No. Notice the ratio of the caps in each leg. This provides approximate log action in the passband being boost/cut.
This is an old circuit, hawking back to the tube days. It has been used in equipment all the way up to the early 90s as far as I know.
I have never used this circuit in a design. Even going back to the 70s (when I built my first preamp) I always used the inverting op amp type of tone controls. They're a lot simpler to customize and only use one cap per control.
Is there any advantage sonically to using one circuit over another? A lot of still popular equipment still uses this circuit. I have had many receivers using this setup and only once did I feel compelled to rip into the tone section and fudge around with it (which I did with success).
This classic circuit has been superseded by tone controls on a chip and preset pushbutton "tone controls" that are hit and miss and leave a lot to be desired.
Till I know, almost all tone controls referred to gnd, are insertion loss and to have the 0db at center of the pot, it must be log scale.And the ratio between resistors and capacitor from pot to gnd and from pot to signal, they must be also log, to have equal boost and cut ranges.
I've taken a lot of them apart. They're not all like that. Also there's shunting resistors thrown into the mix.
Many commercially designed controls are not true Bandaxall design. They are in fact very imprecise and only approximate the performance of the original circuit Bandaxall presented. But they still boost the bass and treble and it's what many of us listened to for many years.
Also remember that in the real world there's no such thing as a true log pot. Measure some old ones out of commercial equipment and see for yourself.
Probably.
What passes for a "log" pot is usually just a two stage pot. It's two linear tracks in series. It isn't really logarithmic at all. 😉
There are many, many variations on the Bandaxall tone control circuit. Some used log pots; some used linear. I'm not convinced that any of them provided a true flat response at any setting, because I have never found one that did. And most of them introduced significant distortion as well. Even my old Nakamichi receiver sounds way, way better with the preamp bypassed and an active tone control circuit (nothing fancy at all) of my own humble design (really a combination of simple Walt Jung circuits) inserted in its place.
This circuit is a variation of what was called "the Bandaxall circuit" that was in vogue for decades. Its performance depends on being fed by a low impedance buffer and feeding a high impedance input. There are countless variations in tube and transistor and (as we see here) op amp circuits. It has been an industry standard fever since its introduction (in the 40s?).
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The circuit I know as original baxandall has a 500K pot with center tap to ground, for treble. But I never could discover for what is this tap. If for grid return, it may be done with a fixed R, if to fix the 0db, it also can be done with resistors externally to the pot.
In many amplifiers of the 80s and 90s with tone control included in the feedback loop, pots include curved "C".
Thank you all, folks.
I think I can manage easily to "pull down" the Bass tone to about 70Hz and the Treble tone up to 12kHz.
This has been very interesting and fun! I can only imagine what other people make with their own projects! 🙂
P.S.: please, confirm if I'm right: moving the hi-band (10kHz) further (to 12kHz) and we don't need to exceed with the pot in +dB (increasing) to achive a high Treble effect, right?
I think I can manage easily to "pull down" the Bass tone to about 70Hz and the Treble tone up to 12kHz.
This has been very interesting and fun! I can only imagine what other people make with their own projects! 🙂
P.S.: please, confirm if I'm right: moving the hi-band (10kHz) further (to 12kHz) and we don't need to exceed with the pot in +dB (increasing) to achive a high Treble effect, right?
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Theoretically, both potes must be independent, but they are more dependent as the frequencies of each network are nearer.
For some interesting info, search for SLOA042 ate National Semiconductors Application Notes.
For some interesting info, search for SLOA042 ate National Semiconductors Application Notes.
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That's also why I started this experiment. At "standard" 100Hz (basses) and 10kHz (trebles) sometimes I have the feeling that only at the end of pot cursion (around +6dB) I can hear some increasing level.
I'll have a look at the SLOA042, Thanks!
This is a very worthwhile effort. Rank and file tone controls affect too broad of a bandwidth, in my opinion. This is especially true of the bass controls, which boost too much mid bass. This results in boominess when the bass is boosted. Most speakers only require modest boost below 80 Hz or so and no boost above 150 Hz. Typical tone controls do not provide anything like this. Many modern feedback type controls start boosting from 1000 Hz on both sides, which makes absolutely no sense at all from a musical standpoint. Of course engineers like nice round numbers and think in decades.
You can make some calculations, but make sure that you like the results. It depends largely on your system; especially your speakers and room gain.
The design of such networks is very well described in the National Semiconductor´s book "Audio". I used the calculation there and gives me good results in my 3 band (100-1000-10000Hz) tone control.
That's why I've never been that happy with typical 100Hz - 10kHz tone controls. 😱
http://onlinetonegenerator.com/
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The work is done. Tone control is a bit more effective, specially on the low frequencies. I just turn the bass pot a bit to have the same effect I had when turning it till the end before changing the capacitors. Bass control is now around 65Hz, while treble is about 12kHz!
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