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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


5 posters

    Ultravalve for $2000

    j beede
    j beede
    j beede


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    • Post n°1

    Ultravalve for $2000 Empty Ultravalve for $2000

    Post by j beede Thu Mar 31, 2011 3:32 pm

    I looked over and listened to the AVA Ultravalve at last year's NorCal audio show in Emeryville and was not particularly impressed. What about that amplifier makes it a bargain at $2000? Maybe Bob should offer an anodized faceplate option for his stereo amps! Can you educate me on this?
    ...j
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    • Post n°2

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by Guest Thu Mar 31, 2011 4:03 pm

    I had one of AVA's preamps about 8-10 years ago and couldn't unload it fast enough. Noisy as hell, no bass, no depth and an abysmal headphone section were just a few of its shortcomings. The company has a loyal and rabid following however. Rolling Eyes
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    Bob Latino
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    • Post n°3

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by Bob Latino Thu Mar 31, 2011 7:18 pm

    I am not surprised that both of the above posters found the "AVA Ultravalve" amp somewhat "lacking" in musical value. The "Ultravalve ST-70" (an oxymoron?) still uses two older design 6GH8A driver tubes. Personally, I don't care how you jerk the circuit around, a 6GH8A pentode/triode tube, as used on the Ultravalve ST-70, is not a good driver tube. It is not linear at all drive levels and rolls off the top and bottom end of the audio spectrum. Coventional wisdom is to use an all triode drive system. The ultravalve also (AFAIK) still uses a bandwidth limiting circuit although I have heard that the bandwidth limiting on the newer untravalve ST-70's is less than it used to be. On the AVA web site they call it > "getting the bandwidths of the power supply, audio circuits, and input acceptance into the right set of ratios so that no input signal short of output clipping could drive the unit into gross distortion at any frequency." I guess this is a rant here but my thought is > "don't use bandwidth limiting for God sakes, just design a friggin circuit that is FLAT and linear at all drive levels and also sounds clean WITH tube warmth thrown in." Now > charge $2000 for this amp ? Huh ? I'll build you TWO VTA ST-70's for that price.

    Personally. I don't thing AVA sells many "Ultravalve" ST-70's ...

    Bob
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    j beede
    j beede
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    • Post n°4

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by j beede Thu Mar 31, 2011 9:26 pm

    The only experience I have with AVA was with the "double Dyna 400" of "100 years ago". It drove the Magneplanar Tympani 1-U very well and was a desireable amplifier in those days. I think the van Alstine theory has always been to filter the input stage so that the power supply can better service the audible spectrum. I suppose the challenge is adding a filter that is abrupt enough to benefit the power supply without impinjing on the audible range in terms of roll off or phase error, etc.
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    Luddite
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    • Post n°5

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by Luddite Thu Mar 31, 2011 10:37 pm

    Bob Latino wrote: I guess this is a rant here but my thought is > "don't use bandwidth limiting for God sakes, just design a friggin circuit that is FLAT and linear at all drive levels and also sounds clean WITH tube warmth thrown in." Now > charge $2000 for this amp ? Huh ? I'll build you TWO VTA ST-70's for that price.

    Personally. I don't thing AVA sells many "Ultravalve" ST-70's ...

    Bob

    Bob,

    I realize there may be a mutual "history" factor involved here, then maybe I'm drawing an erroneous conclusion. Never-the-less, perhaps a wee bit more objectivity could be mustered...IMHO, that is.

    Best Regards,
    Charlie
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    RockyAM
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    • Post n°6

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by RockyAM Fri Apr 01, 2011 6:20 pm

    I'm with Bob on this one. Why not design a driver circuit that doesn't need bandwith limiting instead of using a driver circuit that does need bandwith limiting. This seems to me something like this. Lets say you have an automobile design whose steering mechanism vibrates or shimmys at 80 miles an hour. OK, so lets put a governor on the engine so that you can't go above 75 and you will never notice or have to deal with the problem at all. What you should do is design a better steering mechanisn on your automobile that won't shimmy at 80. RockyM
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    Roy Mottram
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    • Post n°7

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by Roy Mottram Thu Jun 15, 2017 6:51 pm

    just like any other nationally advertised "Hi-Fi" gear. Sells for around 3-4x what it's worth.
    When I tested the AVA circuit back in the late 80s (maybe he has made a few minor improvements since then??)
    here's what I had to say in my Glass Audio article . . .

    Open loop response was a shocker. Bandwidth is only from 50 Hz to 5500 Hz, with good square waves from 100 Hz to 2000 Hz. Open loop gain is only 16.
    The only way this circuit is getting by is thru heavy feedback. Closed loop response does extend from 5 Hz to 22 KHz, with good square waves from 100 Hz to 5 KHz.
    The only difference between stock and AVA is that the AVA is purposely bandwidth limited to keep the circuit operating within its useful range.
    Low end response is rolled off below 20 Hz, and the high end rolled off above 25 KHz (which the circuit didn't reach with the tubes used).

    The bandwidth of the original VTA70 driver board was 7Hz to 70KHz,
    with all of the improvements over the years, I've never retested the bandwidth, but wouldn't expect it to be any less . . .
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    Bob Latino
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    • Post n°8

    Ultravalve for $2000 Empty Re: Ultravalve for $2000

    Post by Bob Latino Thu Jun 15, 2017 9:04 pm

    PeterCapo wrote:Actually, the price of the Ultravalve dropped not all that long ago from around $2,000 to the $1,599 that it appears to be selling for now.  IIRC, I think they said it had something to do with a reduction in their production costs or something like that.

    Yes - The Ultravalve now sells for $1599. Reduction in production costs caused the price drop? I don't think so. This amp was just overpriced to begin with and did not sell at $2K > hence the $400 price drop.

    Bob
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