OB-X Single Voice/Controller Card Build Info Page
Hi all and THANK YOU for being a part of our first of hopefully many DIY synth projects!
This page will replace the need for email blasts and will keep all info in one place.
Since I will be adding to this page as needed, the info will be organized by dates rather than subjects, so if you’re new to the build, it’s best to read the whole thing.
(original email blast info edited for web page)
6/27/2020 Update: PSU and other stuff
Sorry for the delay y’all. That’s a phrase I use often, because often I suck at predicting my availability while also meeting shop deadlines and having 2 kids…
I’ve ordered the PCB’s for the PSU. For our Rev 1 buyers, we’re going to be offering this at cost, which will likely land around $25 or so. Luckily we were able to design something that’s much simpler than I originally thought, and it doesn’t get hot or anything. It uses a 18VAC wall wart and via basic creative circuitry results in an adjustable supply that properly powers the project. It will be mounted in a project enclosure with the MOLEX stuff coming out one end and the wall wart plugging into the other.
To touch on PSU pricing to Rev 1 builders and subsequently Rev 2 builders… we are not factoring the cost of the PCB into the $25 price tag. The PCB will be including as part of the overall kit going forward. The project enclosure, wall wart, and components will simply be added to the BOM for Rev 2 buyers (BOM to be updated when all parts are confirmed). We believe it will cost Rev 1 builders substantially less to get the “kit” straight from us at cost to save on shipping from various vendors.
Mounting the new PCB in a project enclosure properly is the next small hurdle. I designed the PCB’s to fit into a project enclosure from Jameco based on datasheets but with this kind of stuff you never know if thats the most accurate, so once we verify that, we’ll blast again that it’s available and make it all happen. Time’s like this I wish I could just drive to All Electronics nearby and grab what I need, but COVID has put a major damper on that 🙁
We realized (embarrassingly) that the controller card is missing silk screen for the I/O. When we ship the supply stuff, we will also be providing a thin sticker label to compensate for this error.
I’m working to figure out a better resistor value scheme to allow adequate calibration and range for the PW and also to shut off VCO2. This is due to the way the original OB-X shuts off oscillators: When an oscillator is “off”, the computer signals the voice card to switch to pulse wave and also sends 5V to the pulse width control node to effectively null out the oscillator. This isn’t a major issue, but I do still need to adjust some pull up/down resistors on the card.
I’ve noticed that the OB-X card does not reliably sequence from a SH-101, which spits out a gate voltage of about 4.7V. The gate must be 5 or above for it to trigger reliably. I assume it may be possible to add a diode to lift the ground potential to “cheat” your way into 5+V, but I haven’t done that just yet. I imagine most other sequencers nowadays use gate voltages higher or exactly 5V.
Maybe I’m biased because I made the thing but it sounds really sweet and works quite well! I’ve been sequencing it with an Oberheim Mini-Sequencer and it really not only sound like a 1 voice OB-X but also just a great sounding synth. The Sync and X-Mod is super sick. In a lot of ways this makes me wish the actual OB-X could easily disable 7 voices to only hear one card (this can be done, but it needs to be opened up). I can’t wait to hear what y’all make with this! You can hear this on our instagram… we made a “highlight” section on our page with the various videos I’ve posted of this project making sound. https://www.instagram.com/rosen_sound/
9/12/2020 Update: PSU Is Ready!
After needing to adjust the design due to very haphazard project box experiences, the design is now ready for prime time! Photos below….
Notice the SMD regulators… that was the main design change. Using through hole LM317/LM337 would have either required a larger board, or a larger project enclosure… Either way resulting in a large project box. The current draw is low enough that these regulators are sufficient. They’re big enough packages to hand solder, too.
One side of the board has easy pads to connect a power switch, the AC jack, and a fuse.The other side has the output voltages with extra pads to make calibration a bit easier.
We will let everyone know via email how much it will cost to have the PSU shipped to them. Again, it will be at cost which is quite low. The most expensive parts are the enclosure ($5) and the wall wart which isn’t much more.
All that’s left is:
1. Resistor values for controller card
3. Gate levels (if needed, likely not).
10/05/2020 Update: Trump has Covid and all parts of this build are ready for delivery!
Happy to report that at this point the project no longer has any mystery pieces. Rev 2 controllers are in and PSU’s are ready to ship to all builders.
The Rev 2 controller simply rationalizes some cuts and jumpers and the only additional feature is the master volume pot. Adding a master volume to the card itself isn’t hard. We will add the needed pot in your PSU box. To add it, lift the negative leg of the capacitor connected to G2, which is the middle pin on header G. Attach the negative lead to the center of the trim pot. Fudge the clockwise pin to the original hole for the capacitor. Use wire if needed. Attach to the counter clockwise leg to a ground point, which can easily be accessed from G1 and G3. Secure with hot glue or silicone and voila, volume has been added.
– Please don’t delete or sub anything from the mouser cart. We had to re-add a few things. If there is something obsolete, please email me so I can update the cart.
– If you haven’t built your controller card yet, check the cart to make sure you got the linear pots and not audio. If you already put in the audio pots, it’s not the end of the world, but use the linear if possible. For Rev 2 builders, use the audio pot for the master volume
– You may opt to not use hardware to mount the card. Up to you. We seem to get a better fit with no hardware.
– If you’d like a rev 2 board, we will only charge for the board at cost and postage. Let me know.