Harsh noise generated by Buffalo32s DAC

[kiwi_abroad]

Hi All,
I have a problem with my Buffalo 32s DAC, The DAC plays music fine, expect when the source is either paused or volume is reduced to 0, at which point a very harsh static noise is played.

I've tried the forums at Twisted Pear with little help, and am throwing the issue open to see if anyone can help.
All relevant information, with images etc. is in the following forum:

http://www.twistedpearaudio.com/forum/default.aspx?g=posts&t=844

A few notes:

• It does it on two different spdif sources (Sony DVD player and a M-Audio Audiophile 192)
• It does it with both the internal firmware and the volumite
• With the volumite, the noise volume goes up and down with the volume setting
• It does it with the case lid on and off, also someone suggested untwisting the spdif cable between the connector and the PCB, this had no effect.
• The Lock LED remains constantly on (Checked with oscilloscope)
• When I change the sample rate on the M-Audio soundcard (from 44.1k to 192k) the frequency of the static noise goes up. Also setting the spdif bits (consumer/pro, scms) has no effect
• The onboard switch settings seems to have a minor effect on the noise, but not much.
• PS voltages are stable on the scope.

I'm certain that it's not the Analog stage as

1. The noise volume goes up and down with the Volumite, indicating it comes from the Digital processing stage of the DAC, or before.
2. When the spdif signal is unlocked (Source disconnected), the DAC is silent

Please read the TP forum and let me know if you have any ideas on how to troubleshoot this, as it's unusable right now.

 

[rossl]

Have you tried transformer coupling the SPDIF?

Is the SPDIF RCA connector grounded to the chassis or is it floating?

You could try a 100 nF cap in both wires of the SPDIF and make sure both are isolated from the chassis. That would help if you are getting noise current in the SPDIF cable.

 

[BrianL]

Keep on playin'

You say that it's just fine as long as music is playing. Well, don't stop playing!
🙂

 

[kiwi_abroad]

Hi,
I've tested with two sources and two connectors, normal 75r coax and Toslink optical, with identical results. As the optical link isolates the source from the DAC, I suspect that a transformer probably won't do much either.

I have put a 220nF cap is series with the spdif signal, with identical results.😡

I'd love to not stop playing, but can't avoid the silence between tracks.

See the fourm on Twisted Pear's website for some oscilloscope images of the output, and the spdif input signals.

 

[rossl]

then it looks like the digital section is working OK.

could be something isn't soldered down correctly. Get a loupe an look closely at all the solder joints.

maybe the mute output signal from the ESS chip is shorted to something... and it only affects the operation when mute is asserted. Pin 40.

That one is quite a reach but I don't have much else to go on.

 

[BrianDonegan]

I put in a request to check the output of the comparator, but he is moving at the moment so it may be some time before he can do it.