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x0x:vcfmods [2007/09/19 08:22]
creekree
x0x:vcfmods [2008/05/20 23:01]
subatomic
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 Perhaps this page could be split out into a grouping of pages soon. Perhaps this page could be split out into a grouping of pages soon.
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 ==== Filter Modulation (VCO) ==== ==== Filter Modulation (VCO) ====
-This is another relatively easy but awesome mod for the 303. Take the feed from the square wave (R36/Q8) and the saw wave (R105/Q28) and wire one to pin3 of an SPDT switch and the other to pin1 of the same switch. Use a SPDT switch so that you can select the saw or square wave as the modulation source. Connect ​ pin2 from the switch to the 3rd leg of a 50K log pot. Wire the first leg of the pot to the junction of R71/Q9/Q11 (it is best to hook it up here instead of to ground so that it follows the same bias strategy as the env mod does - see page 8 in the 303 service manual: [[http://​dl.analoghell.com/​index.cfm?​id=107]]). Hook up a 100K resistor to the center lug of the pot, the other end of the resistor goes to the junction of R71/​R72/​Q10-base,​ the summing point for the filter frequency control voltage input.  ​+This is another relatively easy but awesome mod for the 303. Take the feed from the square wave (R36/Q8) and the saw wave (R105/Q28) and wire one to pin3 of an SPDT switch and the other to pin1 of the same switch. Use a SPDT switch so that you can select the saw or square wave as the modulation source. Connect ​ pin2 from the switch to the 3rd leg of a 50K log [[http://​example.com|External Link]]pot. Wire the first leg of the pot to the junction of R71/Q9/Q11 (it is best to hook it up here instead of to ground so that it follows the same bias strategy as the env mod does - see page 8 in the 303 service manual: [[http://​dl.analoghell.com/​index.cfm?​id=107]]). Hook up a 100K resistor to the center lug of the pot, the other end of the resistor goes to the junction of R71/​R72/​Q10-base,​ the summing point for the filter frequency control voltage input.  ​
 This will let you select the saw or the square as the modulation source independent of the what you have selected for the VCO.  This will let you select the saw or the square as the modulation source independent of the what you have selected for the VCO. 
 Depending on where all the other controls are set you can get everything from an evil zipper to slowly dripping acid - among other things! ​ Depending on where all the other controls are set you can get everything from an evil zipper to slowly dripping acid - among other things! ​
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 {{x0x:​fmmod_vco.png|}} {{x0x:​fmmod_vco.png|}}
  
-NOTEthe schematic above merely illustrates the text. There has been discussion on the forums lately that it would be  good idea to buffer the waveform output. +UPDATEIt is a good idea to buffer the waveform output. ​Use a 0.1uF ceramic cap after the 100K resistor. The Mod works great and is especially good at high resonance levels, so make sure you include the Resonance Boost Mod also!
  
 +UPDATE2 (by [[http://​www.ladyada.net/​forums/​profile.php?​mode=viewprofile&​u=103|subatomic]]):​ that may be true (that 0.1uF being a good idea) however it doesn'​t sound as good...
  
  
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 If you don't particularly care about the numerology or DevilFish purity, you can simply play with various resistor values until you find a sound that works. ​ Conversely, you could mount a potentiometer instead. If you don't particularly care about the numerology or DevilFish purity, you can simply play with various resistor values until you find a sound that works. ​ Conversely, you could mount a potentiometer instead.
  
-C17 might attenuate the signal too much, so you might need to replace it with a 10uF cap.+C17 might attenuate the signal too much, so you might need to replace it with 
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 + a 10uF cap.
  
 === A Devilfish Like Overdrive === === A Devilfish Like Overdrive ===
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 ==== Resonance Warble ==== ==== Resonance Warble ====
-This is actually ​a PsModbut it is included here for completeness sake. +This is actually ​part of the  [[psmods# Power Supply Mods]]. However, it seems to be //not// working.
- +
-{{template>​psmods#​resonance_warble}}+
  
 ==== Increased Filter Low End ==== ==== Increased Filter Low End ====
 According to RobbinWhittle,​ all you have to do is short out R47 (10K ohm resistor) by a length of insulated wire.  Some other x0xers tried it out, and found that mounting a 4.7K ParallelResistor along with R47 works better (giving 3197 ohms resistance). ​ This will also affect cutoff range to a degree. According to RobbinWhittle,​ all you have to do is short out R47 (10K ohm resistor) by a length of insulated wire.  Some other x0xers tried it out, and found that mounting a 4.7K ParallelResistor along with R47 works better (giving 3197 ohms resistance). ​ This will also affect cutoff range to a degree.
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 ==== Resonance Boost ==== ==== Resonance Boost ====
    
-You can change the value of some of the resistors on the VoltageControlledFilter to boost the resonance. ​ +You can change the value of some of the resistors on the VoltageControlledFilter to boost the resonance. ​ 
 +[[http://​http://​www.ladyada.net/​make/​x0xb0x/​mods.html|The Mods page on Ladyada.net]] suggests: ​
  
   - Decrease R97 to ~7.5K   - Decrease R97 to ~7.5K
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   - Increase R109 to ~22K (perhaps even larger?)   - Increase R109 to ~22K (perhaps even larger?)
  
