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Looking for info on loudness control

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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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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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