Audio Research VT100 MK1 and LS15 HELP!!!

Did you make sure your Sony is set to correctly mix down to stereo in it's menu and not set for surround with bass sent to a sub.

Did you check to see if the shorting pins on the XLR inputs are inserted?
This was already suggested by another poster: did you check this?
All your components should be performing well together.  The DAC is not the reason for your problem.  
Are you 100% sure ALL of your components are connected correctly? 
How confident are you knowledge of how audio connections are made?
I've ARC for decades, with now having current pieces, and have always had exceptional performance. 

You were clear, everything sounded good at the sellers house.  Both channels (I presume) loosing all their bass AT THE SAME TIME is unlikely if it was tubes.  CHECK your connections.

Hey,

So, some thoughts.

If you have some standard electrical wire - i.e. the kind that runs inside the wall - you can use a piece of the ground wire, cut it down and make a jumper wire for the XLR if using SE input. If you have any music on your phone, use a 3.5mm to RCA adaptor and run it directly into the amp. At least you can isolate where the problem actually lies. 

@lowrider57 im waiting for the DAC to arrived.  We’ll see if its fix the problem for good.  Thanks 

The EQ is a good temporary fix. Please keep an eye on the preamp for any shorting out or shutting down due to the tube.
:-)

But I’m still replacing the v3 tube just to be cautious since ARC said that’s not normal. 

@lowrider57 tube V3 in LS15 still sparking when turned on but with the EQ added the sounds boost to an amazing level.  :))

So, there's no tube problem in the preamp?

Guys!! Seems like my bass response problem solved. I installed an EQ and this boost the signal tremendously which now i can do tone control. This is my current set up and it now sounds amazing like it should. Fuller sound with deep bass response and clear treble with details.

CD to EQ to LS15 to VT100 out at 4ohms to R900.

(From preamp to amp using XLR and the rest are RCA interconnect)

Although i solved the bass response problem but I’m not satisfied with the sound completely since the EQ makes the sounds too artificial (even though it sounds very good). I want to be natural sounding as much as possible. Perhaps i should look into a preamp that has tone control? Or i should get a good DAC to boost the signal into the preamp? Any recommendations?

thank you again for being so helpful and wonderful. Love this community. 👍👍

@jea48  Wow! Yes, it appears you were right that you were wrong :-)

And between Chip's comment earlier and my not looking closely enough at the rear panel photos I mentioned it appears that I was wrong as well. What I assumed were separate connectors for the jumpers were just printed symbols.

Thanks for catching that.  

Best,
-- Al

P.S: I'm signing off for the night.

@almarg

No Al, I was wrong. The bad thing is I knew better, LOL.... Like I said I must have had a brain fart moment.

Here is a picture of the back of a VT100

https://www.google.com/search?q=audio+research+XLR+single+ended+shorting+jumpers+for+vt100+power+amp...:


Note the printed picture beside each XLR input connector showing the correct jumper install position for the jumpers.

Edit: No excuse but I know where I went astray, LOL.......

chip_29508 posts   

08-29-2019 
 8:02pm 

So... Just a polite correction. The jumpers do not go in the XLR socket. The receptor is separate and apart. See the manual.

Jim

The jumpers install into the balanced output jacks.... They would have to be removed before the balanced cables could be plugged in.

@jea48  Jim, no, I'm pretty certain that you were right the first time. The OP said that his amp is a VT100 MkI (which I would think is the same thing as a VT100 that has no Mk designation indicated on it). Your comment that I quoted would apply to the MkIII, and perhaps to the MkII, but rear panel photos of the VT100 with no Mk designation show connectors for the jumpers that are separate from the XLR input connectors.

Best,
-- Al
 

My bad! The jumpers install into the XLR balanced input jacks. I must have been having a brain fart. They would have to be removed before the balanced cables could be plugged in.

All my posts about the jumpers being installed when using balanced cables are moot. It can’t happen...
Jim

No, the owner didnt give me anh jumpers

Would it damage the system if i dont have jumper connected while using rca?

