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phono vs line inputs on stereo

Discussion in 'Misc Electronics' started by Steve-o Stonebraker, Jun 11, 2004.

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  1. My apologies if this isn't the proper sci.electronics group for this
    question --

    I have an old one-piece stereo, the kind that's designed to look like a
    rack system but isn't. It has just one set of RCA inputs, which are
    intended for a phonograph. It's my understanding that the phono inputs
    expect a much lower-amplitude signal than a regular set of inputs would.
    I'd like to use this stereo, though, for my VCR, DVD, Nintendo, etc..
    I've done a little searching, and seen a suggestion to go inside and short
    out the phono pre-amp, as well as a couple simple circuit designs[1] to
    un-amp the line to get it ready for the phono's pre-amp.

    Now, I'm a physicist, so I should probably be able to do either of those,
    but my only electronics class was way back in 1996, and I didn't enjoy it
    very much. If there's a cheap little device I can buy that will fix this
    up for me, I'd prefer that. I see that there are separate phono pre-amps
    available to allow a phono to go into a line input, but I don't know if
    the reverse is possible. Or even if I can just hook up a device like that
    backwards and have it work. A non-powered device would be highly
    preferred, naturally.

    Anybody have a suggestion?

    [1]http://www.hut.fi/Misc/Electronics/circuits/phono.html

    --Steve-o
     
  2. Sounds like two resistors should take care of it (called a voltage divider
    or a pad).
     
  3. John Miller

    John Miller Guest

    Because phono inputs are RIAA-equalized, they also need to be bypassed, so
    in addition to resistors (and probably coupling/DC blocking capacitors) we
    need to bridge around the RIAA EQ.
     
  4. Captain Rick

    Captain Rick Guest

    I am not certain about this, but I think that phono inputs generally
    have a tailored frequency response, not a flat one as a standard input
    would, so your sound might be a little weird even with level
    correction...

    RIAA equalization rings a bell, try searching Google for more info.

    I have found a reverser for RIAA, try this - it seems to be what you
    need:

    http://sound.westhost.com/project80.htm

    Cheers,
    Rick.
     
  5. Is it matched for magnetic or ceramic cartridges? How old is it?

    Tom
     
  6. Yeah, that bears some similarity to the design I found. I can try to
    build something myself, I guess. Maybe I can bug the guys in the
    department electronics shop to make a nice little boxed device for me. :)

    Thanks for the suggestions, everyone.

    --Steve-o
     
  7. If you look at the URL he gave above, you will see that there needs to
    be equalization. If you use just "two resistors", then you will get
    terrible sounding audio.
     
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