Tube pre with SS HT- issues

Discussion in 'AV Receivers' started by Yogi, Apr 21, 2003.

  1. Chu Gai

    Chu Gai Lead Actor

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    Sheesh, the things the valve-heads put up with [​IMG]. The ASL's are imported from China so I'm not so sure that Mr. Lau is indeed the designer or simply sourced the product and is OEM'ing it. However I'd expect if he does post that he'd have more than a passing familiarity. It's an avenue.
    Well first Yogi, I'd confirm via email whether or not you're covered. Apart from that, I did a little digging and this is what I came up with as possible things to investigate that could be responsible for your hum. No guarantees...just possibilities.


    1) Grounding issues: Confirm that all connections that go to ground do indeed so.
    2) Defective phase inverter tube: Replace with one known to be good.
    3) Defective capacitor: Generally people wind up replacing all of them (usually not that many) with polyester or polypropylene ones of a higher voltage rating. Not necessary to always replace precisely with the same capacitance...i.e. 0.047 is fine to replace a 0.050.

    There's got to be a Guitar Center near you. While a line attenuator may alleviate the symptoms, another approach is to pick up the Hum Eliminator (Made by Ebtech). It'll go between your amp and pre. Mr. Hamm had great success in using this to alleviate a hum from a different source. Guitar Center has an outstanding return policy, so if it doesn't work you should have no problem getting your money back.
     
  2. Joe Casey

    Joe Casey Stunt Coordinator

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    Yogi,
    Try lifting the ground on the amp(s) only. Might help reduce the hum level.
    I've used varying (price) levels of tubed preamps and heard anything from dead quiet to a minor hum/audible noise floor. As long as the noise does not increase with volume, it really doesn't bother me.
     
  3. Scott_N

    Scott_N Second Unit

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    Brett i've never heard ASL but I have heard Jolida which is in the same price range and I wasn't that impressed. I think Rogue and Opera/Consonance or Audio Electronic Supply are better buys in the low price range of tube gear. ASL may be nice for the price but you do get better parts and build with more expensive gear. I think a preamp is just as important as the amp so I don't see the value of adding cheap gear with high end gear like Yogi has. For myself I hope to have a Cary V12i and a Cary SLP-98L very soon.
     
  4. Brett DiMichele

    Brett DiMichele Producer

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    ScottN,

    When it comes to tube gear there is nothing to this junk.
    I am by far not an electronics expert and I can see by
    looking at the designs that there isn't much to any of them.

    So what does more money get you? a more fancy case and
    maybe WBT RCA out's and in's.. Maybe better capacitors?

    I am not saying to skimp on the front end.. A Preamp is a
    very critical component even more so spec wise than that of
    a power amp and I wouldn't skimp there. But I don't think
    you need to spend 3K to get a good tube pre either..

    FWIW though.. I will stick with S.S Pre's and use tubes for
    the power generation! Works for me [​IMG]
     
  5. Scott_N

    Scott_N Second Unit

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    Brett

    I don't think you have to spend 3k either. I did bring up the Rogue 66 to Yogi which is less than half that price. Tube amps are like SS amps in regard to quality vs price IMO. More expensive designs do have better or at least different sound qualities to my ears. I'm not a rich guy but i'm not going to compromise on sound quality. I have auditioned about seven different brands of tube amps and preamps and none of them sounded the same to me.
     
  6. Brett DiMichele

    Brett DiMichele Producer

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    Scott,

    That's why I said I went S.S.. My $800.00 S.S PreAmp is
    high in the food chain but $800.00 in the tube world does
    not get you into much unless you look at affordable companies.

    In S.S heck a Krell pre only runs ya about $1200.00 or so..

    You can easily drop 3K into a tube pre [​IMG]

    But I belive in value and like you said there are value
    based tube pre's out there.
     
  7. Scott Oliver

    Scott Oliver Screenwriter

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  8. Brett DiMichele

    Brett DiMichele Producer

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    Scott,

    Yeah and you talk about beer budgets? HAH! [​IMG]
     
  9. Martin Rendall

    Martin Rendall Screenwriter

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    Just wanted to weigh in on a couple of things...

    There is a *lot* of markup in the tube gear world. If you want to get what you really pay for, DIY is the way to go. I started by building a Bottlehead Foreplay pre-amp (~$450 after all the popular mods and a stereo attenuator), which measures quite well against commercial gear costing $1-2K. It's no high end piece of gear, but it is an exceptional buy.