No.  It just wouldn't be sonically optimal, and it might result in a bit of hiss and/or hum.  

Regards,
-- Al

Would it damage the system if i dont have jumper connected while using rca?

Damage, no.  Read the owners manual why the jumpers should be installed when using RCA single ended ICs.

Didn't the seller give you the jumpers for the amp? Surely he mentioned them.

@almarg, the random shutdown is resolved for now.  But about the jumper, i dont have anh jumpers connected to the xlr. 

@jea48 well, i dont even have the jumpers. Would it damage the system if i dont have jumper connected while using rca?

@Kentrent, the jumpers must be present on the rear of the amp (in the two places where it says "use jumper for single-ended") if and only if the connections between preamp and amp are made with RCA cables. The jumpers must be removed if the connections between preamp and amp are made with XLR cables.

@jea48
Jim, it looks like I provided an answer to some of the questions you directed to me in one of your recent posts while you were composing that post. So as I said it seems very possible that if the jumpers are installed while the amp’s balanced inputs are being used it "could make the preamp very unhappy." And the caution you found in the manual about not using the mute function while the volume level is high would seem to add credence to that.

Regarding your question about the volume difference, the OP had said earlier that:

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.

... And I note that the seller’s speakers are spec’d as being 6 db more efficient than the OP’s speakers. I’m guesstimating that would account for about 1/3 of that 40% difference. And perhaps differences in the source components and source materials that were used, room effects, and differences in listening distance might be contributing to some extent as well. But in any event it would seem that all bets are off until the issues of the sparking tube and the shut-downs of the preamp are resolved.

Best,
-- Al

kentrent OP35  

 posts08-29-2019  
 9:20pm@jea48 yes.


The shorting jumpers were removed. I used RCA interconnect. This will effect the sound if jumper not removed?

The jumpers MUST BE REMOVED if using balanced ICs
The jumpers Must BE INSTALLED if using RCA single ended ICs.
Jim

I don’t have any jumper connected to those balance output

@jea48 yes. The shorting jumpers were removed.  I used RCA interconnect.  This will effect the sound if jumper not removed?

Just right now, i used another old 80s preamp from Sony and the sound is boomy boost of full bass and tone control was on neutral (imagine if i crank that bass up). So this confirmed the vt100 is working and my LS15 preamp is not giving that sound. Perhaps because of the faulty V3 tube? I already ordered the new tube on the way. I’m hoping replacing this faulty tube will fix my bass response problem.

@ kentrent

I assume you used RCA single ended ICs to connect the Sony preamp to the VT100.
Read my post above ( page 2 ) about if the shorting jumpers were removed on the VT100. If you were using balanced ICs the jumpers must be removed.

Back of VT100
https://www.manualslib.com/manual/907956/Audio-Research-Vt100.html?page=3#manual

@newbee you said it right out of my mind and I couldn’t have said it better.  Yes, i love the vintage tube sound of warm and low soft bass response from vintage MAC1500 but i needed more details.  I thought this ARC equipments would give me that sound im seeking for but its so flat and no bass.  I can understand these equipments are not colored or has any tone control but i feel that the bass should be a little more fuller.  The sound doesn’t feel full like it should coming from a floor stand speakers.   I compared the ARC sound with the 2 Devialet Gold Phantom speakers and the ARC has about 50% less bass.  The gold phantom has good soft bass response i want but it doesn’t has the holographic sounds and details like from the tube amp system.  My goal is to have both in this system but i guess the r900 and Arc don’t work synergistically...?

Just right now, i used another old 80s preamp from Sony and the sound is boomy boost of full bass and tone control was on neutral (imagine if i crank that bass up).  So this confirmed the vt100 is working and my LS15 preamp is not giving that sound.  Perhaps because of the faulty V3 tube? I already ordered the new tube on the way.   I’m hoping replacing this faulty tube will fix my bass response problem.  

