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EKDENTON
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« on: December 12, 2006, 05:33:02 pm » |
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has anyone else here made a Rat pedal before? I made a version of it and it is pretty awesome. The filter control to me at times makes this thig sound like I am also using a wah in a fixed setting, it really focuses on certain frequencies. It has just the right amount of gain to get that controled feedback with the distortion. And the distortion is really smooth. Pretty nice pedal.
I was wondering if anyone here may know how the filter in this circut works. Its the 100k pot to the right of the glass diodes. Changing the setting seems to my ears to change the frequency focus simmilar to what a wah pedal does but, looking at the schematic, it looks like the pot just changes the current to the transistor. How does it filter?
also looking at the 4.7uf and 560ohm and 47ohm and 2.2uf at pin 2 at the opamp. I was wondering why would they wire it like that rather than just using a 43ohm resistor series with a 6.9uf capacitor. Did they run those parallel because its hard to find those values or does that wiring have to do with filtering high and low frequencies.
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« Last Edit: December 12, 2006, 05:34:03 pm by EKDENTON »
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let's rock
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jhadhar65
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« Reply #2 on: December 13, 2006, 11:00:11 am » |
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Hey Ed -
Yeah, I think you could. I'm guessing you mean interstage. A simple interstage cap to ground calculated to work with a resistance to give the desired break frequency would work just fine.
Most production amps that incorporate lowpass, do so by bypassing all or part of the plate resistor for the same effect. Remember that B+ is capacitively filtered, so it's AC ground for all practical purposes. Bypassing only part of the plate resistor by inserting a small value resistor between the plate and plate resistor/bypass cap helps reduces interaction between the added cap and interelectrode capacitances inside the tube.
I only mention that as it may be easier to throw in a single cap rather than the interstage lowpass you've got there.
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adamasd
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Posts: 754
famous half-filled flour sack
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« Reply #3 on: December 13, 2006, 12:44:42 pm » |
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The 100k log pot determins the level that is filtered(more resistance more filter, less resistance less filter).
Almost. The pot and the 1.5k resistor are in series with the cap to ground. The pot sets the cutoff frequency of the filter. The 1.5k resistor makes it so the filter never hits zero resistance.
You can calculate the cutoff frequency of the filter for different values of pot and cap with this equation
1/(2[ch960]RC) R in MegaOhms and C in uF
So as is the filter would start to roll off around 80hz and you can sweep that up to about 1200hz. Since this is a simple RC lowpass filter anything above the cutoff of the filter is 6db quieter then anything below the cutoff frequency. So if the cutoff is 100hz, everything above 100 hz is attenuated by 6db and everything bellow hz is left alone.
Thats the basics, now go search google for RC filter and have gads of stuff to read through and learn more.
And yeah, you could put this in amp, pretty much as is, you just need ot make sure all the parts can take the voltage and you will be fine, give it a try.
adam
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adamasd
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famous half-filled flour sack
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« Reply #4 on: December 13, 2006, 12:48:56 pm » |
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Most production amps that incorporate lowpass, do so by bypassing all or part of the plate resistor for the same effect.
But that is a fixed frequency lowpass. The Rat uses a variable frequency filter with a set amount of attenuation. Alot of the cheaper old guitar amps used frequency controls like this, mostly in the single tone knob amps. Harmony, Valco, Airline, Silvertone, etc. Variable frequency fixed attenuation filters are also common in guitar tone controls.
adam
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tbeck
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"Mars ain't the kinda place to raise your kids..."
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« Reply #5 on: January 24, 2007, 08:53:15 am » |
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Hey, thanks for the nice Rat schematic. I have 2 older Rat pedals that need to be fixed, now I have the means to do so.
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"Ignorance can be cured with education, stupid is forever" Clint Smith--Thunder Ranch owner and instructor.
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EKDENTON
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« Reply #6 on: January 25, 2007, 09:16:29 am » |
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I got to researching high pass and low pass filters and stumbled on this link below that has some interesting information on using clipping diodes in high pass and in low pass filters to clip either the highs and lows or anywhere inbetween. Really usefull if anyone is interested in that type of stuff. The schematic at the bottom could quickly be added to a rat pedal. Actually having two seperate amps with one pot controling the low clipping the other pot controling the high clipping and they added some silicone diodes that can be switched in. http://www.muzique.com/lab/tclip.htm |
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let's rock
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hotguit
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I love tube amps
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« Reply #7 on: January 04, 2008, 09:04:19 am » |
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Hi everybody.
here is a RAT mod i designed to improve tone and give the filter more flexibility
RAT2 HOTMOD (for pcb version 3 RAT)
C3=100 NANO
C5 = 3.3 uF TANT
C6 = 4.7 uF TANT
C8 = 330 PICO
C12 = 47 NANO
IC = LM308 (no metal can)
1 SWITCH ON/ON dual
A) COND MYLAR 562 (5600 PICO)
B) COND MYLAR 822 (8200 PICO)
connect wires from switch central pins to pin 1 and 2 of VOLUME pot
2 SWITCH ON/OFF/ON dual
A) 2 RED LEDS IN ANTIPARALLEL
B) 2 MOSFET IRF 520 AND 2 DIODES GER. 1N100 IN ANTIPARALLEL
(1 mosfet and 1 diode per side)
How it sounds:
LED: warm crunch
MOSFET: wow!!!! warm juicy sound
CENTER: boost
Bye
Hot
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