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Simple hi-fi question

Discussion in 'Misc Electronics' started by Little Monster, May 16, 2004.

  1. Anyone know what typical output impedance is with hi-fi separates? (A
    tuner in this case) I trust it is fairly generic...

    Also building speakers - anyone know correct size of bass reflex tube for
    a 6 inch woofer? I think the one I got (2.5 inch) is way too big - and
    I've lost my speaker design book :-(

    Tia,
    Monster
    --
    I am the sexiest man in the UuuuKaaaayy
    All the girls love me
    And I will never grow Ooollldd
    I am the sexiest man in the UuuKaaaay!

    http://www.the-monstruum.co.uk
     
  2. Nope. Anywhere from 10s of ohms to several Kohms, depending on design
    and vintage.
    No such thing. Depends on the acoustic characteristics of the woofer
    and the enclosure.

    Kal
     
  3. Myron Samila

    Myron Samila Guest

    For the tuning port, you need to know all the Thiele Small paramaters and you can plot the
    expected response curve. The port only works at the tuning frequency. You can actually
    buy adjustable ports, you can lengthen/shorten the tube and "tune" for ideal sound at low
    frequencies. (Fs, Qts, Qms, Qes, Vas, and you'll need the Vb (box volume)). It is easiest
    to plot this with software.

    It is easier to make a sealed enclosure, but the problem is you loose the output you could
    have with a tuned port (at the lowest frequency).

    I didn't understand what you meant in regards to output impedance for hi-fi speparates.
    You mean the output from the tuner (amplified? or just pre-amp signal?). Typically, line
    level is 600 ohms (-10dB) on a device such as a CD player/tuner, etc.. (recent
    electronics). The output of the amplifier is usually designed to run anything down to 4
    ohms/channel (typically). I have a Bryston 3B, capable of 2ohms/channel.

    Hope that sorta helps.
     
  4. Nope. Only in professional equipment. Consumer equipment has no such
    standard.
    Again, your Bryston is quite competent (as is mine) but many (most?)
    consumer A/V receivers and amps cannot handle a 4 ohm load, let alone
    a 2ohm load.

    Kal
     
  5. Mmm, thanks for the feedback. The tuner is a 70's vintage Realistic
    tuner, of fairly compact size. I just supposed that since separates
    generally seem to work well together, there must be some kind of standard.

    Thanks for the "speaker notes" - really wish I had my book on the subject
    now...

    Monster
    --
    I am the sexiest man in the UuuuKaaaayy
    All the girls love me
    And I will never grow Ooollldd
    I am the sexiest man in the UuuKaaaay!

    http://www.the-monstruum.co.uk
     
  6. As long as the input impedance of the device it feeds is higher by an
    order of magnitude or more, there should be efficient voltage
    transfer.

    Kal
     
  7. That is certainly the case, the device it feeds being a valve amp, the
    input is 1M ohm approx. However, the amp does not have volume or tone
    controls, so at the moment the tuner feeds across a 20k dual pot
    (completely guessed value), with the wiper connected to the amp. Trouble
    is, the volume goes up very steeply near the beginning of the track - I
    was hoping if the pot matched the tuner's output impedance a bit better,
    it might make a smoother change. Also, intend extending the simple volume
    pot with a baxandall circuit, and wondering about picking optimum values
    to start with - ie so the circuit has roughly the same impedance as the
    tuner output. Now I am thinking, perhaps what I need is a /higher/ value
    for the volume control, to match the amp's input...

    Monster
    --
    I am the sexiest man in the UuuuKaaaayy
    All the girls love me
    And I will never grow Ooollldd
    I am the sexiest man in the UuuKaaaay!

    http://www.the-monstruum.co.uk
     
  8. The value is probably OK but you need an audio taper pot, not a linear
    one.

    Kal
     
  9. It's log - isn't that pretty much the same?

    Monster
    --
    I am the sexiest man in the UuuuKaaaayy
    All the girls love me
    And I will never grow Ooollldd
    I am the sexiest man in the UuuKaaaay!

    http://www.the-monstruum.co.uk
     
  10. Try wiring the other way around (anti-log). OTOH, if your amp's input
    impedance is 1M, you might also try a 100K pot in case your tuner has
    a very high output impedance.

    Kal
     
  11. Thanks for all the input - must experiment now :) Anti log sounds
    interesting!

    Monster
    --
    I am the sexiest man in the UuuuKaaaayy
    All the girls love me
    And I will never grow Ooollldd
    I am the sexiest man in the UuuKaaaay!

    http://www.the-monstruum.co.uk
     
  12. Guest

    Ideally, output impedance must be zero.
     
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