thanx :)~ ... and now ...

[jc]

thanx very much for all the replies for the 4250 op-amp ... from what I
hear there's bias control on this one ... in the para exciter there's a
1Meg resistor between pin 8 and ground ... I found this curious ! though I
could very well see it setting idling currents in current mirrors
throughout the op-amp and/or in particular the diff-pair at the input (if
I'm wrong I'd be curious to know).

I'm modding a Marshall for this guitar player and he brought in these two
gizmos that impressed me ... one's called a "para.eXciter Mark III" and the
other "Lo-Z pack (to get pure sound)" ... he told me who made it and I
forget the name, Ranger or something ... anyway, both in a stock Marshall
and modded Marshall the para-exciter really shines, it's worth a build IMO
... here's my hand at ascii'ing it ...

** Para Exciter MARK III ** (10Hz-10kHz parametric eq./exciter)

                      |\ 4250
       .47u           | \
 in ----||------------|+ \         4.7u
            |         |   \_____----||---- out
     +9     |         |   /    |
      |    1Meg     --|- /     |
     100k   |      |  | /      |
      |-----       |  |/       |
     100k          |   .001u   |
      |             -----||----
      0            |           |
                  5.1k        5.1k
                   |  ->...<-  |
                   | 470k-470k |
                   |  ^  |  ^  |   (dual 470k pot)
                    --   |   --
                        ---
                        --- .01u
                         |
                         0


... the Lo-Z pack is the same op-amp circuit but wired in unity gain as a
buffer, since Graham dreams of an amp that has that circuit in the front
end we've decided to stick the lo-z pack circuit in his guitar modded to
the para-exciter circuit along with a bypass switch ... later tomorrow I'll
build a clone of it with RC4558's or something and see how it compares ...

----

* About my Fake Book*

I have just printed a new batch of fake books (a whopping ten copies) and
I'm selling them for $20CDN - I pay for shipping ... the book is 214 pages
long and includes 57 music circuits, app notes for novices and data sheets
... almost all circuits are for guitar and bass though some certainly
adaptable to other applications ... sorry to anybody who emailed me when I
was asking 40$ for it (my cost has dropped to 8$ from 22$ and my feet are
back on the ground now :)

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\\\\ http://www.lynx.bc.ca/~jc/    \\\\\\\\\\\\\\\\\\\\\\