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The "Underground" Genesis Phonostage

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  • The "Underground" Genesis Phonostage

    During Myles' visit to Genesis, he listened mostly to my records through my phonostage. The transparency of the phono caught his ear, and he asked me to say something about the design of the Genesis Platinum Phono.

    I am primarily a loudspeaker designer, and this story begins the same way all my electronics designs do. I was dissatisfied with the existing phono stages that I owned and decided that I needed to design my own in order to show off the transparency of Genesis loudspeakers. I started off with designing and laying out the most sophisticated cartridge loading system that I could devise as the phono stages I liked all had sophisticated loading systems (some of them were even remote controlled).

    A couple of months into this, I realized that I hadn't answered the question "WHY?" Why "load" the cartridge output (input to the phono stage) in the first place? It turns out that loading is needed to reduce an ultrasonic resonance peak due to the electrical interaction among the cartridge, the tonearm cable, and the input of the phono stage. This resonance peak is at a frequency that is not audible, but would overload the delicate electronics that amplify the tiny cartridge signal.

    What's more, loading is actually very bad for music! The typical moving coil cartridge generates a miniscule signal. 0.5mV is typical, and some high-quality cartridges can go as low as 0.2mV. Loading dumps part of this signal to ground. The higher the loading (lower value resistance), the more of the current generated by the cartridge gets shunted to ground.
    Without loading, the music is more powerful and dynamic. But the high resonant peak swamps the electronics of the phono stage and makes things sound harsh and hard. You don't actually hear the distortion, but you experience the detriment to the music. High loading reduces detail and resolution, but makes a "rounder and warmer" sound.
    Once I realized this, I set out to solve the original problem – the resonance peak.

    One characteristic of LP playback is the RIAA de-emphasis curve (Recording Industry Association of America’s standard equalization curve – pre-emphasis on recording, de-emphasis on playback) required to amplify the signal from the cartridge. The output of the cartridge is so low that the output voltage needs to be amplified by over 1,000 times (>60dB of gain) to get to the level required by the preamp. However, because of the RIAA curve, it needs to be amplified over 10,000 times (>80dB of gain) at 20Hz. But, it only needs to be amplified by 100 times (>40dB of gain) at 20kHz.

    Hence, there is a 40dB (100 times) difference in gain between 20Hz and 20kHz. With the RIAA de-emphasis curve, the higher the frequency, the lower the gain wanted. That being the case, and the detrimental resonant peak being 30dB at ultrasonic frequencies, could we design an amplifier that doesn't amplify the resonant peak?

    The typical phono stage is designed as a 3-step process:
    • amplify (by 80dB or more) --> RIAA de-emphasis (filter by up to 40dB at 20kHz) --> amplify some more or just output buffer
    There are problems with this approach - the first stage of amplify by 80dB or more would amplify the 30dB resonant peak by 110dB (that is over 300,000 times!!). Here's where the distortion creeps in as the typical amplifier is not capable of 110dB of gain. Then, the musical signal is filtered at the RIAA de-emphasis filter to reduce the midrange signal by 20dB and the high frequencies by 40dB. IMHO filters reduce transparency.

    Why not just design a variable gain amplifier that amplifies the bass frequencies more than the high frequencies, and match this variable gain to the RIAA de-emphasis curve? Then, make sure that the gain at the frequencies where the bad resonant peak of the tonearm cable can come in is low enough that it does not present a problem?

    That is exactly what we did with the Genesis Phono - a single high gain stage where 20Hz has a gain of 80dB, 1kHz has a gain of 60dB, and 20kHz has a gain of 40dB with the variable gain structure matching the RIAA de-emphasis curve. 200kHz and above has a gain of less than 10dB, resulting in the resonant peak no longer being an issue (>20dB less than the midrange and well within the operating parameters of the high gain stage).

    In this case, simple is really better – and following my mantra of “As simple as possible, but no simpler” worked once again.
    Gary L Koh, CEO and Chief Designer
    Genesis Advanced Technologies, Inc.
    www.genesisloudspeakers.com

  • #2
    Thanks for the write up Gary. I have an Experience Audio phono stage and also run it without loading as per Dave Slage and Jeffrey Jackson. Definitely sounds better and more dynamic.

    Comment


    • Dre_J
      Dre_J commented
      Editing a comment
      Thumbs up!

  • #3
    Brilliant. Has this been done before? It seems so obvious, but then again, only after you've explained it.