You guys has been so helpful and awesome... Thank you so much. 

chip_29508 posts

08-29-2019
8:15pm

To clarify my earlier post, test the preamp without a load. No input cables attached. No output cables attached. See if the sparking stops.

If not, steal a 6922 from the VT100. It has 8. Swap it in for the sparking LS15 tube. See if it fixes the sparking problem. If so, put it back in the VT100 and go tube shopping.

If not, steal a 6922 from the VT100. It has 8.

Bad idea. If the 6922 tube is damaged he will have a bigger headache than he has now. First he will have to buy two new closely matched pairs, and I mean each section of each pair closely matched, 6922 tubes and pay a qualified Tech to re bias the 6922 tubes in that channel of the amp.

chip_29508 posts

08-29-2019
8:02pm

So... Just a polite correction. The jumpers do not go in the XLR socket. The receptor is separate and apart. See the manual.

@chip,
Thanks for the shorting pins info.

The OP is using balanced ICs. But with that said are the jumpers removed?

~ ~ ~


@almarg,

What if the jumpers are still installed? The OP is using balanced ICs. Would the jumpers not be shorting out one side of the balanced outputs of the LS15 preamp? That might explain why the OP said he had to crank up the volume so high to reach the desired volume level he wanted.
Wouldn’t shorting the outputs cause problems with that section of the balanced output circuitry of each channel of the preamp? Could that cause the 6922 tube damage?

Back of VT100
https://www.manualslib.com/manual/907956/Audio-Research-Vt100.html?page=3#manual

Al,

Here is a PDF for the SP15 preamp manual. Read the warning about muting the preamp with the volume control turn up.
https://audioresearch.com/ar-package/ls15_manual-pdf/

Jim

The jumpers do not go in the XLR socket.  The receptor is separate and apart.  See the manual.

Excellent point about the jumpers, Chip. Since the OP has been using balanced interconnections between the preamp and the amp he should verify that jumpers are NOT installed on the rear of the amp in the two connectors labelled "Use Jumper for Single-Ended."

If jumpers are installed there while balanced connections are being used one of the two signals in the balanced pair of signals the preamp is providing for each channel would be shorted to ground. Which could make the preamp very unhappy.

Regards,
-- Al

To clarify my earlier post, test the preamp without a load.  No input cables attached.  No output cables attached.  See if the sparking stops.

If not, steal a 6922 from the VT100.  It has 8.  Swap it in for the sparking LS15 tube.  See if it fixes the sparking problem.  If so, put it back in the VT100 and go tube shopping.

So...  Just a polite correction.  The jumpers do not go in the XLR socket.  The receptor is separate and apart.  See the manual.

Sorry.
i did scan them and apparently did a bad job.

Chip, this has all been previously covered. Scan thru the comments.

The balanced input impedance is 200K.  SE is 100K.  Big difference.  
IMHO.  Check that first.

Do you have a multi-meter with spring-loaded hook clips?  If so, check the amp bias to make you have power.

As to the LS15, disconnect it from the amp (power off).  Power it back up and see if the sparking goes away.

Let me know and we can go from there.

Have had a lot of ARC gear over the years.

You can download the VT100 manuals on the Audio Research site.  The manual shows where the jumpers are.

On the rear of the VT100 mki there is a place for inserting jumpers to change the inputs from balanced to SE.  Was the seller using balanced or SE Interconnects?  

Very well stated, @newbee 

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.

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.

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

@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.  

Firstly, I overlooked your comments about the LS15 going into protection frequently. This could well be the result of the V3 6922 flashing/sparking. If the LS 15 doesn't require re-biasing you can easily change this tube yourself with like kind and quality. ARC is correct, this Sovtek 6922 doesn't flash on turn on. FWIW I don't think this tube needs to be re-biased. Ask ARC.

Re the loss of bass response, as stated earlier, I think it is a fundamental difference between your Mac, an old vintage tubed receiver known for overblown low frequency response, and a modern amp/preamp known for its more linear, cool, and for many, clinical response. The basic difference between the two is huge! I suspect that you have just made a fundamental beginner mistake, and we all make them, of assuming that what we hear elsewhere will be what we hear in our own homes, but to our disappointment it does not. Been there, done that!

