3 band parametric eq how to#

When the Wien bridge is combined in a feedback circuit the Q is greatly improved and insertion loss is no longer a problem. ДЇ = 1 / ( 2ПЂ Г— R Г— C ) Where R is resistance in Ohms, and C is capacitance in Farads

3 band parametric eq how to#

For more info on how to build an oscillator, see Project 22.ДЇigure 1 - Basic Wien Bridge, With Amplitude & PhaseДЇrequency is determined by the resistance and capacitance, and they are normally all equal - i.e. In an oscillator, an amplifier circuit is used to provide positive feedback around the Wien bridge, and the negative feedback path needs gain stabilisation to provide a gain of 3, which is just enough to sustain oscillation. This circuit is the 'heart' of nearly all audio oscillators (not function generators - they are very different). As a filter, it's rather dismal, having very low Q (0.32) and a high insertion loss of about 9.5dB. It's a useful circuit, and with the arrangements shown later provides an easily tuned filter with a constant Q (at maximum boost or cut) of 0.88 (close enough to 0.9) - a value that just happens to be very useful in an equaliser because it sounds 'right'. Use of a Wien bridge circuit in an equaliser is not common, but it has been used in a tone control circuit, is the subject of a now expired patent, and no doubt elsewhere as well. I recommend NE5532, OPA2134 or LM4562 opamps, but others will work too, including very cheap or very expensive types.

If decent opamps are used, there should be very little increase in noise, and distortion will remain negligible. Ultimately, virtually all parametric equalisers have lots of opamps, because that's what's needed to get the functionality that users expect. Not that this is a real issue, but it does mean that some people may not be happy with so many opamps in the signal path. If you have a 3-stage equaliser, you have 3 opamps in series.

However, each stage is cascaded because you can't make two or more sections behave properly using a single opamp. Despite this advantage, the circuit itself is fairly economical in terms of components. The adjustable circuit described here has the advantage that the Q remains constant, so it covers the same frequency range (in octaves or parts thereof) regardless of the centre frequency. However, its Q changes as the frequency is varied, and that is slightly annoying.

I have already described a 'quasi-parametric' equaliser (see Project 28), and it does work rather well. However, there are many places where the ability to vary the Q is not needed, especially for general purpose tone controls.ДЇor musical instrument use a flexible tone control circuit is often a must, and especially so with bass guitar which has some interesting challenges. While other filter types can also be used, most are not as well behaved or as flexible as the state-variable topology. Parametric equalisers are often very complex, because to enable variable frequency and Q requires a state-variable filter. It's not perfect (I don't know of any circuit that is), but it is fairly simple to implement and performs well. The main purpose of this article is to introduce the reader to a flexible equaliser circuit that can be used for hi-fi, mixing consoles, instrument amplifiers (especially bass guitar) or anywhere else that a simple and predictable 'parametric' equaliser is needed.