2. amps-preamps
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This One has Me Stumped

I recently purchased a Pass XP-12 to replace my aging ML 38s. After installation, I noticed gobs of high frequency distortion, especially in Operatic female voices.

I measured every component in the signal chain separately. All are performing in spec.The XP-12 has very impressive test results.

Re-installing the 38s gets me immediately back to more mellow sound.

In my system, I have an EQ and crossover between the XP-12 and my Bryston 2.5b^3 power amp. I removed the EQ and the XO, plugging the XP-12 directly into the power amp. The distortion remains.

I am puzzled. I am a measurement guy. I use REW extensively. I can measure and troubleshoot almost any problem in my system. This one is a stumper.

Can anybody suggest a measurement or a way to solve this apparent component mismatch?

 

My system in order from source to output :

Shelter 901 MKIII MC or Koetsu RS MC cartridges

Parasound Zphono XRM phono preamp

Technics SL-1200G TT

Oppo BDP-105 Universal player (digital)

Bryston BDA-3 D/A ( feeds the Oppo signal to the XP-12 or 38s)

Sansui TU-X1 tuner

XP-12 (38s) line amp

dBx 1231 EQ

Rane AC22 2 way crossover

Bryston 2.5B^3 power amp

Usher 604 floorstanding speakers

HSU ULS-15 sub (when using the XO)

 

Thanks,

Kevin

 

128x128Ag insider logo xs@2xkevemaher
hsounds
119 posts
 

Just buy a Pass amp. The 30.8 is a great amp. 
a lot of people do not understand you have to have your amps specs line up with your preamp or DAC/Streamer used as a preamp. 
hegel like higher powered amps and weaker preamps. American equipment typically does the opposite. I have a buddy who has the Hegel mono blocks with the VAC Master preamp. Oddly though it has very similar specs to the Hegel Preamp so it works perfectly. I think the VAC is 9 volts. Where as my audio Research Ref 5se has 12 volts output which sounds amazing with my Luxman M10X amp. 

asctim
429 posts
 

Did you ever get a measurement of the high frequency distortion coming out of the speakers? Was REW showing super low distortion, even though you could hear it coming through the speakers as the sweep was playing? I have found that REW can't always distinguish distortion from background noise or late reflections. 

kevemaher's avatar
Ag insider logo xs@2x
kevemaher OP
71 posts
 

@asctim 

No. Distortion is audible and clearly present on REW data also.

asctim
429 posts
 

 Seems like you've covered the compatibility issues and the distortion shouldn't be happening. I'm sure they'll figure it out. 

The reason I mentioned REW getting confused is that I've had highly audible distortion pop up that was apparently so strange as to be unrecognizable by REW. Flutes sounded like a Kazoo was playing along with them. I thought a driver had a loose spider or something. Turned out to be an odd anomaly  in the digital domain. 

@hsounds 

The 30.8 may have ideal synergy with the XP-12, but the XP-12 should not be causing the amount of distortion the OP is hearing and measuring with any good amp with reasonable input impedance - which he has. Best to take it in and have it checked. 

Ag insider logo xs@2x
jji666
442 posts
 

Similar experience when my source component was overloading my preamp.  I suggest you try every source and see if it's consistent or just a single source.

I suppose the preamp could also be overloading the EQ or your EQ settings are too high relative to the new preamp's signal and overloading the crossover.  Try turning the gain down on everything a bit, including if you have any variable gain on any source so you can be sure you're not overloading the pre. Basically turn it down young man! 

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