I don't think you need a FET input. I'm assuming you're using this tone control with low impedance signals (regular line levels, or the amplified signal coming from a previous stage). Bipolar input stages have very low noise, lower than FETs, as long as you keep impedances low.
The treble circuit has an asymptote in the midband, and the bass circuit has an asymptote in the midband.
So the two asymptotes add together in the midband.
Unless the bass and treble hinge points are sufficiently far apart, the two responses will add, and cause
a substantial midband rise, about symmetrical around the geometrical center of the two hinge points.
I just wanted to point out that this is an application where FET input op amps excel. Reducing bias current through the bass pot is paramount to achieving low noise. With a 5532, raising pot values (say 100K) will greatly increase offset drift as the pots are turned, creating a potential noise problem.
Raising pot values to 100K also allows the use of smaller, cheaper capacitors for the same performance. OPA2134 with 100K pots works perfect with very little offset and drift.
Raising pot values to 100K also allows the use of smaller, cheaper capacitors for the same performance. OPA2134 with 100K pots works perfect with very little offset and drift.
This is the real test result when the pots are entered, the response is somehow flat around 0dB
This is the result when I turned the Treble pot to Max:
As you can see from 20Hz to 1KHz got attenuated by 4dB
This is the real test result when the pots are entered, the response is somehow flat around 0dB (NE5532)
This is the result when I turned the Treble pot to Max:
As you can see from 20Hz to 1KHz got attenuated by 4dB
A much better tone control circuit is realized using Walt Jung's bass and treble controls. The circuit uses separate op amps for each control. There is zero interaction between the controls, and the precision is much better. Of course, it uses two op amps and a lot more parts.
I'm totally ok with those minor deviation , I just wondered why the whole band width got attenuated by 4dB when I turned the Treble pot to the max position .
Center:
Treble at max:
I see, but this design works great in Multisim simulation , that's why I wondered
The circuit you show is quite conventional and is essentially the same circuit used it a lot of consumer equipment. The Walt Jung circuit doesn't necessarily sound better but it does work with a much greater degree of precision, which looks better in the measurements.
Extreme precision just isn't necessary in a circuit like this. It won't "sound" any better. That being said I use Walt Jung's circuit because I'm an engineer and I'm downright nerdy about electronics. If I were building a precision circuit (like for a recording studio) then I would definately opt for Jung's controls. They can be cascaded to make a high precision, low distortion equalizer.
Extreme precision just isn't necessary in a circuit like this. It won't "sound" any better. That being said I use Walt Jung's circuit because I'm an engineer and I'm downright nerdy about electronics. If I were building a precision circuit (like for a recording studio) then I would definately opt for Jung's controls. They can be cascaded to make a high precision, low distortion equalizer.
May be an interaction with the bass circuit, and the input impedance of the op amp.
This type of EQ circuit does exactly as you describe. The interaction is mainly from the bass filter damping characteristics. You will need to tweak component values to minimize the issues but I doubt you'll get the dip down to less than 1-2 dB.
I think you can use a lower shunt resistor (R5). You are probably coming from a very low output impedance, and line level impedances are usually one order of magnitude less (around 10k). This won't make any difference as to the midrange drop, but you'll have somewhat less noise.
As for the midrange drop, this is basically a Baxandall circuit right? Some midrange drop is to be expected.
Yes it's Baxandall design.
Interesting that the circuit works correct in Multisim simulation
Exactly, in my case the circuit works fine and the tone control pots did not affect the entire signal, but the "Overall gain" is changing when you turn the pots, especially the Treble pot. If I want to be more specific when you turn the Treble to max the overall gain gets attenuated by around 4dB. In picture one, the pots are positioned at center and the entire response is around 0dB, and in the second one the Treble pot is it it's max and the "whole signal" attenuated by around 4dB, while the tone control is boosting the High-Band correctly. I'm pretty sure that I made the circuit right.
The circuit works fine and the tone control pots did not affect the entire signal, but the "Overall gain" is changing when you turn the pots, especially the Treble pot. If I want to be more specific when you turn the Treble to max the overall gain gets attenuated by around 4dB. In picture one, the pots are positioned at center and the entire response is around 0dB, and in the second one the Treble pot is it it's max and the "whole signal" attenuated by around 4dB, while the tone control is boosting the High-Band correctly. I'm pretty sure that I made the circuit right.
