简单的音调控制电路

Tone control circuits are basically filter circuits which are used to filter audio frequency signals so that only the desired range of frequencies are allowed to pass to the amplifier and the loudspeakers. This enables the listener to customize the music output with either a high level of low frequency content through bass boost, or an increased level of high frequency content through a treble boost.

音调控制通常是大多数的重要特征audio amplifiers,而这些通常可用的低音和treble controls, competent at delivering around 12dB approximately of boost or cut above their specific frequency bands.

While these are extremely straightforward circuits, numerous tone control layouts apparently reveal rather unconventional control features when you do a few mindful inspections with them! The thing is typically an absence of symmetry in the boost/cut characteristic.

这可能不是真正的危险缺点，但是这确实意味着关键控制配置不会提供所需的扁平频率响应。问题背后的一个原因是，几个音调控制电路往往是被动类型，因此它们是通过具有适当的源和负载阻抗来确定的。两者中的故障都可能导致音调控制响应的不良变化。

Passive Tone Control

Figure below exhibits the circuit diagram of a basic passive tone control which might work fairly good given that the signal supplied to it is from a low source impedance and passes into a relatively high load impedance.

Due to the passive characteristics of the circuit, it isn't actually appropriate to assess in terms of the controls delivering boost and cut. Such designs will always present losses, and if configured to offer bass or treble boost it is in reality delivering diminished losses instead of a authentic boost to the signal level. This may not be strictly academic, and the technique in general has to be built to consider the fundamental loss of around 12dB associated with such designs.

Active Tone Control

被动音调控制网络可以连接到线性放大器（通常是操作放大器）的负面反馈回路，以创建一个active tone-control circuit. But instead of attenuation, this circuit gives signal gain.

The amplitudes of the output signal are fully regulated through resistor R5 in case the input signals to the circuit shown below are small enough for the capacitors C1 and C2 to function as open circuits.

这是因为电容器C2从输出中分离出电阻R6。输出信号的幅度完全由电阻R6在足够大的输入频率下完全控制，以使两个电容器作为短电路的行为。在这种情况下，电阻R5通过C1短路。

The values of R1 and C1 decide the low-frequency (bass) circuit cutoff, whereas C2 and the quantities of R1 to R3 define the high-frequency (treble) circuit cutoff. The next figure below reveals how the design in the above figure can be incorporated into an active tone control circuit which may amplify or reduce bass or treble signals by up to 20 decibels (dB).

Although comparable to the above this active tone control circuit indicated in the next in figure looks even more flexible. It contains an extra filter control circuitry that is centered within the audio spectrum's 1 kHz midband. The midband may be enhanced or reduced by up to 20 dB using this network.

通常建议，不再像被动电路混乱，而是像以下电路图中所示的那样，选择一个主动色调控制电路。

这只是一个被动色调控制，从非反转OP放大器的反馈电路以及输入缓冲区阶段连接起来，以确保通过适当低源阻抗操作主音调控制电路。

这提供了一种倒置的结果，其中从音调控制供应供应提高了反馈和增益减少，而从控件中的削减可提供减少的反馈和增加的增益。如果考虑到这些因素，将两个电位仪连接起来，则它可能能够通过控件提供正确的结果（这意味着锅的顺时针移动将产生增强；抗锁定的旋转将提供切割）。

指示的音调控制电路供应略高于12dB的增强功能，并在音乐范围的相对范围内切割。

Simplified Tone Control Design

The next figure below exhibits the circuit diagram of a simplified Active Tone Controls using a single op amp, which is a standard set up possessing bass control VR1 and treble control VR2.

当VR1和VR2的刮水器臂完全转向左侧时，它会产生最大的反馈，从而产生完整的低音和高音切割。

When the wipers are moved at the opposite side of their rotation we get lowest feedback and thus highest bass and treble boost. The controls don't have any substantial impact at central audio frequencies (around 800Hz), and offer highest boost and attenuation value of approximately 12dB.

The total level of cut and boost is actually offered at the two extremes of the music frequency range, and 12dB is around the maximum that will actually be required in real life use.

1C1 is wired in the inverting mode, and its non-inverting input is as a result easily biased to 50 % of the supply voltage through R1 and R2. C2 is used for decoupling any noise that might normally be supplied to the non-inverting input through the supply rails through R1 and R2, or picked-up because of to stray coupling.

The amounts of noise and distortion generated by the circuit are minimal, even while the pot controls are adjusted for getting highest possible boost (which still allows the the circuit to have just an extremely minimal level of voltage gain).

As soon as one or both of the tone controls are adjusted for a cut, IC1 offers a closed loop gain of lower than unity. Using certain inside compensated operational amplifiers a closed loop gain of smaller than unity may trigger instability, and the internal compensation is simply for closed loop voltage gains of unity or higher.

在电路中已经实验了许多TL081 CP IC，并遇到了零并发症。

The circuit may additionally perform nicely using a 741C IC, and in real life use is unlikely that any kind of recognizable drop in efficiency would actually be noticeable employing IC 741. However, the noise and distortion quantities will probably be somewhat greater compared to the IC TL081CP.

