Simple Scratch and Rumble Filter

This is 12 dB per octave and the beginning of the add-on Rumble filter, which can be connected to "Tape" or the institution responsible for the amplifier.

And 'the usual quadratic filter circuit having a passive high pass filter formed by the ability of C3 and C4 series and parallel resistor R2 and R3 (the latter is also used to bias the transistor Q1 source follower). Passive filter of this type gives only very slowly to the original roll, and the final reduction was only 6 dB per octave. Boot Strapping resistance is then used to improve performance. Above the cutoff frequency, where profit is the district would otherwise drop slightly, R1 is the effect of strengthening the signal. Well below the cutoff frequency, the loss of C4 leads to the signal emitter of Q1 is significantly below the junction of C3 and C4. This leads to some of the signals at the intersection of C3 and is pushed through the R1 and R1 with C3 effectively forming a second network-pass filter. This eliminates the sluts, the number of the original film (in fact, is a small and insignificant in a maximum of about 05dB above the cutoff frequency) and accelerates the depreciation rate for a nominal 12 dB per octave.

The low pass filter works the same way that the high-pass, except, of course, the elements of R and C of the filter have been implemented to provide the correct action of the filter.

With the component values ​​specified for Rumble filter response drops below unity at about 45 Hz, where -6 D13 just above 30 Hz, then drops to a nominal 12 dB per octave. The filter response from zero to unity gain points around 6k5Hz time 6dB points at about 10 kHz, then drops to a nominal 12 dB per octave.