    Comment


    • garylkoh
      garylkoh commented
      Editing a comment
      I don't know if this has been done before. When I researched phono circuit design, I didn't see anything like this. Most designs added complexity to patch problems.

    • Dre_J
      Dre_J commented
      Editing a comment
      I can't say for sure that your specific design choice has been done before Gary. (I haven't seen the schematics or the million others in the ether for comparison)

      My added comments that are below saying you found something that works for you (and it was excellent you did) were mostly to say that there are other designs that operate just fine without loading options. Like Mark's post above.

    • garylkoh
      garylkoh commented
      Editing a comment
      Thanks, Dre. As you said, I found something that worked for me and I'm just explaining how my phono stage works. There are other excellent designs out there, and I'm sure that many of those work as well as my design if not better. When I needed a phono stage, I had a few in-house, but decided that it might be faster (more to my own tastes) if I designed my own. Not to knock available commercial implementations. That's why I don't have it on my website, and I call it my "Underground" phono stage.

  • #4
    Most MC carts are going to have non flat response in the audio band if run unloaded, I don't understand how this works unless its not RIAA curve
    Magnepan 1.6 QR Loudspeakers, Amherst A-2000 MOSFET 150 WPC Amp, Conrad Johnson PV-10A Modded Tube Line & Phono Stage, Electrocompaniet MC II Class A Head Amp, Audio Technica AT-OC9XML Cart (Stereo) , Graham Engineering 2.2 Tonearm (Stereo) , VPI Aries-1 Turntable (Stereo) , VPI Clamp, Denon DL-102 Cart, (Mono) , Luxman Tonearm (Mono) , Kenwood KD-500 Turntable (Mono) , Michell Clamp, Marantz 20B Analog FM Tuner, Pioneer SACD, Onkyo DX-6800 CD Transport, DIY 24B/192K DAC, Sennheiser HD-650 Headphones, Headroom Max Balanced Headphone Amp, DIY Silver Interconnects

    Comment


    • Dre_J
      Dre_J commented
      Editing a comment
      Not necessarily true. You may be thinking of Moving-Magnet cartridges. Non-linear MC-cartridge frequency sweeps are rarely associated with this issue. It's usually how the phonostage was designed that effects the perceived interaction with the cartridge. Not the RIAA curve.

  • #5
    As far as MC carts go, its been discussed in another thread that in general, load them to little and you get boosted highs, load them too much and you get rolled highs.
    Magnepan 1.6 QR Loudspeakers, Amherst A-2000 MOSFET 150 WPC Amp, Conrad Johnson PV-10A Modded Tube Line & Phono Stage, Electrocompaniet MC II Class A Head Amp, Audio Technica AT-OC9XML Cart (Stereo) , Graham Engineering 2.2 Tonearm (Stereo) , VPI Aries-1 Turntable (Stereo) , VPI Clamp, Denon DL-102 Cart, (Mono) , Luxman Tonearm (Mono) , Kenwood KD-500 Turntable (Mono) , Michell Clamp, Marantz 20B Analog FM Tuner, Pioneer SACD, Onkyo DX-6800 CD Transport, DIY 24B/192K DAC, Sennheiser HD-650 Headphones, Headroom Max Balanced Headphone Amp, DIY Silver Interconnects

    Comment


    • garylkoh
      garylkoh commented
      Editing a comment
      I believe that would depend on the phono stage as I hadn't found boosted highs with my design and my speakers are extremely sensitive to boosted highs.

  • #6
    Thanks for sharing Gary.
    Hugh Nguyen
    ACA

    Comment


    • #7
      Thanks for the write up Gary I liked it I would love to hear it some day

      Comment


      • #8
        Refer to post #10 here to illustrate the point Gary was making between loading, frequency response and ultrasonic peaks.

        https://www.audionirvana.org/forum/t...-cables-matter


        Phonocable capacitance changes both the amplitude and frequency of these peaks.. Indeed, I remember Jonathan Carr also saying that the FR for MCs within the 20-20,000 is essentially linear.

        As Gary said, it's a tank circuit and the capacitance of the phonocable also comes into play here. The lower the phonocable capacitance--->medium value resistors. Higher capacitance cable--->low value resistors and dynamics and resolution can suffer. But as Jonathan also points out, phonostages all vary in their sensitivity to overloading too.

