I need advice on a possible miniature tube preamp for electret mic

Discussion in 'The Projects Forum' started by Geek, Sep 17, 2009.

  1. Geek

    Thread Starter New Member

    Sep 17, 2009
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    I'd like to use one of the Panasonic omni electrets for an onboard acoustic guitar mic.

    I read about a 5672 pentode tube that appears to have extremely low voltage consumption that could possibly work.

    I'm a long time hobbyist, and I can follow a schematic. But I don't have the ability to design something like this. So any advice or links will be appreciated.

    I've added the 5672 spec sheet below, as well as specs for a Panasonic WM-64PN electret capsule.




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    Last edited: Sep 17, 2009
  2. Geek

    Thread Starter New Member

    Sep 17, 2009
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    I found some specs on the tubes.

    [​IMG]

    Subminiature type used in power output stage of subminiature equipment. Requires either a subminiature socket or direct soldering of the wires from the tube to circuit components.
    Mechanical Data

    Outline ....................................... 2-1
    EIA Base ...................................... 2E31
    Electrical Data

    Heater Voltage ................................ 1.25 DC V
    Heater Current ................................ 0.05 A
    Maximum Ratings (Design Center Values)

    Pentode
    Plate Voltage ................................. 90 V
    Grid No. 2 Voltage ............................ 90 V
    Characteristics and Typical Operation

    Class A Amplifier
    Plate Voltage ................................. 67.5 V
    Grid No. 2 Voltage ............................ 67.5 V
    Grid No. 1 Voltage ............................ -6.5 V
    Transconductance .............................. 650 µMho
    Plate Current ................................. 3.25 mA
    Grid No. 2 Current ............................ 1.1 mA
    Load Resistance ............................... 20K Ω
    Power Output (approx) ......................... 0.065 W
     
  3. Geek

    Thread Starter New Member

    Sep 17, 2009
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    And the specs for the Panasonic WM-64PN
    This is pretty much within a hair of the majority of the Panasonic omni electrets.

    [​IMG]




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    Last edited: Sep 17, 2009
  4. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    Wow, tube!

    What's wrong with using a FET and a battery?

    It's how the professionals do it.
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    The old Neumann U-47s and their ilk had built in tube preamps, but they had pretty big cases.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Be careful of that echo!
     
  7. Geek

    Thread Starter New Member

    Sep 17, 2009
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    Cuz i've convinced myself that it matters.

    :p
     
  8. Geek

    Thread Starter New Member

    Sep 17, 2009
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    Care to explain? I don't know the first thing about this.

    :confused:
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    Take a look at post #5. KL7AJ included his line in a quote.
     
  10. Geek

    Thread Starter New Member

    Sep 17, 2009
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    Oh, duh. I thought that was a reference to some sort of delay effect that the tube would introduce.

    I told you guys I'm a newb, lol.


    The Geek sn comes from computers, where I seem to know what i'm doing. :cool:
     
  11. Geek

    Thread Starter New Member

    Sep 17, 2009
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    Look what I found. Takamine did pretty much what I was thinking about here.
    http://www.metromusic.net.au/catalog/product_info.php?products_id=804

    Takamine players will find a most useful array of features to enhance their recording or live performance applications when using the cool tube these are the features to bear in mind:
    • A chromatic tuner available at your fingertips keeps the guitar in tune.
    • The tuner is capable of being calibrated from A438, to A445. An LED display reveals the note being played and directs the player with illuminated arrows that show sharp and flat.
    • The EQ section utilizes a shelving, graphic EQ, which can cut or boost bass and treble frequencies.
    • The mid range is shaped using a semi-parametric EQ section comprised of a rotary knob used to choose the mid point of the midrange frequency.
    • The midrange frequency can be cut or boosted with the mid slider. The range of frequency covered by the rotary knob is 200hz to 8.5Khz.
    • The tonality of the preamp is further enhanced by the use of the rotary knob labeled “Cool Tube” With this control, the player chooses the depth of effect the tube places on the signal generated by the proven Takamine “Palathetic” pickup.
    • With this knob the player can choose from a high degree of “CUT” for aggressive strumming; expanded “sweetness” and harmonic density with fatter lows and rounder highs; or levels of rewarding richness for finger style players.
    • An auxiliary input jack and volume knob, which can control an additional add-on pickup of your choice.
    • This facility can accept a magnetic sound hole pickup, or a soundboard transducer. The AUX control knob is used to blend the add-on signal with the Takamine pickup.
    • A small switch in the back of the preamp can be used to match the varying outputs of different pickups with the preamp.
    • The output volume slider can then control the blended signal. The CTP-1 is powered by 4 AA batteries, which will deliver approximately 24 hours of playing time.
     
