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

I've taken the xp-12 into the Pass factory. Kent gave me a quick tour of the production area. I explained my observations and measurements to the tech who will be testing the xp-12.

They've had it for about a week. I do hope they have found something wrong.

@jji666 I've measured signal levels throughout my system with an AC voltmeter, osclloscope and RTA. The measured input and output voltages are well within normal range for each component.

I hope that Pass has an answer.

Pass Labs found a gain module that was out of spec. The preamp was manufactured in 2019. Passed replacd the module with the current production module and tested. My XP-12 is now in spec.

I've not set it up in my system yet.

Pass was very responsive and discovered the problem very quickly and was honest and straightforward about what they found and what they would do to fix it.

Excellent service! Very trustworthy.