Harmon Kardon Tone Control Circuit

Tube : 12AU7/12AX7

Frequency Response :

The vertical scale is linear in dB from minus 9 to plus 18 with marks every 3 dB. 

Frequency is from 10 cycles to 100 kc on a log scale. 

There are 5 curves making the shape of an hourglass turned on its side. 

• The top curve starts at 10 cycles and plus 15 dB. At 50 cycles it is at 13 dB and falls until it reaches a minimum at 850 cycles and 1.5 dB. It rises again reaching 8 dB at 10 kc and topping out at 9 dB at 25 kc. It falls to 7.5 dB at 100 kc. 
• The second curve starts out at 10 cycles and 6.5 dB, 50 cycles, 5 dB, 100, 3 dB, 200 cycles, 1 dB 400 cycles 0 dB. At 1 kc it is at 1 dB, at 2 kc, 2 dB and 10 kc 2.5 dB. Past 20 kc it starts to decline and is at 0 dB at 100 kc. 
• The third curve is a straight line at just a scoash over 0 dB. 
• The fourth curve starts at minus 4.5 dB at 10 cycles. It is minus 4 at 50 cycles, and has risen to 0 dB at 300 cycles. It rises about half a dB above zero and crosses zero again at 1 kc. It is at minus 1.5 dB at 10 kc and minus 2 dB at 100 kc. 
• The fifth curve starts at minus 8.5 dB at 10 cycles and is at minus 8 dB at 50 cycles. It is at minus 3 dB at about 250 cycles and rises to a maximum of minus 0.5 dB at 850 cycles. It falls to minus 3.5 dB at 10 kc and minus 4 dB at 100 kc. End verbal description.