T. Mueller wrote on Tue, 11 March 2008 14:34 |
zmix wrote on Tue, 11 March 2008 10:50 | I think an interesting way to implement this EQ would be to run the output of each filter to a rotaty switched resistive ladder attenuator feeding a SPDT center-off switch. The center lug of the SPDT/CO switch would be connected to the attenuator following the filter's output. The outer lugs of the SPDT/CO would feed Pins 2 and 6 of U2.
This way you would have a three position switch determining whether each band was going to "Cut" or Boost" or, in the center position, be "out".
This also effectively doubles the number of positions available on the attenuator.
EDIT: I see that Mike Pecchio had a similar idea here.
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PLEASE pardon my lack of understanding; still learning. Am I reading this right in that you're describing a way to implement attentuation with more precision/resolution to the filters? I read Mike's post; sounds like a fun project.
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My suggestion is probably simpler than you think it is..
Basically in this EQ, as in most active EQ circuits, the input signal is split off into two paths, one straight through to the output amp and one through an EQ filter, either a shelf or a bell (peaking) filter.
If you combine these two paths at the output amp, you will get an additive effect at the frequency of the filter.
If you invert the polarity of the filter 180˚ you will have a subtractive effect at that frequency.
In the stock circuit, each filter's "cut/boost" control is essentially a pan pot which directs the output of the filter to either the inverting input of the output amp (for cutting) or the non-inverting input (for boosting).
If you use a toggle switch (after the filter's ouput attenuator) to direct the filter's output to either the inverting or the non-inverting port in the output amp, you can use the entire travel of the "cut/boost" pot or alternately all of the positions of the rotary "cut/boost" switch towards your desired result.
To simplify it further, suppose you have an 11 position switch for the cut/boost function.
In the original schematic this will give you 5 cut positions and 5 boost positions and the middle postion is 'flat'.
In version I suggested you will have 11 positions of cut or boost and you don't waste one position to have a 'flat' setting (since the cut/boost selector toggle has an 'out' position).