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Verito 1: Phono integrated amp from LKV Research

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  • Verito 1: Phono integrated amp from LKV Research

    LKV Verito 1

    Story of a Successful Design

    Bill Hutchins, Chief Designer, LKV Research

    Last summer LKV Research introduced its latest new product, an amazing little integrated amp we call the Verito 1. I love this little guy and think it may just be the best design I have yet done. I want to offer the Audio Nirvana community some insight into this design.

    My goal was to create an integrated amp that included both a great sounding moving coil phono stage and a true high end power amp. Of course, it would also need to be very attractively priced. Here is how it worked out.

    I wanted a power amp section that delivers not only really musical sound, but also power to handle insensitive speakers and challenging musical dynamics. Unfortunately, the audiophile standby Class A and Class AB designs that offer great sound and real power are hot, heavy and often expensive: not well suited for my purpose. The relatively new Class D technology is an obvious candidate, offering cool running, light weight and relatively inexpensive amplifier modules. But, what about sound?

    For about 5 years I have been acquiring and testing Class D designs from several manufacturers. The best sounding of the lot was the UCD module from a company in the Netherlands called Hypex Electonics. But even that design seemed to me to fall just short of the best Class A and AB amps I have heard. I was about to give up on Class D when I learned that Hypex had come out with a thorough redesign that embodied new technology devised by Bruno Putzeys. Called NCore, this technology solved some of the last remaining problems with Class D power. I got hold of a couple of samples, went to work and then listened. After an extended period listening (mostly to vinyl) and soliciting the reactions of some folks with pretty good ears, I was convinced. At last, a Class D amp design that sounds every bit as good and in some ways better than anything else I have heard (or built). So, we finally had our power amp stage.

    https://www.audionirvana.org/filedat...982&type=thumb

    It’s not hard to complete an integrated amp by adding to the power stage a pot and a couple of op amps. Bingo! You’re done. But what I wanted was a great integrated, one that could compete in sound quality with the best separates around. For that I needed to design two excellent separate components, a preamp and a phono amp, and then find ways to include them in the same enclosure with the Hypex module. What I did was take the circuits from LKV’s Line One preamp and Veros One phono amp and modify them to be suitable for the integrated. In doing so I retained their essence: Class A zero loop feedback differential amplification executed using tightly matched jfets and other discrete components along with excellent passive parts including in the signal path 1% tolerance metal film resistors and polypropylene capacitors. In the process I actually improved the circuits in important ways.

    Of course, an integrated amp with aspirations to the top of the high end performance tree had to have an MC-capable phono stage. Yet many current phono-integrateds lack a key feature: an input for a low-output moving coil cartridge. These days of vinyl revival, an MM-only component is really just an entry level box. So the Verito 1 has a really nice MC/MM capable phono stage with the gain, low noise levels, and flexibility to handle low output moving coils, e.g., 0.3 mV input, as well as MM cartiridges. And boy, does it deliver the music: natural detail, clean transients, accurate musical tones, tight bass and lovely highs.

    The Verito 1 sells for $2700 with phono stage, $2200 without.




  • #2
    If anyone has questions about the Verito 1 or LKV in general, feel free to email (Bill@lkvresearch.com) or call me (603 730 7400). Bill

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    • #3
      This looks very interesting, thanks Bill.

      Comment


      • #4
        Looks like a sweet little unit! How many wpc does the integrated put out Bill?
        Myles B. Astor, PhD, Administrator
        Senior Editor, Positive-Feedback.com
        ________________________________________

        -Magico S5 Mk.2 speakers with SPod feet
        -cj 40th Anniversary ART300 monoblock amplifiers
        -Ensemble Fuoco hybrid integrated amplifier
        -cj GAT preamplifier Series 2 preamplifier
        -Doshi V3.0 phonostage
        -VPI Vanquish direct-drive turntable
        -VPI 12-inch 3D Fat Boy dual pivot tonearm, VPI 12-inch 3D Fat Boy gimballed and SAT LM-12 arm
        -Lyra Atlas SL, Fuuga, vdh Colibri Master Signature, MOFI Master Tracker, Sumiko Songbird cartridges
        -Technics RS1506 with Flux Magnetic heads, Doshi V3.0 tape stage (balanced)
        -Assorted cables including Transparent XL Gen. 5, Allnic cables, Skogrand, Viero, Kubala-Sosna, MG Audio, Audience Au24SX, Genesis Advanced Technologies Power Cords
        -Accessories including Stillpoint Aperture panels, Cathedral Sound panels, Furutech NCF Nano AC receptacles; Silver Circle Tchaik 6 PLC, Symposium ISIS and SRA Craz racks, Audiodharma Cable Cooker, Symposium Ultra and assorted SRA platforms.

