Volume drops out with tube phono pre

Discussion in 'Audio Hardware' started by subframe, Mar 1, 2015.

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  1. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Hi everyone, I'm having some problems with my phono stage, perhaps some of you knowledgeable folks can help out.

    I bought a used NVO SPA one phono pre from a dealer last year. It's a fantastic unit, and simply sounds amazing. But it's developed an issue where intermittently, the volume drops out completely for perhaps a second. This might occur once every couple of hours. The dropout occurs in both channels.

    Since this thing has 13 tubes in it, my first thought was a bad tube. I've replaced 5 of them and I'm waiting on new tubes to swap out another 4 (if it's not a bad tube, at least I'll have backups :D). So far, the problem has persisted. However, I'm relatively new to tubes, and have only a rudimentary knowledge of electronics, so if anyone has any thoughts on what could be going on here, or how I might isolate the issue, I'd appreciate the help.

    Thanks
     
  2. Raylinds

    Raylinds Resident Lake Surfer

    Typically, phono stages have a set off tubes for each channel, so the fact that both channels are cutting out makes me doubt that it is a tube. What makes you sure it is the phono stage?
     
  3. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    The problem has never happened when using my DAC as a source. I suppose the problem could be with my TT/cart/tonearm, but it's hard to see how a problem like this could originate with any of those. That said, I suppose it's possible, so I'll keep an open mind.
     
  4. deadcoldfish

    deadcoldfish Senior Member

    Location:
    Santa Rosa, CA
    swap the inputs used by the phono and the DAC and see if the dropouts persist.
     
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  5. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Aha that is the obvious test, I'll try that this afternoon
     
  6. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Finally got a chance to test that out. I switched the inputs the DAC and phono were connected to on my preamp. The problem still occurs with the phono pre, and not with the DAC.

    Any other thoughts on what might be going on here?

    Note that about half the tubes in the SPA one are given over to voltage regulation, if I understand correctly.
     
  7. russk

    russk Forum Resident

    Location:
    Syracuse NY
    I'd assume the cart is at fault since the tubes passed the swap
     
  8. skriefal

    skriefal Senior Member

    Location:
    SLC, Utah
    Have you tried swapping the interconnects? It's unlikely to be the problem, but not impossible.
     
  9. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Okay, so my system has changed quite a bit. New speakers are in the house, and my amp and preamp have been replaced by an integrated.

    The problem still occurs, but my new speakers reveal that what I thought was the signal cutting out, is actually a very low-frequency thump. I can see the cones moving in and out when it occurs, and it occurs in both channels.

    So, any thoughts on what would lead to intermittent low-frequency thumps?

    I haven't swapped interconnects, but I did change speakers cables. I've also swapped all the tubes in the signal path, leaving only the tubes in the regulator circuit unchanged in my phono pre.

    Thanks!
     
  10. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Bump now that people are actually awake :)
     
  11. Mr Bass

    Mr Bass Chevelle Ma Belle

    Location:
    Mid Atlantic
    Are you getting the thump only on certain records or randomly? If it is particular records then it might be a tonearm resonance issue. If randomly then it sounds like an electrical problem with the phonostage, not a tube issue. You are not getting any blown fuses I gather?

    Try turning up the volume slowly with the phono stage on but NO record playing. Do you hear anything other than tube rush?
     
    Last edited: Apr 25, 2015
  12. Analogman

    Analogman Well-Known Member

    But easier to see how tubes, in BOTH channels have just suddenly turned into interrupter switches? That open and close at precisely the same times?
     
  13. Analogman

    Analogman Well-Known Member

    So at any point in all of this has the MUSIC ever stopped when this even occurs?
    You had initially said that the "volume" "drops out" whatever that means; be more specific
    Drops out as in an instant of silence, or drops out as in someone quickly turning things down and then back up?
    If it is an INSTANT of silence accompanied by the woofer pump, it's a power supply problem

    But you're going to have to provide a little more coherent information
     
  14. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    The problem is not restricted to particular records, and in fact occurs with no record playing. I hear nothing but the expected noise when the volume is cranked with no record playing.

    With my previous speakers it sounded like the signal dropped out altogether for a second - an instant of silence.

    My new speakers reveal that what is actually happening is the signal drops out accompanied by a momentary very-low-frequency thump. When it occurs, the music stops playing for the duration.

    I guess it would be what you're describing as an instant of silence, with simultaneous low-freq thump.

    If I'm looking at a power supply problem, how would I begin troubleshooting?

    Thanks!
     
  15. Analogman

    Analogman Well-Known Member

    I tried to find a schematic of your phono section
    Unsuccessful at doing so
    But if the photo below is of your unit, you need to take it back to where you bought it to allow them to handle the diagnosis/repairs
    I read the overview, what little there was All I can find about your machine is reviewer palaver; nothing useful
    It is an extremely "over engineered" design, involves a great deal of PC board construction and also appears to employ several Solid State devices
    Complicated to say the least
    Your issue could be emanating from one of many "points"
    I doubt very much if it's going to be an easy "find", maybe a very easy "fix" but someone familiar with this model should look at it and save you a lot of grief and time wasted
    I think you would be best served with that approach
    Sorry for your problems

    [​IMG]
     
  16. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Fair enough, I'm not qualified to fix it anyway, whatever the problem may be. I'm mostly curious as to what's going on for educational purposes.
     
