Noisy volume pot with some tubes but not others

mariner4 · 6th August 2011, 10:11 PM

Hi, guys!

I built a version of Andrea Cuiffoli's no-compromise headphone amplifier (pictures in the picture thread). Schematic at HeadWize - Project: No-Compromise OTL Tube Headphone Amplifier by Andrea Ciuffoli

I have the following small problem:

When using a WE 417A as voltage gain tubes, the volume pot is silent when turned. When I replace them with JAN-Raytheon 5842 tubes (recommended for this amp), I hear noise while adjusting the volume. The sound is great with both tubes and the amp is very quiet when the pot is not being turned.

Can someone with more experience than me help analyze this situation? It's not really a big deal, but it's something I don't understand.

Thanks!

DigitalJunkie · 7th August 2011, 02:02 AM

The pot is being used as the grid-leak resistor,running DC through the pot.
To get rid of that,you could add a coupling cap,and a new grid-leak resistor on the input grid to ground.

mariner4 · 7th August 2011, 02:34 AM

This makes sense. When I was constructing the amp, a friend was skeptical about DC coupling of the input, but I ignored his advice since it worked so well with the WE tubes.

I guess this means that the Raytheon tubes have stronger grid leak than the WE... I will measure it.

mariner4 · 7th August 2011, 03:25 AM

And, of course, thank you for the reply!

Quote:

Originally Posted by mariner4

This makes sense. When I was constructing the amp, a friend was skeptical about DC coupling of the input, but I ignored his advice since it worked so well with the WE tubes.

I guess this means that the Raytheon tubes have stronger grid leak than the WE... I will measure it.

6th August 2011, 10:11 PM	#1
mariner4 diyAudio Member Join Date: Mar 2011 Location: New York	Noisy volume pot with some tubes but not others Hi, guys! I built a version of Andrea Cuiffoli's no-compromise headphone amplifier (pictures in the picture thread). Schematic at HeadWize - Project: No-Compromise OTL Tube Headphone Amplifier by Andrea Ciuffoli I have the following small problem: When using a WE 417A as voltage gain tubes, the volume pot is silent when turned. When I replace them with JAN-Raytheon 5842 tubes (recommended for this amp), I hear noise while adjusting the volume. The sound is great with both tubes and the amp is very quiet when the pot is not being turned. Can someone with more experience than me help analyze this situation? It's not really a big deal, but it's something I don't understand. Thanks!

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7th August 2011, 02:02 AM	#2
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	The pot is being used as the grid-leak resistor,running DC through the pot. To get rid of that,you could add a coupling cap,and a new grid-leak resistor on the input grid to ground.

7th August 2011, 02:34 AM	#3
mariner4 diyAudio Member Join Date: Mar 2011 Location: New York	This makes sense. When I was constructing the amp, a friend was skeptical about DC coupling of the input, but I ignored his advice since it worked so well with the WE tubes. I guess this means that the Raytheon tubes have stronger grid leak than the WE... I will measure it.

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