How to Feed Audio to an Old HIFI?

Discussion in 'Audio Hardware' started by Eugene's DIY Den, Mar 21, 2019.

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  1. Eugene's DIY Den

    Eugene's DIY Den New Member Thread Starter

    Location:
    Ireland
    I have a 1993 vintage Sony system with a turntable. The only inputs are phono pre-amp inputs, no line ins.
    I'd like to be able to hack into the amplifier, so is there any point in the amplification stage where the impedance and sensitivity is compatible with a line out signal? I was thinking of sacrificing the turntable input so maybe I could connect in at the output of the preamp stage.
    Has anyone ever tried this?
     
  2. R. Totale

    R. Totale The Voice of Reason

    If the circuit is at all conventional, the output of the phono preamp will essentially feed the top of the volume control. The wiper of that control will be followed by any tone controls before it hits the amplifier section. Inserting a switch to feed the top of the volume control with either your external signal or the phono preamp output (with the external signal's ground at the bottom of the control) may work. The incoming signal will see the nominal value of the volume control as its load, which is likely to be high enough not to bog the external signal down. You'd probably want to run the external signal through a cap on the way in to strip off any DC.
     
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  3. Eugene's DIY Den

    Eugene's DIY Den New Member Thread Starter

    Location:
    Ireland
    Ok, thanks I'll suss that out and maybe try and track down a schematic also.
     
  4. BrentB

    BrentB Urban Angler

    Location:
    Midwestern US
    Is there a cassette deck? If so you could consider an adapter to go into that like the old car ones. Basically a cassette shell that has a stereo lead wire usually with a 1/8" jack on the end.
     
  5. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    The only likely candidate is an all-in-one rack system like a HCD-D109. It actually has four possible inputs, three of them being internal, and being switched by a mc14052 stereo multiplexer chip. One simply needs to lift any of the connections to the other internal components and repurpose them.

    [​IMG]

    You can see the X0-X4 inputs on the chip, their input pins, and the legend that shows which input matches which pins.

    The tape would be the easiest input to re-purpose, it has its own connector leading from the main board that carries both a line in and a tape out signal that both could be brought to rear RCA jacks.
     
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