  12. Geek

    Thread Starter New Member

    Sep 17, 2009
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    Anyone know if those Takamine electronics would be available separately?
     
  13. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    I find this thread fascinating. Being an old dog, it's nostalgic for me, but it begs that a long time question be answered here. Let's face it, you could sit an Audiophile in front of a lab grade Spectrum Analyzer, comparing a BJT, FET and Vacuum Tube amp, with identical frequency responses, and you will not convince him!... So what is it then?

    It's been well over 30 years since I transplanted myself and the wife to South Florida but I still remember what a Winter was like. Back in those cold northern days I loved the warmth and glow that emanated from my Hallicrafter SX42, which my Dad bought new in <= 1945 and passed down to me in 1967. It was my first receiver after I received my Novice Ham license. However, the warmth from those tubes was not analogous to sound! :D

    BTW, the SX42 had a companion speaker with an electromagnet where we're accustomed to seeing a permanent magnet.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    From the page you linked to:
    But keep asking them - maybe they'll change their minds.

    Sorry you haven't had much response to your project. This is really more a general hobbyist and student site than one for audiophiles and professional musicians; though we do seem to get a few occasionally.

    The last tube project I did was a homemade audio amplifier that I built around 1970. There really hasn't been much call for that sort of thing in the last 40 years, except for the high-end audiophile and professional musician market.

    Tiny tubes like that don't seem to need a lot of power at first glance, unless you're using batteries to power them with. You would soon find yourself spending a lot of money on batteries with even that small tube in a preamp. They're also pretty fragile, particularly when they are warm.

    You'd be better off to stick with a solid-state preamp, and effects pedals or "stomp boxes", and connecting them to a tube/valve amp.
     
  15. Geek

    Thread Starter New Member

    Sep 17, 2009
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    I would have no problem going with a solid state preamp version of that one.

    I just found another link about that Takimine tube one, and it apparently eats four AA batteries per day.


    So it looks like back to the drawing board.
     
  16. Geek

    Thread Starter New Member

    Sep 17, 2009
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    I don't doubt that I could be fooled. I remember the big challenges that Bob Carver did years back, when he said he could model any tube amp made.
    I don't recall which one he wound up going after, but no one could pick it the difference in a blind test. And the one he modeled was one of the mega dollar tube amps.
     
  17. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Don't despair. Before long you will have all sorts of solid state preamps posted here. What the members here are going to need are some specifics to where all the effect controls tie into the amp circuitry.
     
  18. Geek

    Thread Starter New Member

    Sep 17, 2009
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    I am seriously a newb on electronic circuitry.

    So here's what I have and what I want to do. And this basically means no tube amp at this point.

    I have a thin bodied acoustic electric.
    I want to be able to plug it in, not for final recording necessarily, but occasionally to lay down preliminary tracks.
    It will also be handy for times I just want to run the guitar through some basic effects while i'm playing.

    I want to use electret capsules, maybe 3 or so of them.

    I would like to be able to adjust individually, the bass and treble. Having a midrange eq like the Takimine would be awesome, but not required.

    The guitar already has a piezo saddle setup. And I would like to blend that in with the electret capsules.


    The smaller the better!


    Oh, and a beer dispenser if possible. :D
     
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