    After a stunning success, and realizing the incredible potential for two channel listening, I went ahead and bought ungodly expensive parts for a new build, and a slightly different design (for those in the know, think "Soul Sister"'ish). I have about $1500 worth of parts in a couple of boxes, including a very professional enclosure, waiting for my "building" mood to hit. I fully expect that this pre-amp will be as good as some of the best stuff out there, and I'd hate to think if what it would cost commercially.

    Tube designs can appear deceptively "cheap". Many are simple, and that's their elegance and strength. A very complicated tube pre will, IMHO, disappoint. Or cost a fortune. Or both!

    Regarding changing the capacitors. Not a bad suggestion. A couple of thoughts: the power supply section will have electrolytic caps. You can replace them with something better, but don't replace with caps with a much higher voltage rating, as electrolytics don't operate as well when they are under powered. So if they are 400V caps, maybe go as high as 450V, but you're probably better sticking at 400V. The other thought is to do some research on what you choose to replace them with. It's amazing how much the character of the sound can change based on the caps... especially the output coupling caps (C4 and C7 in the schematic), and the interstage caps (C2 and C6).

    I looked at the schamatic for the AQ2004, and I'm nobody, but I don't really like the design. There's a lot of gain in the amplification sections with requires a big voltage drop on the input signal. And the one 12AX7 is shared by both channels. I don't believe the signal separation is that great for this tube. Anybody think otherwise?

    Martin.
     
  10. Brett DiMichele

    Brett DiMichele Producer

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    Martin,

    Check out this schematic and tell me what you think of the
    design and what caps you would switch over to.

    http://www.westol.com/~brettd/temp/schematic.jpg

    When I upgrade the tubes that's when I will probably do a
    cap and resistor upgrade. I am in no hurry since the caps
    in the audio path are paper in oil already and it sounds
    dynamite as is.. So that's a future project with no set date.

    I am just looking for opinions..

    As for Caps.. Jensen, Wima, Rikken, AuriCap, AudioCap, Sonicap,
    BlackGate,Solen

    Who do you use?
     
  11. Martin Rendall

    Martin Rendall Screenwriter

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    Brett,

    I'm in no position to be making recommendations... believe me! Anyway, it's not like there's much consensus, especially when you start talking esoteric resistors.

    Looks like a nice PP design to my uneducated eyes! Is this DIY, or a commercial amp? It looks like it would be a fairly inexpensive DIY project, excepting possibly the trannies! Is it a monoblock design?

    Martin.
     
  12. Brett DiMichele

    Brett DiMichele Producer

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    Martin,

    These are my ASL Monoblocks 20WPC Class A the price was
    $500.00 for the pair brand new (I honestly don't think you
    could build them this nice for much less than that.. Like
    you said the trannies are pricey!)

    It's fairly all P-P the tubes sockets are on a PCB and they
    do have the caps and resistors on the PCB but it's well laid
    out and all of the other P-P wiring is done nicely.

    Like I said about the caps, the critical caps are already
    very good Paper In Oil units they aren't typical cheapie
    elecrolytics except outside of the signal path. But I would
    just for the tweaker in me, rewirie them later on with some
    better single conducor PTFE Sheilded wire and replace the
    ceramic resistors with Mills and upgrade the caps and tubes.

    These are amps I am not parting with so I could care less
    about hurting resell by making changes to the cases or
    anything.

    They sound superb! Every time I fire them up just to listen
    to a "couple" songs it winds up with me laying back in the
    love seat (sweet spot!) and being there for hours on end..
    I just get shivers with some pieces of music [​IMG]
     
  13. Yogi

    Yogi Screenwriter

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    woww you guys are so far ahead in this game. I am also thinking of replacing the multicaps to Auricaps and see if I notice a difference. I also plan on upgrading all the wiring to silver wiring. Do you think these things would make an audible difference. I am willing to try this on this preamp as I got it pretty cheap and so I am not afraid to experiment. Last night I also went into the preamp and liften all the circuit boards off ground so the chassis is still grounded but the circuits arent but it still didnt get rid of the hum. In any case I have stopped worrying about the hum as it doesnt scale with volume and at the volume I listen to its not distracting.

    Keep the discussion rolling guys. I am enjoying every bit of it and learning.

