[Iniamyen]

I guess the real question is what is acceptable DC offset period?

I just finished assembling my new Alien, voltages are good (4.7V and 3.3V), but I'm getting about 2.5mV and 6.5mV of DC out of the channels (with respect to ground out.)

If this is within acceptable ranges I'll just **** and enjoy.. I already hooked up some earbuds and at least it didn't fry them. I also measured the resultant DC offset from Alien -> PIMETA -> meter, and it has the same values, which I thought was odd.

What do you all recommend?

 

[mark10001]

Is the output AC coupled. What does your output circuit look like?

 

[Iniamyen]

The output of the Alien DAC is using the 33uF Nichicon Muse's for CL/CR that Jeff provides in the kit. They should be eliminating any DC offset but based on my measurements they aren't. So, either I've mis-soldered something, or my meter has a few mV of offset to it. I'd be willing to just chock it up to my meter but the fact that they are different values has me concerned.

 

[error401]

Measure DC offset with a load attached to the output. Otherwise you're probably measuring residual charge in the output capacitors.

 

[Iniamyen]

Looks like the problem was solved by just asking the question! When I went back to measure it, before adding a resistor, it had disappeared. Now it's flickering +/- 2mV which is what I've seen with my meter before. Thanks for the help!

Oh and it sounds really good too!

 

[StanRex]

Could anyone enlighten me a bit on the procedure to follow to measure DC offset?

I hookup my Alien DAC to my PC and my headsix.

Measure between OG and GND and OR and GND on the alien DAC.

Am I supposed to measure the DC offset while music is playing or not?

Because if I mesure it while itunes is playing some music, the values I get when setting the multimeter on 200mV just dont stop changing, which makes it a bit hard to properly measure ^^

But when no music is playing I get 0mV between ground and both channels.

So I was just wondering how exactly I'm supposed to measure things

Thanks in advance

 

[Fitz]

You have to measure it without music playing, otherwise you're measuring the music and not the DAC itself...

 

[StanRex]

Ok that makes sense. Thanks for the info Fitz!

 

[threepointone]

There's a 330K resistor from output to ground in the Alien DAC. When you first turn on the Alien DAC without a load, the capacitor will be slowly charged by the 2.5V bias coming out of the DAC through the 330K resistor. The time constant is 10s, which basically means the DC bias will go down to a couple of millivolts pretty darn slowly (takes about a minute to get down to 2mV offset).

If you plug in a cheap pair of headphones for testing, the offset voltage should settle to around 0 in a fraction of a second (the small "pop" you hear would be the capacitor charging to 2.5V through your headphones, effectively "removing" the bias)