Saturday, 14 December 2013

Proco Rat 2

Now, there is only couple of small changes to the output buffer and volume control when compared to the original Rat. The volume control looks like it could give you some trouble with the output level. If it does, just snip the 10K resistor from volume 3 to ground. I would personally use linear taper for that too.. If you want to turn this in to Turbo Rat, then just swap the 2M2 resistor for 220K and use 3mm red LEDs for clippers. Or use 1N34A germanium diodes to make it YouDirtyRat. (fixed clipping info accordingly)




45 comments:

  1. I always thought that turbo rat used leds for clipping. Was I wrong?

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    1. You Are right.
      check out my build notes and the multi rat schematic with the various options. I had some really great results. Goes really well with a VOX amp and humbuckers.

      http://fuzzquest.blogspot.com/2012/11/the-flying-rat.html

      Great layout Mirosol, highly recommended build.

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    2. Hmm..
      This image found from the most reliable source, the internet :) lists Turbo Rat clippers are Ge:
      http://www.diystompboxes.com/pedals/rstrand/rat/pcratrev.gif

      But then again, the lists are different here:
      http://www.diystompboxes.com/pedals/rstrand/rat/rat_versions.htm

      Could be that it is with LEDs. I don't have any original Rat unit myself, so i have to rely on the internet... So i'm not sure. :)
      +m

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    3. turbo rat is with led's. you dirty rat is with germanium! Thanks for the layout !

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  2. I tought Prco You Dirty Rat was Ge. Give your opinion, If you had a handful of diodes 1n270, as you implement these on the circuit?

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    1. Does a mix of 1n270 and 1n914 sounds good for you?

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  3. Fixed the description accordingly.

    Note that i placed the diodes so that they can be taken on a switch :) So swap the 2M2 for 220K and have your way with the clippers.
    +m

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    1. Could please anybody give some explanation how to implement the switch / how to take the diodes on a switch? Thanks a lot for any help!

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    2. No help please? Or any adwise where to find an answer?

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    3. HI. Just remove D1 & D2, take a wire from where one side of D1 (or D2) to a switch (pin2) and another wire from where the other end of the diode was to the switch (pin 5).
      Place your diode choices across pins 1 and 4, and 3 and 6 for a DPDT switch and hey presto.
      Use this link for an example
      http://tagboardeffects.blogspot.co.uk/2014/05/blakemore-effects-rous.html

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    4. Thanks for your help! I`m just on the beginning to understand those things. One more step!

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  4. There are also a lot of mods which can be implemented, of course, like the Ruetz mod for chaning the 47R resistor to a pot for smoother overdrive.

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  5. I guess you can verify it. Built it and all functions work. Not 100% sure on the filter thou. Seems to be cutting to much treble. I'll check my values.

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  6. Call it good. I think the doides on a switch would be well worth building in also. Got a nice little bit. Thanks guys.

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    1. Cheers!

      The Filter control is something that i've hated on every Rat i've ever build (which is the reason i'm still prefering my build of Arion MMP), so i do believe that is a feature. You could swap the pot for 50K or even smaller to make more usable.
      +m

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    2. I've built the early version from here for a friend. After some playing around we decided to use a 1nF cap instead of the 3.3nF, that gives you a much more useful tone/filter range too. Also it is worth to play with the clipping section in the basic Rat layout, as that can really give you different tonality. In the latest one he decided for a Si + LED combo, but my personal favourite is the Si + Ge combo.

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    3. quick question, does the resistor change for turbo version apply to dirty rat too or is that 2m2?

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  7. Played with this some more. Sounds good on a Vox type amp. One question on the resistor change. There are two 2.2m's on the board. Which one gets changed?

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    1. The one going from input to ground (the one on the left) is just a pulldown resistor, so that won't make a big difference. Try the other one.

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    2. Yup. The other one from vref rail to 1K resistor.
      +m

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  8. Hi, I've just build this board, but got several problem at first. First is the feedback which is ear piercing. Then the sound drops of gets cut when I strum power chords like chug-chug. I've made some changes and somehow improves playability and tone. But still I get a bit of sound drop/cut on power chords.
    I replaced the 1uF electrolytic with 100uF; the 2.2Mohms with 1Mohms and will soon try the 220K. I put a 1nF cap on LM308 pins 3 & 4. I also did a 1K pots Ruetz mod. I also put in switch for clipping selection, 1-RedLED/RedLED; 2-BlueLED/Zenr-Zener; 3-Si-Ge/Si-Ge.
    The RedLED/RedLED is not lit when I use it but has sound. The BlueLED blinks fine when selected and I like the sound. The Si-Ge/Si-Ge is weak in volume.

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    1. What have you done to get rid the feedback? mine is squealing in a insane way, when the cable is unplugged. What can be done to solve this?

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    2. Running a buffered pedal in to mine took care of that

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  9. I can literally tune my squealing. I'm not sure why. Please help, Anyone.

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  10. is there a difference between lm308n and lm308 ?

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  11. This comment has been removed by the author.

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  12. This layout seems to be missing a 1nf cap to ground after the 1k resistor feeding the noninverting input of the op amp. This maybe the cause of the squeeling some people have noted when nothing is plugged into the input.