    Regards,
     
  14. Chu Gai

    Chu Gai Lead Actor

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    Yogi...ya knows I likes ya, after all you got nice speakers. But what's bothering me is that you've dropped 400 (i think) on the unit
    you've got a hum coming out of one side that hasn't been addressed. tube lover or not, that's a problem.
    you're looking to sink more time and money maybe into tubes, maybe into investigating replacing various components.
    I'm kinda thinking Yogi, that you might be throwing good money after bad and that maybe an option to consider is to sell the unit.
    Look my friend, time is money, money is money, and you just might well find yourself in a situation where that hum's gonna get worse. Considering that unless you get very deep into electronics and start understanding circuitry and picking up a 'scope, the best you can hope for is tinkering. Kind of like doing stuff to a car and never really knowing if you've actually improved it's performance or not.
    Putting aside for the moment my own personal opinions on tubes, there's no reason to my mind, if you're looking to get into the whole tube thing that you've got to settle. Let's be honest, if you'd bought a SS unit and had a slight but noticeable hum coming out of one channel, you'd be looking for the nearest warranty place.
    Just my 0.02.
     
  15. Yogi

    Yogi Screenwriter

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    Well to tell you the truth I only dropped $200 on the unit and for the sound I think it was worth it. The reason I am willing to tinker with it is because the most I lose is $200+ some additional components. And if nothing works out I can always sell it (provided I dont break it) for maybe a little less. So I still might tinker with it for some learning experience.

    I know time is money but if I learnt something, I figured I'll get some power because knowledge is power. And with power comes money or the capability to make money so I might after all recuperate my losses this way. Talk about twisted logic [​IMG] silly me, I guess dwelling too much into tubes does that to your brain.

    In any case Chu you do have a point and I might just upgrade to another 'better' preamp.
     
  16. Martin Rendall

    Martin Rendall Screenwriter

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    Chu Gai may have a point.

    But you both should consider that there are unfortunately no standards in terms of line voltages or impedences in home audio. This has the extremely unfortunate effect of making some equipment work well together, while other equipment works poorly together.

    What I'm getting at is that the hum which you hear when you put your pre through a high gain SS amp may not be audible if put through a lower gain tube amp. On the other hand, it may be. I personally think it's fairly problematic to have a tube pre feeding an SS amp. First, tube gear tends to run on higher voltage signals (2-3 volts), with pretty high impedences expected on the receiving end (100K Ohms). SS gear on the other hand tends to require lower voltages (1 - 1.5V) and lower target impedences (10K Ohms). So the two may not mix well.

    So what I'm really getting as is that a tube pre into an SS amp is problematic, while neither piece of equipment may have actually exceeded their design requirements.

    Attenuators on the amp input are a great solution in this case.

    Martin.
     
  17. Chu Gai

    Chu Gai Lead Actor

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    maybe the learning might come from taking a basic adult ed course in electronics coupled with a lot of independant reading, scouring forums, older radio magazines. myself, i think with enough persistence osmosis has a way of getting knowledge into our heads. then maybe your satisfaction will come from building your own unit from scratch. tough to say Yogi, like HG said, 'you've got to find your happy place' [​IMG]
     
  18. Brett DiMichele

    Brett DiMichele Producer

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    Yogi,

    I didn't ask this and I didn't read back through to see if
    anyone else did and this may seem like a trite question.

    Did you unhook all of your source components from the pre
    and just leave the speakers and amp wired up to it and see
    if you still get the hum? Disconnect the cables from the pre.

    I was thinking maybe a cable could be the culprit? Probably
    not but it's worth a shot.

    I got my new PreAmp today (WAHOO!) and in my cable making
    haste I fudged up my XLR to Phono cables comming out of my
    Tube EQ going to my Tube Amps and I have a massive hum on
    both channels (easily 75Db worth) [​IMG] this is what happens
    when you get a new toy and rush.. Ohh well, back to the soldering
    gun tomorrow morning to fix my mistake LOL!
     
  19. Yogi

    Yogi Screenwriter

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    Brett, I do get hum without any source components connected to the preamp. The preamp and the amp connected by themselves hum, even with the pre turned off (but only in one channel). The only time there is no hum is if the power cord going to the preamp is disconnected.

    Last night I carefully noted with my ear attached to the tweeter, that there are two hums superimposed on top of each other. One is a constant buzz that is independent of volume level and another is a soft hiss that scales with volume. The hiss is very low level and even with the preamp at max volume, is at a lower level than the buzz. So all I listen at three feet away from the speaker is the buzz components of hum (buzz+hiss). Woww now there are three terms to deal with:

    Hum = Buzz + Hiss. [​IMG]
     
  20. Brett DiMichele

    Brett DiMichele Producer

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    Well Snizzle My Nizzle that bites!

    If it's any conselation I redid my wires today and I am
    still getting a hum in my speakers (never got it before)
    although if you saw my wiring you would say "well DUH no
    wonder" [​IMG]

    No time to neaten wires right now... that comes after the
    new rack is in place.


    I sure wish I knew what was causing your BumbleBizz err I
    mean Hum,Buzz,Hiss [​IMG]
     

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