-Just an addition here. You really don't have to bother with anything but decreasing R97. Changing it to 5K or 6K is about as low as you would want to go, and definitely a switch to choose between the factory setting of 10K and the new hi-res would be a good idea. +**NOTE:​** ​You really don't have to bother with anything but decreasing R97. Changing it to 5K or 6K is about as low as you would want to go, and definitely a switch to choose between the factory setting of 10K and the new hi-res would be a good idea. 
-An elegant way to do it is to use a 4.7K resistor in series with a 5K trimpot. This way you can adjust the maximum Reso boost to your liking. ​+An elegant way to do it is to use a 4.7K resistor in series with a 5K trimpot. This way you can adjust the maximum Reso boost to your liking ​without the need to solder and desolder different values of resistors
  
 {{x0x:​reso_boost.png|}} {{x0x:​reso_boost.png|}}
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 +**Extra results:**
 +[[http://​forums.ladyada.net/​viewtopic.php?​t=5215|Momerath says in this post]] that he likes **r46 = jumper / r97 = 8.2k** as default (always on) on his box... Also he says "6.8k [for r97] was ridiculous if i recall"​.
 +[[http://​forums.ladyada.net/​viewtopic.php?​t=5215&​postdays=0&​postorder=asc&​start=15|charlie_says confirms it's good]] and says "you tend to get self resonance at the (very) top end but, I don't seem to have lost anything that I had before, and some combinations are definitely fuller. " ​ and  "but overall I think it's worth doing." ​    
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 +[[http://​www.ladyada.net/​forums/​profile.php?​mode=viewprofile&​u=103|Subatomic]] tried mome's mod, and found that it can be a bit whistly, but good, I went with a pot though so I could tweak. ​ To explain Mome's use of shorting out  r46... ​ It's the 
 +[[http://​www.ladyada.net/​wiki/​x0x/​envelopemods#​increase_accent_range|"​Resonance Increase Accent Range Mod"]] it seems to add more squelch on the accent, it's kinda subtle, but I could notice it most when the cutoff was way down it seemed to let through more resonant "​scream"​ (sounds like "​wow"​)...
  
 ==== VCF External In ==== ==== VCF External In ====
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 The signal where R121 and R122 meet is where the audio from the VCF comes out.  One could in theory, wire a Jack between this and IC15.  Hell, you could probably wire in a Tip/​Ring/​Sleeve Jack and provide both VCF out and VCA In functinality here.  You may need to wire some value of resistor and/or capacitor before the jacks however! The signal where R121 and R122 meet is where the audio from the VCF comes out.  One could in theory, wire a Jack between this and IC15.  Hell, you could probably wire in a Tip/​Ring/​Sleeve Jack and provide both VCF out and VCA In functinality here.  You may need to wire some value of resistor and/or capacitor before the jacks however!
  
-==== Pole selection ==== 
  
-<note important>​ **VerifyMe** and **WorkOnMe**:​ This mod needs to be worked on a little more, and have someone with more experience and mojo flesh out the details </​note>​ 
  
-The x0xb0x/​tb303 has a 4 pole filter (24db/oct), but due to design flaws has more of an 18dB/oct response. ​ Theoretically one could introduce the signal after each pole, thus turning it into a 2 pole or 1 pole filter. ​ You could either have the pole selectable by switch, or even seperate inputs if you desired. ​ This may, or may not sound good.+
  
 ==== '​Fixing'​ the '​Flawed'​ Filter ==== ==== '​Fixing'​ the '​Flawed'​ Filter ====
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 From a different webpage, apparently if you replace resistor R 97 (10k) with 6.8k (or 5.6k) it will allow the filter to self oscillate. From a different webpage, apparently if you replace resistor R 97 (10k) with 6.8k (or 5.6k) it will allow the filter to self oscillate.
 +-> this is the Resonance Boost Mod!]]
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-==== Audio Input into resonance feedback loop ==== 
-<note important>​ **[[WorkOnMe]]** and **[[VerifyMe]]:​** This mod needs to be worked on a little more, and have someone with more experience and mojo flesh out the details </​note>​ 
  
-Audio Input to the resonance feedback loop would be achived around C15.  One could wire a jack with resistor and cap in there as well. 
  
 ==== CV for Cutoff ==== ==== CV for Cutoff ====
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 For DevilFish like filter tracking, this is a little more complex, as we need to scale the voltages. ​ This would probably mean using a pot as part of a voltage divider, and possibly multiplying the CV in before going through the divider. For DevilFish like filter tracking, this is a little more complex, as we need to scale the voltages. ​ This would probably mean using a pot as part of a voltage divider, and possibly multiplying the CV in before going through the divider.
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 +==== increase resonance feedback ====
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 +reported by bcbox [[http://​forums.ladyada.net/​viewtopic.php?​t=5316|in this post]], the following is a cut-n-paste of his post.
 +<note warning> **VerifyMe:​** Please remove this tag if you verify this mod works as described </​note>​
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 +you can increase resonance feedback by changing C21 and R122
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 +Replace R122 with 68k
 +Replace C21 with .015uF
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 +this will increase resonance feedback while keeping the frequency response the same. The sound level will stay more constant as you increase resonance - not so much of a drop off.
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/home/ladyada/public_html/wiki/data/pages/x0x/vcfmods.txt · Last modified: 2016/01/28 18:05 (external edit)