Another carvin eq question

[screamersusa]

I'm looking at building 4 preset eqs using the carvin schematic. I cant find the silverkiss.
I'm using +12 or 15v or bipolar 15v.

http://imageshack.us/f/262/carvin2.png/

I suck at math so I'm wondering if someone could figure out the values to make the
mid switchable between 400hz and 800hz? I believe it is 500hz so 500hz/800 should be ok.
I'd like to change the presense to a hi mid at about 1.4k/800 switchable.

Could I simply add a dual gang pot on the mids to move it around??

[PRR]

> make the mid switchable between 400hz and 800hz? I believe it is 500hz so 500hz/800 should be ok.

Higher pitch is smaller capacitors.

So 0.022 and 0.01 become 0.011 and 0.005. (0.01 and 0.0047 standard values will do.)

> Could I simply add a dual gang pot on the mids to move it around??

No.

You could use dual-gang *variable capacitors*. However you need numbers like 0.01uFd which is 10,000pFd, and variable capacitors tend to be 100pFd tops, 365pFd for the special case of AM radio, and 1,000pFd for custom transmitters. Prices are in the stratosphere (nobody makes big ones any more, and old/surplus has become precious). Dual-gang is rarer, dual-different gang very rare (again, exception AM radio where 365p+180p was standard).

Also big variable capacitors suck ALL the buzz out of the air and drop it on your signal. The H-P 200AB oscillator had a huge (7 inches long?) variable capacitor. It was in a shield box inside a near-sealed case; if you opened it to repair it the buzz was huge.

There's other ways to make a practical vari-F EQ, using more opamps. Practical but a lot of work. Anything more than 2 or 3 bands, I've always bought (or scrounged) EQs, not made them.

The Boss GE7 7-band EQ pedal is a pretty effective tone-control for most musical purposes. I got mine decades ago, I was shocked that they still offer it, around $110 new, $60 eBay.