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Bias Tremolo+Half Tube Return FX Loop for 2204

Discussion in 'Shock Brother's DIY Amps' started by XTRXTR, Feb 7, 2021.

  1. XTRXTR

    XTRXTR TDPRI Member

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    Do you think its possible?

    I want to add one 12ax7 to my 2204 with 1/2 used for a Bias Wiggle Tremolo and the other 1/2 for the return buffer for an FX loop. The send / return coming after the MV and pre PI

    My Digitech 1101 Effect loop specs:
    Loop Input:
    Impedance: 16K Ohms unbalanced or 20K Ohms balanced
    Nominal input level: +4 dBu or -10 dBV
    Maximum input: +23dBu (Level switch at +4 dBu)

    Loop Output:
    Impedance: 600 Ohms
    Nominal output level: -10 dBV (Unity gain from guitar input in BYPASS)

    I know there is a lot to unpack in this idea but do you think its possible?

    I believe the Drake PT 1202-324 has the heater and HT current head room for two 12ax7 tubes to be added based on the JCM 800 model 4210 aka 2205. The 2204 and the 2205 have the same PT, OT and Choke but If I can get away with one tube...why not? Two tubes could do it with one for the send and return and one for a opto coupled/LDR tremolo like a deluxe reverb. The added complication of that last scenario being that both the tremolo and the FX loop would would splice into the circuit at the same point. I've got plenty of space on the chassis.

    Thanks for your effort and consideration
     
    Last edited: Feb 8, 2021
  2. Paul-T

    Paul-T Tele-Holic

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    London
    If you're considering an opto coupled trem, do check out this design. I also have this thread bookmarked for tube effects lloop.
     
  3. XTRXTR

    XTRXTR TDPRI Member

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    Jul 13, 2020
    Location:
    Northern Colorado
    I don't know, I am rethinking the wiggle bias tremolo and favoring a signal mixing tremolo like the deluxe reverb. I was thinking about certain type of sounds to play around with like a slow tremolo blues inside a reverb or a time delay effect. If the bias is controlling the output tubes it won't sound right - something like someone turning the volume up and down manually. Where as the signal tremolo getting reverb or echo afterward would sound more natural. Like playing blues tremolo inside a large stairwell. Bridge of Sighs comes to mind. Maybe Ill add a switch that can add or remove capacitance values in case I want a very slow tremolo or very fast.

    This means using two tubes.
     
  4. Bitsleftover

    Bitsleftover Tele-Holic

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    Oct 17, 2016
    Location:
    The North of England
    I added this tremolo into my Plexi micro and it sounds great.
    It loaded the signal down slightly as per the diagram so I used a 250k intensity pot instead. It messed with the sweep slightly. Ie. Not much happens for the first 1/3 of the dial. But no noticeable reduction in signal now. I love it. I tapped it straight into the signal where it exits the normal channel volume pot.
    Like you say, It allows reverb to be added after the tremolo for a very natural effect. EF062FFE-1902-475B-9E69-5A6AB40DE13D.jpeg
     
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