spaceludwig said:
OK, so initial breadboarding done with resistors and pots to be added shortly (no pun intended...)
Had a question regarding the Mid EQ: Is there a readily available formula or calculator sheet available like Ian has for the Hi/Lo sections?
[edited for spelling]
Unfortunately there is no ready reckoner for the mid band. The reason is that the same value inductor is used for several frequencies. What that means is that the Q is different for each frequency that uses the same inductor. If we had the luxury of a unique inductance value for every frequency then we could keep the Q constant in which case there would be a simple ready reckoner you could use for frequency.
However, I can give you some general guidance that will allow you to work out the inductor value at a given frequency for a given Q.
The basic equation is Q = 2*PI*F*L / R
where F is the frequency and R is the characteristic resistance of the EQ circuit. For the mid boost, R is about 8500 ohms.
You can re-arrange this to give you L:
L = Q*R / 2*PI*F and since we know R and PI this simplifies to:
L = Q*1353 / F
So if we want a Q of 1 at 3KHz we get L = 1353 / 3000 = 0.45H
So pick a value of Q (1 is not a bad start) and use the formula to calculate L for the required frequency.
Note that high values of Q ae not a good idea at low freqeuencies. For example, the Q of the 200Hz boost in my design is about 0.2.
Hope that helps.
Cheers
Ian