Audio Research VT100 MK1 and LS15 HELP!!!


I recently bought this set VT100MK1 and preamp LS15 and while I was at this seller house he demonstrated the sound from his online Tidal on TV connect optical to the DAC Luxman DA - 06 then this go to the preamp LS15 and out into the VT100. This set up sounds amazing at his house. However, when I came home play CD from the Sony X1100ES Blu-ray player RCA output into the LS15 and out to the VT100 and it sound horrible - no bass at all in any type of music.  The sound sometime muffle and not clear and most importantly the bass missing tremendously. Im using a pair of KEF R900 Speakers. What is wrong here? can anyone help me correct the sounds? it is because I didn’t have the Luxman DA - 06 DAC? or it is because I don’t have those fancy hundred - thousands of dollars cable?  or the CD source is playin at 41khz /16 bit not high enough signal?  

This is my first system and I don’t know why I can’t get that high fidelity sound from the ARC equipments.  I'm waiting for the Audioengine B1 to arrive so I can stream Spotify into the LS15.   What is wrong with my set up?  Thank you in advance for helping me solve this.
kentrent

@newbee thanks for your explanation.  But the different is so huge.  It’s like the ARC has no bass at all.  The Mac1500 does have tone control but i flat them just to compare and it still boost a large amount of bass.  I called ARC and they said that tube 6922 doesn’t requires re-baised but that’s not normal for it to sparks.  I called Kef and they said not recommended to use the speakers in 4ohm when the speakers are rated at 8ohms.  
Assuming that the sparking is occurring most of the time (which would not be normal), rather than just briefly during the first minute after turn-on (which might be normal, as has been said), it is conceivable that both the sparking and the shut-downs are being caused by poor contact between some of the pins on that tube and its socket.

If you haven’t already done so I repeat the suggestion I and others made earlier of taking off the top cover and checking that the tubes are securely inserted in their sockets, and that they don’t seem so loose in their sockets that they come out with essentially no resistance.

When you do that, be sure to follow the cautions Jim (Jea48) stated earlier: Unplug the component from the AC, and wait for a while after doing so before touching anything inside. He suggested waiting for 30 minutes in the case of the amp; somewhat less than that would probably be ok in the case of the preamp (although keep in mind that the tubes will be hot for a while after the component is turned off). And be sure that any tubes which are lifted out of their sockets are returned to the exact same socket.

(Jim, thanks for stating those cautions, which I should have thought of saying myself in my earlier post).

We know in this case that the amp and the preamp were working before they were transported from the seller’s house to yours, at least for the amount of time you spent listening to them at his house. Which reinforces the possibility that something happened during transportation, or during setup at your house. Such as a marginal contact between the pins on a tube and its socket turning into a problem.

Good luck. Regards,
-- Al

Also speakers are rated at 8ohms though
As I stated before, KEF may rate the speaker as a 8 ohm nominal load, but you look at the impedance curve to determine which tap to use (to start with).  The frequencies in the bass and mid-bass range are at approximately 4 ohms. This is the critical area of the frequency spectrum because it is harder to drive the speaker to reproduce good low-end response.


Well I did a little on line reading regarding your speakers which causes me to suspect the combination of your ARC stuff and the KEF may be your problem. Your speakers seem to be considered ’neutral speakers’ (at best). You seemed to like them when driven by a (very) warm vintage receiver). You are hearing the results of you amplification choices quite clearly. You seem to like a warmer toned system’s sound but with better resolution than you get with the old Mac.. Very common in audio.

Now you change to electronic’s which, tonally speaking, might be voiced to be neutral (at best, IMHO, very cool). So you are doubling down, so to speak, and get the sound inherent in both. For you this sound is not synergistic in that it doesn’t produce the tone you want, not that either the electronics or the speakers are wrong, they just don’t sound as you would like when combined. I would suggest that most of us have been there and done that. I certainly have. That is why most folks will recommend ’matching’ your speaker and electronics. Arbitrary buying will not get you there.

BTW, regarding 4 ohm taps. I’m a bit put off by KEF’s ’recommendations re using only the 8 ohm taps. I could understand why they think your speakers might sound best a 8 ohms (perhaps they think the 4 ohm tap might unbalance their preferred sound) but I know of no reason you should not try them. Your speakers may have have a nominal 8ohm rating but this is far from indicating that they have a minimal 8ohm ’curve. Reviews point out that they have a minimal ohm droop to 3.8 ohms. Were I you, I would research this issue before I just walked away from it based on someone from KEF’s opinion. I like warm toned systems and have most always operated off 4ohm taps.