  17. Analogman

    Analogman Well-Known Member

    It is in all likelihood going to be an issue with the power supply, B+ etc............the problem is, the way that amp is constructed it could be in any number of spots and as simple as a joint that needs to be re-flowed (soldered)
    Someone with product familiarity may even already know of pattern failures or weak spots with the unit and that knowledge could save a great deal of time (and money)

    That is the one draw back with equipment that is built basically by hand and by a small enterprise; finding anyone that's even willing to work on it...........not because they can't find the problem, rather a matter of finding it in a cost effective manner

    Many times (and if it were me doing the work) it would be a matter of actual time and materials and that's not something that I (and a lot of guys) want to get into

    For one, even finding a schematic or manual for the piece may prove to be a challenge, in and of itself

    Talk first with your dealer and see how they "sound" (how they would handle it); you may even be better served contacting the guy that built it (that is what I would suggest) That little amp is NOT a conventional design
     
  18. Mr Bass

    Mr Bass Chevelle Ma Belle

    Location:
    Mid Atlantic
    From Positive Feedback article Jeff Day Sept 2013:
    In Issue 57 I introduced you to a talented fine audio constructeur, Andreas Hadjiminas, working out of Nicosia, Cyprus. I was particularly impressed with his NVO Audio SPA-II (Stereo Phono Amplifier-II) that contained an astonishing twenty-two vacuum tubes!

    You are encountering first hand probably the balancing of sonics with reliability. I'm sure the sonics are special. The big boys such as Sony prize reliability and so they will cut some corners on sonics if they have to in order to achieve it. The small high end companies prize sonics more but don't have the manufacturing and quality control typically to ensure high standardization from unit to unit and very high reliability. There are firms in the middle who achieve better sonics with better reliability but usually the cost is quite high since they can't amortize their costs over many units. You were wise to get it used at a reduced price. I hope the problem is easily identified by the distributor who certainly can contact the builder in Cyprus.
     
  19. Analogman

    Analogman Well-Known Member

    That's just not true, 'cause it ain't necessarily so
    Not too much of SONY'S statement pieces during their real high performance years ever even made it to these shores
    SONY also enjoys some of the finest engineers in the World who's names you will probably NEVER know
    The problem with "statement" pieces (no matter who makes them) is, are the parts still going to be available in 5 or 10 years if I like the piece and keep it? (especially chips and specialty transistors)
    Any cost cutting done today (mass market product) is simply a matter of profits and price point building targets; not an accurate statement to hit 'em with that big of a benefit

    I agree with the main points of your post; "serviceability" and "customer support" should always factor into buying decisions, especially when buying Audio from the "Second World"

    I know this first hand, I bought one of "JJ" Electronics piles of crap tube amps, the "828" sight unseen and unheard, all based on a glowing Vacuum Tube Valley review (which later proved to be utterly worthless on ALL counts) Bought it new
    Of course one of the biggest problems with that amp was the "JJ" KT88s (absolutely worthless in no uncertain terms) but it was constantly developing other issues about every 30 days as well

    His amp would/could have periodic issues simply because it so convoluted a design, whether it sounds good or not..............more parts there are, the more to go wrong

    A Sonic Frontiers amp and the "JJ" also both taught me this lesson; I do not ever want to own again any tube amp with tubes mounted on PC boards no matter what country it came from; only exception for me would be a kit that I could build and repair later when it broke down; of course with a phono stage that's not that big an issue (heat).............still

    So, no indictment here; I just hope he's able to get his phono stage repaired and done so hassle free

    Complicated and convoluted circuit design is not a requisite for good sound quality, not even for FANTASTIC sound quality
     
  20. subframe

    subframe Forum Resident Thread Starter

    Location:
    Bay Area
    Thanks all. I got in touch with the distributor, and he's already been in contact (on a Saturday no less :righton:) so I expect this will be resolved and maybe I can still learn a little something along the way.

    Buying second-hand has been a fantastic way to learn what I prefer and don't like. I don't mind depreciation if I will get full use out of something, but during the learning process, I've been happy to reduce my financial risk :)
     
  21. Analogman

    Analogman Well-Known Member

    "Second hand" is the way to go; no shame in taking advantage of others who will never be satisfied anyway (status symbol seeking, flavor of the month crowd)

    It's a relatively current product breaking into a tough market, and that's a good thing; I would think they'd want you happy and it sounds as if they will see to that

    I hope your issue is quickly and well resolved
     
  22. Jack Flannery

    Jack Flannery Forum Resident

    Location:
    Houston, TX
    Why don't you buy a cheap phono pre and see if the problem goes away?
     
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  23. NTO

    NTO Active Member

    Yes,only 6 tubes are in the signal path. 2x6c45pi , 3x12ax7 and 1x12au7
     
  24. Larry I

    Larry I Senior Member

    Location:
    Washington, D.C.
    Like analogman, I would guess this is a power supply problem, or an issue with some kind of protection circuit cutting in because it either properly, or improperly, is detecting a problem. It is common for a protection relays to become touchy with age and trigger when they are not suppose to act. Alternatively, something else might be awry that sends a pulse that causes a relay to trigger properly. If you are correct that only 6 of 13 tubes are in the signal path, there would be a LOT of tubes--rectifiers and regulators-- that are in the power supply. Perhaps one or some of these are acting up and sending a pulse that is causing the temporary shutdown. I would not be inclined to suspect any of the signal tubes; the complete shutdown of both channels suggests powersupply/protection circuit. Before replacing any of these tubes, try cleaning the tube pins and sockets. Bad connections in the sockets can be a source of intermittent pulses and problems. This often shows itself after the unit has warmed up. If that does not cure the problem, I would try replacing power supply tubes. If you have the ability to test capacitors, also check out the electrolytic capacitors in the power supply.
     
  25. NTO

    NTO Active Member

    subframe,has the problem been solved?
     
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