Preamp specs to match a power amplifier

October 10, 2021
 by Paul McGowan

5 comments on “Preamp specs to match a power amplifier”

  1. If I chose to hook my Schiit Vali2 headphone amp up to my Jolida JD-1000P all tube power amp and sat that high gain low gain switch to high, and turned the volume half way up, it would crank out 6volts with a minimum input of 300MV from my JVC cd changer.
    It would make that amp put out 180 watts.
    That is pretty darn loud!
    Yay thoe I don’t do that, because I live in a bad aria.
    And noone that lives outside of my home, needs to know what kind of sound equipment I have in here.
    Because, that’s just inviting some stupid person to brake in to your home while you’re gone, and still all of your stereo equipment.
    That’s why among a lot of other reasons, I don’t play my music as loud as I yoost to.
    When people see my wife out and about, sometimes, they ask her, “what kind of equipment does your husband have in that house?”
    And when she answers them, her answer is always, “none of your business!”
    You can’t really trust anyone out there.

  2. We can do some fairly straightforward maths here (or math for those in the US):

    1200 W in 4 ohms is equivalent to a sine wave with RMS voltage of 69 V, and a peak of 98 V. A gain of 30 dB is a voltage ratio of 31.6 times.

    For full power, the pre-amp needs to drive a peak of 98/31.6 = 3.1 V. Any preamp that can drive 3.1 V will be able to access the full power of the M1200.

    However, Paul has often said that an amplifier sounds best if it is operated well below maximum power, and 1200 W is an incredible amount of power, so it wouldn’t really be a problem if the pre-amp put out a little less, except that it would be nice to have some additional headroom in the preamp too.

    If all of the amplifiers have the same 30 dB gain then for a given preamp they all provide the same output at any given position of the volume control. There’s no reason why an M1200 owner should expect to be carefully manipulating the volume control over the first few degrees of rotation. The difference with an M1200 is that the owner can turn the knob further in a clockwise direction without hearing distortion.

  3. Even though I’ve had pre/power separates in the past, what I do like about a ‘straight through’ well designed integrated is that the pre section is designed *exactly* to feed the dual mono power sections.
    500 watts continuous per channel into 8 ohms at <0.01% THD from 20Hz-20kHz is perfect for me.
    Paul is spot on about the 'headroom factor' 🙂

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