What is the effect of a 22K res in series with a 25K volume pot?

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andyr

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Joined 2003
My preamp has a 22K res in series with a 25K volume pot, for each channel. Can anyone explain what having this res there, does?

My thinking is that when the pot is fully wound round (ie. maximum volume, so the pot is out-of-circuit), the signal is still going through a 22K resistor - so I must be getting some signal attenuation.

The reason for my question is that I would like to achieve a bit more gain from my preamp - and I'm thinking that reducing the value of these resistors ( or removing them) would do this? :confused:


Thanks,

Andy
 
A

andyr

Member
Joined 2003
nigelwright7557 said:
I think the phono stages need to see 47k hence the 22k and 25k pot.
Its all about impedance matching.
Click to expand...

Yes, I understand about Zin but AIUI while the Zin of a phono stage is, typically, 47K ... its Zout has no such specific requirment but should be at least 10x (and preferably 20x or more) less than the Zin of the preamp?

Given that the Zout of the phono stage is 100ohms, the 25K of the pot itself should be more than adequate?

Even if the Zout of the tuner & the CDP are as much as 1K (which is unlikely, I suspect), the 25K of the volume pot should still be sufficient?


Thanks,

Andy
 
A

AndrewT

R.I.P.
Joined 2004
The Zout of the pot is seen as the source impedance by the receiver.
The Zout of a pot reaches a maximum of [Rpot+Rs(before the pot)] / 4
When you add that 22k in series with the 25k pot you have increased the maximum Zout max to ~12k
Zout min = 0r0.
That will give a very variable low pass filter as seen by the receiver.
 
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