Audio preamplifier help needed

Discussion in 'The Projects Forum' started by barried, Apr 19, 2015.

  1. barried

    Thread Starter New Member

    Apr 20, 2013
    I have recently completed a new stereo system using class D which works really well. I have routed the output of my digital tuner via a switch to either a DAT recorder or a CD recorder to enable quality recording of classical music from the ABC in Australia. The tuner puts out 800 mv and this is a little low to get a full signal on either the DAT or CD.

    Can anyone suggest a circuit for a stereo preamp which will accept 800 mv input and provide line output, which I guess is 2 volts? Since I have plus and minus 15 volts available in the unit it would be good if the preamp ran on that.

    Thanks for your help.

    Barrie Davis
  2. cornishlad

    Active Member

    Jul 31, 2013
    If both your voltage figures are of the same type - eg. both peak to peak you only need a gain of three. I would try a TL072 in the most basic opamp circuit with the feedback resistor chosen to get the appropriate gain. What you don't want is excessive gain which could introduce noise. can't say more been called to go out ..
    Last edited: Apr 19, 2015
  3. crutschow


    Mar 14, 2008
    For the lowest noise, use the TL072 op amp suggested by cornishlad in the non-inverting gain configuration running from ±15V with 0.1μF decoupling caps from the positive and negative power pins directly to ground.
    For a gain of 2/0.8 = 2.5, connect a 2kΩ resistor from the (-) op amp input to ground and a 3.01kΩ resistor from the (-) input to the output (film type resistors).
    Add a 100kΩ resistor from the (+) op amp input to ground.
    Connect the (+) op amp input to the digital tuner output.
    Last edited: Apr 19, 2015
  4. Veracohr

    Distinguished Member

    Jan 3, 2011
    Professional line level is referenced at +4dBu, which is 1.228Vrms. Consumer line level is referenced at -10dBV, which is 0.316Vrms.