ONE LINEAR AMP from Massdrop has input impedance of 1k ohm???

Discussion in 'Advice Threads' started by SHAWN P. WATSON, Mar 8, 2021.

  1. SHAWN P. WATSON

    SHAWN P. WATSON Acquaintance

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    So is the convention that an AMP must have an in input impedance 10 times higher than the output impedance of the DAC that is connected to it TRUE?

    The published specs over on MASSDROP of the ONE LINEAR AMP show an input impedance of 1k ohm.

    Problem is that my iDSD BL has it's DAC's output impedance as 240 ohms. So 10X that would be 2.4k ohms which breaks the rule of optimal impedance matching? Will this create audible distortion or something? Similarly, I was considering buying an SU-9 DAC which is 122 ohms but still an impedance mismatch.

    What is weird is that the Drop THX789 amp shows input impedance of 50k ohms balanced or unbalanced. You would think that the ONE LINEAR AMP, which was supposed to be a single-ended version of the THX 789 would have similar specs for input impedance?

    So I guess my question for those more technically minded is: "What will be the outcome of this impedance mismatch?" and "Will it be audible?"
     
    Last edited: Mar 8, 2021
  2. 7seven

    7seven Acquaintance

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    Some loss of gain on the input.

    1V from 240 ohm would drop to about 0.8V with a 1K input.
    The input and output impedances here are probably just set by resistors which would behave the same way a potentiometer would.

    My guess is that 789 50K input impedance comes from extra input circuitry to convert an SE input to balanced and also buffer a balanced input.
    Buffering the SE input on the ONE probably measured worse so they omitted it
     
    Last edited: Mar 9, 2021
  3. rlow

    rlow A happy woofer

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    Are you sure it isn’t a typo on the Drop site? Did anyone ask? I’ve not heard of a 1k ohm pot.

    Also, why is this a thread?
     
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  4. 7seven

    7seven Acquaintance

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    It isn't necessarily a pot... the mechanism is the same though. A 240ohm output resistor in the DAC and a 1k input resistor feeding a low impedance amplifier input, forming a voltage divider.

    Topping L30 also has 1K input impedance (2.5K actually), it was necessary to get their extremely low noise measurements.
    Im not sure but I think it actually had practical benefits in some cases, with noise being audible even at extremely low levels with hyper sensitive IEMs on a lot of amps.
     
    Last edited: Mar 9, 2021

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