Advice on RAT

[Papa_lazerous]

Ok I think its time I build me a RAT, done a bit of searching and I've found a few schems. Both are hosted on this site.

One is just ProCP RAT drawn by RG the other is effectively the same Circuit but called Mulit RAT and has a rotary switch to change clipping type.

Just a few questions though, is the LM308 critical?  or can I use another OpAmp?
Also on RG's drawing it states a few other parts can be used in place of the specified BF245A

In short is it worth ordering parts from small bear and getting orignal specified components or should I just build with what ever I have laying around?  I dont know much about this effect and where its magic comes from so I figured someone here may have messed about with one recently.

I've heard sound clips and I dont know if I'd want to mod it much but then I may play once I build it

[Barcode80]

any compensated single opamp will work. google for suggestions.

[Meanderthal]

 The LM308 is a non compensated  single opamp. Not many of those around... An LM301(or 201) would be a drop-in replacement, but I believe you can use an ordinary compensated opamp like the LM741, just eliminate the compensation cap(30pf).

Slightly OT, but the other day I took my son to a Guitar Center to use his christmas gift card. I wandered over to the pedal counter(and remembered to buy that one-spot I've been wanting), and there was a bin of old used pedals. Among the usual abandoned DOD and Boss pedals was this long, heavy black thing(can't remember the name, but the back identified it as a bass RAT) from the RAT family with Mucho knobs and an effects loop. I'm thinkin'- Cool! So I ask how much for this thing? $180.00! USED and BEAT! Have any idea what that thing was? It looked interesting, weighed about 10 pounds, was intended for bass, yet somehow I never heard of such a beast...

Sorry, it's just that I'm a bit curious...

[Meanderthal]

 Ok, I answered my own question by going to the ProCo site- It's called the Juggernaut, and Proco still makes them. Nifty!

Sorry again about the Off Topic...

[jrc4558]

I used a TL080. Much quieter and same low slew rate. Use a 22pf cap pin 1-8

[Branimir]

I use 741's for my Rat's,I don't put the compensation cap.

Pedal has the same character, a/b tested it to the stock Rat, and it sounded a tad brighter, but I think that difference could be approximated with turning the filter knob towards bassier side...

LM308 costs 8 or 9$ here, and 741's are usually around 1$, and fortunatly I have a full stash of ole' 741's in my basement, so it came out rather cheap...

[Cardboard Tube Samurai]

My advice... The GGG layout version of the Rat is a pretty easy build and it also allows you to use a DPDT switch instead of a 3PDT (which makes it slightly cheaper) courtesy of having the indication LED running straight off the board. Despite a couple of de-bugging problems I had, it was one of my favourite builds (I have actually made a couple of them). The LM308 was pretty easy to source here (Australia) and I would suggest using it if you can source it. My Rat sounds awesome and has a permanent place in my set-up! I changed one of the pot values as I found it gave a better response/sound, but I can't for the life of me remember which pot it was nor what value I put instead... I halved the value of one of them but can't recall which... I think it might have been the 'filter'

[Sweetalk]

I build it with the LM308 and it's awesome, I paid it around $0,66!!!!, badly they had only one . With the other opamps doesn't sound as awesome as with the LM308, can be the cap across pins 1 and 8.

Anyone tried the version with two fets??... any difference in the sound?, I was thinking in putting some kind of booster in the in because sound a lot better with a overdrive (gain 0, level high) before him...

[WGTP]

I built mine with a TL070 that plugs right in.  Jack Orman at AMZ recommends the NE5534AP.  Both require the compensation cap that the LM308 does.   The LM308 probably has a more wooly sound. 

[oldrocker]

I originally built mine using the 741 but I'm now using the 308.  I couldn't hear a huge difference between the 741 or the 308.  My 308 is not the metel can type it looks like the 741 chip.  Does anyone know the difference between the metel can type and the black plastic ones?  If I could get my hands on some metel can type I would like to hear what it sounds like.  Mr.Wampler from Indyguitarist.com said there isn't much difference but I just wanted to hear if anyone has done an A B comparison of metal can and non-metal 308's.

[Pushtone]

No survey of the RAT would be complete without checking out  dano12's Four Knob Rat (FKR) at:

http://www.beavisaudio.com/Projects/FKR/

there is a link on the home page to a demo video.


ah heck, its easy to miss so heres the FKR video link
http://video.google.com/videoplay?docid=4031088502218202410

[Barcode80]

i'm going to be building one with the metal can type since tungngruv sent me one (thanks man!). i'll try to post some sound clips whenever i do.

[Mark Hammer]

Some folks would maintain that the LM308 is critical to the character of the Rat.  Indeed, if you read the interview with the designer in Art Thompson "Stompbox" book, it would seem that the peculiarities of the LM308 are critical to at least one of the properties of the Rat.

Why?  The Rat uses two ground legs in its noninverting gain structure, one of them setting the 308 up for a gain of several thousand (at max) for higher frequencies.  The compensating cap, meanwhile, restricts the gain-bandwidth product such that there isn't a chance in hell of the 308 being able to produce that much amplification of those frequencies.  The result is a kind of "misbehaviour" from the chip that is distinctive, and produces a weird sort of background "wooooo" tone.  This according to the designer.

Now, NONE of that is to take away from the fact that it is also *just* an op-amp with the gain differentially cranked, and fed to a diode pair, followed by a variable lowpass filter and a FET output buffer.  So, indeed, a great many of the properties of the Rat likely *can* be achieved by use of just about any externally compensate op-amp, like a TL070/080, or even half of an internally compensated op-amp like the venerable jrc4558.  You just won't get ALL the qualities of the original.  If the missing qualities don't really matter to you, then you aren't missing anythingand any old op-amp will do.  If one of the things you like about the Rat is the result of the intrinsic properties/weaknesses of the 308, then I suggest you get one.  It's a bit like the difference between a cheese, tomato and lettuce sandwich on white bread vs whole wheat.  For some folks the essence of the sandwich is in the ingredients in the middle and the beard type is moot.  For others, the "right" bread has gotta be there or else it just ain't the same sandwich.  Figure out which of these you are and purchase/build accordingly.

[Papa_lazerous]

Thanks for the advice,

I just decided to order the parts from small bear, hopefully I'll see them in a week or so....  Selected Air mail seems it depends how stacked he is with orders on how quick I get stuff.

I may build it from the tonepad layout, mainly becaue the schematic is nicely laid out and clear to see where as the others I have seen werent as structured IMHO, if anyone knows of a good reason I should build to a certain layout then speak now lol

[brett]

Hi

recommends the NE5534AP

For the record, the NE5534 has low input impedance (100kohms ??) and will drag down high frequencies.  Probably not good for a standard Rat sound, but ok for a tone rich in mids.
cheers