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    1. james must be right. Increase that cap value in case you face lots of noise, at the expense of decreasing the max gain available :P

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  13. I just finish building a second one of these and it's really gated, like, I get sound if I hit the strings then it cuts out. I checked for solder bridges, what super obvious thing am I missing?

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    1. Yes, hopefully very obvious. It's just the simple matter of checking the circuit through until to find it. Double, triple check all your cuts and layouts. Then move onto component values, off board wiring, etc. Take a break, and come back to it fresh. Check FET orientation, are you using an alternative op amp? Some wont use the the compensation cap 33pf.

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  14. I went back through it tonight, everything checks out, I even compared it to the last build I did. I can't figure it out. I'm using the correct fet and opamp. I either messed up a cut somewhere or one of the caps I didnt replace is faulty. Luckily I socketed the fet and opamp.

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  15. Did another build, it fired right up. Thing is such a beast

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  16. Hi I've just finished my second build of this circuit neither working correctly. The circuit shows no sign of Volume gain until about 3 o'clock on the volume pot, but the main problem is that when I turn up the Distortion I get a really high pitched squeal which lowers in frequency the more the Distortion pot is turned up. I am using the OP07 Opamp if that helps, also I have tried more than one opamp with no difference, tried different JFET's and checked their orientation and run a knife between the tracks. Any Ideas?

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    1. http://www.analog.com/static/imported-files/data_sheets/OP07.pdf
      http://www.ti.com/lit/ds/symlink/lm308-n.pdf

      OP07 is not pin to pin equivalent with LM308. Since the LM308 compensation pins are used for offset nulling on OP07, your behavior is expected. There is no straight on replacement for LM308, so to get your circuit working right, you'll need LM308 chip. Or you could read the application notes on OP07 datasheet to figure out how to set up an offset nulling trim for the OP07. I'd still recommend getting the correct chip as the Rat won't sound like a Rat without LM308.
      +m

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    2. Thanks, for some reason I thought they were pin equivalent as I see some people use them. That will teach me not to check my data sheets.

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    3. It can be used, but not as is. The circuit will need tweaking for it to work properly with OP07 (or any other single opamp). LM308s are widely available through ebay and the prices are not that bad either.
      +m

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  17. Cheers for setting me right miro. I'll get some and see what happens

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    1. If you use a 308 and still get the squealing try putting a buffered pedal in the chain.

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    2. Also, try using a linear pot for the volume pot

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  18. Right Got me some LM308 opamps and stuck one in, and it's acting exactly the same as it was with the OP07. Volume and Tone seem to be working but all the Distortion pot does is turn the pedal into a really shitty frequency generator :( I'm going to put it to one side until i don't feel like destroying it and then i'll post pin voltages for the opamp and JFET

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  19. Hey guys, shouldn t the clipping filter cap / res pairs be matched the other way around (that is, 2.2uF / 47 Ohms and 4.7uF / 560 Ohms instead of 2.2uF / 560 Ohms and 4.7uF / 47 Ohms)? At least that s the way it appears in most schematics... I have implemented the original rat version from your vero layout and the pairs there are also the opposite way than what appears here.

    Given the chance, I cannot even start telling you how great your work is. I m grateful!

    Kind regards :)

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    1. i know that the original rat was setup that way, but i do not believe the rat 2 is. what you could do is take the rat 2 layout as it is and put sockets in place of the resistors and swap them to be like the original, or it gives you the ability to try different values and see what you like.

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    2. Hi Zach and thanks for your comment :) What makes you believe that rat 2 is not set up this way? I haven't found any schematics showing it any other way... Swapping the resistor values would give you a 721Hz and 129Hz pair of low pass filters instead of 1539Hz and 60Hz - and this filters the input to the opamp (see here : http://www.electrosmash.com/proco-rat). The higher of those is practically almost identical to the Ruetz mod with the 1K potentiometer set somewhere halfway (see here in the 1k potentiometer section : http://www.diyguitaramp.com/rat.html) thus making the rat much more of a gentleman and I m not sure that this is the sound that most people expect to hear, at least at the start :) I d be interested to hear your opinion on those above, and please contribute any sources if available! The rat is such a great pedal!!

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    3. no problem buddy. i looked those sites and didn't see the schematic for the rat 2. now, there could be different versions of the rat 2, and have slightly different values for certain areas. i do believe that there is more of a difference between the rat and rat 2 then just the clipping section, just MHO, but i could be wrong. like i said i would just socket the resistors and put them as they are in the rat and see what happens. when i built my rat, i altered those resistors to help make it better suited for bass, but by doing this i also altered the gain.

      about that 1n cap. without seeing the schematic it's hard to say it belongs there. you can put a socket in that area for that cap, and see how it sounds with and without it. usually layouts don't get verified if there's something wrong with them, so i would say it's same to assume it shouldn't be there. but experiment and see what happens. i know there is a lot of sonic differences between the rat and rat 2, so the things you're seeing could be the reasons.

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  20. There s also a 1n cap missing between IC pin 3 and ground, as James Nettleton and a few others noticed. And while i m at it, you might want to use a larger value for that cap in case you are facing lots of noise, at the expense of reducing the gain :)

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