Audio Research REF 75 vs VAC Phi 200

I have no view as to which amp is better. I would caution you though that the amps may have different electrical attributes that may affect speaker compatibility. Specifically, output impedance, damping factor, and power supply size. If possible, try to audition the amps with your speakers.

Actually, based on correspondence I have had with another member about his VAC tube amp, I understand that his amp has a variable negative feedback (NF) control. As is usually the case, NF often times reduces an amp's output impedance and correlatively increases the amp's damping factor (DF).

Ok ... where I am going with this point is amp/speaker compatibility. As I wrote in my post above, I am not familiar with VAC amps. However, if they use little or zero NF, then an inference is permitted that they also have a "high'ish" output impedance and a "low'ish" DF. These attributes could result in acoustic colorations if the speaker's impedance characteristics vary considerably as a function of frequency.

In the case of the member mentioned in the first paragraph, his speaker choice was quite deliberate. Namely, one having "gentle" impedance characteristics that make for an easy to drive load with a minimum of acoustic coloration.

By contrast, most ARC amps use more NF and consequently have "low'ish" output impedance and "high'ish" DF for tube amps. As a result, this class of tube amps performs somewhat "SS-like" and can couple with a broader range of speakers.

That is the longer version of what I had in mind. I try not to be a name dropper. I'm sure the member I referred to above knows who I had in mind. If he wants to chime in, he should of course feel free.

Thanks Al. Your point underscores the importance of knowing what a speaker designer had in mind when voicing the speaker.

Of course, one may trip into a great sounding speaker that can do triple duty, i.e., mate with: (i) a very low output impedance SS amp, or (ii) a high output impedance tube amp, and/or (iii) a "low'ish" output impedance tube amp. Presumably, such an all-star speaker would have: (i) a ruler flat 8 ohm impedance function across the acoustic spectrum; (ii) a zero phase angle function across the acoustic spectrum; and (iii) high sensitivity.

And we should all believe in the Tooth Fairy too. :)

Oregonpapa ... what is the ARC CD-7se? Are you referring to the CD-7 with the upgraded power supply: (1) 5881 tube and (1) 6H30 tube??

Glad to read that the KT-150s are working out. Still scratching my head about why ARC continues to hold back officially blessing the KT-150 for use in its current amp lineup.

Yeeesss .... I've read the hearsay reports that so and so at ARC said the KT-150 are ok. I want to see it come in writing from ARC. They've had that tube in life testing for two or three lifetimes already. I doubt this type of conduct would have happened under Mr. Johnson's watch.

@Oregonpapa ... I've read the same about the CD-6 being totally solid state. Can't speak about its sound. In fact, it's the SS version of the Ref CD-9. I believe the CD-6/9 use a quad mono configuration for its Burr Brown chip sets. Supposedly better sounding than the CD-8, which is my CDP.

FWIW, Kal from ARC thought I would get more bang for the buck improvement going the Ref 150 SE upgrade route than messing with my CDP. And as I posted elsewhere, I look forward to reading your comments about your Ref 75 SE when you get it back from ARC.