New Original Filter Board. Dual SKF. Complete

Hello everyone.

It’s been awhile since I let anybody know how things were progressing with this. Almost two years, I’ve been busy and a lot has happened since my first post in September 2014. For those who remember my post from back then, here’s an update. For those who don’t, I’ll try to bring you up to speed.

Anyway, I had been working on a filter board based on the Korg 700S for awhile. It was using the firmware settings for the Dual SVF gilter to change filter responses and routing. Eventually, I had to take a break from it because I had too much happening in my personal life. When I finally was able to start work on it again, I found that an OS update had made a lot of the work I had done on my computer inaccessible. I salvaged what I could and worked my way through that. I had some boards made, and found that I had missed a few careless errors. So those boards were unusable for anyone who doesn’t want to do a lot cutting of traces and soldering wire jumpers.

Earlier this month, I finally was able to get those errors corrected and new boards made. I’ve made one, and it works great:)

Here’s a quick rundown:

It has the same functionality as the Dual SVF board but includes only very easy to find parts. (However, there are a lot of them.) I don’t have a Dual SVF to compare it to, but from the demos I have heard. The character is significantly different.

It is not meant to be a clone of any existing design, but it is based largely on the diode ring filters of the Korg 700S and Korg MS-50. The VCA is based on early Korg designs as well.

SKF stands for Sallen Key Filter, but I decided to informally call it “Three Ring Circuits” for a few reasons. First of all, it has three diode rings (One for each filter, and another for the VCA), and obviously “circuits” sounds like “circus”. It’s also a bit of an homage to the early Human League song “Circus of Death” which prominently features the Korg 700s. In keeping with this theme, I changed the ghost to an evil clown.

If anybody is interested, I would like to offer the boards for sale once I’ve sorted out the details of how to handle that. I’d feel bad about selling the boards without a manual, so I would like to finish the manual pretty soon. I’m giving some consideration to putting kits together. That may be more work than I can handle though, so I don’t want to make any promises about that until I know I can keep them. I’ll let everybody know when I am ready. I expect it to be some time this month.

I’ve added a few new demos to my soundcloud page.
Danchenka Soundcloud

And here are a few pictures.

Congratulations! It’s amazing to see continued development for the Shruthi-1 in 2016 :slight_smile:

Wow! Great work. I agree, it’s cool to see shruthi projects are still ongoing.

Yeah nice work! I’m definitely interested if you make this available.

Thanks for all the kind words of encouragement.

Yeah, still going in 2016. This was supposed to be done in 2014, but more important stuff got in the way. Still, it was very important to me to get it finished. Anyway, I’m glad to see people are still paying attention. I know a lot of stuff has changed around here since the last time I was here.

This sounds really cool.

@Danchenka Great work, look great! I’m not in the market for another Shruthi-1 filter board at the moment, but I’m really interested to hear how it sound sounds.



Good work. I’m up for one or two.

Great, well done! I am also up for one or two.

Two years’ delay is nothing. I’ve got projects I started five years ago that aren’t even close to being done :slight_smile:

It all sounds great. Good work!

I love it! Too bad I’m such a slow solderer and in progress building the standard dual SVF.

Better too slow than too fast;)
This one has 477 solder pads. A few are optional, so you’d be looking at around 470 solder joints. I finished mine all in one sitting with just a few breaks. I think it took about 8 hours.

Ooh, depending on price I’d be interested in a kit or lone board.

Nice! A board or two for me.

I’d like a board too. Seems I’ll never build my last Shruthi!

Hi everyone. It’s been awhile. The time has really gotten away from me.

I just wanted to let everyone know that I am making my dual diode ring filter boards available for purchase. I have 20 kits, and 30 boards available. I’m also uploading the manual, kicad project, gerber files, and spice files that I used during development. Please feel free to give them a look. I need to figure out a better hosting solution, but for now, I’m just zipping everything up and uploading it here

I think the bar has been set pretty high by all the previous boards in terms of the quality of the manuals, and I set out to write one that would meet the same standards. To be honest, I think it falls a little short, but I did my best. I’m not an engineer, and the manual is not meant to be an academic technical explanation of Sallen-Key Filters. However, if anyone is interested in building a board, it’s definitely worth reading.

I’ve been wanting to share this with others for a long time, so I really hope people enjoy it. I’m really excited to see what people can do with it. I’m also excited to put everything I’ve learned making this to use in other projects. I know I’m a lurker with just a few posts, but I hope anyone who is interested will see all the work I put into the board and won’t be reluctant to get in touch with me and try out the new board.

I’m putting purchase info in the Market forum. I hope that’s ok. Since, this isn’t a Mutable Instruments product, I think that’s technically against the rules. I hope I can get away with bending that rule just a little bit. To me it makes more sense to put purchase info there, where people who are interested can see it, than it does to clutter up this post with irrelevant info.

If there are any questions at all, please feel free to ask me here.

Cool! You could setup a github repository for it. That solves the hosting problem, allows to add the build guide as a wiki article and makes it much easier to find and modify for others.

Thank you for your work, I really like the detailed manual!

Yes, I had given a github repository some consideration and looked into it before I posted this.
It would certainly be an improvement over the current situation. I just haven’t done it yet because it looks like there is a lot of stuff to learn, and only so much time to do it. I’ll see if I can wrap my head around how all that works when I get a little more time.

Started reading this thread, thought “Wow that seems really cool, I should express interest![](” and then got down to the post I made in August. Hah, well I’m still interested)