Rat build w/pics

[tungngruv]

I perfed up a Rat based loosely on Tonepads layout. It turned out pretty well. I made the diodes choices footswitchable (2x1n914 and 1n914/LED combination), and used the "Ruetz" mods ( I added a SPST switch to remove the 560R from the circuit and a DPDT middle "off" switch to either remove the 47k from the circuit, leave it in or replace it withh a 1K pot). I had hoped I could use this as a "dirty channel" so my Marshall could remain clean but it really sounds best used as a boost to an already distorted signal. I also seem to have a "%^&*ed wah" tone coming from it, this might be due to using a .0047uf instead of a .003uf. I also noticed that this pedal has tons of fuzz to it (too much?). It sounds best to me with the gain around 11:00. I also used a 308 from Steve at Smallbear. The Rat really does sound good, I just have to figure out the tone issue.  I'll try to get some sound samples up later this week.

[MartyMart]

Hey, nice build
You could try a 2n2 and a 1n in parallel to get closer to that cap value ?
or ... three 1n's  I often have to do that and it works fine.
Nice lookin "metal can IC"  I didn't see one of those before

MM/

[Yun]

Hey, nice build
You could try a 2n2 and a 1n in parallel to get closer to that cap value ?
or ... three 1n's  I often have to do that and it works fine.
Nice lookin "metal can IC"  I didn't see one of those before

MM/

OH MAN!  i havn't seen one of those IC's in AGES!  i didn't know that they still made em like that 

[markm]

Is that a 308 in that there metal can???
I've been playing around with this circuit lately, don't ask me why 'cause I'm a Country Picker but, It sounds real good!

[Connoisseur of Distortion]

very nice build, extremely neat!

[BDuguay]

Clean, clean, clean!
Nice.

[Seljer]

I've got 2 of the LM308 in the metal cans too

(my rat, which I'm not really pleased with)


do you mind check the voltage on the pin 3 of the thing (the non inverting input)? for some reason its showing my 1/4 of the input voltage on both of the rats I have built

[tungngruv]

I'll check the voltage tonight and post it. The 308 cans are from Small Bear. Killer,right?

[Seljer]

I got mine from Banzai in germany (I was expecting regular DIP8 type ICs but I eventually also managed to get one into a socket  )

[tungngruv]

Hey Seljer, I'm going to replace the gain pot with a different value. The gain past 11:00 is way too fuzzy and muddy. I'm probably going to replace the filter caps with Melanheads "Headcase" values to reduce the muddiness. Other than those issues, I think it sounds really good.

[tungngruv]

Seljer wrote:

do you mind check the voltage on the pin 3 of the thing (the non inverting input)? for some reason its showing my 1/4 of the input voltage on both of the rats I have built

Pin 3 on mine with an 8.85 volt battery is showing 4.01volts. I hope that helps.

[hilbi]

Hello Tungnruv,

any update on muddyness issue with rat? I have built one myself and experiencing same issues, fuzzy sound above 11 o clock with drive settings.

[theman]

Hello Tungnruv,

any update on muddyness issue with rat? I have built one myself and experiencing same issues, fuzzy sound above 11 o clock with drive settings.

i just built one, and the compensating cap between pins 1 and 8 makes a huge difference. it is supposed to be 30p. i used a high quality silver mica here. i originally had a 100p in there, and the sound was way too bassy and woofy with the gain at max. it was only tolerable with the gain less than 2 o'clock. after i changed it to 30p, it was much better, and better still at lower values. as mark hammer has mentioned in a previous thread

see http://www.diystompboxes.com/smfforum/index.php?topic=48346.0

the datasheet suggests that this cap really changes the frequency response quite a bit when the gain is very high (as is the case with the rat).

i also tried a metal can lm308 vs the ic (from national), and the ic sounded better to me, but that was only after a quick listen. the metal can pins have to be twisted a bit to fit the 8-pin ic config, but it can be done. i don't think there's any real mojo lurking here, however ...

[hilbi]

I used two 15pf in paralel as compensating cap for my IC lm308, the sound is not bassy, more fuzzy in my case, as is with the original rat I also have.

[dosmun]

Try adding a pair of LED's in the feedback loop as PaulC mentioned in another thread.  That gives it a little extra crunch.

Some cool info here:
http://www.diystompboxes.com/smfforum/index.php?topic=47379.0

[Rafa]

Well looks great but it took me a while to realise that the tin can was the IC

[Mark Hammer]

The compensating cap alters the open-loop bandwidth (i.e., how much gain you could ideally expect if the chip was set to absolute maximum gain by having no negative feedback from the output to input whatsoever).  As the cap value goes up, there is much less gain available at the sorts of frequencies we usually need to have around in order to hear fuzz.

Reducing the cap value too much, though, may have the effect of: a) losing the unique character of the Rat (that lovely background "whoooooooo"), and/or b) producing more fizz than you want.

If you DO try to experiment with lower comp-cap values, you will need to keep a damper on the sorts of oscillations possible at those gain factors.  You can do this by increasing the value of the 100pf feedback cap, or increasing the value of the .0033uf tone cap.  Increasing the 100pf cap will trim back more high end as you increase gain, and increasing the .0033uf cap will let you trim back treble at any gain setting.

So, as an example (and this is off the top of my head, and completely untested), reducing the comp-cap to 22pf might be complemented by increasing the feedback cap to 150pf and the tone cap to .0039uf.

All of that being said, the Rat seems deliberately designed to be just at the cusp of breaking out into oscillation at max gain, but with that oscillation held tightly in check by the compensation cap and use of a chip like the 308.