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In Reply to: RE: Opps!, ordered wrong value posted by Cousin Billy on January 03, 2016 at 07:08:11
While you do go to 1Hz with 0.22, they don't sound as good otherwise, and with the 0.1 uf units, the squarewave tilt at 20Hz is unmeasurable. This means no phase shift at 20Hz, which is how you get impact.
Increasing the value will mess with the timing constants in the circuit which will increase the IMD.
Thanks for that insight. I once read about "slugging the bass" which amounted to using an excessively large value coupling cap. What's that all about?
Sometimes an amplifier could do with a larger coupling cap as the timing constants in the power supplies will allow it.
The issue is that the amp should not have bandwidth that goes below that of the power supply! No power supply is truly DC (batteries are) as they all have some sort of low frequency timing constant.
If the amp has bandwidth below that of the power supply, the result will be that it has the ability to modulate the supply. If it can do that, the noise in the supply will cause intermodulations to occur.
Now our amps don't have a particularly low THD figure as modern amps go, but our IMD figures are just fine in that regard. This is because we pay attention to this rule. There is a myth that if your THD is not low neither will be the IMD. In solid state amps that are direct-coupled input to output (meaning that they by default exceed the LF timing constant of their supplies), this does occur but it does not have to be that way if the amp has well-managed timing constants.
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