Rat mod to improved clean up tome when riding guitar volume?

A forum devoted to mod, tips and suggestions for upgrading and rehousing your VERY CHEAP commercial stompbox to near boutique excellence.
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oczad
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Post by oczad »

I have a cheap rat clone and i'm quite happy with the tone as it when using it with my guitar on 10. ALL my guitars have treble bleeds and when i roll off the volume for clean tones which my amp does quite well, it's cleans up nicely and gets nice and chimey. But not with the RAT. Had the same issue with original RATs and ones i have built. The tone gets dull like you turned your tone control too far down. I have tried every setting possible on the amp and pedal but it's just one of those things where thats the nature of it and nothing works far as twisting knobs etc.

So i'm wondering if anyone who's had the same issue knows of a mod that fixes this "issue" and could point me to a schematic. Thanks in advance...

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thesmokingman
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Post by thesmokingman »

the rat isn't a design capable of what you want from it.

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Cybercow
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Post by Cybercow »

See what JHS has to say about the "Pack Rat" mod. It clearly changes up the Rat's dark familiarity. The first step is use a cleaner single opamp like an OP134 or NE5534; both of which have a much higher slew-rate.

You may want to look at how the opamp is biased too. But it's still a Rat circuit at heart and likely not much to be gained there.

Then add some clipping options to change from diodes to LEDs and a 'no clipping elements" option for a cleaner boost.

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phatt
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Post by phatt »

As you have built some Rat circuits, I would try putting a simple buffer in front. Just look at Tube screamer for clues.
Or as mentioned, try another opamp.

As for the guitar treble bleed trick yes it can help but there are other things you could try.
I swap the tone side of my Strat switches which works better than treble bleed.
I did see a name for this mod once,, can't recall it?
Most 5way switches are dual circuits and the tone out terminal is usually connected to the PU output terminal which goes to the Top of the Volume.
Separate the 2 outputs of the 5way Sw
Then take the Tone output side of switch directly to the Centre Lug of the Volume Pot. Done.
There is now no treble loss to my ears at least,, It works well with my rig and my Strats. YMMV. :thumbsup
I have no idea if it works on HB PU's.
Phil.

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PedalJerk
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Post by PedalJerk »

There are a few things you can do to improve the Rat's cleanup with the guitar's volume knob:

1) DECREASE the input impedance by reducing the input pulldown resistor and the opamp input biasing resistor from 1MegOhms to 470kOhms each. Sounds counter-intuitive, but this makes it behave more like a Fuzz Face in that when your guitar volume is all the way UP, the signal is loaded down more, so you get a dark dirty sound with the same pedal settings, and as you turn down your guitar volume, the additional series resistance to the circuit input INCREASES, thereby slightly brightening the tone of your reduced volume. You could even go down as low as 100kOhms, though you may have to play with the input coupling cap to maintain the same level of low-end.

2) Replace the 1nF shunt cap at the Rat's opamp input (the one in series after the 1k input resistor) with something like a 220pF. This will interact with your guitar volume knob in a manner more akin to the Miller capacitance of a tube amp input stage. The stock 1nF rolls off QUITE a bit of treble with a guitar pickup directly feeding it and tends to shift the pickup resonance slightly lower into the midrange (which, admittedly, is part of the Rat's signature tone). But a smaller value cap here makes it clearer and more "transparent" sounding, especially with guitar volume roll-off.

YMMV, of course.

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PedalJerk
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Post by PedalJerk »

https://www.electrosmash.com/images/tec ... -stage.png

In the partial schematic above, the components to be changed would be reducing R1 and R2 (and possibly increasing C1 to compensate), and reducing C2. Suggested starting values:

R1, R2 -> 470kOhm (brings input impedance down below 235kOhms)
C1 -> 47nF (maintains same bass response as 22nF does with a 1MegOhm R2)
C2 -> 220pF

I'd start with just swapping C2 for the lower value first and testing to see how far you need to go with the changes.

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jonfoote
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Post by jonfoote »

On mine i replaced the 1Meg to vBias (R2 on electrosmash schematic) with a pot. Really helps me control the amount of bass going into the opamp and becoming a flubby mess (but its still there if you want it). Set really low the output is really thin, then into chimey, about 9/10 o'clock it can get 'nasally' and from 12 o'clock onwards its the stock RAT sound. Cant remember if I changed C1 or not, if i did it wasn't by much

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RandyFay
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Post by RandyFay »

Just doing a few quick calculations.
The issue is the .001 cap will roll off HF at very differing -3db points depending on the source impedance. And a guitars volume put can be quite - a 500k pot will be 12fk output Z. Plug that in to the RC filter calculator and you can see a whole lot of roll off.
I propose changing the 1k series resistor to something like 27k then may 330pf instead of the .001 (1n), then experimenting from there. That combo will give a -3db point of around 5khz with the guitar's volume pot halfway. Maybe more rolloff is desired.
But I don't think it is such a good thing to have it so variable with the source impedance.

edit: I am also looking at the tone control. not well thought out IMO. min setting the -3db point is less than 500hz. max setting the -3db is over 30khz. lets tighten that up a bit.

I propose a 25k tone pot and a .0068uf cap. At min setting the -3db is now about 1khz and at the max setting the -3db point in 17khz.

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nooneknows
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Post by nooneknows »

I've just modded my rat , my aim was to increase bass, so I changed the 2.2uF cap on the feedback loop to a 4.7uF and I increase the input cap to 1uF, I think it's now perfect for my rig (it's more a fuzz now , so it may not be good for everyone) but I' incidentally have noticed it works way better with guitar volume changes, my two cents

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