Simple SE volume pot value???

BillEpstein · 1st November 2010, 01:41 AM

Stole the 50K volume pot out of my SSE a while back for another project. Decided to put one back this weekend to use the amp connected to the TV.

All I had was a 10K so I wired the pot outputs with 43K resistors. Getting a "kinda muffled" (that's an audiophile term) sound. Pretty good KOA resistors but maybe I should remove them and leave the pot at 10K?

tubelab.com · 1st November 2010, 01:48 PM

Quote:

All I had was a 10K so I wired the pot outputs with 43K resistors.

Two possibilities. Likely the 43 K resistor is working with the Miller capacitance of the 12AT7 to form a low pass filter, killing your treble response. Eliminate them (short them out). The other possibility is thet your source doesn't like a 10K ohm load. This is unlikely if it contains sand based life forms.

The volume pot value for most tube amps (and all of mine) is bounded on the lower end by what the source can drive. I have used a 500 ohm pot on an amp that was fed by a Sony Discman's headphone jack. It is bounded on the upper end by the miller capacitance of the input tube. 100K is about the limit on the SSE and SSP (12AT7) and 50K on the TSE (5842).

BillEpstein · 2nd November 2010, 01:17 PM

Thahks, George

BillEpstein · 3rd November 2010, 04:15 AM

I clipped the resistors and the amp is singing all the notes again. While I was there I moved the on-off switch from back to front and it's still dead quiet. You just can't make this circuit hum!

jrenkin · 10th January 2012, 07:47 PM

May I ask a question along the lines of this thread?

the high frequency response of the input stage (TSE in this example) would be calculated using the Rin and miller capacitance of the tube.

I just want to make sure I have this right, or correct what I have wrong.

So to figure Rin, i would use the output impedance of my source (low, maybe 100 ohm), the value of my volume pot (50K, although in actually listening this number would be lower), plus the 5842 grid stop (4.7K ohm) in parallel with the the grid leak resistor (121k ohm) or roughly 37k ohm or so.

I don't have the equation or calculator with me, but I suspect this is a cutoff (-3dB) of around 75kHz for the input stage of the TSE with a 50K volume pot. Higher at true listening volumes?

If this is right, that would make problems for a different input tube, such as a D3a which has a much highr miller capacitance, or could I increase the grid leak some?

1st November 2010, 01:41 AM	#1
BillEpstein diyAudio Member Join Date: Feb 2004 Location: The Great Smoky Mountains	Simple SE volume pot value??? Stole the 50K volume pot out of my SSE a while back for another project. Decided to put one back this weekend to use the amp connected to the TV. All I had was a 10K so I wired the pot outputs with 43K resistors. Getting a "kinda muffled" (that's an audiophile term) sound. Pretty good KOA resistors but maybe I should remove them and leave the pot at 10K?

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2nd November 2010, 01:17 PM	#3
BillEpstein diyAudio Member Join Date: Feb 2004 Location: The Great Smoky Mountains	Thahks, George

3rd November 2010, 04:15 AM	#4
BillEpstein diyAudio Member Join Date: Feb 2004 Location: The Great Smoky Mountains	I clipped the resistors and the amp is singing all the notes again. While I was there I moved the on-off switch from back to front and it's still dead quiet. You just can't make this circuit hum!

10th January 2012, 07:47 PM	#5
jrenkin diyAudio Member Join Date: Nov 2007 Location: Denver, Colorado	May I ask a question along the lines of this thread? the high frequency response of the input stage (TSE in this example) would be calculated using the Rin and miller capacitance of the tube. I just want to make sure I have this right, or correct what I have wrong. So to figure Rin, i would use the output impedance of my source (low, maybe 100 ohm), the value of my volume pot (50K, although in actually listening this number would be lower), plus the 5842 grid stop (4.7K ohm) in parallel with the the grid leak resistor (121k ohm) or roughly 37k ohm or so. I don't have the equation or calculator with me, but I suspect this is a cutoff (-3dB) of around 75kHz for the input stage of the TSE with a 50K volume pot. Higher at true listening volumes? If this is right, that would make problems for a different input tube, such as a D3a which has a much highr miller capacitance, or could I increase the grid leak some?

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