50k or 100k output impedance.

mattjk · 14th January 2008, 05:07 AM

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.

sharpi31 · 14th January 2008, 07:59 AM

50Kohm sounds too large to be the output impedance in a phono preamp - could this value be the input impedance?

What is the phono preamp connected to? Where is the volume pot in relation to the other items in your system (between what and what)?

mattjk · 14th January 2008, 04:53 PM

Hi,

It is an art audio vinyl one phono amp. It is set up with 2 25K resistors at the output terminals, totaling 50k. There is an option from the factory to add a volume pot, which is also 50k, but I have a 100k Noble on hand which I wanted to try.

jnb · 14th January 2008, 09:30 PM

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.

analog_sa · 14th January 2008, 10:15 PM

Quote:

Originally posted by mattjk
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.

mattjk · 14th January 2008, 11:06 PM

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.

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

14th January 2008, 05:07 AM	#1
mattjk diyAudio Member Join Date: Aug 2004 Location: Huntington Beach, Ca	50k or 100k output impedance. 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.

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14th January 2008, 07:59 AM	#2
sharpi31 diyAudio Member Join Date: Oct 2005	50Kohm sounds too large to be the output impedance in a phono preamp - could this value be the input impedance? What is the phono preamp connected to? Where is the volume pot in relation to the other items in your system (between what and what)?

14th January 2008, 04:53 PM	#3
mattjk diyAudio Member Join Date: Aug 2004 Location: Huntington Beach, Ca	Hi, It is an art audio vinyl one phono amp. It is set up with 2 25K resistors at the output terminals, totaling 50k. There is an option from the factory to add a volume pot, which is also 50k, but I have a 100k Noble on hand which I wanted to try.

14th January 2008, 09:30 PM	#4
jnb diyAudio Member Join Date: Dec 2006	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.

14th January 2008, 11:06 PM	#6
mattjk diyAudio Member Join Date: Aug 2004 Location: Huntington Beach, Ca	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. Here is a picture of a similar unit with the optional volume pot installed. As you can see, the 4 resistors are removed.

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