The output impedance of the source is 32 ohms and the input impedance of the amp is 100k ohms according to the manuals.
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Strictly speaking, the output impedance still won't tell you much about the output's actual driving abilities. That said, any source brave enough to have only 32 ohms of output impedance (sounds more like a nominal load impedance to me, actually), would be likely to have a decent amount of oomph, easily driving 10 kOhms and possibly even <1 kOhms still.
An possible alternative (which you may not wish to do), is to mount the volume pot. INSIDE your power amp, effectively turning it in to an integrated amp., then the concern over passive volume control pot. resistance value mostly goes away. The key is whether or not the pot. forms an RC low-pass filter with the interconnect cable capacitance (commonly, approximately 50pF per foot), producing an audible high response roll-off. The higher the pot. resistance, the worse the roll-off if it is mounted before the interconnect cable. When mounted after the interconnect, such a roll-off is not produced. Which enables the pot. resistance to be chosen so as to provoke the lowest line driving circuit distortion. However, the higher the pot. resistance the more it will produce measured thermal noise, which still may not be audible as an increase.
100k is usually capable of discernable hiss at the tweeters, as that's about 70µV RMS at the output of a typical power amp. Typically you'd only hear this fairly close to a speaker.
100k pot has its max effective noise resistance of 25k, when set to 50k+50k position, and that noise gets amplified about 25 times in a typical power amp.
I reckon if noise is an issue (all depends if you are irritated by the hiss close to the speakers), change to 10k.
100k pot has its max effective noise resistance of 25k, when set to 50k+50k position, and that noise gets amplified about 25 times in a typical power amp.
I reckon if noise is an issue (all depends if you are irritated by the hiss close to the speakers), change to 10k.
On the bjt IPS example, say with a unipolar input and not complementary with some degree of bias current cancelation, is the base bias current not isolated by the input coupling cap? So this ips bias current would be determined by a resistor that is connected to the ips base and usually connected to the ground reference returned through the emitter? The base bias current would not be determined by the source or the pot in this case?
This is how a jfet IPS has an advantage over a bjt type.
This is how a jfet IPS has an advantage over a bjt type.
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DC - yes.
AC - no.
Any dynamic cancellation of input bias current nonlinearity requires matched impedances.
If you look at Samuel Groner's measurements of BJT input opamps, the input bias current related effect shows up as the flat area at lower frequencies in the input impedance distortion graph; higher up, input impedance starts to dominate.
Their JFET colleagues show almost none of that shelf (it is eventually limited by common-mode distortion) but the capacitive part tends to be stronger by about a factor of 3, with very few exceptions like the OPA627 and its bootstrapped cascode input.
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