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        • guss2
          guss2 commented
          Editing a comment
          I think it's 180 wpc Myles.

      • #5
        Guess2, you are right. About 180 into 8 ohms, 250 into 4, 200 into 2 ohms.

        Comment


        • #6
          Specs alone don't define a design's sound, but they might give those interested a feel for the Verito 1's capability. Here are its other specs, based on our measurements. Verito 1 - SPECIFICATIONS final.docx

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          • jonathanb
            jonathanb commented
            Editing a comment
            There's less power at 2 ohms (200w) than 4 (240w)? That's not a typo?

        • #7
          No typo. A power amp's ability to deliver power is determined by ohms law (voltage in Volts multiplied by current in Amperes). Every amp has a maximum voltage and maximum amount of current that it can deliver. Its max level of one or the other of theses factors will determine the limit as to how much power it can deliver. Which factor will be the limit into a particular speaker depends on the impedance that speaker presents to the amp. As the impedance of the speaker a power amp is driving goes down, the amp must deliver more current at a given voltage (Ohms law). As long as the amp has more current to deliver than the speaker wants, the power that amp can deliver is limited by the maximum voltage it can produce. In this situation the amp is said to be voltage limited. The power delivered will increase as the speaker impedance decreases because the current delivered increases, the voltage stays the same and the power (Volts times amps) goes up. But, once the current demanded by the load reaches the maximum amount the amp can deliver, the power is limited by the maximum current capability of the amp and the max power will drop as the load impedance decreases. So, at 8 ohms, the Verito can deliver more current than is needed at its maximum voltage. Its power is limited by the maximum voltage it can deliver. At 2 ohms, however, the Verito runs out of current before it reached maximum voltage and it is therefore current limited, In that situation the power delivered drops as the load impedance drops.

          In essence, the Verito delivers about 200 watts of power (+/- a bit) into 8, 4 and 2 ohms. Pretty good for an integrated amp. And you ought to hear it!

          Comment


          • #8
            The Problem with Class D (well at least for me) has always been in the Filtering at the output. Can you say something about that? The amp looks so tidy I'm am sure you would have something interesting to say on that Topic...
            Regards Billy

            Comment


            • #9
              Billy, Yes, the LC filter at the output of class D amps can be a big source of trouble. They can and do restrict bandwidth, increase output impedance, cause hi-end frequency response to be load dependent, add distortion and hack our elections. Well all but the last . Some Class D amps dispense with the filter and rely on the natural hi frequency increase in speaker impedance to attenuate the "ultra sonic" switching noise the amp generates. This turns out to be a pretty good way to design a harsh sounding amp, so let's discard it.

              Enclosing the filter within a global feedback loop would be one way to eliminate or at least greatly reduce the ill effects of the output filter. But most Class D designs take feedback after the output mosfets and before the LC filter, meaning that the feedback has no effect on the problems that filter creates. There are two reasons for this approach. 1) The output filter introduces almost 180 degrees of phase shift in the high frequencies, and that in turn will give you horrible oscilation (instability) ifyou feed it back to the input of your amp. 2) Typical feedback circuits are not very effecrtive at high frequencies because the open loop gain of the amplifier drops a lot as frequency increases . As it drops the amount and therefore the efficacy of the feedback drops.

              [Parenthetically, I believe that this drop in the effect of negative feedback as frequency increases is one of the reasons that many feedback circuits don't sound good. This and other effects are why for low level (ie, phono and pre amp circuits) I prefer not to use feedback. But as I will try to explain below, this problem has been solved by the designer of the Hypex NCore class D amps.]

              Now back to the LC rfilter problem. Bruno Putzeys, the designer of the Hypex class D amps, has devised a pretty remarkable feedback loop that olves these problems in the NCore modules. A much oversimplified version of what he did is as follows. Using some very powerful math anda lot of ingenuity he has designed a 5 pole feedback filter that that overcomes both of the problems described above. First, the gain of his class D circuit does not fall off before 20K Hz. The feedback therefore continues to be equally effective theoughout the audio spectrum. This means the sound quality is maintained through that spectrum and the high frequency problems associate with other feedback circuits are eliminated.

              Second, his 5 pole filter (lots of math) along with other techniques avoids the instability created by the LC filter's phase shift. This allows him to take the feedback AFTER THE L/C FILTER. Now the filter is within the feedback loop, which can act to reduce output impedance, restore proper (ie, neutral) frequency response, and minimize distortion. This solves most of the LC problems laid out above. He is still working on the hacking problem

              The result is just amazing. For the first time when I listened to my prototype with the NCore module, I heard a feedback amplifier that rivals a really good Class A design, but without all the limitations of those devices. When we introduced in California, the most common response was amazement: "I never thought Class D s\could sound like that."

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