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In Reply to: RE: Rothwell In-Line Attenuators posted by Tre' on March 3, 2025 at 07:59:43:
Tre said:
"Above is a (approximately) 10db attenuator (1/3 of the input voltage) but the input impedance of the amp will be in parallel with R2 so there will be more than a 10db loss.
In this example if the input impedance is 10k then the value of R2 becomes 5k (10k//10k) and the db loss is now 14db (1/5 of the input voltage). If the input impedance is something different, then there will be a different amount of db loss."
A few basic questions . . .
My understanding, based on our previous discussion elsewhere, is that putting a voltage divider on the preamp / source side of an interconnect affects the output impedance of the preamp / source. And that it also interacts with the capacitance of the interconnect itself, which affects the low pass rolloff point.
In that scenario (voltage divider on the preamp / source side) does the value of R2 also change the input impedance of the amp?
My understanding was that, if the voltage divider is on the amp side of the interconnect, it has no effect on the output impedance of the preamp / source and it doesn't interact with the capacitance of the interconnect.
Do I have this right?
Also, it would seem to me that there wouldn't be any advantage in lowering the input impedance of the amp significantly. Especially if it is low to begin with, as is the case with a SS or Class D amp where 10k to 20k is typical. Wouldn't lowering it further just make it harder to drive?
If minimal change to the input impedance is desirable, wouldn't it be better to use higher values for R1 and R2?
For example, if you used 2M for R1 and 1M for R2 it would result in the same amount of attenuation and the input impedance of the amp would be 9.9k rather than 5k.
It seems like the main concern would then be the effect on the low pass rolloff. For a tube amp it might be easier to determine that since tube data sheets list capacitance specs. But what about SS and Class D? Do manufacturers publish those specs or can they be easily measured?
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- A Few Basic Questions - FlaCharlie 09:27:49 03/08/25 (0)
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