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Origin 20 voltages - not what you expected

Discussion in 'Marshall Amps' started by NotSure, Jun 11, 2021.

  1. NotSure

    NotSure Member

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    I've read on other threads people asking for the voltages on the Origin 20. There has also been speculation as to how Marshall is doing their power scaling. It is not what it was thought to be!
    Here are the voltage readings on the plates for V1 - V5, going from "low" power mode to "high" power mode:
    V1 ------- low ------ mid ------ high
    pin1------175v------166v------151v
    pin6------152v------145v------133v

    V2 ------- low ------ mid ------ high
    pin1------274v------262v------236v
    pin6------151v------145v------131v

    V3 ------- low ------ mid ------ high
    pin1------39v-------70v -------149v
    pin6------39v-------72v -------150v

    V4 ------- low ------ mid ------ high
    pin3------307v------293v------262v

    V5 ------- low ------ mid ------ high
    pin3------309v------295v------262v


    Do you see what I see? V3, the phase inverter, is being choked out in low to mid power mode! That's how Marshall is getting the volume drop. It also sheds light on how important the phase inverter is to the overall sound of the Origin series amps. I'm sure you can get some very different tone out of them by trying different valves in V3.

     
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  2. fitz288

    fitz288 Well-Known Yinzer Silver Supporting Member

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    Interesting.
    Assume that I have no idea what this means (leap of faith) - what types of tubes should do what?
    I replaced all 3 stock ECC83 with JJ ECC803S's and my novice perception is that it increased the gain.
     
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  3. BRMarshall

    BRMarshall Active Member

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    NotSure, thank you for sharing this information. I’ve had my 20H for about a year and generally have run on the low power setting - going to try something different tomorrow.
     
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  4. NotSure

    NotSure Member

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    The stock Chinese 12ax7 in the Origin 20 P.I. is already a more brittle-sounding, high gain tube. I would imagine running it at such low voltages only makes it sound more thin and brittle, so it's a recipe for the common complaint that the Origin 20 sounds "thin" to a lot of people. The simple fix: put in a Sovtek 12AX7LPS. That particular 12AX7 is a great phase inverter for any guitar amp. But especially for the Origin 20, the longer plates will help to overcome the "thinness".
    Since the JJ ECC803S is a "long plate" tube, that's no doubt why you did notice an increase in gain. So you won't notice any difference with the Sovtek 12AX7LPS. You've already fixed the problem!
     
    Last edited: Jun 12, 2021
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  5. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    .
     
    Last edited: Jun 12, 2021
  6. fitz288

    fitz288 Well-Known Yinzer Silver Supporting Member

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    Cooool! - Some science to back up my unsubstantiated claims!
    3x JJ ECC803S + 2x JJ E34L + EQ in the loop = Origin20H goodness.
     
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  7. Timo V

    Timo V New Member

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    There's more than that to it. Power tube screen voltages are regulated with MOSFETs. Screen voltages in my Origin 50 are 64V, 173V and 434V (low>mid>high), my SWAG is that PI voltages are regulated too to keep distortion ratio between PI and power tubes constant. In my ORI50H voltages in V1 and V2 are solid, no matter what power setting.
     
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  8. NotSure

    NotSure Member

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    Thanks for posting. I should check the screen voltages on the Origin 20 to see what's going on in there. Obviously the voltages aren't going to be anywhere near the Origin 50, which looks like it pushes 434v! That does bring to light one of the major shortcomings of the Origin 20: the power transformer.
    Let's face it. It's small and wimpy. My plate voltage findings above prove that. Whereas Timo V mentioned his V1 and V2 plate voltages are solid throughout the power settings on his Origin 50, with the Origin 20, the B+ suffers as the P.I. and the output tubes start drawing more current. That's a clear indicator of an undersized power transformer.
    So my two main recommended mods for the Origin 20 would be:
    1) definitely the P.I. tube (Sovtek 12ax7LPS or JJ ECC803)
    2) for the tech savvy, an upgraded power transformer that can handle more current and keep that B+ stable, as in the Origin 50.
     
  9. Markfresh

    Markfresh Active Member

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    Hi,
    Is it possible to just swap the P.I tube and nothing else to make the 20h sound better.
    I was going to do what fitz suggests but now this comes to light, im wondering if replacing all tubes would make much more of a difference then just the replacing the P.I.
     
  10. fitz288

    fitz288 Well-Known Yinzer Silver Supporting Member

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    Any or all of these tube changes make subtle but noticeable improvements IMHO.
    Because the Origin really only gets native overdrive tone when it's loud, the louder you get this amp, the more you will be able to compare the difference.
    OD up front, EQ in the loop, is "much more of a difference" at any volume.
     
  11. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    How are you deciding that the power transformer is underrated? I’m not seeing any voltage measurements for idle vs full clean rms vs full power output. A lot of the Marshall Plexi’s sound signature comes from the voltage drop as the amp transitions through it’s power output. A 50 watt plexi drops approximately 60 volts on the first filter node from idle to full power and a 100 watt plexi drops approximately 100 volts from the same node. This movement of voltage gives you the dynamics and sensitivity and keeps the amp alive vs being stiff and sterile.
     
  12. Timo V

    Timo V New Member

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    Judging by the its 20 Wrms power rating (i don't have an amp to verify) Origin 20 works in a deep class A mode, so the current draw does not fluctuate with signal, and there is no power supply sag.
     
  13. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    Lol
     
  14. Timo V

    Timo V New Member

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    Why? I'm just guessing because i don't have that amp. If i did i would measure plate supply voltage, bias point and output transfomers impedance. Then i would be able to draw the load line for the amp to be certain if tubes are in cut off at any point of signal swing at maximum output power.
     
  15. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    I’ve never witnessed any push pull amp that operated in class A only. They all pass into class B right about full rms output and if it’s got el84’s it’s doubtful that it can make 20 watts rms unless it’s got over 400 volts on the plates. Either situation is going to be way outside of the recommended design of an EL84.
     
  16. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    In a power amp current draw is directly related to signal strength and frequency.
     
  17. OriginOfTheSpecies

    OriginOfTheSpecies Active Member

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    EL34's or compatible in the marshall 20 watters.
     
  18. Timo V

    Timo V New Member

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    Origin 20 has 2 *EL34s*, and such a low output power of 20 W, and a low plate voltage of 262 V ( see NotSure's post) makes it suspect of working in class A, but like i said, i don't have means to verify.

    Yes, but it's also a function of chosen bias point and output transformers impedance. Bias any amp high enough idle current, and it operates in class A ( and in most cases your tubes die very quickly if plate voltage is too high, and/or transformer impedance is too low to support safe operation.)
     
    Last edited: Jun 14, 2021
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