Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Bantam DAC help please
New Posts  All Forums:Forum Nav:

Bantam DAC help please

post #1 of 11
12/18/10 at 4:54pm
Thread Starter 

Me and my friend built 2 Bantam DACs today from the kit on Glass Jar Audio, but we're having some problems with both of them. I have viewed the troubleshooting on the bantamDAC website and searched this forum, but to no avail.

 

The computer recognizes both DACs as a Burr-Brown Japan PCM2702, Generic USB Audio. The LED lights up.

 

DAC A:

-Weird loud buzz sound from left output(several layers of low and higher pitches vibrating it seems), quieter high pitched whine in right.

-No music output, and changing volume does nothing.

-Voltage across C11 regulator (IC1) is 2.37V(should be 3.30V)

-Voltage across C13 regulator(IC2) is 2.27V (should be 4.75V)

 

DAC B:

-No sound whatsoever from either left or right output.

-No music and volume change does nothing.

-Voltage across C11 regulator (IC1) is 3.30V (correct according to bantamDAC website)

-Voltage across C13 regulator(IC2) is 0.841V (wtf)

 

If you need me to take any other measurements or pictures please ask.

Reply
post #2 of 11
12/18/10 at 5:07pm

Photos help.

Reply
post #3 of 11
12/18/10 at 5:29pm

Yes, as FA says - we need photos.

 

Honestly, with the voltages you are measuring, you've got some bridges/poor soldering somewhere.  A few good, clearly focused photos should help us spot the problems.

Reply
post #4 of 11
12/18/10 at 5:33pm

large sized pictures, no tiny thumbnails.

Reply
post #5 of 11
12/19/10 at 9:42am
Thread Starter 

IMG_1031.JPGIMG_1032.JPGIMG_1033.JPGIMG_1034.JPG

 

The voltage across C13 seems to jump when i measure it, goes to 3.3ish then off and jumps around a lot.

Reply
post #6 of 11
12/19/10 at 11:07am

C16 goes on the R8 pad, not on the C16 pad.  Refer to Step #10 here:

http://www.diyforums.org/BantamDAC/BantamDACsteps-2.php

 

It won't affect your problem (not doing the above certainly will!), but you also need to do Step #8a on the same page.

Reply
post #7 of 11
12/19/10 at 1:41pm
Thread Starter 

Thanks so much.

 

While what I do hear sounds great, there is zero bass whatsoever.

Is this just because I'm plugging a headphone(ad700) into the dac?

It definitely gets loud enough, and the bass seems too weak for it to be just because of a lack of amplification it seems.


Edited by ryli - 12/19/10 at 2:21pm
Reply
post #8 of 11
12/19/10 at 2:37pm
Quote:
Originally Posted by ryli View Post

Thanks so much.

 

While what I do hear sounds great, there is zero bass whatsoever.

Is this just because I'm plugging a headphone(ad700) into the dac?

It definitely gets loud enough, and the bass seems too weak for it to be just because of a lack of amplification it seems.


The DAC is not meant to drive headphones.  It has no amplifier and depending on the heapdhone load, you may damage the DAC.

 

Strictly from a theoretical sense, if you used the film caps, there will be a very high bass cutoff when driving a headphone load directly.  As I said, though, you should stop trying to drive a headphone directly with the DAC.
 


Edited by tomb - 12/19/10 at 2:41pm
Reply
post #9 of 11
12/19/10 at 3:08pm
Thread Starter 

I was mostly just using the headphone to test that it was working, and i didnt plan on using it for long term.

Does this mean that it is alright, and theres no problems?  The low range seems to be completely non existent.

Is there something that can cause that to happen, or is it normal?

Reply
post #10 of 11
12/19/10 at 5:36pm
Quote:
Originally Posted by ryli View Post

I was mostly just using the headphone to test that it was working, and i didnt plan on using it for long term.

Does this mean that it is alright, and theres no problems?  The low range seems to be completely non existent.

Is there something that can cause that to happen, or is it normal?


When you combine a Resistor (headphone impedance) with a Capacitor (the output caps on the Bantam), it forms an RC circuit.  One of the interesting traits of an RC circuit is that the current it allows to pass through the circuit is frequency-dependent.  In the circuit that's formed when you connect the output of the Bantam to a headphone, the frequency that it doesn't allow through is bass.  IOW, it forms a high-pass filter (only high frequencies pass through).

 

You can calculate for the frequency where there's -3dB loss (the loss gets greater below that) using this equation:

79e190943633c91aa660a4a9351087ab.png

 

If you've used the recommended Vishay-Roederstein caps at 1uf, that's the value for "C" - 1 x 10^-6.  The headphone impedance for your Audio-Technica AD700's is 32 ohms, that's the value for "R".  So, we have 1/(2*pi*32*1E-06) = 4973Hz.  So, essentially the circuit you form with your headphones and the Bantam has a cutoff frequency of almost 5KHz.  Needless to say, you're not going to hear much low bass, bass, mid-bass, high-bass or even low-midrange.

 

Most headphone amps average an input impedance of 50K ohms.  Put that in the same equation above, and you get 3.18 Hz, a very, very low bass frequency - very close to DC, certainly well below 20 Hz, the considered low of the audio frequency band.

 

I hope that explains it for you ... now get an amp for that thing! wink.gif
 


Edited by tomb - 12/19/10 at 5:37pm
Reply
post #11 of 11
12/19/10 at 8:17pm
Thread Starter 

That was really helpful, thanks so much!

Im possibly thinking of attaching this to a Millet Max, but that's for a later time. =)

Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Bantam DAC help please