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Old 21st September 2006, 06:18 AM   #1
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Default Looking for info on loudness control

Hello,

I recently finished my first vacuum tube line preamp. Its a simple design, with a regulated power supply and a couple of 6SN7GTs, one for each channel, gain 10. Im very happy with the results, except when Im listening at very low volume, during late night hours. I feel that a loudness control would be helpful in such moments, but I wasnt able to find a suitable circuit anywhere.

Can someone help me and point out a book or website with a schematic or formulae for a simple passive loudness control? Or, even better, for a tube based active variable loudness control?

Thanks in advance,
Norman
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Old 21st September 2006, 12:43 PM   #2
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This is a link to a page on Steve Bench's site. It includes some circuits, although passive rather than active.

http://members.aol.com/sbench/freqres3.html
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Old 24th September 2006, 05:07 AM   #3
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Thanks Robert, that hit the spot!

The only bad thing is that I use a 100k volume potentiometer, and those circuits expect a 500k pot.

Perhaps someone can help on this subject? Any tips on recalculating those circuits?

Thanks in advance,
Norman
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Old 24th September 2006, 12:04 PM   #4
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Default convert to 100K pot

To convert the designs from a 500K pot to a 100K pot, divide all resistances and inductances by 5, and multiply all capacitances by 5. This will result in a circuit with the same frequency response, but 1/5 the impedance.
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Old 26th September 2006, 11:37 AM   #5
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Hi Norman

Have a look here:

Volume pot with 4 legs ?!!!

Wayne
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Old 26th September 2006, 04:43 PM   #6
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A kluge that has been used with some success in the past is to use a parallel combination of resistor, cap and half of a dpdt switch connected between chassis ground point and the cold (gnd) end of the volume pot.

Start with a resistor of about 10K and a 0.12uF cap, increase cap to lower maximum boost frequency. Adjust both to taste.

Increasing cap value lowers point at which boost ends. F=1/(2piRC)

Larger resistor increases amount of boost, decrease cap value by ratio of r_old/r_new. So double resistor, halve cap value..

Smaller resistor reduces boost, increase cap value as by above. Halve resister, double cap value.
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