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Thread: Best tube type for ART Pro MPA II preamp?

  1. #1
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    Best tube type for ART Pro MPA II preamp?

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    Hello friends,

    I know the ART MPA uses 12ax7 tubes, but I know 12at7/12ay7/12au7 would have less gain and would has cleaner sound, less compression and more headroom.

    The question is - what type of tube do you recommend?
    -Is it 12ax7 because it's designed for it, or a lower gain one?
    -If a lower gain one - then which one?

    I want to buy different 2 types, 1 for each channel, to have different sounds. but I want the ones that will suit the preamp best.

    Thanks alot,

  2. #2
    Beck Guest
    There's really no best tube, but I would stick with the 12AX7/ECC83 class tube for units like the MP. I can give you my preference for a brand that I use in most every tube device these days. The JJ/Tesla ECC83-S is absolutely without question my favorite tube for both starved plate and high plate designs. In fact, one of the sweetest sounding tube pres I own is is the PAIA dual tube mic pre Model 9407K that I built and heavily moded from a kit. It's starved plate, but you wouldn't guess that from the silky smooth sound. These come stock with the common cheap Sovtek or Chinese made 12AX7 variants. After a lot of experimentation I settled on the JJ/Tesla ECC83S. It's very true to an old Telefunken design, but much less expensive and every bit as capable. Very impressive. You could pop in a 12au7 and get something interesting I suppose, but personally I wouldn't waste too much time with the others you mentioned. There's enough variety in the character of different 12AX7/ECC83 types to keep you busy for a while experimenting.

  3. #3
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    Aug 2004
    Wagga Wagga, NSW, Australia
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    5751 - I've not tried one in an ART preamp although I've preferred them in other 12AX7 preamps I've used.

  4. #4
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    Oct 1999
    Eagle Winged Palace of the Queen Chinee
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    I think you are incorrect in assuming that t/y/u type tubes would have higher headroom than the x type. The lower output of each of those tubes than the x type should inherently indicate lower headroom before distortion. I think you are confusing headroom in tube guitar amps with clean gain/headroom in the application involving the ART mic pre. In order to reach the same output level with a lower-value tube type you would have to drive the tube in question harder--- thus reducing the amount of headroom in order to achieve similar output, and likely increasing the compression characteristic of the lower-value tube as well. Just an observation.

    For x types I would recommend the Tung-Sol 12ax7.
    "By the time these guys are finished people will be clamoring for death panels so they can petition for a mercy killing."

    Tiz Walstib

  5. #5
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    Jul 2005
    Central Illinois
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    Thom Davis of ART shared this with me a number of years ago:

    "The ART MPA (II) circuits were built for the 12ax7.

    All the others mentioned provide less gain than the 12ax7 thus require more gain/boost to acheive same output as the 12AX7.

    As you increase the make-up gain to equal the output of 12ax7 you also increase the inherent noise of the MPA (II) Circuitry which is, then, added to your program material."

    FYI, the 7025 tube has the same gain factor as the 12ax7 but its is built specifically as a low-noise tube and could be considered as another choice.

    I agree that the current Tung-Sol 12ax7 is a very nice low-cost replacement tube and there are some nice lower cost 7025s being made as well

    If you have some major spare cash, the UK made Mullard "NOS" 12ax7 or 7025 have a very nice warmth to them but you are looking at posssibly $50-$150 or more per tube.

    (FYI-"NOS" means New/Old Stock and that means an older tube from the 1950's/60's/70's that was never sold or used thus it is still "New")

  6. #6
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    Apr 2002
    Ontario, Canada
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    I modded mine with some 12ax7 Fender Groove Tubes I had lying around and I found an improvement. As you will read, if you do your research, where the tubes are placed in the MPA II's schematic, they really won't change your sound all that much. I'm pretty sure anyone who says "oh absolutely must use THESE tubes, they're warm and juicy" or "oh I use THESE tubes, they're fat and chimey", etc, etc are all cases of "The Power of Suggestion", for this mod anyway. The only real sonic difference I really heard was that it helped rid me of some brittleness I was experiencing when louder notes were sang on vocals. The tracks were never clipping and I wasn't overdriving the gain,. but at times I'd get this thin, sharp, fizzy sound in the high end, likely due to cheap Chinese parts, especially the tubes. I found it is a lot smoother sounding now. I think the rule of thumb here is, ANYTHING will sound "better" than the cheap Chinese tubes that ship with the unit. It's an easy mod and I'm sure they almost expect you to do it.
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