Cavan Fyans at the time of writing this is a PhD student at the Sonic Arts Research Centre. His personal site along with detailing his extensive academic work also outlines a number of his DIY electronic instruments. My favorite is the “Tape Box 2” which as the name suggests is an updated version of “Tape Box 1″. It’s perfectly simple, does what it should, and doesn’t distract with excessive controls, knobs, and gimmickry. I also have to give him a thumbs-up on his use of high quality pictures documenting his work online. Nothing makes me more disappointed than a thumbnail that leads to a picture of… a thumbnail.
I pretty much use my laptop for everything with the exception of sound design and experimentation with the outboard gear in the studio. I’ve wanted for some time to be able to capture audio on my laptop to jot down quick ideas but like most laptops the only input it has is a microphone input which simply just doesn’t cut it when trying to record line level inputs. It definitely doesn’t cut it if I want to betray good-practice and record the signal from a headphone jack which sometimes is the only option. And for some unknown reason this “top of the line” laptop doesn’t have a means to switch the mic input, to a line level input: a major irritation.
I got thinking and remembered I had a Direct Box lying around that gets infrequent use. I also recalled I had a balanced-to-unbalanced converter jack… you know, one of those five dollar jacks from radio shack that’s about the size of a roll of dimes. I figured I could take an unbalanced line level signal, run it through the DI to bring it to a microphone level signal. but then the signal would be balanced so I needed to make it an unbalanced signal again. The DI box has a switch for a -20dB and -40dB pad which is great when taking a hot signal from a headphone out. And lastly, I threw in an additional 1/8″ output jack so I could just plug it into the laptop microphone input.
These whirlwind passive DI boxes cost approximately $30 and can be found just about anywhere online. Amazon has one for 29.50. But, I suspect you could make one yourself for far less than that as there are only a handful of parts… a transformer, some jacks, a couple diodes and a couple resistors for the input pad.
This is the adapter with its guts removed. I’m just looking for the transformer.
Using a stepped hole cutting bit I drilled a new hole for the jack. If you don’t own a hole cutting bit I highly recommend them. Perfectly sized holes every time without the drift you find when using a regular bit. Not to mention is spares your regular bits the abuse of using them on metal.
I remember I though this thing was so rad when I first bought it back in 97-98ish. These days it pretty much collects dust except for the occasional use of its arpeggiator. Nonetheless I thought it would still benefit from some blue LEDs under the keys. What can’t be seen is the addition of two Burr Brown OPA132 Op Amps to the output section. They won’t do much for the timbre of the lousy PCM samples but they do make the outputs sound brilliantly crisp.
Back in 1997 a company called Music and More (MAM) created a tb303 clone called the MB33. They licensed their design to another company called Freeform Analogue Technologies who dubbed the same clone the Freebass FB383. I guess it’s a clone of a clone? Both were identical and affordable during a time techno was all the rage and everybody and their brother HAD to have a tb303. Despite the overused sound and the long past death of techno these little boxes still have a good deal to offer…. Especially at current prices…. Originally around $400… I picked mine up for $10.00 on eBay, albeit broken. Due to poor manufacturing many of these guys are broken these days and don’t produce any sound however, you can still tap into their analogue resonance filter to add some nice tone to just about any instrument and add a excellent tool to your studio. The mods that follow show you how… and it will cost you pennies.
Assuming you’re familiar with the FB383/MB33 you’ll know there is an external input on the back to patch a signal through the filter section of the unit. Assuming your unit works you know that when you connect a signal the internal synth is disabled which makes racking the unit a major hassle. By adding a filter on/off switch you can keep your unit racked and patched to a patch bay and use the filter easily. If your FB383/MB33 doesn’t work, like mine, then it’s basically a signal on/off switch. I plan on making a cv input for the oscilator and when i do, this mod will still be neceassry if i want to rack the unit.
The photo above is a shot of the finished mod. You can see more details, photos, and descriptions at the link below.
As with most external filter units, you need to trigger the envelope section before you will hear any sound. So if you have an input signal patched and the envelope is not triggered you hear nothing. To do this you have to supply a voltage to the bias input of the Operational Transconductance Amplifier (OTA). Instead of applying a direct voltage I opted to use a pot to drop the voltage at the base of a transistor controlling flow to the bias input… drop the voltage and current flows to the bias input. With higher voltages you get some gritty distortion which isn’t so bad in some cases. I soldered one lead of the pot to ground and one to an easy to reach lead on the end of a 0 Ohm resistor. That’s what you see in the photo above.
As before, you can see the full set of photos by the link below.
This one is pretty self explanatory. There is a resistor in place that restricts the resonance a bit. By bridging this resistor you can get some nice thick resonance and even some self-oscillation. Instead of simply bridging it though I added a switch to allow for ‘normal’ and ‘boost’ modes for a variety of applications.
As with the previous mods… photos and details by the link below.
When initially looking into information on the FB383 I immediately figured out that nobody has any. Nobody. There was virtually no information available on the net with the exception of a brief background on MatrixSynth and some information on possible mods (for a fee) at Circuitbenders.uk. Of course there were reviews at typical locations like hyperreal and harmony central but other than that it was limited. I managed to track down someone familiar with MAM products through the company that ate them, Musonik, and figuring that somewhere someone would have service manuals, design specs, part sources, etc. I was wrong. Nothing.
So given the good number of these machines out there and the likelihood that there were a fair number of folks in need of a signal flow diagram I made a high resolution circuit overlay of the Freebass FB383 (MAM MB33). It’s not a schematic but it’s about as close as you can get. I’ve found it immensely useful and have it available here for any and all to put to good use. Enjoy!