• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

50k or 100k output impedance.

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Are you saying that these resistors are going from the output terminal to ground? It sounds like they are not essential, per-se, but serve a secondary purpose.

It sounds as if you could replace them with a pot. I don't think you will have a problem with 100k. The differences would be minimal. I could say that the noise would be higher and the distortion would be lower, but I doubt that the average person would notice.

I'd be more sure if you had a schematic.
 
mattjk said:
I have a tube phono preamp and it is currently set to 50k for the output impedance.

I was playing around with a 100K noble volume pot, and it sounds fine.

My question is, what affect, if any would going to 100k have on the circuitry?

Thanks.


More info about the topology is requred. The notion that the output impedance may be 50k is quite preposterous for such a fine component. For any component in fact.

My guess is that the optional pot is sandwiched between the output of the riaa stage and possibly a cathode follower. The value is quite likely not critical.

A pic of the board will confirm this.
 
The output comes from the two large coupling caps, and into 4 resistors, which as I mentioned are 25k each. One goes to ground, and the other goes to + left and right.

Here is a picture of my board without the volume pot.

large.jpg


original.jpg



Here is a picture of a similar unit with the optional volume pot installed. As you can see, the 4 resistors are removed.

original.jpg
 
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