can i use opamps instead of muamps in this schematics?

[Unkn0wn Art1st]

I don't have so many jfets (original version needs 9 couples of jfet), so I'm thinking about using opamps.
Did i draw it correctly? Is it possible at all?

[anchovie]

Those aren't mu-amps, they're pairs of N and P FETs.

If you want a cab sim that uses opamps, try the Runoffgroove Condor or this: http://www.diystompboxes.com/pedals/schems/msim.jpg

[Unkn0wn Art1st]

sorry for the wrong term, i'm a dummy
i already made the Condor and Marshall cab sims, and find them very useful. but then i discovered this cab sim, that implements the mesa boogie cabinet's frequency responce. the clips are very interesting, they are different than regular cab sims  produces. so i wanna give it a try. i used to work with opamps in such circuits, so i try to remake this schematics.

[Earthscum]

not sure about this, but ya might be able to do that with 2 cd4007's rather than all those separate fets, if you by some strange coincidence have some.

[Unkn0wn Art1st]

no, i haven't, but thanks

[darron]

every opamp stage will add a buffering effect too... might offset your tone a bit?

i'd say get some fets in. they are cheap... that way you have the confidence that the circuit is really doing what it is meant to.

[PRR]

> Did i draw it correctly?

Not quite.

Each FET pair here is a unity voltage follower buffer.

Therefore you strap "Out" to "-In", and put signal in at "+In". (You have the "-In" and "+In" reversed, and lack the strap.)



In either case (FET or opamp) you will have trouble with buzz from non-perfect wall power supplies; the added 100K+10uFd will clean this.


> might be able to do that with 2 CD4007s

No, or not dead-easy. This plan needs unity-gain followers. CMOS logic is all high gain inverters. Yes, you could cascade two CMOS stages to invert-invert, and use NFB to define unity gain, but the NFB resistors load the R-C networks. While "any" analog function may be built with inverters, sometimes it isn't easy (why we have differential opamps).

> get some fets in. they are cheap...

Yes and no. These P-channel JFETs may be awful hard to find today. I can't even type that Cyrillic part-number, and I don't know what sort of specs the original parts are.

I can guess (from too many long nights) what it wants. I also know that Erno Borbely specialized in JFET complements... but I just discovered that he is going out of business. So an opamp version may be the best bet.

[edvard]

I wouldn't give up hope on P-channel JFETs just yet...
http://www.mouser.com/Semiconductors/Transistors/Transistors-General-Purpose/JFET/_/N-7h69m?Keyword=p-channel&FS=True
You'd have to dig through the datasheets to find which N-channel is the complement, but once that's figured, it oughta work just fine.
Hopefully...

[Earthscum]

> might be able to do that with 2 CD4007s

No, or not dead-easy. This plan needs unity-gain followers. CMOS logic is all high gain inverters. Yes, you could cascade two CMOS stages to invert-invert, and use NFB to define unity gain, but the NFB resistors load the R-C networks. While "any" analog function may be built with inverters, sometimes it isn't easy (why we have differential opamps).

Good point. I've been using inverters alot lately and kind of grew a 'second nature' regarding using them for RC networks, so I kinda forget until I have to start crunching numbers to get something working right that these are a actually pain to work with.

[Unkn0wn Art1st]

PRR, thanks for such detailed answers i'll make your opamp mod soon
and thanks guys for advises, very appreciated