My x0xb0x

I spent the last year+ without a workshop and focused on finishing my thesis and finding a job. But now that I've moved across the country, settled into a new job, and set up my work space it's time to start hacking again! First project.... a x0xb0x.

The x0xb0x is a clone of the Roland TB-303 synth. Back when I was making music on a daily basis, I owned a 303 and loved it! Then when I had no job and was studying full time I had to sell it to pay the rent. I got it for $600 but now they are selling for $2000 and up! Not yet thank you...

Some time around the early to mid 2000's the x0xb0x came around as a promising, moderately priced, faithful DIY clone of the 303. I think the first kits cost ~$300 and were back ordered as they sourced parts. Needless to say in undergrad and grad school I did not have $300 to toss away hoping that I would get a synth kit soon. But I did know that the most unique thing about the 303's sound was the modified Moog ladder filter it used. And since the x0xbx0x project was open source I was able to source all the parts I needed to make 2 filters.

Cut ahead to now... I realized now that I have a job I can afford to buy the circuit board and case and hardware for the x0xb0x, and I had almost everything I needed from the rare parts sitting in shoeboxes in my room. So I revived the project. It took a couple weeks since most of my resistors and miscellaneous parts were sill across the country in m brothers house. I had to make about a dozen small orders to digikey and mouser but it's done! And more importantly it worked completely on the first try!

I did put a bit of planning into the construction. The resonance circuit of the ladder filter needed the highest gain transistors. Since I had to source some replacement parts there was on average a transistor beta ~50 lower than  the original parts, but the spread of the beta overlapped. So I built a simple test circuit to measure the beta of every transistor and binned all the transistors I used putting the highest beta parts into the most critical spots.

One last mod that I need to make is to reduce some of the resistors on the filter to increase the gain at resonance. I noticed that at low resonance and low cutoff the filter sounds very good and very close to the original 303. But about 3/4 of the way to max resonance and cuttoff the filter just stays put where the original 303 would scream!! I'm hoping this last mod will make my x0xbox sound more like a real 303.