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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

    Damping Factor

    harpy
    harpy
    harpy


    Posts : 94
    Join date : 2012-02-04
    • Post n°1

    Damping Factor Empty Damping Factor

    Post by harpy Fri May 25, 2012 9:01 pm

    I was looking at the specs of a Mk-III and it said it had a damping factor of 15. Is that a factor of 15? I always see the period behind it and wondered if the meant anything other than the end of a sentence.
    My Rotel has a damping factor of a 1000 with 200 watts driving very inefficient speakers. When I tried the stock Mk IV’s I thought they sounded superior. I was just wondered why I would think they would outperform a modern amp (at least to my ears). I am crossed over about 65 hz with an SS amp doing the bass though.
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    Roy Mottram
    Roy Mottram
    Roy Mottram
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    • Post n°2

    Damping Factor Empty Re: Damping Factor

    Post by Roy Mottram Fri May 25, 2012 9:56 pm

    do a google on damping factor and you'll get about a million links, read the first 4 or 5 and you'll have a great understanding of it!
    Tube amps usually have a low damping factor, and SS amps usually have a much higher damping factor.
    How they interact with the speaker itself makes a difference.
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    harpy
    harpy
    harpy


    Posts : 94
    Join date : 2012-02-04
    • Post n°3

    Damping Factor Empty Re: Damping Factor

    Post by harpy Sat May 26, 2012 12:14 am

    I see. Thought this was interesting talks about the ST-70:

    http://homepage.mac.com/tlinespeakers/vaughn/downloads/Damping-Factor.pdf

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    Roy Mottram
    Roy Mottram
    Roy Mottram
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    • Post n°4

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    Post by Roy Mottram Sat May 26, 2012 12:39 am

    excellent article, pretty well sums up everything!
    Now just remember that our VTA ST70 amp is a whole different animal than a Dynaco.
    The only thing it has in common is the chassis, transformers, and power tubes.
    The rest of the circuit is all new. Better power supply, better lo-gain triode preamp, proper phase splitter,
    low negative feedback, very wide bandwidth, resulting in good tight bass, an open natural midrange, and clear clean highs
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    Alan-14
    Alan-14
    Alan-14


    Posts : 46
    Join date : 2012-03-31
    Age : 63
    Location : Melbourne - Australia
    • Post n°5

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    Post by Alan-14 Sun May 27, 2012 4:28 am

    Yes a very good article ...

    Which begs the question to Roy & Bob ... what sort of speaker efficiancy should we be looking at for optimal performance with the VTA ST-70 or ST-120 amps?
    Would the amps be able to drive and control low efficiancy speakers of low to mid 80's db or should we only be looking at higher efficiancy speakers of over 90db?
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    Bob Latino
    Bob Latino
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    Location : Massachusetts
    • Post n°6

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    Post by Bob Latino Sun May 27, 2012 8:26 am

    The VTA ST-70 and ST-120 both have a damping factor of 16 which is about the same as the original ST-70. The VTA amps do not, however, have the circuit design flaws (weak power transformer, small amount of DC storage, mediocre performing driver circuit) of the original ST-70 amp. I probably shouldn't say "flaws" but you have to understand that the original ST-70 was designed (in 1959) to hit a price point not for "best sound quality". In its day it was an OK amp because the signal source of the day (vinyl records) did not really tax the amp's power supply and driver circuit. The original amp does not stand up well to digital signal sources which have 90+ dB dynamic ranges.

    To deal with your question about driving low efficiency speakers you should consider
    1. The size of your room ?
    2. How loud you play the music ?

    As an example .. On my downstairs system I now have a pair of VTA M-125's driving a pair of 86 dB efficient Magnepan MG 3.6R speakers in a 14 X 28 foot listening room. With a good sized room and inefficient speakers you really need power.

    This is only my opinion but > in a smaller room say 10 X 12 foot or 12 X 15 foot the VTA ST-70 will work just fine with speakers that are 89+ efficiency. In a slightly larger room and with speakers ranging down to about 87 dB the VTA ST-120 will work well in a room of 200 to 250 Sq feet. With larger rooms and lower efficiency speakers you need more power. The old saying > "You can't have too much power" is true because more power gives you more "headroom" or a better ability to respond (when necessary) to musical peaks.

    There is a manufacturer of high efficiency speakers in the 100 dB range who uses a 35 WPC VTA ST-70 to demonstrate his speakers. I asked him why he doesn't use a smaller 2A3 (3.5 WPC) or a 300B (8 WPC) SET amp instead? His answer > "The VTA ST-70 has more headroom than the SET amps especially in the lowest octave".

    Bob


    Last edited by Bob Latino on Sun May 27, 2012 6:15 pm; edited 1 time in total
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    Alan-14
    Alan-14
    Alan-14


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    Age : 63
    Location : Melbourne - Australia
    • Post n°7

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    Post by Alan-14 Sun May 27, 2012 11:12 am

    Thanks Bob ... I'll have to get my tape out and measure my room ... and somehow work out my speaker efficiancy Smile
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    thevic24
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    Join date : 2010-01-31
    • Post n°8

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    Post by thevic24 Sun May 27, 2012 7:00 pm

    For what it is worth...

    My main room is 18.5 X 11.5. I have the ST120 driving a pair of Mirage M5's which are 85db.

    In my application, I can shake the house at any time I like!

    I even have a "stock", rebuilt ST70 that even dose quite well considering....
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    • Post n°9

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