A potentiometer has three terminals. A resistor has two.

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Posted by Al Sekela (A) on January 30, 2010 at 14:32:48

In Reply to: Hmm THAT'S interesting... can you elaborate please? posted by hukkfinn on January 29, 2010 at 16:10:40:

The way a potentiometer is usually employed as a volume control is with the full range of the potentiometer (end points) connected as a load to the driving section, and the tap connected to the input of the driven section. The driving section design depends on there being the full value of the potentiometer resistance always present, no matter where the tap is placed by the user.

Now, it is possible that the original design only used two terminals of the pot, with a fixed resistor from the input of the driven section to ground. In this case, the mod was correct and maintained the original circuit topology. If so, your sonic observation has to do with the characteristics of the Vishay resistor and is not a fault of the modifier.

However, if the original design followed convention and the modifier changed the topology, then the sonic problems could be a result of the changes.

Tubes have essentially infinite input resistance, and grid-to-cathode resistors are usually of very high value. Their operating behavior depends on the load resistance. Making a significant change in the load resistance of the driving stage could cause problems.

I suggest contacting the manufacturer or designer if you don't get a satisfactory answer from the person who performed the modifications.

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Follow Ups Full Thread

Topic - Should I expect much of a break-in with a new hi-quality resistor? - hukkfinn 03:54:51 01/29/10 (9)

I would have tried PRP or Caddock. - Al Sekela 15:23:12 01/29/10 (6)

Hmm THAT'S interesting... can you elaborate please? - hukkfinn 16:10:40 01/29/10 (5)

A potentiometer has three terminals. A resistor has two. - Al Sekela 14:32:48 01/30/10 (4)

Thanks very much. Question.... - hukkfinn 18:27:32 01/31/10 (3)

All resistors have some sonic character of their own, - Al Sekela 15:16:38 02/01/10 (2)

Thanks, that's really helpful. Sorry to be such a newbie. - hukkfinn 18:58:21 02/01/10 (1)

Everyone is a newbie sometime. - Al Sekela 15:26:27 02/02/10 (0)

RE: Should I expect much of a break-in with a new hi-quality resistor? - bacobits 08:35:42 01/29/10 (1)

Nope, different unit. - hukkfinn 09:03:56 01/29/10 (0)

Follow Ups

A potentiometer has three terminals. A resistor has two. - Al Sekela 14:32:48 01/30/10 (4)

Thanks very much. Question.... - hukkfinn 18:27:32 01/31/10 (3)

All resistors have some sonic character of their own, - Al Sekela 15:16:38 02/01/10 (2)

Thanks, that's really helpful. Sorry to be such a newbie. - hukkfinn 18:58:21 02/01/10 (1)

Everyone is a newbie sometime. - Al Sekela 15:26:27 02/02/10 (0)

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