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previous: Igor Hi Mark!I'll use TL072 or T... -- 5/28/2003 11:08 PM View Thread

Re: Boss GE-7 equalizer

5/29/2003 3:13 PM
Mark Hammer
Re: Boss GE-7 equalizer
To the best of my knowledge, you can use it without any attention to offset null. That first op-amp is simply a plain vanilla gain-of-11 input stage with a few bells and whistles. Turning it back into a simple non-inverting gain stage with a TL071 and none of the unnecessary components (the cap between pins 1 and 5, and the 22k resistor to ground) should have precious little effect on its performance. I imagine some of that stuff is there because the unit normally uses FET switches, and every such product needs an input stage that anticipates the impact of the FET switching, since that input stage will remain on all the time. If your intent is to use a simple DPDT stomp switch to bypass the unit, then do not expect it to behave differently as an EQ using the stock circuit than with just a simple 4.7k/470R/.015uf network. The output of the chip (pin 6 on a TL071) will go directly to the 10k resistor after it.  
The stock unit is arranged as most such units are with each band covering the same width in terms of octaves and being spaced equidistantly. There is nothing that requires you to do so, though, and many writers in the area of equalization will note that it can often be good practice to have your band non-equidistantly placed so as to be able to devote only as much coverage to the easy-to-deal-with bands as you need to and have a little more dial-it-in-and-dive-in capability in the critical bands. If you have the space and inclination, it would not be wrong at all to stick in some switches to be able to change the centre frequency of the 400hz and 800hz filters to move them a little higher or lower. Check out the articles on EQ-ing at RG Keen's site on how to select them or tinker with the bandwidth.

Igor Hm, I want to use FET switching on ... -- 5/30/2003 11:17 PM