Emotiva BasX PT1 preamp - first impression, two-preamp fix

[charles2]

Got the BasX PT1 to be a line stage preamp in a stereo hi-fi system. After several dozen hours of use, it was still too bright. I tried reducing the treble, but that did not solve the brightness problem well.

I put a Xiangsheng 728A preamp between an external DAC and the PT1. The Xiangsheng is a tube preamp, 12AT7×2, 12AU7×2, and 6Z4×2. The setup had no operational problems. The brightness was cured, but at the expense of muddy sound. I could toggle the Input setting on the PT1 between this setup and the PT1 straight. The PT1 remote made it easy to do. Sometimes I preferred the latter, sometimes the former – but I didn't really want to be going back and forth.

At this point I began to think about sending the PT1 back. Then I had the idle thought that I might put the Xiangsheng in the path after the PT1 instead of before it. Would that really make a difference? In desperation I tried it, and I found my solution. The brightness is gone, the sound is well-defined, and it is a little richer than the PT1 by itself.

I have no idea why the order of the preamps in series makes so much difference.

[MusicHead]

I suppose the input/output impedances of those three components play better together in this sequence than the other.

[garbulky]

Dec 10, 2021 13:18:06 GMT -5 charles2 said:

Got the BasX PT1 to be a line stage preamp in a stereo hi-fi system. After several dozen hours of use, it was still too bright. I tried reducing the treble, but that did not solve the brightness problem well.

I put a Xiangsheng 728A preamp between an external DAC and the PT1. The Xiangsheng is a tube preamp, 12AT7×2, 12AU7×2, and 6Z4×2. The setup had no operational problems. The brightness was cured, but at the expense of muddy sound. I could toggle the Input setting on the PT1 between this setup and the PT1 straight. The PT1 remote made it easy to do. Sometimes I preferred the latter, sometimes the former – but I didn't really want to be going back and forth.

At this point I began to think about sending the PT1 back. Then I had the idle thought that I might put the Xiangsheng in the path after the PT1 instead of before it. Would that really make a difference? In desperation I tried it, and I found my solution. The brightness is gone, the sound is well-defined, and it is a little richer than the PT1 by itself.

I have no idea why the order of the preamps in series makes so much difference.

What’s the rest of your system?

[charles2]

Dec 10, 2021 20:16:53 GMT -5 MusicHead said:

I suppose the input/output impedances of those three components play better together in this sequence than the other.

Rated impedances:

Xiangsheng 728A:
Input impedance: 100K ohms
Output impedance: 600 ohms

Emotiva BasX PT1:
Input impedance on its line inputs: ?
Output impedance: 1000 ohms (per emotivalounge.proboards.com/thread/58998/released-basx-stereo-preamp-tuner?page=2)

my power amp:
Input impedance: 100K ohms