 This is especially so when the seller has taken great care to match and set up his audio system. A good audiophile can obtain excellent results from fairly ordinary stuff because of his basic understanding of his stuff,  how it all synergizes, and the requirements of his room for proper set up.

That said, in order to optimize the bass response of your current stuff, I would run your speakers off the 4ohm taps. I would buy a SPL meter and a test disc  and insure that you speakers are not located in a bass null (and at the same time help pin down getting the best overall frequency response). I would also buy Robert Harley's book on audio for a good primer about audio. 

Same set up, I switched out the arc and use the mac1500 and has a lot of bass response especially low. Switched back to arc and it has about 60% decreased in bass. All speakers wires are all properly connected. Can someone here explain this?

https://classicreceivers.com/mcintosh-mac-1500

http://sportsbil.com/mcintosh/Receiver/MAC1500/MAC1500_ser.pdf

But what about the LS15 preamp?

You didn’t just switch out the VT100 amp.
You switched out the preamp, amp, and balanced ICs.

Just curious, what do you have the tone controls set at on the MAC receiver? Flat, ( 0 )? How about the loudness button? In, on? Out, off?



You need to find someone to come into your home to help you to resolve your problem.

It sounds like you're at a point where it needs to go in to a repair shop for a diagnosis.  If there's that much difference in sound quality and you've tried all the obvious things, it's time to get it looked at.

If you’re hearing 60% more bass by only switching the amps, then the issue is not speaker/room set up. Assuming the tubes are fine, I would suggest trying to borrow a preamp or an amp from someone and try to isolate the bottleneck systemically. Interconnects, power cords, or speaker cables can affect bass quality but not anywhere close to +/- 60%, in my experience.
Keep at it and good luck.

I called ARC and asked them about the tube flashing/sparking and they said that’s not normal.  

As for the set up, i placed the speakers about 7-8 ft apart in a 18ft x 20ft room.  

Same set up, I switched out the arc and use the mac1500 and has a lot of bass response especially low.   Switched back to arc and it has about 60% decreased in bass.   All speakers wires are all properly connected.   Can someone here explain this?

FWIW, Some European sourced small tubes do flash on turn-on. Not at all unusual and it is not significant. I suspect, as others, that your problem may be speaker location (set up in your room) combined with the basic difference in the sound of your new electronic’s. Audio Research components are not known for warmth and unless your system and speakers set up are synergistic and properly set up they can sound cold and clinical, much as you describe, especially compared to your old Mac. I’m an old ARC advocate but I dropped out of that line some years ago for just that reason. It is also possible that your ARC amp is just not one that works well with your KEF’s.

Take a break from your assumption that your components are faulty and that someone has lied to you. Think more about speaker set up and trying to get them (and your listening position) to sound better by properly locating them in your room, Do some research on set up. If you think you need help with that issue, just ask. Many folks here would be happy to help.

Good luck.

kentrent OP31 posts

08-29-2019
8:42am

@audioconnection the tube flashing and sparking is normal?

In your case, imo, no

kentrent OP31 posts

08-28-2019
10:14pm

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... :((

The preamp protection circuit was/is shutting down the unit.I would not power up the preamp again until you install the new tubes. Hopefully the bad tube didn’t take out a resistor.

As for why the 6922 tube shorted, went bad? I have had new 6922 short after just a few hours of use. It happens.

Just curious approximately how many times have you turned on, and turned off, the preamp since you brought it home. Repeated power up can cause stress on a tube.

Did you read the owners manual for the preamp?

@audioconnection the tube flashing and sparking is normal? Also speakers are rated at 8ohms though 

((And tonight I discovered the LS15 one of the tube (V3) has white sparks when i turn on.)))Some tubes flash upon turn on which is normal. Make sure you're on the 4-ohm taps and your speaker wires are in phaseand speakers not too far out into the room.