MODS I have done so far

[intellijel]

Hi there,

I have done the following mods now:

1. CV in (with full protection) to Filter Cutoff
2. CV in (with full protection) to Pitch CV
3. Filter Overdrive using 3.3K resistor in series with 250K pot
4. Internal Filter FM
5. Muffler Distorition using 1n60 germanium diodes

* I also did the extend filter cutoff and envelope range mods

1. CV in (with full protection) to Filter Cutoff
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This mod works great, I need to be careful of my CV sources DC offset or else plugging something in drops the VCF cutoff range. This is a great mod and works really well.

2. CV in (with full protection) to Pitch CV
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This input is super sensitive. If I have a cable plugged in I can modulate the pitch by touching the connector on the other end. With filter FM and Pitch FM at the same time I get very crazy sounds... nice for techno.

3. Filter Overdrive using 3.3K resistor in series with 250K pot
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At full, the sound is very boomy and distorted with a warm feel. At mid range there is some bite but it is subtle and at full off it sounds like the default 303. If you use a pot with a switch built into it, then you would have a way to fully cut VCO going into the Filter.

4. Internal Filter FM
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I tried several different ways to do this including Pre and Post VCA signals as sources. Without AC coupling and taking the VCF direct out connected to VCF CV in (via 100k) resistor you get only a weird low clicking sound out of the x0xb0x ---not good---. Same thing happened with AC coupling.
Next I tried post VCA but the VCF cutoff was dropped lower due to difference in ground refereces. When I added AC coupling (2uF cap) I was able to get some modulation but it was not such a dramatic effect.
Finally I used the VCO out as the source with 2uF cap for coupling going into 100k resistor attached to base of q10. I used a 250K pot to control modulation amount and it works great! It is a really useful control and scuplts the frequencies in an interesting way.
I recomend this but playing around with AC cap values may have more desireable effect.

5. Muffler Distorition using 1n60 germanium diodes
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If you are clever you can do this circuit with 3 position switch and just two diodes (not three)
Having the two different setting is effective. At different ocatves they both have very different effects. The clipping sound is reasonably tube like.

I have two holes on my front panel for two more pots to put in. I may do slide timing and soft attack controls. I definitely want to add the Sweep Speed control and High resonacne/Sweep Type switches.

I also find the FM related modulation has the most interesting effects on sound. I am not looking for harsh distorted basslines, I am way more into trippy plastikman style riffs with which I can continualy evolve and change (make them come alive).

Any ideas for cool mods? I thought of putting a ring modulator in there (using small transformers). Speaking of transformers, I wonder if that is what Robin Whittle used as "unique" AC coupling from psot VCA.

[Jonnay]

How did you handle CV protection?

As for cool mods, Self frequency modulation might be interesting, or even a suboscillator.

[intellijel]

For Cv input protection I used the methods described on www.musicfeomouterspace.com and the x0xm0dz wiki

1. CV Tip--> Cathode of 1n1418 --> anode to ground
2. CV Tip--> Cathode of 9.1V zener --> anode to one side of 10K resistor--> other side of resistor to ground.

The first should shunt any negative voltage and the second should regulate any voltage exceeding 9.1 V

Works well so far.

[intellijel]

oops the wiki: http://wiki.jonnay.net/x0x/

The other link should have been:
http://www.musicfromouterspace.com/anal ... CTCVINPUTS

[greg]

self fm is not that interesting in my experience. i don't know why the yamaha fm feedback paths produce complex sounds. if you think about the way a waveform would modulate itself, it just ends up slowing down the low portion of the waveform and speeding up the high portion, effectively thinning out the sound. a saw wave begins to approach more of a curved skinny saw. try it out though, it may be worthwhile.

i've thought about adding a simple tri/square lfo that can go into audio rate to mine. the ASM-1 LFO is a very simple design i've used before.

[controlvoltage]

If you wanted to get fancy (and add more parts) perhaps self-fm thru a lag/slew generator would be more complex and interesting... but maybe the answer is ultimately just to build a 2-oscillator b0x with oscillator sync. FM and ringmod possibilities...
well that's my goal anyway

[intellijel]

I am abandoning oscilator FM, I get interesting enough results with filter FM and other mods.

However, I would definitely like to build a sub oscilator. I think this would be a super useful effect (and very musical). I am going to try that single chip option linked off the wiki.