Digital Distortion

Posted by: sjust on 21 May 2009

Not sure if I understand what is happening, and would love feedback from the knowledgeable, here.

My config is:

MacBook sends Apple Lossless sound to Airport Express. That sends to a Beresford DAC. That connects to the 552. Normally, results are very good. In rare (reproducible) cases I get significant distortion (some vibraphone tunes as a good example). Turning down 552 volume does not help. Turning down volume in iTunes (to 8/10) (and turning up on the 552) cures the problem.

I thought turning down in iTunes "castrates" the digital signal, and is not recommended.

Any good explanation ? Theoretical or practical ?

Stefan
Posted on: 21 May 2009 by james n
Output from the Beresford DAC too high and either overloading the input of the 552 or you've just got a bad beresford. Do you get the same problem if you use the headphone output of the beresford ?

James
Posted on: 21 May 2009 by sjust
my only headphone is a stax - which connects to the line output, so can't test the phone output, but your explanation (too high output voltage) sounds logical to me.

cheers
Stefan
Posted on: 21 May 2009 by james n
Do you get the same problem with the Stax running from the line out of the beresford ? I take it that these are fixed line out (the headphone is the only variable ?)

James
Posted on: 21 May 2009 by james n
Just looked and the beresford has fixed and variable level line outs - which are you using into the 552 ?
Posted on: 21 May 2009 by js
He should use fixed as it's lower and better. Beresford can't throw enough from any output to overload the input so it's probably just clipping on the variable turned up all the way or just defective. If it's distorting from the fixed it probably low voltage somewhere in the unit. If your using the stax in loop before the 552, try taking it out and see what happens as ther may be a line stage there though it's usually not the case. They will likely sound better of the 552 tape out as buffer anyway. Sometimes more in the circuit is actually better but you'll have to try and see.
Posted on: 21 May 2009 by sjust
Thanks for your thoughts, questions and remarks.

I am using the fixed output (seemed to sound better than the variable). Nothing else connected to the Beresford.
When using Stax at Beresford line out, results are same. Distortion goes away with 80 % signal from iTunes.
Stax normally not connected to 552. If connected, then to tape out.

cheers
Stefan
Posted on: 21 May 2009 by james n
The stax connected directly to the Beresford would be a useful test - if you get the same distortion then the beresford is at fault.

James
Posted on: 21 May 2009 by pcstockton
Try something, anything, other than iTunes. This should isolate the player, and it corresponding volume level) as a potential issue.

-Patrick
Posted on: 21 May 2009 by sjust
Patrick,
had similar issues when connecting a TEAC streaming device (instead of the Airport Express) to the Beresford (just more extreme), so I really see the reason in some overload. What is puzzling me, is the fact that by reducing the digital bandwidth, it is cured. Must be in the analog signal reconstruction, then.

cheers
Stefan

quote:
Originally posted by pcstockton:
Try something, anything, other than iTunes. This should isolate the player, and it corresponding volume level) as a potential issue.

-Patrick
Posted on: 21 May 2009 by pcstockton
... or a bad DAC.

FYI, I have the B-ford as well.
Posted on: 22 May 2009 by JYOW
Am I reading right that the OP has Airport-Beresford connected to a 552?
Posted on: 22 May 2009 by js
Probably as a stop gap until he finds something worthy for the purpose. Please, no posts to what others feel may be worthy. It's his decision and we all know what options are out there.
Posted on: 22 May 2009 by JYOW
Sorry I didn't mean to sound condescending, especially since I cannot afford a 5xx. Just saying that one shouldn't be surprised that a Beresford DAC would show its limitation in such a high end system. It did in my entry level 202/200 system as well.
Posted on: 22 May 2009 by js
As it should. Smile
Posted on: 23 May 2009 by sjust
Amen
Posted on: 24 May 2009 by garyi
If it were itunes the only thing I can think of is if you open the EQ there is a gain level on the side. itunes obviously only controls volume to lower than the system volums (computer) and max volume on itunes is only the volume at what ever you have the system set at. The gain level will however overdrive the signal. Check that the eq is off.