Rebuilding a rat.

[msurdin]

Hey all,

So the first time I almost got there building the rat.
There are a couple things i was after that I couldn't get.

Quiet. Mine was quite noisy.
Note definition. The have been a couple people's rats I have heard that when The distortion was all up you could still make out all the notes.
No mud, even with the tone down and distortion up.

High pitched squeal on some of the ICs

Thanks

Matt

[msurdin]

bump.

[bipedal]

Per the Debugging thread, a lot more info is needed about what you've built.  Version/layout?  Any parts subs?

Also, you noted comparing the sounds of your build with others' Rats, so I gotta ask: were the comparisons made with same guitar/pickups/playing style/signal chain/amp?  Were the other Rats "stock"?

I owned a Rat for a long time.  Sounded thin, fizzy, and nasally with my Strat -- never could get a sound I was happy with.  A humbucking guitar helped me get a lot more usable tones out of that pedal -- meatier, better note articulation across the board, and (obviously) quieter.

I haven't tried any of these, but some interesting looking mods...

- Jay

[msurdin]

The changes I have made are follows.
C11-10uF... thinking this might be a prob
D2- 1N34 Germanium.
C6,C5,C7,C10 are tantalum.
D5 is 1N4001

GGG Rodent Layout.
http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=92&Itemid=26

Like I said, I want to be able to get a lot of gain, but being able to have note definition even in chords and having it quiet is important.

Thanks

Matt

[soulsonic]

Instead of a germanium, I would use two 1N914 in series for D2.
I would try changing the value of R5 to 100 ohms.
C11 shouldn't cause any problems unless you have a noisy power supply plugged in.
You may consider lowering the value of C4 to as low as maybe 10pF. The value in my modded Rat is around 2.5pF, but that's kinda pushing it.
Squealing problems are usually solved by shorter, neater wiring. Also, shielding the input and output wires are important with high gain circuits like this.

[msurdin]

I tried a few different ICs for this and some of them didnt give me any sound..

[aankrom]

I rescued a Peavey Hotfoot that was half-submerged in standing water in my basement. The Hotfoot is almost exactly like a ProCo Rat II. The one with FET buffers. The differences are the RC networks in the feeedback loop of the opamp - really just small ones, but you can mess around with these a LOT to get what tone you want. It may even be worth adding some switches to you bnox if it's easy on a Rat. It's not so easy with the way the Hotfoot is layed out.

I had to take every single part out. The pots weren't submerged but I sprayed a lot of WD40 in them. I actually managed to get the stock footswitch and mechanism to work after repeatedly spraying in WD40 and turning it on/off/on/off/on/off... I noted the values of each part as I removed them and used the Rat schematics I found online to put it back together. The LM308N that was in it was fine after a good clean-up, but I just happened to have a nice metal can LM308AH. I did not A/B test them because I could not bend the pins of the can chip to fit reliably in a socket. I almost never use sockets for guitar effects anyway. In fact, whenever I get a DOD effect (which always seem to have sockets on every IC) - or indeed any effect that uses a lot of sockets for IC's - to tweak, the first thing I do is desolder all of the IC sockets on the parts I don't plan to fiddle with and solder them right in and then when I have a setup I like, I take out ALL of the sockets. I tend to leave BBD devices in sockets if they came with them... But I digress...

Rats and Hotfoots benefit from having bigger coupling caps on the inputs and outputs. On the outputs at the very least. They make distortion two ways: one is trying to squeeze too much gain out of an op-amp with a superslow slew rate. There's something magical about the LM308 in this regard, but too much and it sounds brittle and like there's a lot of high-order harmonic artifacts (but there does seem to be some extra mojo in the metal can LM308AH - which may be the A suffix rather than just it being in a can...). The second way is the all too familiar 2 diodes in reverse phase shunting the signal to ground. If I remember correctly, mine had a 1N4001 and a 1N4148 which should have made for some decent subtle asymmetric clipping, but I went 1 or 2 or 3 better and made 2 little PC boards: one a string of 5 Germanium diodes, the other a string of 3 Germanium diodes. I tried a lot of different combos, some mixing Silicon diodes in with the Germanium, but the long strings of Germanium diodes gave the best tone. I would like to do a more exhaustive comparison between ther effects of the ratio of the number of diodes in each string, but as it is when the distortion setting is at its lowest I get mostly mellow 2nd order harmonics from asymmetric clipping, but when I dial in more I get more 3rd harmonic mixed in with the 2nd order and there's much more of a "diode compression" effect. I chose to use long strings of Ge diodes so that I could get some relatively clean tones (without a whole lot of success to tell the truth), but also responsiveness to playing dynamics (with much much more success in this area). I didn't use 1N34's either. I used some HP units from a vintage piece of precision HP test gear (along with over 50 2N274's). I tried some 1N272's, but I liked the HP Ge diodes better.

I wonder if it makes much difference relaying my experience with a Peavey Hotfoot comparing it to a ProCo Rat II since with the Rat the op-amp is inverting and with the Hotfoot it is non-inverting. I found that odd, but it's possible I just traced the PCB without enough attention that time. Because it's uncanny how almost exact the rest of the circuit is.

[ambulancevoice]

I tried a few different ICs for this and some of them didnt give me any sound..

well, the lm308 isnt a regular opamp, different pinout and features, look at its data sheet (google) and you will see

[msurdin]

I changed out the Germanium for a 1N914.
When in series thats 2 together in the same place right? I just want to check. What will this add?
I liked it with the 1N914, it does not have the warmer over the top gain.. but the bad tone control, lots of mud is not there.
Being able to get some more extra gain in there would be great.
I liked how the gain the the 1N34 was a bit like a fuzz... but not really.
Anyway to get that without the problems the 1n34 caused?

Thanks

[msurdin]

After more playing with it, it sounds like it still is darker then it prob should be..
anything certain that would do this? The Tantalums?

[soulsonic]

Yeah, if you can, try some regular electros there. Most tantalums don't sound good at all.

[msurdin]

Is it really true they don't have a very very long life? I've read some things about that...
I will place some orders for new parts...

I have a couple of those box caps on the board, and a few film ones.. Would the difference cause a problem?


Thanks

[msurdin]

Is there a different value pot that I can use for the drive so i is more sensitive...
It seems like the last 50% of the gain pot all i the same..
I mean I dont want to not loose the amount of gain a rat gain control should have... but I want to have a lot more control..

[tonefreak]

I know it might be a little too late now, but maybe build it stock and then put mods in.

100pf to 10pf is something I have done... look into some of Jack Ormans mods, which I used to mod a Proco RAT I have.  I will never strip paint again...

[msurdin]

Well I changed the tantalums to electrolytic and the tone is back, not really muddy.
Its dark until 60-70% normal for rats?
Get that Squeal when the tone and gain are at 100%
I changed to shielded wire, How do I shield the inputs? I am using switchcraft jacks now, will nutrik jacks make a difference? I have stereo, just really cant figure what points are what...

When the tone is down and gain up it is very "sloppy" or "muddy" Is there a way ti get more definition?
Is there any different IC that can get gain-y, but is less then a LM308? I really want the gain to be some wear between a Distortion + and Muff.

Hope that makes sense

Matt