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Thread: Tweed Twin power reduction

  1. #36
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by The Dude View Post
    What I didn't get from the start is, why doesn't he just turn it down? I can't see that it would be much different than adding a MV (to a Twin, anyway).
    My thought too. It's not as if he's ever had the chance to crank it into clipping for practice or gigs. If he has then maybe.?. But otherwise it's the same dirt box no matter where you set the volume control on the amp.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

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    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  2. #37
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Randall View Post
    He is turning it down to a ridiculous amount. Last gig he reports to 1.5 - 2 on volume. Getting no preamp love at those levels. I think we can all agree this is not ideal, and why not get a different amp, but as I have told him, I am his amp tech, not his therapist. His money is good, if his knowledge and judgement is not.
    Put a 10% taper volume pot in his amp. He'll think your a magician

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

  3. #38
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Chuck H View Post
    Isn't the output impedance of the "circuit" the PI output impedance parallel with the 220k bias resistance? And where is the signal "divided" to? A more easily understood voltage divider divides to 0V, but in this case it would have to be divided to the opposing phase. That seems like local NFB and should reduce the circuit impedance IIRC. I'm seeking clarity because I always saw this circuit as phase dependent like Rob's site says.
    Sorry for slow response. Notifications are a feature of the site that could do with tweaking as they stop if you don't keep checking back to see what it happening.

    There is nothing magic about 0v, it's just a reference. If it helps you can call the bottom end of the MV 0V and you'll see it more clearly. Local (voltage) NFB (i.e. on the PI stage) would lower the output impedance but would not change the divider operation. That said the NFB would stop when you hit clipping on the PI.

    If you put a pot bewtwen the two phases and looked at the wiper I'd happily call that phase cancellation. But now as I say it, it seems like it's mostly semantics.

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  4. #39
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    But now as I say it, it seems like it's mostly semantics.
    I would say there is not any more phase cancellation/mixing involved than in any PP stage where the (reflected) load is connected between opposite phase plate signals.
    In fact a LTPI can be viewed as a PP amplifier and this MV would be its main load. Volume reduction is achieved by brute force downloading the PI.

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    Last edited by Helmholtz; 06-19-2019 at 05:53 PM.
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  5. #40
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    I'd probably give trying a bigger PI bias resistor a shot if he comes back to you.

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  6. #41
    Supporting Member Randall's Avatar
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    Text from customer today. "Randall, I love the master volume. Thank you".

    Halelujah!

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    It's weird, because it WAS working fine.....

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