        Gary should also mention that he makes a phonocable too that goes with the phonostage.
        Myles B. Astor, PhD, Administrator
        Senior Editor, Positive-Feedback.com
        ________________________________________

        -Zellaton Plural Evo speakers
        -Goldmund Telos 300 stereo amp
        -Goldmund Mimesis 37S Nextgen preamplifier
        -Doshi EVO and Goldmund PH3.8 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 Lambda, Fuuga Mk. 2, vdh Colibri Master Signature, MutechHayabusa, MOFI Master Tracker, Sumiko Songbird cartridges
        -Technics RS1506 with Flux Magnetic heads, Doshi V3.0 tape stage (balanced)
        -Assorted cables including Transparent XL Gen. 6, Skogrand, Viero, Kubala-Sosna, Audience Au24SX, Genesis Advanced Technologies and Ensemble 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 3 racks, Audiodharma Cable Cooker, Symposium Ultra and assorted SRA OHIO Class 2.1+ platforms.

        Comment


        • #9
          Thanks, Myles. The biggest push-back I've been having from both dealers and customers is the phonocable that I designed to go with the phonostage. Instead of RCA's or XLR's, it is attached to the phonostage using a LEMO connector (the one I found most transparent at the millivolt level). As a system, it has low capacitance, but as inductance is trade-off to capacitance, I balanced the trade-off between acceptably low capacitance and acceptably high inductance.

          Unfortunately, some customers own tonearm cables that cost more than my phonostage and cannot accept that the "free" tonearm cable that comes with the Platinum version of my phonostage sounds better than their mega-buck ones. I keep telling them that it's only because they were designed together, but they still can't accept it and keep trying to find a "better" (i.e. more expensive) cable.
          Gary L Koh, CEO and Chief Designer
          Genesis Advanced Technologies, Inc.
          www.genesisloudspeakers.com

          Comment


          • #10
            Originally posted by mylesbastor View Post
            refer to post #10 here to illustrate the point gary was making between loading, frequency response and ultrasonic peaks.

            https://www.audionirvana.org/forum/t...-cables-matter


            phonocable capacitance changes both the amplitude and frequency of these peaks.. Indeed, i remember jonathan carr also saying that the fr for mcs within the 20-20,000 is essentially linear.

            as gary said, it's a tank circuit and the capacitance of the phonocable also comes into play here. The lower the phonocable capacitance--->medium value resistors. Higher capacitance cable--->low value resistors and dynamics and resolution can suffer. But as jonathan also points out, phonostages all vary in their sensitivity to overloading too.

            Gary should also mention that he makes a phonocable too that goes with the phonostage.
            at what load?
            Magnepan 1.6 QR Loudspeakers, Amherst A-2000 MOSFET 150 WPC Amp, Conrad Johnson PV-10A Modded Tube Line & Phono Stage, Electrocompaniet MC II Class A Head Amp, Audio Technica AT-OC9XML Cart (Stereo) , Graham Engineering 2.2 Tonearm (Stereo) , VPI Aries-1 Turntable (Stereo) , VPI Clamp, Denon DL-102 Cart, (Mono) , Luxman Tonearm (Mono) , Kenwood KD-500 Turntable (Mono) , Michell Clamp, Marantz 20B Analog FM Tuner, Pioneer SACD, Onkyo DX-6800 CD Transport, DIY 24B/192K DAC, Sennheiser HD-650 Headphones, Headroom Max Balanced Headphone Amp, DIY Silver Interconnects

            Comment


            • #11
              Originally posted by JCOConnell View Post

              at what load?
              The loads are listed on the graph.
              Myles B. Astor, PhD, Administrator
              Senior Editor, Positive-Feedback.com
              ________________________________________

              -Zellaton Plural Evo speakers
              -Goldmund Telos 300 stereo amp
              -Goldmund Mimesis 37S Nextgen preamplifier
              -Doshi EVO and Goldmund PH3.8 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 Lambda, Fuuga Mk. 2, vdh Colibri Master Signature, MutechHayabusa, MOFI Master Tracker, Sumiko Songbird cartridges
              -Technics RS1506 with Flux Magnetic heads, Doshi V3.0 tape stage (balanced)
              -Assorted cables including Transparent XL Gen. 6, Skogrand, Viero, Kubala-Sosna, Audience Au24SX, Genesis Advanced Technologies and Ensemble 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 3 racks, Audiodharma Cable Cooker, Symposium Ultra and assorted SRA OHIO Class 2.1+ platforms.