Frequency Response

下面的下图显示了几个对照锅中的估计频率响应，当它们被排列以获得最高的增强和切割时。这些响应包括非常出色的对称性，并且电路提供的特性一旦在中心位置进行调整后，该特征就非常接近平坦的响应。

话虽如此，请记住，电位计的公差可能会在20％左右的情况下非常广泛，而且调整的物理中心点不可能是正确的电气中心点。

Any kind of errors caused by this situation within the theoretically flat frequency response could be rather insignificant though. Building of the tone controls provides hardly any issues.

的电压增益很微不足道,即使control is adjusted for getting optimum boost, there could be absolutely no risk of instability.

How to Connect the Pots

Make sure that the pinouts of the pots controls are connected the right way round.

Referring to the two op amp tone control circuit, treble control VR1 delivers boost when its wiper is moved towards the C3 end of the rotation, or oppositely the cut is set when the control is rotated towards the C6 end.

In the same way, bass control VR2 offers boost when the pot wiper is moved towards the R3 end of the rotation, or oppositely the cut is set when it is adjusted towards the R6 end of the rotation. Observe that you will find a little amount of voltage gain of approximately 5X from the circuit at the 0dB reference level.

3 Channel Tone Control (Bass, Treble, Presence Controls)

The next concept explains a 3 channel tone control circuit, which can be used for generating bass and treble control responses and in addition to this, the circuit can be also used to produce presence control, or the mid frequency control.

The input music signal is applied through connector SK1 to the 1st op amp stage configured around IC1. This is wired as a non-inverting amplifier with a gain that is fixed through the ratio of resistors R3 and R1. For this 3 channel tone control circuit the gain is fixed at unity.

The first op amp stage needs to be kept isolated from the next stage due to prevent loading effects. The ICI output is applied through 3 frequency shaping circuit configurations to IC2. The three tone controls are constructed around the pots RV1, RV2, RV3 which additionally form the part of the feedback path of IC2, which is configured like another inverting op amp stage.

使用的部分around the three potentiometer are selected such that it delivers the intended frequency and tone control results.

Simple Transistor Tone Control Circuit

这个简单的晶体管控制电路可以轻松包含在任何音乐系统中，例如立体声放大器，迪斯科舞厅或无论如何。这是因为它具有较大的输入阻抗（超过100K），最小的统一电压增益和低输出阻抗。

The standard bass and treble controls can be seen incorporated in the unit. These filters have around 12 dB of boost and cut at 100 Hz and 10 kHz respectively. The noise and distortion levels involved in this transistorized tone control circuit tend to be incredibly low because of the massive amount of negative feedback utilized and due to the fact that the circuit is able to deal with output signal levels at many volts rms, without clipping.

晶体管Q1是在简单的发射机追随器缓冲区阶段配置的，该阶段为设备提供了增加的输入阻抗。电容器C2将Q1输出与音调控制电路连接。该设计是一个主动音调控制电路，可为放大器提供频率选择性的负反馈。使用Q2的放大器是直接连接到Q3的标准公共发射极阶段的标准公共发射器阶段，这是发射极跟随的输出晶体管。后者为设备提供低输出阻抗。

This tone control circuit is somewhat easier than the typical Baxandall setup, however it is still able to provide a highly realistic performance. Pot RV1 is configured to adjust the bass range of the circuit while pot RV2 controls the treble control.

Feedback is enabled to the highest levels when the potentiometer sliders is shifted to the extreme right, while the feedback becomes the lowest when the pot sliders are rotated fully towards the left.

Needless to say the tone control circuit gain is inversely proportional to the feedback level. Meaning when a maximum feedback is generrated it corresponds to the highest possible cut and not a full boost. The tone control's current consumption not more than 1mA per supply volt.

三冠王助推器的吉他

To increase the higher order harmonics and create a more dazzling sound, a treble booster circuit could be used with an电吉他（以及音乐设备）。这种电路在低音和中间音频频率的大部分部分上具有相当平坦的响应，在上层和下三倍的频率下具有显着的提升。

In order to provide high stability and a reduced noise level, it is common to place just a little amount of importance on the upper-treble. This also avoids the output from appearing excessively harsh.

The frequency response is seen in the graph below.

该设计本质上是在非反转模式下运行的操作放大器。

R4 and R5 bias the non-inverting input through a decoupling network consisting of R3 and C3. DC blocking is provided by C4 and C5 at the input and output, accordingly.

With SW1 in open condition, R1, R2, and C1 provide nearly 100 percent negative feedback, providing the circuit unit gain and a flat response. By closing SW1, part of the feedback via R1 and R2 is decoupled at frequencies greater than just few 100 Hz, resulting in the desired ascending response. At peak treble frequencies, feedback through C1 enables the response to fade away over around 5.5 kHz, preventing the extremely high frequency harmonics from getting over emphasized.