What makes the Bloom around instruments . . .

Kell_man,
I get that same 'bloom' you refer to when I use my Burson integrated. I don't feel it's distortion but the amps ability to pick up that last bit of info off the recording, intact, and sending it along to you speakers. That bloom is specific, and independent of everything else on the recording so it can't be distortion since its image and placement specific and nothing else is displaying it.
A very well regulated power supply can be the answer or if you believe what Burson says (and I do), being an all discreet design of high quality doesn't hurt.

I own a Pass XA30.5. To my ears, it sounds pretty neutral. I'm not doubting you about the difference in bloom you heard between the Pass and the Spectron. But I am wondering whether the difference in bloom is attributable to something that the Pass amp ADDS or to something that the Spectron amp SUBTRACTS. Here are two possible scenarios:

1. The Pass amp ADDED bloom to the system, whereas the Spectron amp did not.

2. The Spectron amp SUBTRACTED bloom from the the system, whereas the Pass amp did not.

I don't know anything about the Spectron amp, other than its excellent reputation. But as an XA30.5 owner, I can say that it does not seem particularly additive, at least not in the way I associate with descriptors like "bloom," which makes me think of euphonic harmonic distortion. This observation about the XA30.5 is confirmed by Stereophile's measurements, which show that its harmonic distortion is mostly 3rd order, and that it is otherwise rather harmonically neutral.

In light of that, I am inclined to believe that scenario (2) is the more likely of the two, and that the Pass amp's advantage over the Spectron was that it was allowing the bloom from the recording, or from other components, to be heard, while the Spectron was masking it. Of course, this is speculative.

It would be interesting to hear more about the system used to audition the two amps.

Bryon

Thanks for all of the responses. It makes sense.

Since it appears that it's a product of either my AC, Spectron or both, that's where I'll start to look.

It can't be the Wadia S7i since the bloom was there with the Pass but not with the Spectron.

Chuck

Bryon, I also think Chuck's speaker cables and such are more resolving than your anti cables. So maybe more details/resolution are heard in Chuck's system. Your two systems and rooms are different. Just a hunch, what do you think?

I run a 6SN7 preamp in front of a pair of digital monoblock amps and asked the same question.

Secondly, has anyone really heard bloom in a live amplified/un-amplified performance ?