Input Z

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jandrews

Input Z
« on: 4 Jul 2023, 07:42 pm »
Hi Boris
Is the input impedance of the Spark 10kΩ regardless of where the volume pot is set… or is it dependent on how open or closed the volume knob is?
Thanks
JS

Audiovista

Re: Input Z
« Reply #1 on: 5 Jul 2023, 12:34 pm »
Hi,

The Spark's input impedance is fixed and does not depend on the volume control position.

Best,
Boris

jandrews

Re: Input Z
« Reply #2 on: 12 Jul 2023, 05:41 pm »
Thank you Boris
I asking bc I have been planning on make a couple of simple in-line high pass filters to put in front of the Spark to roll bass off around 70Hz for my speakers, and offload all the lows to my subs (using the speaker level connections) ...but after opening the amp and thinking about it further; Wouldn't I be able to accomplish the same thing more efficiently but replacing the input caps that are already there with a much lower value?  for instance, the same M-cap but in .22μf value?
thanks
JS

Audiovista

Re: Input Z
« Reply #3 on: 12 Jul 2023, 08:57 pm »
Replacing the input capacitor is a sound idea  :D

However, a word of caution: such simple filters will cause gradual phase change around the new crossover frequency which may make subwoofer integration difficult. For start, I would suggest an experiment: add the target capacitor (0.22uF from your example) in line with the input and then see how it works with your subwoofer. Experiment with the best sub crossover frequency and phase to see if you are happy with the results. Then, if happy, you can replace the Spark’s input caps.

You may find that your satellite speaker’s low end rolloff is a better match with the sub.

I am curious!


jandrews

Re: Input Z
« Reply #4 on: 12 Jul 2023, 09:56 pm »
Yes , I am under the impression the filter introduces a 45° shift around the cutoff and the phase on the sub needs to be adjusted accordingly.
But I like your idea of starting with the cap inline first

Audiovista

Re: Input Z
« Reply #5 on: 13 Jul 2023, 05:46 am »
Right, and the phase starts shifting much sooner, even one octave lower than the cutoff frequency. It comes down to personal sensitivity to the phase. I am not very sensitive, but there are people who can clearly hear it and it ruins the experience for them.

The speaker design and room acoustics also play big role when subwoofer is added, so experiment is the way to go. And it’s fun.  :D