zapco crossover mod help

[IMSTOOPID]

I need some help... please..

I have the schems (partial) for a zapco crossover circuit I need to modify.

I want to change the variable freq range from 55-270 to something fixed like 4K
I also want to replace the crappy TL074 op amps with some 627 or 2132
or what ever I can.

I'm a ME and forgot most of my electrical circuit design I took in college(I remember p=i^2*R) but I do know which end of a soldering iron is hot!

so any suggestions guys..THANKS.. now to figure out how to post schem!

[Perry Babin]

I think you can use the formula R=1/(2*pi*f*c). The R would be the total resistance between the output of one op-amp (where a pot is now connected) and the inverting input of the next op-amp. C would be the capacitor used for feedback on the op-amp. F would be the desired crossover point.

It seems to work out with the pot set to the highest frequency (pot shorted). Using the above formula, it comes out to 266Hz. It would work for 55Hz if the pot is 50k ohms.

[IMSTOOPID]

thanks.. I haven't torn into the amp yet.. but that seems logical..
any suggestion on the TL074..I can solder in adapters if needed..
my issues is I'm not sure but I think newer op amps draw way more current?
plus I have another crossover that uses them that I'd love to replace

[Perry Babin]

You can look up the current draw in the datasheets. I doubt that it will be a problem.

[IMSTOOPID]

well rather than setting a fixed value.. until i get my system woking what Do i need to change to keep the 50K10 pot in and change the freq range to like 2-5K>

also what can I put in place of the tl072 and ne5532's dual 627's or 2134?

I can solder but no circuit guru! I do know I can hear the diff in head phone amps and crossovers between op amps though.. thanks

[Perry Babin]

To change the frequency range, you'll need to replace the two capacitors connected between the output of the op-amp and the inverting input of the same op-amp (C69 and C87 locations, for example). Reducing the capacitance will increase the frequency range. Punch the numbers into the formula to get the frequencies).

Replacing the op-amps isn't likely to make an audible difference and could make things worse if the op-amps are unstable in the circuit.

[IMSTOOPID]

PERRY: thanks.. Yes I will replace the pots with a fixed resistor network one I get the system set where I want it. I do know the zapco works on 15-16V because of the Slymbilink balanced line inputs. I just want to raise the freq and I know that in every active tweet/mid crossover I have ever heard with TLOX opamps they sound crappy. Low freq has not been a problem and this unit is set up currently(from the factory) to run from 55 -270HZ. I was just wondering if there was a easy drop in that sounded a little cleaner. Thanks a bunch.. do I set the cap value for the center freq of the range or basically set it for 4k.. Not sure what resistor value to use in the formula sine a pot is involved.

[tsmith1315]

The corner frequency scales linearly and inversely with the cap values. For example, to increase the range values by 10, decrease the cap values by 10x for a range of 550-2660Hz.

To get the lower end of the range up to 2kHz, scale the cap values down 36.4x. That would define the top end of the range as 9672Hz with your existing pot.

[IMSTOOPID]

473J = 0.047uf? this doesn't seem right but that's what's in there.

.0015uf ok I'll start lookin!

[IMSTOOPID]

well I got one I'll post for the C2k..
If you are interested. It has the ranges I just got to figure out how to turn one section into a bandpass!
I'm gonna keep those amps.. and sell the ref360.

However the TL072 and 074's and 5532 are gonna get replaced If it does kill my current draw.