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x0x:vcomods [2007/04/04 06:08]
hl-sdk
x0x:vcomods [2016/01/28 18:05] (current)
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 ==== Detent Tuning Knob ==== ==== Detent Tuning Knob ====
 When we designed the x0xb0x, we put in a non-detent tuning pot because that was what the original 303 had. However, this may drive you a little crazy. Panasonic part number P3I9503, an equivalent 50K linear potentiometer with a center detent, is available from DigiKey. Note that you may have to retune the synth once in a while to keep the center detent '​correct'​ When we designed the x0xb0x, we put in a non-detent tuning pot because that was what the original 303 had. However, this may drive you a little crazy. Panasonic part number P3I9503, an equivalent 50K linear potentiometer with a center detent, is available from DigiKey. Note that you may have to retune the synth once in a while to keep the center detent '​correct'​
 +
  
 ==== Slide Timing Adjust ==== ==== Slide Timing Adjust ====
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 Note: this mod will mess with your tuning a little, especially when the pot is turned all the way up. And there'​s no way to easily fix it.  Note: this mod will mess with your tuning a little, especially when the pot is turned all the way up. And there'​s no way to easily fix it. 
 +
 +Alternatively,​ I think this is a very bad way to do this. I would go about it by changing the value of c35, which is actually responsible for the creation of slide. If you want to squeeze out some hardcore math, find the cutoff frequency of the lowpass formed by c35 and whatever comes before it (DAC network). It could be 2.2K, making the cutoff ~328Hz, which makes sense I guess. I'm sure someone with more math experience could calculate how much time it would take for the voltage to change. Anyway, on to the mod:
 +
 +Put capacitors in parallel with C35 to make slide time longer, place them in series to make it shorter. I'd suggest values from .1 to 10uF
 +
 +Note2: normaly the frequency of the slide time Filter (C35 and unknown resistor(s)) is 7.2 to 7.5Hz (this is based on actual measurements of the output, not the schematic or circuit) thus with the 0.22uF cap the resistance is 100K (wherever it is)
 +for a ~twice slower slide use a ~0.44uF cap
  
 ==== CV In ===== ==== CV In =====
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 Wire a jack to a 100K resistor, and then wire that to the base of Q29 Wire a jack to a 100K resistor, and then wire that to the base of Q29
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 ==== Self Frequency Modulation ==== ==== Self Frequency Modulation ====
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 === Questions to answer before performing this mod === === Questions to answer before performing this mod ===
-I have no idea how this circuit is affect by current. I don't know the current that should be going into CV, or the current that is output by the VCO.  You might be able to fry your VCO if you arn't careful+I have no idea how this circuit is affect by current. I don't know the current that should be going into CV, or the current that is output by the VCO.  You might be able to fry your VCO if you aren't careful 
 + 
 +I dont know if "To CV" is as easy as hooking up the circuit to Pin 5 of IC 11. We need to sum the voltages basically. I don't know if this is the proper way to do it.
  
-I dont know if "To CV" is as easy as hooking up the circuit to Pin 5 of IC 11. We need to sum the voltages basicly. I don't know if this is the proper way to do it. 
  
 ==== Sub Oscillator ==== ==== Sub Oscillator ====
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 === Questions to answer before performing this mod === === Questions to answer before performing this mod ===
  
-Because the Oscillator outputs between 5 and 12V the voltage needs to be biased (like the Self Frequency Mod above) so that it is 0V and 5V respectively, and perhaps ​re-biased ​back.+Because the Oscillator outputs between 5 and 12v the voltage needs to be biased (like the Self Frequency Mod above) so that it is 0V and 5V respectively. It does not need to be re-biased ​because the filter is AC coupled, and then biased, allowing you to feed AC coupled signals into the VCF. 
 + 
 +One way to easily do this is just divide the signal by by voltage divider by a ratio of 4, giving a signal between 1.25v and 3v. That is very iffy, and it would be better to divide by 2 and run the CD4024 off of 12v, making LOW be 3v and HIGH be 11V. 
 +This is from the datasheet and it all depends on your VCO putting out the correct voltages. I'm sure no matter what though, that it will sound crazy. 
 + 
 +Voltage Divider circuit:  
 +{{http://​upload.wikimedia.org/​wikipedia/​commons/​thumb/​8/​8f/​Voltage_divider.svg/​100px-Voltage_divider.svg.png}} 
 + 
 +Even though this is untested, it should work.
  
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