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xdissent 24th November 2003 04:09 PM

is my new design on the right track?
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below is the input stage of a guitar pre im building - basically i need it to be a line driver (about 0dbV out). i need it to accept line or inst levels (hence the hi/lo gain switch) and be as hifi as possible... or as reasonable i should say. i've set the low freq rolloff at around 15hz so i can use the same circuit for a bass guitar and the hi freq rolloff is around 33kHz just cause i want it to be super bright if possible. so... is my gain control idea ok? i mean, with the hi/lo switch ON, it should have a gain of about 1 with the volume control almost all the way down. i chose this type of gain control on the first op amp because although i need to provide high gain for the 100mV typical output of a guitar, i wanted to have as little gain as possible if its not needed. this way the gain is only set to about 2 with the volume all the way down, which can then be reduced to 1 when you switch the hi/lo toggle to on (while still keeping the lowpass freq about the same). am i missing an easier way to do this? i didnt want to do this before the first op amp because i want the input impedance to be as constant as possible regardless of whether or not im using line or guitar inputs. its ok that i cant provide for any LESS gain than about 1, because it will never be driven any harder than about 1V anyway. any suggestions. am i ok noise-wise? oh the buffer at the end is pretty important too. is it best to have the 22k there or should i just short over it?

xdissent 24th November 2003 09:19 PM

2 Attachment(s)
this is with peak detector and schmitt trigger led driver.... any thoughs?

Richard C 24th November 2003 11:27 PM

C4,R8 and R9 are redundant.:)

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