Combining Pultec EQs

I would like to combine both the Pultec MEQ5 and Jakobs Gyraf EQP 1 type curcuits to give an all inclusive EQ capabiluty. These circuits are interactive so I think maybe paralleling the two might work. I drew upa schematic with my thoughts:http://users.adelphia.net/~thomasholley/Pultec.gif

I would appreciate your comments, thought and advice.

Thomas,

That won't work, as the eq's are ment to pass through the signal they're not messing with. This means that by adding the two output signals you cancel (most of) the eq'ing.

The only sensible way would be to have the two circuits in series.

But be sure to drive the circuits with low impedances - the input impedance of the PEQ is 75R worst/case, and around 500R for the MEQ.

I don't think either of these circuits' outputs would like being directly/psssively loaded with the input impedance of the other - so you will probably have to provide impedance conversion (and makeup gain now that you're there) between the two sections.

Which also means that you could as well have two separate units, maybe sharing box+psu

Jakob E.

[quote author="Viitalahde"][quote author="gyraf"]the input impedance of the PEQ is 75R worst/case[/quote]

What's the worst case? (=what kind of an EQ curve?)[/quote]


imagine full boost @ 16k with narrow BW (q pot = 0ohm) and full hi cut at the same time: the impedance @ 16k will be = R5 = 75 ohm, maybe little higher since the cap and inductor reactances wont be 0ohm.

steff

You could use maybe a Forrsell opamp inbetween the EQP and MEQ, then run the regular tube section for the output amp. A rather cool hybrid, eh?
Since the MEQ and EQP have different amounts of cut and boost, 10 db vs 16 db, it makes sense to series them, and add the inbetween amp for 10db makeup, then the EQP amp for 16 db gain.
If you want to ditch the extra innerstage tranny on the EQP, use a common mode line amp on the output.
Or another transistor amp.
You could also add an opamp circuit for bypassing the input transformer, an option Manley uses I believe.
cj

Looks like I should either make two boxes or put the circuits in series.

If I used series circuits I could save on a powersupply but I still would have a lot in one box. I could maybe use an SRPP like Jakob's for makeup between EQ's and another at the end of the chain. Different gain settings of course.

Crap, I have to think about this a bit. I don't know it it is really worth trying to cramp things up like this.

Yeah, I mean just build 2 1U boxes and put them on top of each other.
Maybe have an interconnect for the pwr supply.