Rat mods... will this work?

[Just1More]

Firstly, a big thanks to Dano for all the information on your web site about your FKR mods, builds and general electronics info.  Your site has been a really valuable resource to simply explain how some of this stuff works.  Great stuff!! 

This has inspired me to try a few changes.  I plan to build a Rat with some of Dano's FKR mods in a 125-B box (I just like smaller enclosures) using the Tonepad board.  Basically as described in the project with the following alterations:
1. Add a switch to select clipping between LEDs (Turbo Rat), no clipping, or vintage rat.
2. Add a second switch to select between standard (symmetric) and asymmetric clipping in vintage mode.

My plan is to remove D1 and D2 from the board and replace with this:


I'm pretty new to all of this so I was just wondering if someone could verify that what I am attempting to do is likely to work.  I think this is how the switching will look. 



Is this ok or is there a better way?  Feel free to correct if I've got this completely wrong.  I realise that SW2 could be a SPDT, but I figured I have a reasonable chance of directly connecting the components to the switches this way without having to use a separate small board to mount the components.

Thanks heaps

Johno

[John Lyons]

Asymetrical clipping is when you have two diodes in on direction and one in the other dirrection.
For Sw2 you have two and two which are doing the same thing, both symetrical.
The schematic is incorrect.

Looks ok otherwise.

John

[anti-idiot]

Asymetrical clipping is when you have two diodes in on direction and one in the other dirrection.
For Sw2 you have two and two which are doing the same thing, both symetrical.

but he can use Ge/Si combination...

[sevenisthenumber]

Symmetrical is when two of the same diode are running together as in the stock rat. Asymmetrical is when 2 different diodes are running together.
Here are some possible asymmetrical combo's. Ive tried most all of these and they all ave a great sound to me. Also remember that LED's light up in the RAT circuit as you pick. You can wire them to be seen if you want by drilling a hole and mounting one of the clipping LED's through the case (ala Keeley seeing Eye Mod)

1) Stock + LED
2) Stock + 2 LED's in series
3) Stock + 2 LED's in Parallel facing opposite directions.
4) 1n34a + LED
5) Stock + NOTHING
6) LED + NOTHING
7) Stock + 2 (1n4148's) in series

Another great mod is to put 2 diodes (try different ones) in parallel, but facing opposite directions, solder to lugs 1 and 3 (the
outside lugs) of the gain pot. For a "smooth/compression" adjustment, install a
2nd potentiometer, 50k or so , in SERIES with these diodes.

[dano12]

Don't overlook rotary switches--they simplify so much. E.g.:

[Just1More]

Asymetrical clipping is when you have two diodes in on direction and one in the other dirrection.
For Sw2 you have two and two which are doing the same thing, both symetrical.

but he can use Ge/Si combination...

Yeah sorry about that - probably should have included it on the original post.  I was planning on making one of the pairs Ge/Si.

Thanks for the suggestion about the rotary switch too Dan.  I hadn't really considered that, but I could probably accommodate the various clipping options on a smallish stripboard and have 6 different options if I used one of these...

Incidentally, today is Chinese new year and it's the year of the rat!  Must be a sign...

[kismet78]

Don't overlook rotary switches--they simplify so much. E.g.:

I don't think I could fit a rotary in my Rat 2. Please don't tell me you've done it. I just finished a round of clipping mods on my rat tonight. I stuck with a slew of spdt toggles though, but check out the fancy switch label I made:

http://www.kyletompkins.com/wp/?p=535

[tehfunk]

I am liking the labeling you did, looks great! how does it sound? or should i say they?

[Just1More]

Haven't had very much time lately, but I finally got this thing finished!! 



Here's the guts.  It's not as neat as I would like (and not as neat as my first build) but I had to cram quite a lot in there.



It was inspired by Dan's FKR.  Obviously it wasn't going to be possible to put all of that into a 1590B sized box so some features had to go.  I built it as described above in this thread.  The LEDs for the turbo mode are mounted on the outside for extra mojo.

Sounds great btw.  Highly recommended.  The asymetric clipping mode is probably my favourite at present, but the no clipping option might provide some useful overdrive type alternatives to my Fulldrive2.

[kismet78]

Haven't had very much time lately, but I finally got this thing finished!! 



Here's the guts.  It's not as neat as I would like (and not as neat as my first build) but I had to cram quite a lot in there.



It was inspired by Dan's FKR.  Obviously it wasn't going to be possible to put all of that into a 1590B sized box so some features had to go.  I built it as described above in this thread.  The LEDs for the turbo mode are mounted on the outside for extra mojo.

Sounds great btw.  Highly recommended.  The asymetric clipping mode is probably my favourite at present, but the no clipping option might provide some useful overdrive type alternatives to my Fulldrive2.

Why did you external mount both clipping LEDs? I thought only one of them usually lights up. At least that's the way mine is.

[Mark Hammer]

1) Symmetry/asymmetry depends on the equivalence or inequivalence of forward voltage for the diodes in question.  Certainly one quick way to get it is by means of different numbers of diodes, but an Si in one direction and a Ge in the other will also get you asymmetry, as will two Si diodes that differ in forward voltage because of normal component tolerances.

2) There are limits to how useful and audible multiple selections of diodes will be or can be.  What one is varying primarily is the clipping threshold and output level.  LEDs will get you less clipping overall, and a hotter output.  If what one uses a rotary switch for is to vary tonal quality as well as output level, fine.  If the goal is to have many different tonal qualities, holding level constant, you're barking up the wrong tree.  Moreover, given that a fundamental part of the Rat is the compensation loop and the restriction of how fast the chip can slew, I'm not all that sure that selecting between diodes will do anything OTHER than trade clipping amount for volume.  Think of it this way.  If you had a bunch of sprinters and long-distance runners, and you made them run 200 metres as fast as they could, yu'd probably see a difference int heir performance.  If you made them run 10 metres, you probably would find very little difference.  If opart of the difference between diode types is the manner in which the "knee" occurs when they go into conduction, it strikes me that the circuit itself should permit the speedy ones to show you that speed, and in the stock Rat circuit they can't do that.

[Just1More]

Why did you external mount both clipping LEDs? I thought only one of them usually lights up. At least that's the way mine is.

They both light up on this build.