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It was the output tubes all along...

I think I finally reached the balanced sound I have been seeking for years.  I've had my VAC 200 IQ's monos for about 7 years.  When auditioning the amps I was comparing these to a similar priced Pass solid state amp.  I liked the bass of the Pass, but really liked the tube sound of the VACs.  The VAC's come stock with KT 88's which seemed a little tame to me at the time.  Mike at Suncoast Audio was incredibly generous with his time during this process and rolled some KT-120's and then finally the new KT-150's over the course of a couple of hours.  The KT-150s added the bass slam that was equal to the Pass but had the nice warmth of the tubes to boot.  Sold!  Kevin Hayes was great-switching out the KT-88's for the KT-150s when my units were manufactured.  This was my first big boy purchase-a move up from an older MacIntosh unit.  We moved a few times and 5years ago I was able to build a listening room with optimal dimensions in what will be our last house.  By this time Mike had been able to secure lightly used Magico S7 speakers for me and things sounded pretty good. I've sequentially added rugs to the wood floor, first reflection point GIK art work, and other acoustic treatmens.  The bass was a little prominent, so I added bass traps as well as The Swarm subwoofers.  Things sounded great.  Then I added the secret sauce-VAC Master preamp with phono.  I was stunned at the sound I was hearing.  I added Valhalla 2 interconnects and speaker cabling with further improvements.  However, I started to notice the bass had become somewhat intrusive on about 30% of my records (mostly classic rock, jazz, blues).  I paid extra attention at live events to see what proportion the bass occupied in a variety of musical events.  About this time I found several excellent discussions on tube rolling here on Audiogon.  I paid extra attention to the posts of @Mulveling as he has owned most of my current equipment and has lots of experience with different tube combinations.  I played with some NOS input tubes which further improved the sound stage and overall timbre, but the pesky bass persisted.  It got in my head big time.   I stopped listening to the music, rather focusing on where and when the bass would vie for sonic dominance.  I reread some of the tube articles where @Mulveling stated he didn't care for the sound of KT-150s and found the best sound was achieved with KT-120s. I talked to Kevin Hayes who prefers the KT-88s.  What to do?  At this time I was sure I needed a tube change, but not sure where to go. I spoke with Mike from Suncoast, who actually had come previously just for a listen.  He liked the bass, but suggested I try the KT-170's.  He said it was the best sounding and tight bass he had heard and a has a set up featuring them in his shop.  I polled this group, but there was no one with an opinion on the virtues of the KT-170 over the KT-150 tubes.  Sooo. I am now 400 hours in with the KT-170's.   The bass is spectacular! Fast and full and but balanced. Didn't lose the slam.  No more subterranean rumbles, either.  The sound stage is broad with good depth and instrument placement. The mids and highs are great.  I had one audiophile friend over for a 3 hour listen.  He had heard the system before the tube switch and had commented after prompting that he didn't like the bass sound at all and it wasn't 5 minutes in that he exclaimed that the sound "was perfect".  I am now hearing only music. Using the retrospectuscope, as my system incrementally became more revealing, the faults of the KT-150 slowly emerged.  I see no detriment to any aspect of my sound after making the switch to the 170s, only a much much better bass.  Hopefully this post can help inform others as to what to expect with the KT-170 tube, especially if they are running KT-150s. I did check with Kevin at VAC who indicated there was no conflict with this tube, as the parameters were similar to the KT-150, but this may not hold true for other systems-so please check if you decide to try the KT-170's.  However, it's still not clear what tube is actually the best for this system...

orthomead
ghdprentice
6,915 posts
 

Congratulation. Thank you for sharing your experience. It is really valuable for folks to see the dedication and work that goes into crafting the perfect system for yourself. I know, I have at times been really close with some aspect that needed tweaking and just pure effort and persistence ultimately triumphs, congrats.

Also, Magico are really sensitive and revealing speakers… getting the input perfect for them is really required. I have heard a lot of bad sounding Magico… not because the speakers are bad, but they reveal nuances many other speakers will not.

wsrrsw's avatar
wsrrsw
995 posts
 

Also went from KT88's to KT170's. There's magic in the 170s.

peter_s
1,333 posts
 

I will need to contact Kevin Hayes and ask whether I can use KT 170 in my phi 200 amplifiers. Can you suggest a good source?

mijostyn's avatar
mijostyn
8,546 posts
 

@jasonbourne71 1+

However, the S7 has a very flat 4 ohm impedance curve. You probably still have a lot of room for improvement. A good friend of mine has S7s. I am working with him to get the best out of them. I think you should try KT88's and I would match them even though your amp does not require this. All 8 should match! Small differences in amplitude response will affect imaging. Another approach, the one I take is to measure the system by channel at the listening position, but I have the ability to correct any amplitude problem, you do not. The amount of power your amp makes is totally dependant on the power supply. With KT88s in mono configuration your amps put out 200 watts which with subwoofers is more than enough to do the job.  

The swarm is a great system for bookshelf speakers. It is nowhere near powerful enough for for the S7's. You need at least four 12" drivers. Two Magico S subs or two Martin Logan BF 212s would do the job. My friend has four 13" JL Audio subs which I am not crazy about because of reliability issues. I believe the S sub has a complete crossover in it. The BF 212 only has a low pass filter like your swarm. This is not satisfactory particularly with your amps. You need a complete two way crossover with complete bass management. I would put the subs outside the S7s in corners. This only works if you can correct time and phase. I would cross at 80 Hz. What are your program sources? 

Done correctly, your system will be able to play Vini Vici at 100 dB and blur your vision or the Melos String Quartet at 85 dB and make you cry. 

lewm
12,933 posts
 

Tube amps are generally not the best choice for any speaker with a nominal impedance of only 4 ohms. Not only is the impedance a problem but also such speakers tend to be relatively inefficient. However it is not correct to say as a general principle that 1 ohm output Z is some sort of cutoff point. Mate that amplifier with an efficient 16 ohm speaker or even an 8 ohm speaker where the impedance at bass frequencies remains 8 ohms or higher, and the match can be superb.

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