Soekris Dam Dac

[randytsuch]

Hey Rick
I accidentally put 9V on it, after that it just sits there and taunts me for being stupid lol.

In thinking about it, I like the convenience of PC audio. So I'll sacrifice some sound quality for convenience if I have to.

Randy

[nige2000]

Hey Rick
I accidentally put 9V on it, after that it just sits there and taunts me for being stupid lol.

In thinking about it, I like the convenience of PC audio. So I'll sacrifice some sound quality for convenience if I have to.

Randy

ah thats unfortunate,
been in the same place several times

id imagine a nos droop correction and buffer for the soekris should be high up on the list

[randytsuch]

Nos droop correction? No idea what that is

I never played with sync clocking. So plan to get some potato chips and try that along with fixed clock and still need to finish my usb hub which I started a long time ago lol

But since you brought up the output side I'll dig up some buffers and throw them in the mix

[rickmcinnis]

Never heard of it either but I bet you know about as much as I do now.

Plenty to read about.

First thing I looked at was abraxalito's blog at DIYaudio, though I didn't read close enough to know how to do it.

I am interested but being in analog mode I will wait till I have to look at it.

Like everything else there are some who dismiss it. Quickly read a thread where a big blowhard dismisses NOS entirely notwithstanding correcting the droop. He said all NOS is unfinished design. I was not convinced but he seemed really emphatic.

Of course, there is always the chance he is right ...

[abraxalito]

NOS droop is something mathematically defined - because the DAC puts out 'stair steps' the HF response gets 'rolled off' due to the width of the 'stair'. Narrow 'stairs' (such as you get with more oversampling) give progressively less and less roll-off, which is why its only really an issue for NOS - because it has the fattest 'stairs'. The effect with NOS is about 3dB roll-off in the high treble region. With 2X OS its about 1dB and above that, virtually negligible.

I am guessing that the reasons NOS is dismissed have to do with the complexity of the output filter? In my most recent experiments with TDA1387 I've found it sounds better at 2X OS than NOS, which is rather handy for the output filter (it can do a text-book perfect job with only 3 inductors) but adds cost from needing a digital filter.

NOSdroop.png (5.02 KiB) Viewed 949 times

Here's what I use for NOS droop correction - its essentially a Sallen-Key 2nd order low pass filter with a higher Q than normally seen in order to give a boost at the corner frequency. Its designed to be fed from a 2k I/V resistor. The output is taken from source of M3.

[nige2000]

what are these fets k339s or k35's
whats the value of c7?

will the soekris impedance 625z have any effect on that circuit or can it be applied as is?

[abraxalito]

what are these fets k339s or k35's
whats the value of c7?

As drawn (with 20mA bias) its better suited to the K339s. If you wound the bias down (under 10mA) then K35s could be used.
C7 is 6.5nF

will the soekris impedance 625z have any effect on that circuit or can it be applied as is?

Sure it will have an effect - 625ohm output impedance is significantly lower than 2k so you should increase the 1k resistor to 2k4 to compensate.

[nige2000]

thats great

can u clarify why this below is not a good idea again
it uses the existing batt supplies was my thinking

[abraxalito]

If you want to keep the power supply ripple as low as possible you need to pay attention to where the output current flows. Return it to the +ve supply and you'll see there's only a CCS in series with the load, meaning constant current drawn to the limitations of the CCS. You can watch the supply ripple in LTS just put some series resistance inside your voltage sources.

[gstew]

Hey Rick
I accidentally put 9V on it, after that it just sits there and taunts me for being stupid lol.

In thinking about it, I like the convenience of PC audio. So I'll sacrifice some sound quality for convenience if I have to.

Randy

Randy,

Sorry to hear about that. I even missed that you had an SDTrans. How much had you modified it? Probably a stupid question, but any chance that you just blew the regulators and the basic chips are still there?

Greg in Mississippi