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
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No, the CD player into those SE1 input of the LS15.  why is has no bass?
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No, not that.  CD player rca into SE1 on the LS15.  I just don’t understand why it has no bass.  
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Has two output.  Main and record. I used the main XLR to the amp vt100.  
You should be getting quality sound using your CD player.
What RCA interconnects are you using? Have you tried using a different input on the preamp?

Check to see if the tape monitor is set to off.



When u said rca interconnect meaning the type of cable im using? Im using generic brand rca cables.  
Nothing wrong with using cheap cables! Make sure both speakers are connected in the same polarity from the amp - positive to positive, negative to negative. + to + and - to - !
If the speakers are not in phase the sound will suffer - poor imaging and lack of bass!
Use the 4 ohm taps on the amp because those Kef's dip to low impedances!
Not to insult your intelligence, but are you sure your speakers are connected correctly?  Looking at those speakers, they have internal jumpers and you need to turn the screws to connect the jumpers if you don't have the speakers bi-wired.
I did try all of that. Speakers setup connection is correct. I did link them and not biwire.  
I did try all of that. Speakers setup connection is correct. I did link them and not biwire.  
OK- so you checked the phase of the speakers, and by that I mean you changed the phase on **only one of them** and played a bass track and there was no improvement. Right?
Is the room rectangular? Are the speakers facing into the long dimension of the room (If not, bass will suffer)?
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.

Regards,
-- Al
  
Let the OP send some pictures of the back of the preamp, back of the amp and back of the speakers, showing how he has them connected! 
+1 almarg! I too had that thought about tubes coming loose while being moved!
I will take pictures of the back and set up so u guys can see when i get home from work today.  Some people on Facebook ARC fan group said I don’t have good speakers but I doubt it. What do u guys think? 
There’s nothing wrong with your speakers. I’ve heard the R900 with a 30W tube amp and it was a very pleasant listening experience. The R series is the entry-level for KEF, so there is some cost cutting to the cabinets and bracing, but not the drivers and crossovers. These speakers are revealing, dynamic and throw a huge soundstage.
Although listed as an 8 ohm speaker, the impedance curve indicates a large part of the all-important low and mid-bass frequencies are at about 4 ohms. So the 4 ohm taps should be tried first, as stated in the above comments.

@lowrider57 thanks for your input. I will try the 4ohm today.  This wont damage the speakers since it rated at 8ohm? 

The thing i discovered is when i connected to the Mac1500 (1965 model from mcintosh) and it does produces fuller bass and treble.  Sounds very nice using the same Blu-Ray player.  But using with the ARC the bass just strip down a lot. So im worry that maybe either the LS15 or the VT100 are having defects that im not aware?  I dont want to be negative and assume seller is selling because of this issue... but i just cant help it thinking about it.  
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?



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?
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?
 
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
@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?
@lowrider57 he was using rca into the preamp not balance.  I asked him and he said the DAC will fix my problem. Im not sure if he’s right
The only difference is the dac most likely has a higher gain than your CDP.
That doesn't explain why you have poor bass response. 
A CD is always a good reference to use when testing a system.
@lowrider57 u are absolutely right about the Dac help gain.  At the seller house setup, he only turn on 30% and i can hear music pretty loud. But when my setup i had to crank up to about 70% to hear loud.  So definitely this confirmed that DAC increase gain.  But i cant explain why my arc setup is low bass response.  I’m kinda sad and disappointed that i spend a lot of money but im not getting the sound i want.  Idk what’s wrong... 
Do you have any other sources? TV, turntable, tuner. 
Maybe the Mac 1500 has a preamp output you can plug into the amp.
@lowrider57 i will try different source today to see if the sound changes.  Maybe ill use another bluray player 
But i cant explain why my arc setup is low bass response.  I’m kinda sad and disappointed that i spend a lot of money but im not getting the sound i want.
Again- did you swap the phase on **only one loudspeaker**?
If you did both you would not find anything out. You have to swap the phase on just one.
@atmasphere im not quite understand what you’re saying... can u explain. Thanks 
kentrent OP12 posts    

08-28-2019   
 3:46pm


 At the seller house setup, he only turn on 30% and i can hear music pretty loud. But when my setup i had to crank up to about 70% to hear loud.

Are you 100% sure you have the speaker cables connected to the VT100 amp terminals correctly?
( 0 ) is common, neg ( - ). Make sure both speakers neg ( - ) is connected to ( 0 ) common on the amp.
Pos ( + ) on the 8 ohm or 4 ohm terminal on the amp.
Verify 100% you have them connected correctly.


Also make sure the interconnects are plugged in all the way.



@atmasphere im not quite understand what you’re saying... can u explain. Thanks
@kentrent  Yes:

Play a track with bass that you know.
Go to the back of one speaker, left or right doesn't matter. Reverse the speaker connections.

Play the bass track again. Did it get better? If yes => good, if no=> it was right the first time.
kentrent,
When using the Mac do you have the tone controls set flat or are you boosting the bass??
If you are boosting the bass try it with the tone controls set flat and compare that to the ARC.

@andirocks with the MAC it has tone control: treble and bass.  Good idea i will try it and let u know.  Thanks 
@kentrent

Are the amp/pre amp plugged into a power conditioner?

If so, plug them into the wall, at least the power amp.
@pokey77 no power condition. Power right into the wall. Im not getting bass.  
@jea48 so i arranged the wires like you said as follow:

speakers neg ( - ) is connected to ( 0 ) common on the amp.
Pos ( + ) on the 8 ohm terminal on the amp. This resulted same bass but when I reversed the wire it like slightly increased bass.  Why is that? Just slightly not a lot.  I compared this sound to the Devialet Gold Phantom and the phantom has so much more bass.  
Where did the Gold Phantom come from? What kind of inputs does it have?

Can you repeat Jea's test but this time use the 4 ohm taps. The bass on your speakers is about 4 ohms.

I think you should test the tubes some more.  It doesn’t matter that they are new, they can still be broken. 
Are the VT100 SE jumpers in or out?  

FYI.  I have had a VT100 mkiii and LS25 for years.  And, I own the Luxman DA-06.  Output is twice + that of your Sony.

May be able to help.
Aren't there those little U shaped shorting pins that go in the XLR jack if you use the RCA inputs?  Or was that only on the amp, I can't remember, been too long since I owned ARC gear
@lowrider57 i owned the gold phantom so i compared it to the arc and kef r900.  The gold phantom has a lot of bass streaming from my iphone.  Even when i connect the same sony to the Mac1500 amp it still has a lot better bass comparable to to the vt100.  Could it be something wrong with the vt100 and ls15?
So as i was doing all these troubleshooting the LS15 keeps shutting off randomly every few minutes.  This prob new since i got it yesterday.  What is this guys? Im beginning to worry... :((
@chip_2950 

what do u mean SE jumper on the VT100?
Jumpers are used in the amp XLR inputs when you are using RCA cables. But you're using XLR between amp and preamp, correct?

Have you been interrupting power to the preamp, eg, pulling out the AC cable, powering the preamp or amp on, off quickly?
There is a safety mode on the preamp if power is interrupted.


http://vpiforum.com/viewtopic.php?f=7&t=8590