2. tech-talk
  3. 151063-1641

CD distortion through preamp

I apologize for the long post. I’m trying to make this as brief as possible while providing all the necessary info.

The equipment: preamp is Audio Research Ls25 mkii, pass x250.5 amplifier, and bryston Bha headphone amplifier, Wilson watt puppy speakers. All connected with balanced cables. I needed the fixed output to rip records, so the headphone amplifier is connected to the 2nd variable output.

The issue: I’ve had problems with CDs distorting when the music (dynamics within the performance) gets louder. The distortion is mostly noticeable in the mid to upper range and it’s through both the speakers and headphones. No issues listening to records or dac when it is hooked up to the computer with usb. But when I tried using the CD player as a transport to the dac, the distortion returns.

here’s what I’ve tried without success:
-new tubes in ls25
-3 different CD players
-tried rca cables
-different inputs

I also tried a Bryston bp25 solid state preamp and had no problems. It seems like the ls25 is the issue. 

Any thoughts or suggestions?


tripg
kijanki's avatar
kijanki
4,394 posts
 
@tripg   I glanced over manual and found warning, that mkII uses different tubes than mkI.  Are you sure you have 6H30 tubes installed?

Manual say that single ended inputs can handle up to 14V (28V for balanced) at the lowest gain position (6dB).  I cannot imagine it being overdriven. Likely there is something wrong inside (wrong or faulty tubes etc.)
mike_in_nc
1,121 posts
 
As I glanced through the manual, the function of the gain control was not crystal clear, by a long shot. I thought it said that the preamp would limit the signal above the "gain" chosen; i.e., that something with high output (like a CD player) should be run at the higher "gain" settings.
tripg OP
21 posts
 
Mike_in_nc,
if I understand you correctly, I don’t think it works that way. When you raise the gain setting from lo to med or high the volume definitely jumps up a notch. 
tripg OP
21 posts
 
Al,
you were correct!!!!

And looking back, it makes a lot of sense.

I haven’t always experienced this issue and I’ve been using this preamp/amp combination for years. I switched the headphone amplifier to a variable output about a year ago. If I had a better memory, I’d likely recall that’s when the problem started. Although I still think it’s odd the DAC didn’t distort like the CD player. I’d think their outputs would be the same. I’m just happy it works correctly now!!!

I can’t express how grateful I am. Thanks AL!!!!

Luther
Post removed 
More to discover