#1
i got my hands on a bunch of intigrated circut 5w amps that are basicly 8 pin mini amps, i was wondering do intigrated circuts need resistors or do they adjust automaticly, the amp draw is only 4ma at 18v and it will operate nicely off a 9v battery (right in the middle of its voltage range) but im not sure if it needs a 2k ohm resistor or what,
so if someone knows i could use a little help.
#2
You will obviously need a feedback of some kind and at least a few pull down resistors. A few coupling capacitors too.

That's the bare minimum but I'd be inclined to add a volume control and perhaps even a tone stack or something.

What are the chips called?

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#3
they are texas instraments (www.ti.com) chips, i get them for free and the model # is opa134pa they are a intigrated circut (ie not a transistor) www.ti.com says all of the filters are on the chip. im not useing a volume pot untill i make it work without. and i plan to put the whole thing in a altoids can and use it as a stompbox.
#4
those are 8pin opamps, and you connect them just like any other opamp.
Datasheet: http://focus.ti.com/lit/ds/symlink/opa134.pdf

if you're not familiar with opamps, read up on them and simple opamp circuits:
http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm
for example

and remember, opamps have maximum output current, slew rate, maximum voltage output (9v with a 9v battery) and follow unity gain

i'll be honest... op amps aren't that great, besides a small boost + tone controls with just opamps and some resistors/capacitors, there isn't all that much you could do with just opamps. I guess you could make a fuzz box or something.
Last edited by greenbox at Jun 7, 2006,
#5
Quote by greenbox
i'll be honest... op amps aren't that great, besides a small boost + tone controls with just opamps and some resistors/capacitors, there isn't all that much you could do with just opamps. I guess you could make a fuzz box or something.

You can do loads of things with op-amps.. You can make phasers, OD pedals, boosters etc. You just need to use the right circuits.

As for making a booster out of them I'd suggest an MXR microamp type circuit, I'd reccomend copying a schematic rather than designing your own at this stage because it comes across as though you wouldn't know how to design a booster (but go ahead prove me wrong!)

http://www.generalguitargadgets.com/diagrams/microamp_sc.gif < there's the schematic for one. They are quite nice designs and you could try swapping a few components after it's made to get some different flavours... As you've got lots of these chips you could make a few OD/distortion boxes too if you wanted.



Oh and btw they aren't 5w output op-amps, I was going to suggest making a practise amp.
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#6
Quote by power freak
You can do loads of things with op-amps.. You can make phasers, OD pedals, boosters etc. You just need to use the right circuits.
Oh right, phasers too! Also, I'm sure there're a few more, but that pretty much covers the basics in terms of pedals (I still think opamps are limited, but that's because I discriminate against them )
#7
Quote by greenbox
Oh right, phasers too! Also, I'm sure there're a few more, but that pretty much covers the basics in terms of pedals (I still think opamps are limited, but that's because I discriminate against them )

Are you a transistor junkie then?

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#8
Haha, yes, in a sense.
I actually found out recently that (some) tubes are actually kinda like FET's.


Anyways, the point here is, you have opamps, you can make pedals. Let us know if you decide to start some project, and good luck!
#9
^Tubes and JFET's can be interchangeable with each other! Check out the www.runoffgroove.com amp/pedals. Those things are awesome.

Too lazy to check the datasheet, but watch the impedence, going from high impedence(guitar pickup) to low can cause pretty dramatic treble loss.
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#10
Quote by That_Pink_Queen
^Tubes and JFET's can be interchangeable with each other! Check out the www.runoffgroove.com amp/pedals. Those things are awesome.

Too lazy to check the datasheet, but watch the impedence, going from high impedence(guitar pickup) to low can cause pretty dramatic treble loss.

I think greenbox is talking about the small low-voltage tubes like those used in the Zendrive-2? They're quite expensive and often hard to find but a lot of DIYers use them and now a few small boutique companies are using (Hermida in the zendrive-2 is the one I remember being a hermida \/\/hore.)

Also personally I wouldn't copy an amp design "in FETs" as they do on run off groove, I'd much prefer to design a common source from the ground up, then at least you know you're working in a nice range (clipping FETs although nicer than BJTs still isn't the nicest thing IMO.)

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#11
Hmm, well, all tubes can be replaced by JFETS to a certain degree was my point.
As for those submini tubes, I know what you're talking about...IIRC Seymour Duncan came out with an OD that used those little tubes, it got pretty good ratings actually.
Enough spam now!

An EQ is a good thing to have...geofex has a good EQ base that you can add as many sliders onto as you want.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.