing.
thanks

[leo]

Did you select the jumper/link in the socket for co-ax input?

[robertor]

hi leo,
where is the supply input socket(+5 -12 +12 etc etc) there is also the socket for the choice of input.
correct?
. . . like this(over view) 3 points.
one side coax and one side optical: correct?
when i jump the 2 legs for the optical input i find about 3-3,5v where is the led, when i jump the coax 1,2-1,25v in the same place.

[robertor]

today the last famous words of my lampucera have been: bzzz tick tock bzzzz and after the SILENCE.
i think once and for all dead.
thanks for support and sorry.

[Bodran]

It could be caused by a few things, example incorrect or drifted value resistor in the output stage, fb resistor etc, one channel of the dac chip output maybe faulty or maybe loaded down too much.
Also check the soldering especially around the dac chip

Is the input voltage to the left and right channel op-amp the same? (inverted and non inverted input not the supply)
The voltage regs feeds both channels so if one was faulty it would affect both channels

Hi Leo,
Thanks for taking the time to help here.

Problem solved. You are gonna love this ……..….. it was the crappy pin connector on the cable from the board to the RCA, specifically the half on the cable.

Your suggestions stimulated me to action, so I looked up the datasheet to identify the input pins and off I went. This is how I measured the op amp input and output voltages. Please tell me if method is valid.
I used the stereophile test disc on track 20 repeating at constant volume. Measuring AC voltage from each individual pin to AG at the output RCA, all four inputs, pins 2, 3, 5 & 6, were equal at .057v and output pin 1 was .335v while pin 7 was .331v. Is 4mv difference significant?

So it’s not the dac or the op amp lets check the output at the RCA, there is a big difference l versus r which after all is the problem. Now where is it? I separated the halves of connector J6 and measured l & r outputs to AG and they were equal. Bingo problem isolated. So I pulled the pins from the other half and gave them an extra crimp and now all is well.

Coming back to the supplied power supply if my measured -16.4v is correct then somehow they make the -12v higher than the +12v, even though both are 12v regulators (7812 & 7912). Is that possible? Then -5v is derived by a drop across R23. Does that leaves -12v remaining or is there something else dropping it back to -12v?
Regards,

[audio1st]

Hi Alan,
The -16.4V is incorrect. I think that is the same voltage you would have before the 7912 reg..
Check the soldering of the 7912 regs centre pin (ground)..

[Bodran]

Hi Alan,
The -16.4V is incorrect. I think that is the same voltage you would have before the 7912 reg..
Check the soldering of the 7912 regs centre pin (ground)..

Thanks Barry
The transformer datasheet confirms that 16.39v is the secondary no load voltage. My mistake was that the pin out of 7912 is different to 7812. For 7912 the center pin is the input. When I measure the correct pins the voltage is fine.
Regards,