Audio Research REF 75 vs VAC Phi 200

I don't think you can go wrong with either of these amps. I personally like Vac equipment a lot and have found that Kevin Hayes of Vac is a really great guy to deal with.
Alan

Vac is a much better amp!!

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.

The AR has very few rolling opportunities with the KT120s and 6h30s, pretty much stuck with very few choices unlike the VAC.
One positive, I could drive the AR to manufacturer for service.

Both are excellent amplifiers, you really can't go wrong with a choice. I prefer the VAC to ARC, but it's really personal preference in the sound I like (I've always felt ARC was more tilted to the highs, even their newer models, and I like a full midrange, which I definitely get from the VAC). As far as tube-rolling, while you certainly can do it with the VAC, I haven't had the urge to do so, which is unusual for me.

One thing that Bifwynne points out is a definite consideration with the VAC, as it is very sensitive. I have a Shindo preamp with a lot of gain, and I could barely get the volume control to 7 o'clock before it was at a comfortable volume. I actually have put in attenuators at the amp (something that is built in to VAC's Phi 300.1) to get a little more play in the Shindo volume control. On the other hand, using a TVC passive (Promethius) as my preamp has resulted in no such problems, so you may need to consider the output from your preamp in making your choice.

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.

Bruce (Bifwynne), your discretion is appreciated :-)

As the aforementioned unnamed member, I'll second all of the excellent comments offered by Bruce and by Russ (RCPrince). With a slight modification to Bruce's statement that "these attributes could result in acoustic colorations if the speaker's impedance characteristics vary considerably as a function of frequency." At the end of that sentence I would add the words "unless the particular speaker is known to work well when paired with an amplifier having highish output impedance." Some speakers whose impedance varies widely as a function of frequency will still work well when driven from a high output impedance, and in some cases better than when driven from a low output impedance. It depends on the intention of the designer, as Ralph (Atmasphere) has said a number of times.

Specs don't appear to be provided for the Phi 200's output impedance or damping factor, or for the amount of feedback it uses, but it's probably safe to assume that the amount of feedback is considerably less than the 15 db used in the Ref 75, and its output impedance is somewhat higher than the 1 ohm (damping factor 8) specified for the Ref 75's 8 ohm tap (or the 0.5 ohm output impedance the Ref 75 can be presumed to have on its 4 ohm tap).

Also, consistent with the comment by Russ, VAC amps seem to generally have gains that are significantly higher than average, and the Phi 200 is no exception (30/36 db or 31/37 db, depending on what document is looked at, for the balanced and single-ended inputs respectively; and, no, I don't have that reversed). The gain of the Ref 75 is spec'd at 25 db balanced.

So if your preamp has relatively high gain, say upwards of 10 db, and/or if you are using primarily digital sources, and/or if your speakers have relatively high sensitivity, that would work in the direction of favoring the ARC.

And if your speakers have wide variations of impedance as a function of frequency, and they are known to work well with solid state amps (meaning that they match up well with amplifiers having low output impedances/high damping factors), that would also work in the direction of favoring the ARC.

Otherwise, my personal instinct would be to go with the VAC, although I suspect you would probably do well either way, as Alan and Russ indicated.

Best regards,
-- Al

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. :)

Being within driving distance of the company for service means a lot. Therefore I'd audition the ARC and if you love the sound, go for it.

I recently read a thread where people were having issues with their ARC amps, and it was mentioned that some preamps do not play well with ARC amps and could cause problems with them. I have no idea about the details of this or if it's correct, but I'd at least look into this and see if your preamp is a good match if you ultimately decide on an ARC amp. I'm sure others know a lot more about this, but just wanted to bring it up just in case it's a legitimate issue. Best of luck.

Good point by Soix.

Here is the thread that he appears to be referring to. Apparently the manuals for some ARC amps indicate that if non-ARC preamps are used with them damage may occur. The link opens at a post in which I speculated about possible explanations.

Whatever the reason may be for their statement, my suspicion is that it would be unlikely to be an issue with most non-ARC preamps, but I suppose it conceivably could be an issue with some.

Best regards,
-- Al

I have a REF 75 and there's nothing in the manual warning about using the amp with non-ARC preamps.

I don't drive it with a ARC preamp.

The REF 75 only has balanced inputs, so you do need a preamp with real balanced outputs.

I haven't heard the VAC amps in my system, but I own the
REF 75. Don't judge the REF 75 until you change out the
tubes for KT 150's - available from Upscale Audio. While
the REF 75 is amazing with the stock KT 120's, it is in a
different league with the KT 150's. If you go with the KT
150's, you'll have to leave the top cover off of the amp
because the new tubes are a bit too high. Sounds better
with the cover off anyway, so ... so what?

My current system:
ARC REF-3 pre amp
ARC REF-75 amp
ARC PH-8 phono
ARC CD-7se
Well Tempered TT. Original issue and highly modified.
AT-0C9 MK III cartridge.
Speakers: Legacy Signature IIIs biwired with Cardas
binding posts.

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.

I fully endorse Oregonpapa's comments on the ARC and KT150 tubes. I can not comment on the VAC, which is not imported to the UK, but the Ref 75 is by a big margin, the best amp I have had in my system, though it is the most expensive.

On the subject of pre-amps, I run mine with a clone of the Music First Audio Baby Reference and it is a great combination, a cleaner more neutral and less coloured sound than the ARC Ref 3 pre I compared it with.

Oregonpapa, I have read elsewhere that KT150's in the Ref 75 do NOT require the top to be left off. Can you clarify your comment? Are you saying the top won't go on due to tube height, or that you are not comfortable with proximity to the cover? On another forum, a member took temperatures on a Ref 75 cover with KT 120's and 150's and found them to be the same.
A lot of people who might try this tube may be disinclined due to a requirement to leave the top off, so please clarify. Thanks.

David12, I've never listened to a Ref75 but have read the glowing reviews.. You said it was the best amp by far in your system. By comparison can you tell us what other amps you've had that it bested? I'm trying to get a point of reference.

Bifwynne ...

Yes, its the CD-7 with the upgraded power supply and tube upgrades. Big jump in sound over the stock CD-7. In fact, quite amazing. I have it on good authority that the newer CD-6 is more analog-like ... and it has no tubes.

Dbarger ...

Yes, you're correct. The top WILL fit on with the KT-150's in place, but just barely. Even so ... leave the top off. The amp sounds better sans the top ... just like turning the meter lights off. Same thing for all of ARC's display lights.

Also, just in case you folks haven't seen this in some of my other posts; move the tube dampener rings up to as close to the top of the tubes as you can get them, and be sure that both rings are solidly touching each other. This provides for a nice overall improvement in sound.

Happy listening ...

@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.

Bifwynne ...

According to my source, the CD-6 is a fantastic CD-Player. I'm tempted, but I really love the sound of my upgraded CD-7. It really jumped by a large margin when I installed the REF-75 into the system. It was like an entirely new CD collection ... and I have a couple of thousand of those silver discs. (Are we nutz, or what?) Based on that, I think Kal gave you some straight-up advise.