2. amps-preamps
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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
lowrider57's avatar
lowrider57
5,393 posts
 
OK, that's a good start to troubleshooting, but since the Mac is a receiver you've removed both the amp and preamp from the system.
Have you re-seated all the tubes in both components? Gently wiggle them out (not all the way) and push them back into the tube sockets. There's also a good chance you've got a bad tube in one of the critical stages.

Can you call the seller and tell him what you are experiencing?



kentrent OP
71 posts
 
The seller gave me receipts that all new factory arc tubes were replaced Late December 2018.  So its roughly 8-9 months.   I also tested at his house before buying and it sounds amazing.  Do u think because i dont have the DAC Luxman D-06? Because he was streaming from Tidal optical into that DAC and into the LS15.  I don’t understand why when the units set up in my house it doesn’t sounds like that.  Would the DAC  makes that much different?
lowrider57's avatar
lowrider57
5,393 posts
 
No, I don't believe it would. I'll assume he was using balanced connections from dac to ARC preamp. That would provide higher gain to the preamp and then the amp.

RCA out of your CD into the proper RCA preamp input should result in good sonics at a lower level on the volume control.
Have you tried all the inputs to the preamp and made sure the tape monitor is off?
 
jea48
4,268 posts
 
almarg8,964 posts

08-28-2019
10:40am

One thing I would do is to remove the top covers of the two components and make sure that the tubes are securely inserted in their sockets. Especially in the case of the amp, given that all of its 16 tubes are mounted horizontally, which might have made them susceptible to coming loose when the amp was transported.


@ kentrent


If you pull any of the tubes from the VT100 make sure the tube goes back into the same exact tube socket the tube was removed from. Exactly the same tube socket.

Especially the small 6922 signal tubes. Failure to do so can cause damage to the amp. The 6922 tubes are biased for the circuits they are installed in.
Also before you pull the top cover unplug the amp from the power wall outlet. Let the amp set for about a half hour to allow the high voltage electrolytic caps to drain/bleed off. The DC plate voltage for the power tubes runs about 450 volts DC.

Did the guy you bought the amp from tell you about how many hours are on the 6550 power tubes and the 6922 signal tubes? If not you need to find out.

6550 power tubes have an average life of 1500 - 2000 hours. The 6922 tubes average life around 4000 - 5000 hours.

Jmho, you are not knowledgeable, experienced, to replace and bias the 6922 tubes. You will need to pay to have it re-tubed by a professional when it comes time.

Total retube of VT100 Mk 1 & Mk 2
http://mycollins.net/audio/artube1.html

~

As for the speaker jumpers. Can you here any bass, music, at all coming from the bass drivers?


Jim
kentrent OP
71 posts
 
@jea48 

the tubes was replaced 8 months ago with brand new tubes from arc. I do hear bass from the bass driver but overall sound quality the bass is missing that punch greatly compared when im using another amp like the old vintage 1965 MAC1500    

The difference between my set up and the seller is he he Tidal streaming into the DAC then goes into the preamp LS15.  Could it be the DAC that i didnt use and the source is Sony Blu-Ray player?
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