New tube in amp, smaller soundstage from speakers

[ebrandon]

A couple of days ago I did some tube rolling, replacing an NOS GE 12AX7 with a Mullard in my Elekit TU-8600 integrated amp. My speakers are Klipsch LaScalas.

The Mullard sounds “better” to my ears in almost every way - I’m just enjoying the music more.

But one unwelcome change is that the soundstage has collapsed. With the GE tube the sound filled the space, extending well to the left & right of the speakers. With the Mullard tube all the sound is between the speakers with most of it coming tightly from the center.

Thinking about it, I’m beginning to suspect that there’s no way this could have happened by the new tube being in any objective signal amplification sense “worse”. It can only be a result of the sound being more in-phase than before, right?

So am I right in thinking that “better” amplification is leading to less soundstage? Or am I thinking about this wrong?

Is there some deficiency in a tube’s performance that could lead to a smaller soundstage? What could it be? What would the mechanism be?

 

[killdozzer]

Not an easy question. A lot of this is very vague and susceptible to subjective interpretation. Not all may even agree that the "sound stage" has indeed "collapsed".

I can only guess replacing the tube can't be done quickly enough to a reliable comparison. Anyway, if all relevant specs are the same, as they should be when replacing a part, no change should be expected.

 

[lovinthehd]

I prefer rolling joints...

 

[PENG]

A couple of days ago I did some tube rolling, replacing an NOS GE 12AX7 with a Mullard in my Elekit TU-8600 integrated amp. My speakers are Klipsch LaScalas.

The Mullard sounds “better” to my ears in almost every way - I’m just enjoying the music more.

But one unwelcome change is that the soundstage has collapsed. With the GE tube the sound filled the space, extending well to the left & right of the speakers. With the Mullard tube all the sound is between the speakers with most of it coming tightly from the center.

Thinking about it, I’m beginning to suspect that there’s no way this could have happened by the new tube being in any objective signal amplification sense “worse”. It can only be a result of the sound being more in-phase than before, right?

So am I right in thinking that “better” amplification is leading to less soundstage? Or am I thinking about this wrong?

Is there some deficiency in a tube’s performance that could lead to a smaller soundstage? What could it be? What would the mechanism be?

To me it sounds like the tubes have quite different frequency response characteristics, likely in the mid range. You should be able to narrow down the reason by plotting some FR graphs. Do you use REW?

 

[highfigh]

12AX7 have been very inconsistent- that's why so many opinions exist about their sound. Some prefer GE/Sylvania, Mullard (especially the Blackburn), Telefunken, Phillips Bugle Boy, whatever, for various reasons.

I would ask why you felt it necessary to change anything- the difference may be in the frequency response of the tubes, maybe they tailored the amp's design to the Mullard, maybe one of the tubes and the circuit interact differently- it would be a good idea to put them in a good tube tester, to see if there's any differences.

 

[ebrandon]

It would be worth comparing the frequency response between the two tubes with REW, and I’ll do that.
But experience leads me to believe the FR plots will look identical.
i suspect some other mechanism is at work, and was hoping people here might have some ideas as to what it could be.