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    VTA 125 amplifier

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    alnini

    Posts : 1
    Join date : 2012-12-20

    VTA 125 amplifier

    Post by alnini on Thu Dec 20, 2012 1:59 am


    Has anyone done a Hz test on these amps. What about distoration figures at different Hz? I remember when I was in high school the class built a Dynaco 70. It had a Hz of 10-40kHz. All these current run amps barely get past 20-30k Hz range. I like to listen to something other a CD. This kit looks interesting, but I want a amp with a topend in the 40-60k Hz. Woes anyone remember the William's? One of the problem is the distoration, high. If I have to build a amp from scratch, well, I have a circut that is good from 5-156k Hz FLAT! At 20 Hz the distoration is .54% &.58%. These figures are at full power 50 watt. The VTA 125 has over twice the power. This circut can be uped to 100 watts or more.

    Alnini




    Alnini

    Bob Latino
    Admin

    Posts : 2377
    Join date : 2008-11-26
    Location : Massachusetts

    Re: VTA 125 amplifier

    Post by Bob Latino on Thu Dec 20, 2012 9:47 am

    alnini wrote:
    Has anyone done a Hz test on these amps. What about distoration figures at different Hz? I remember when I was in high school the class built a Dynaco 70. It had a Hz of 10-40kHz. All these current run amps barely get past 20-30k Hz range. I like to listen to something other a CD. This kit looks interesting, but I want a amp with a topend in the 40-60k Hz. Woes anyone remember the William's? One of the problem is the distoration, high. If I have to build a amp from scratch, well, I have a circut that is good from 5-156k Hz FLAT! At 20 Hz the distoration is .54% &.58%. These figures are at full power 50 watt. The VTA 125 has over twice the power. This circut can be uped to 100 watts or more.

    Alnini




    Alnini

    Dynaco specified a response of 10 Hz to 40 KHz for the ST-70 but never specified the power level at which this reading was taken. It was probably at one watt. The original ST-70 with the 7199 driver circuit had a rolled off top and bottom end that got worse as you turned the volume up. This roll off was noticeable espcially if you had good speakers that had good frequency response at the frequency extremes.

    I don't really know what the frequency response is of the VTA M-125 amp and what the distortion ratings are at different frequencies because I don't have the equipment here to make those tests. During the development of the VTA M-125 the only thing I used to "test" the amp was a piece of gear that I keep with me at all times - my ear. If it didn't sound quite right, I made changes to the circuit until the amp DID sound right.

    You and I will probably disagree on this but some amps that MEASURE GOOD on a test bench do not SOUND GOOD when playing music. One of the best examples of this was in the mid '60's when Dynaco came out with their first solid state amp - the Stereo 120 ... The Stereo 120 had a frequency response of 5 to 100 KHz and less than .5% distortion from 15 to 25 KHz at full power. Wow I said, I have to listen to this amp! When it did come out I was able to listen to the amp one day at Lafayette Radio in Worcester, MA. I would have to say that probably the Dynaco Stereo 120 was the worst sounding amp I have ever heard. All those great specs and it sounded like crap. Harsh, brittle, irritating sound. I though to myself at the time > "This is the future of Hi-Fi?"

    Remember one thing ... Great specs do not necessarily make a great sounding amp.

    Bob

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: VTA 125 amplifier

    Post by GP49 on Thu Dec 20, 2012 1:15 pm

    YES, back in those days frequency response was typically measured at one watt output.

    "POWER RESPONSE" was measured at (IIRC) half power.

    The Dynaco Stereo 120 did get better-sounding in later production, with circuit refinements and
    improved (and closer-specified) solid-state devices. If you looked at distortion products on the
    early ones at low output, where most REAL listening is done, it didn't measure all that well.

    It was more respectable in its latter versions. What audiophools would do with the early ones
    was to incorporate the changes (some of them different from what the factory did) that "scuttlebutt"
    said were for the audio improvements, without the changes made for stability and reliability.
    Their modified amplifiers almost invariably blew up.

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