[Curtisbeef]

Every now and then my DAC turns stops working and i have to unplug it and plug it back in and it starts working again... its happened 2 times in the hour i have been using it scene built.

Also when having my amp and head headphones hooked up to it when i plug in the USB it makes a loud pop... i dont know if it supposed to do that... just wondering ...

 

[Curtisbeef]

I fixed the problem that was making it stop working... it was a problem with winamp.

But now after extended listening i get large periods of Crackling sometimes it just goes away and sometimes it gets so bad i have to unplug it let it sit for a second then plug it back in. what could be the problem...

Edit: also the Crackling is only in the Left channel Right channel is crystal clear.

Edit2: Checked the DC offset on the Right channel it stays at 1-2mV but on the Left channel it spikes as high as 4-5mV.. is that bad?


Thank you

 

[Curtisbeef]

Now my DAC wont even stay on for more than like 30 seconds.... I have no idea why its acting so unpredictably...

I pug it in it works Perfectly... crystal clear for 10-30 seconds then all the audio drops out.... and i hear nothing but a low static.

I really have no idea what the problem could be... anyone out there that can help?

 

[Toomonoforstereo]

I would like to see a design of the alien dac which has seperated analog and digital ground, so that only the digital part is running on usb power. Hopefully this will reduce the need of a low pass filter on the output. For now my amplifier clips on the high frequency noise generated by the alien dac.

I removed the caps after the reg101 and this helps.

It would be interesting if more have the need for this. If so it might be possible to release an update of the circuit board.

 

[tomb]

Quote:

Originally Posted by Toomonoforstereo /img/forum/go_quote.gif I would like to see a design of the alien dac which has seperated analog and digital ground, so that only the digital part is running on usb power. Hopefully this will reduce the need of a low pass filter on the output. For now my amplifier clips on the high frequency noise generated by the alien dac. I removed the caps after the reg101 and this helps. It would be interesting if more have the need for this. If so it might be possible to release an update of the circuit board.

I think you may be missing a couple of things.

There is no need to separate the digital and analog grounds - they are essentially the same thing. Secondly, the AlienDAC already provides the feature for separate digital and analog power supplies by using the regulators. The 5V reg may be supplied with an external 5V source - 9V battery, whatever.

Neither of those is what causes the need for the DC coupling caps. The PCM chip itself is designed to be fed with +5V, thereby establishing an internal voltage reference of ~2.5V as analog signal "zero". This means the analog output coming from the PCM chip itself is offset by 2.5V. Unless a second stage is used that can zero out that offset, then coupling caps are required.

As for the high-frequency noise and your amplifier clipping, I would suggest that you have a problem in how you've built the Alien or how you have it connected to the amp. That is not normal - at all.

BTW, an updated design to the PCM2702 DAC is the BantamDAC.

 

[Toomonoforstereo]

Ok sorry for not beeing fully clear. The caps I was talking about are the ones direct after the regulators (the panasonics), not the output caps.

I'm aware of the dc ofset to remove the need for a dual power supply.

As soon as I connect a battery as power source the module opperates very unstable. (left and right out of phase)

The hf noise I measures was in the 2 to 4 mhz range which is not that strange for sigma delta designs, the newer pcm versions have filters build in hence the lower signal to noise ratio of the later ones.

Has anyone a solution for the sudden white noise periods when running with cool and quiet on?

Thanks for the name of the updated design I will investigate that one.

 

[tomb]

Sorry, but it still sounds like you may have something messed up in the build. It's true that the output caps are optional on the REG chips, but hf noise up that high is not something I've heard about before. Further, the newest versions of the PCM2702 have worse noise specs, not better. The PCM2702 has a 105 SNR, the PCM2704, 2705, 2706, and 2707 all have 98 db SNR.

 

[Jam_Master_J]

Building an Alien DAC + Pimeta. Do I need the BUF 634 on the DAC if I'm isolating the output jack completely from the case?

 

[pinkfloyd4ever]

The Alien and the Bantam are the same circuit other than a couple of differences in cap values, correct? I know the regulators are different packages, but they perform the same right? Obviously the Bantam's layout is smaller.

I guess I could've saved some time and just asked: With the same brands and type of caps and resistors, are the Alien and Bantam essentially identical performers?

Can the Bantam be used with virtual ground amps? I've don't recall reading that it can't, but I remember on the Alien you have to use an additional IC (buffer), and I don't see a place for that 4th IC on the Bantam

 

[pinkfloyd4ever]

bump for my and jmj's questions

 

[Ashkii21]

I have the same question. Can the Bantam amp be used with a virtual ground amp?

 

[tomb]

Quote:

Originally Posted by Ashkii21 /img/forum/go_quote.gif I have the same question. Can the Bantam amp be used with a virtual ground amp?

Yes. Absolutely.

Sorry I didn't see these questions before. The BUF634 option is a power option if the AlienDAC is powered from the amplifier's power supply. There is a grounding conflict if this is done with a virtual ground amp. Being much smaller, the Bantam does not use the various power options available on the AlienDAC - only USB-power is used for the BantamDAC.

It has nothing to do with how an Alien or BantamDAC connects through the audio connections - that is no different than any other source.

Quote:

I guess I could've saved some time and just asked: With the same brands and type of caps and resistors, are the Alien and Bantam essentially identical performers?

Yes, this is pretty much a valid statement. However, we think we've had enough time now to optimize the parts selection for some better performing parts on the Bantam - such as the TPS chips, the output film caps, etc. Also, even though the Bantam doesn't have the different power options available with the AlienDAC, the Bantam's small size allows different building options - such as the BantamCableDAC.

 

[schubert]

I've built an Alien DAC form a Glass Jar Audio kit. I opted for regulated USB power. The voltages tested fine on the bench and at the computer (4.7V at the 5V pad, and 3.3V at the 3V3 pad), the computer recognizes the chip, but I get no sound. Does anyone have any ideas about what I should look at?

 

[schubert]

It works fine now that I cleared all the solder bridges from the main chip. I tried it in a USB 2.0 add-on card - terrifically noisy. A USB hub was better but still noisy. No problems with the computer's main USB ports though, and it sounds great.

 

[tomb]

Quote:

Originally Posted by schubert /img/forum/go_quote.gif It works fine now that I cleared all the solder bridges from the main chip. I tried it in a USB 2.0 add-on card - terrifically noisy. A USB hub was better but still noisy. No problems with the computer's main USB ports though, and it sounds great.

Yes, many hubs have questionable quality power supplies (or booster circuits) that add a lot of noise to the analog power output. As you've found out, you're better off using a USB connection that's native to the motherboard.