#1
Ok, follow me here.

Actually, a little of my background. I will give you the short and sweet version of my resume. I graduated from electronics tech school in 1987, but I have never worked a single day as an electronics tech. I have been an electrical technician ever since. I work on powere generation and distribution systems, very BIG AC-DC conversion systems for powering motors larger than your car, etc. So I am at a loss when it comes to this little stuff.

I cracked open my old textbooks and saw that "the gain of an op-amp is determined by it's external resistors".

Does this mean that if I have a circuit with an 8 pin op-amp, I can just grab any old op-amp off the shelf and solder it into place and it should work just fine?

The reason I ask is this: in Seattle back in the mid-nineties, music stores almost literally couldn't give away those DOD Grunge pedals. The prices on them started out at about $100 and every time I went in the store, they were ten bucks cheaper. Finally, they were $9.99 and I bought one.

Well, the tone is kind of plasticy, and despite all the distortion, it doesn't sustain as much as you would think, so, since I have other pedals, I thought I might screw with it a bit. Maybe get it to sound nicer.

So, then I read this interview with the Analog Man. I did a quick search on eBay for some of the JRC4558 chips. I found them, but they wanted too much for them. Then I found the other chip he mentioned, the Malaysian 4558 op-amp made by Texas Instruments, and I found those on eBay for 25 cents a piece. So I bought 10 of them.

Now I am wondering if I can put them into my DOD Grunge pedal. If the gain of an op-amp is determined by the external resistors, it seems like I should be able to.

Thanks.
Lois: How am I supposed to live in this town if I'm a social pariah?

Peter: What's that? That them little fish that eat cows?
Last edited by McDuffie at Aug 9, 2006,
#2
you can most likely use those jrc chips (and you can buy them here {http://www.smallbearelec.com/Detail.bok?no=213} on smallbear for way less hassle) but maby only run 3 or 4 in parallel if you want more than one. and you should seriously think about getting some transistor sockets so you dont have to worry about burning an op anp. as for the "the gain of an op-amp is determined by it's external resistors" bit it is true but an op-amp doesnt have infinite gain and i think they might be talking about the potentiometer that controls the gain in the pedal. but hey you have the degree so you problably allready know this.

~jacob t.
#4
^ well im working on my 4th but my first one didnt exactly work so i guess 3. the one im working on now is a true vintage wah (ie no fazel inductor) its going to have a big a$s coil inductor with a slug of iorn moving in and out to make it change inductance, but its still being worked out on paper, im definately gonna make a thred on it.
~jacob
#6
Quote by sempri_fi
hey you have the degree so you problably allready know this.

~jacob t.


No, I don't have a degree. I received a certificate from a technical school.

And it was a very, very long time ago.

And since obtaining the certificate, I have never once worked with chips, with the excepton of building an off delay timer based on a 555 chip.
Lois: How am I supposed to live in this town if I'm a social pariah?

Peter: What's that? That them little fish that eat cows?
#7
^^you could build it in a used and gutted morley volume pedal, that would be the cheapest way i can think of, and ive built a footswich for my amp (cuz i wasnt paying 30 bucks for one) but thats so simple that i dont think it counts.
~jacob t
Last edited by sempri_fi at Aug 9, 2006,