I don't think I said it was the best way, just that I did it - it actually worked very well.
I'm adding an analogue volume control to my current project and will be using a balanced 'U' shunt attenuator between the LP filter and the buffer input.
Shunt attenuator (1 resistor) changes the LPF -3dB frecuency, ladder attenuator (2 resistors) not changes the LPF -3dB frecuency.
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Now I'm confused. Thinking about this, wouldn't a 50K potentiometer always be a 50K load? Merlin's second diagram looks just like a potentiometer to me too - I'm assuming each pair or resistors always add up to the same total resistance so switching between pairs of resistors changes the potential divider ratio, just like a wiper in a pot?
Somebody educate me please
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In the second graph the input impedance is always the same since always the sum of both resistances is equal (10K, 25K, 50K, etc depending your attenuator choice)
So, going back to iperv's comment about my replacing the 47K fixed resistor with a 50K potentiometer, it worked OK because it is OK...
It's not the same: fixed resistor source and load sees the same impedance, potentiometer: source sees the same impedance but load don't sees the same impedance.
See attachment - regular potentiometer.
The best way is, of course, the ladder one.
EDIT:
With regular potentiometer R1 and R2 vary with volume changes, so Zin from source is:
R1+R2*RL/(R2+RL) = not constant.
EDIT2:
It is not a big problem due to the LPF (relative) high frequency.
Even if you change a little the Rin, frequency is always high enough to regular operation.
The best way is, of course, the ladder one.
EDIT:
With regular potentiometer R1 and R2 vary with volume changes, so Zin from source is:
R1+R2*RL/(R2+RL) = not constant.
EDIT2:
It is not a big problem due to the LPF (relative) high frequency.
Even if you change a little the Rin, frequency is always high enough to regular operation.
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How is that possible? both circuits are simple potential dividers, electrically the same. If they're electrically the same then they must behave the same.
Thanks iperv, I think your equation is the information I was missing. I'll run some values through that a bit later so I can see what is going on.
Ray
How?
Assume a fixed RL. If you have two potential dividers (#1 and #2) and at any given point, R1(#1) = R1(#2) and R2(#1) = R2(#2) then Zin(#1) must = Zin(#2), regardless of whether R1 and R2 are defined by a potentiometer or fixed value resistors.
What configuration of 'no-DAC' are you using after your Amanero? What music player software?
@vladimirb0b:
Hi ... It is a CR circuitry where - to my knowledge - the 47k resistor to ground and the input impedance of the subsequent circuitry (amplifier / preamplifier or ??) forms a parallel impedance. The capacitor in series with the signal then has a varying impedance depending on frequency (high pass) and thus sets a lower cut off frequency.
To my knowledge the formula for calculating this is identical to the formula for an RC filter (?) ... The difference being that the ordering of the active components leads to either a low pass (RC) or a high pass (CR) filter ...
@Ray: Thanks for the tip on the RC filter internet calculator. As it is I actually have set up an excel spreadsheet to calculate various calculations that I often need - including the RC filter results. But I appreciate the consideration ;-)
Cheers from Denmark,
Jesper
Hi ... It is a CR circuitry where - to my knowledge - the 47k resistor to ground and the input impedance of the subsequent circuitry (amplifier / preamplifier or ??) forms a parallel impedance. The capacitor in series with the signal then has a varying impedance depending on frequency (high pass) and thus sets a lower cut off frequency.
To my knowledge the formula for calculating this is identical to the formula for an RC filter (?) ... The difference being that the ordering of the active components leads to either a low pass (RC) or a high pass (CR) filter ...
@Ray: Thanks for the tip on the RC filter internet calculator. As it is I actually have set up an excel spreadsheet to calculate various calculations that I often need - including the RC filter results. But I appreciate the consideration ;-)
Cheers from Denmark,
Jesper