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Placement of trannies and choke - my first layout

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  • Placement of trannies and choke - my first layout

    Hey,

    What do you think about the placement of the trannies, choke and tubes in this layout? Any obvious hum-makers? Should I use bigger chassis? Its my first layout... but its inspired by Matamp guts though.

    The layout picture

    The software (DIYLC) I used to draw this was a little bit limited.. Some of the wires should be shielded, 2-conductor, twisted, two-colored, underboard etc..

    I've marked some distances between transformers and tubes.
    Last edited by jussi; 06-12-2013, 08:50 PM.

  • #2
    Well... It's one of those things that needs to be tried before it can be poo poo'd. Most trendy builders that locate a tranny near the input seem to choose the OT rather than the PT. There's a good reason. If the final is out of phase with the input there won't be any PFB induced problems. But the PT being close to the input can result in hum regardless of phase. It's generally considered bad practice to locate the PT on the input side of the amp. But such rules have been successfully broken before without problems. Your layout does offer a little room. You can try it and see, or modify to idealize. It's up to you.
    "Take two placebos, works twice as well." Enzo

    "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

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    • #3
      Do you mean with "input side" the preamp stuff or just the input jack? The OT is at the same side as input jack and preamp is at between the trannies. I was thinking about 18" x 9" chassis instead of that 16" x 8" but it would be quite big 20W amp

      This amp in the picture is told to be "dead quiet until you hit the strings". It has 19" x 10" chassis but the trannies are way bigger too..

      Last edited by jussi; 06-13-2013, 02:37 PM.

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      • #4
        Hey, sorry 'bout that. Must have glanced too quick. Your drawing looks alright with one exception. Re route the NFB lead up and away from the input. It's not even attenuated before it gets to the board so it's like having a speaker lead crossing the input lead!
        "Take two placebos, works twice as well." Enzo

        "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

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        • #5
          The heater wire string should not go through the preamp tubes first then the power tubes. You have it wired backwards. If you do them all in one string then it should go through the power tubes first then the preamp tube stages with the amp's input tube going last in the chain. This way the preamp tubes aren't forced to pass, and pickup the hum caused by, the high current required by the power tubes. In your case, with the preamp tubes in the location and order that they are, it would be best to branch the heater wire string at the PT beginning, with one branch going to the power tubes and the other branch going to the preamp tubes.

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          • #6
            I have a similar question so I will ask it here instead of opening a new thread.
            I'm building a traditional head amp.
            The PT is on the AC end opposite end from the input.
            Normally the OT would be next then the Choke.
            Would it hurt anything if I go PT choke then OT?
            T


            "If Wishes Were Horses, Beggars Would Ride!" Scottish Proverb 1600s
            Terry

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            • #7
              Should be ok. Many Traynor amps are like that but they are more of a Fender like layout.
              WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
              REMEMBER: Everybody knows that smokin' ain't allowed in school !

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              • #8
                Originally posted by Russ View Post
                The heater wire string should not go through the preamp tubes first then the power tubes. You have it wired backwards. If you do them all in one string then it should go through the power tubes first then the preamp tube stages with the amp's input tube going last in the chain. This way the preamp tubes aren't forced to pass, and pickup the hum caused by, the high current required by the power tubes. In your case, with the preamp tubes in the location and order that they are, it would be best to branch the heater wire string at the PT beginning, with one branch going to the power tubes and the other branch going to the preamp tubes.
                Thanks for the tip. I've updated the layout picture now.

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                • #9
                  Nice layout picture, Jussi. What did you draw it with?

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                  • #10
                    Originally posted by ReadyTeddy View Post
                    Nice layout picture, Jussi. What did you draw it with?
                    I used DIYLC which is a free software. Its nice but has some limitations.

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