[Yoda]

I am interested in adding the option of variable eq to my Cornet2 to work w/ older records.  I have a separate pre w/ plenty of gain,  want to keep it stereo (w/ mono switch in tact), so would I simply add the eq circuits times 2, similar to what is described in the monogram pro? 

http://www.hagtech.com/pdf/monogram.pdf

Matt

[hagtech]

The monogram was designed with a 12AT7, I think.  So the EQ component values will be different.  I did some other wierd things with the monogram I can't remember.

But yes, it should be possible.

jh

[Yoda]

Cool,

ok -how where would I begin w/ the math to calc the new values?

Matt

[hagtech]

Use the calculator at www.hagtech.com/equalization.html.  Start by assuming the output resistance of the 12AX7 is 100k ohms.  Put that in parallel with the plate load and the grid bias resistor of the following stage.  That's your R value.  It'll give you a C value.  Ok, now increase R until you get a standard value of C.  Use that series resistance between plate and C to make up the additional amount.  Unfortunately, you have to recalculate everything because the grid resistor on the following stage is no longer in parallel with plate.

You do this for both sections (different sets of turnovers).  Now, once you get RIAA, then modify values proportionally to get the non-RIAA stuff.  They don't have to be perfect, just get close.

Usually takes awhile to do this.  And then, after you build it, you have to tweak values some more.  I use an inverse filter and 1kHz square wave.  Any deviation is immediately apparent.

jh