              Comment


              • #12
                Originally posted by MylesBAstor View Post

                The loads are listed on the graph.
                those graphs cant be responses of the cartridges, as they all go flat to over 1 MHz which is not possible.
                Magnepan 1.6 QR Loudspeakers, Amherst A-2000 MOSFET 150 WPC Amp, Conrad Johnson PV-10A Modded Tube Line & Phono Stage, Electrocompaniet MC II Class A Head Amp, Audio Technica AT-OC9XML Cart (Stereo) , Graham Engineering 2.2 Tonearm (Stereo) , VPI Aries-1 Turntable (Stereo) , VPI Clamp, Denon DL-102 Cart, (Mono) , Luxman Tonearm (Mono) , Kenwood KD-500 Turntable (Mono) , Michell Clamp, Marantz 20B Analog FM Tuner, Pioneer SACD, Onkyo DX-6800 CD Transport, DIY 24B/192K DAC, Sennheiser HD-650 Headphones, Headroom Max Balanced Headphone Amp, DIY Silver Interconnects

                Comment


                • MylesBAstor
                  MylesBAstor commented
                  Editing a comment
                  No that is exactly what J. Carr is trying to show. BTW, Jonathan is one of the top cartridge and phonostage designers.

                  Also can see the same thing on a couple of other sites. http://www.hagtech.com/loading.html

                • JCOConnell
                  JCOConnell commented
                  Editing a comment
                  I believe in both of these cases, they are assuming the voltage source, the cartridge generator, is a perfect voltage source, when in reality it is mechanically limited with regards to frequency response. Carts are not flat to over 1 MHZ. I don't believe test records have ever been cut with 1 MHZ grooves, lathes cant do it either. I'm not doubting the sound quality of his designs or products or credentials, I just don't see the theory in the explanation. This hagtech site states mc carts have very wide theoretical electrical bandwidth, I can agree to that, its got mechanical limitations however.

              • #13
                Last edited by Doxycc; 02-06-2017, 12:51 AM.

                Comment


                • garylkoh
                  garylkoh commented
                  Editing a comment
                  I like them very much! The CH Precision P1 is awesome in current-mode (and there's no way to load it in that mode). It has automatic loading configuration in standard-mode.

              • #14
                Gary, what types of output connectors do you offer and what is the MSRP?
                Magico M-Project, CAT JL7SE, CH Precision L1/X1/P1, Kronos Pro Limited Edition/SME 3012R/Atlas SL/Opus-1, Schiit Yggdrasil, ZenWave D4 ICs & SCs

                Comment


                • #15
                  I love Gary's "Underground" Genesis Phonostage. And I have heard/owned several versions as they have evolved. The various versions were compared to FM Acoustics and Burmester phonostages with the Genesis unit surpassing them at a much lower price. The current Platinum version with special cable (5-pin DIN to LEMO connector), massive external power supply (similar to his power amplifiers), acrylic suspension and Absolute Fidelity power cable add up to an awesome performer.

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                  Speakers/Amps: Genesis G2.2 Jr with Powered Servo-Sub Bass, Genesis GR1440 Mono Amps, 5,000 watts total power
                  Preamp: SMc Audio VRE-1C Preamp (fully balanced inputs and output)
                  Analog 1: VPI Signature 21 Belt-Drive Turntable w/ 10” 3D Printed Fatboy Gimbal Arm and Ortofon MC Windfeld Ti Phono Cartridge driving Lehmann Silver Cube Phono Preamp
                  Analog 2: VPI HW-40 Direct-Drive Turntable w/ 12” 3D Printed Fatboy Gimbal Arm and Ortofon MC Anna Diamond Phono Cartridge driving Genesis Gold Phono Preamp
                  Analog 3: Studer A810 R2R tape w/ Bridge Console. Using built-in tape preamp
                  Digital: Lumin Network Player with Lumin NAS
                  Cables: Genesis Advanced Technologies/Absolute Fidelity Interface Interconnects, Speaker, Phono and Power
                  A/C Power: Extensive System Upgrades, Sub-panel w/hard-wired power cables, and IsoTek Super Titan Passive Power Conditioning for Amplifiers
                  Accessories: Custom Acrylic Equipment Stands, Klaudio Ultrasonic RCM

                  Comment

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