Why preamps have high outputs

June 1, 2021
 by Paul McGowan

9 comments on “Why preamps have high outputs”

  1. A little more then 21 years ago, I was talking to a guy at Peavey Electronics.
    I was asking a question about my Classic 5050 all tube power amp that I bought from them back then.
    I wanted to know, how much power would I get from that amp, if I put 15 volts in to its inputs.
    The guy told me, “that’s not a line level signal.
    That is way above a line level signal.”
    He also went on to tell me, “15 volts=18 watts.”
    But even I know that you have to have a certain amount of currant to get that.
    But my Mcintosh C-2200 preamp wasn’t putting out any currant, but it did give me 15 volts.
    And I do know it’s true that any amp on the planet is gonna be looking for a line level signal.
    He didn’t tell me somethingg that I didn’t already know about that.

  2. The other issue is that most amps have high input impedance. Headphones are a great example in that the higher the headphone impedance is the more output the headphone amp needs to put out.

    It is better to have your gear “loafing along” rather than playing at or near full output. Headroom is good.

  3. Great video Paul. I think this sums it up well, and it may be why I love old tube pre’s with lots of line level gain. It’s effortless. Thanks for all your insights. Cheers!

  4. Which is preferable? An output that saturates at 2 V, but is extremely linear for all voltages less than 2 V, or an output that can drive 12 V but is slightly non-linear over the first 2V?

    1. Just thought about it and I assume it puts out 2 volts until you get to around the 2 o’clock position then 18 more volts crammed in the rest of the way never to be used.

      1. That’s a good point, and makes me wonder why a preamp would be designed to induce power amp clipping, especially without being able to tell when that clipping begins. This would seem to be a problem with lower power amps and inefficient speakers, where one needs to crank it up.

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