Roland filters clones with LM 13700

[alanwilder81]

hello chaps,

i decided to open a separate thread to discuss the Roland filters cloning.
i've come across some nice 70's schematics, but they all employ the rare OTA 3080.
I also found modern schems from Mutable Instruments that specifies the LM 13700 instead. I have no experience in building either of the above, so i would like to hear from more knowledgeable guys for opinions and experiences. Any help is very welcome

[ringroad]

The FC System X 100m VCF clone uses a couple of LM13700s, might be worth looking at that. Their State 700 System 700 12db filter clone also uses a LM13700.

The Curetronic 121 VCF clone used BA6110 chips, which you might still be able to get hold of. Curetronic don't do the boards any more, but you might be able to work out the schematic from their board pattern:
http://www.bild-schall.com/media/assets/assembly-instructions/Assembly_Instructions_100M_121_VCF_2010.pdf

I used CA3080s in my System 700 703e 24db VCF clone, but since then I got the impression that they've got rarer, dunno if Rochester are running out or something - I'd be tempted to try and fit it with LM13700s to see if it sounds any different.

[alanwilder81]

thanks ringroad,

they say the LM 13700 is right up to 3080's specs,just less noisy.Nowadays,the latter being as rare as the purple unicorn, it's worth experimenting a bit with the 13700.
I am looking for filter schematics, would you have a chance to get me some related to the above projects?
thanks !

[ringroad]

musikding seem to have some CA3080 in stock; is expensive though

http://www.musikding.de/CA3080

I don't have any schematics for the Frequency Central version of the 100m VCF or 700 VCF: just check the Roland service manuals for the originals, or you might be able to buy PCBs for them.

Florian Anwander has some schematics for the System 700 (in the 703A/B/C/D, R33 should be 1K, btw).

[alanwilder81]

thanks ringroad !

So you are a lucky owner of one of those babies. Jeez. Early Human League heaven

[Cfish]

Let's see if I can get this voodoo to work and make a link

Understanding and using OTA opamps. By Ray Marston

http://www.nutsvolts.com/uploads/magazine_downloads/11/April%202003%20Ray%20Marston%20-%20Understanding%20and%20Using%20OTA%20Op-Amps.pdf


If it does, is the best article I have ever seen on OTA opamps. Might help settle a lot of fears about using 13700

Not sure if link will bring up part 1 and part 2 . Part one is 3080 part 2 is 13700. If you leave out the diode input pin and don't use the output buffer, they are the same thing

[Cfish]

Here is a link to part 2

http://www.nutsvolts.com/uploads/magazine_downloads/11/May%202003%20Ray%20Marston%20-%20Understanding%20And%20Using%20OTA%20OP-Amps.pdf


I actually have this printed out and laminated as part of my home made quick reference guid. I don't understand all of it. But the more I work with it the more I understand

[alanwilder81]

hey Cfish

thanks a lot for that material. I'd already had a look at this wonderful work some time ago.A bit forgotten though as i never bought the LM 13700 to work with.
I agree,it's an excellent piece of science that sheds some light on the OTA s we all know and love, and unravels some myth around them !

[alanwilder81]

anyway,we havent spoken for a while. How are you doing with your synth ?

[Cfish]

I'm making progress. In my second rack I'm trying to get a firmer grasp on the cd4xxx series of cmos ic's. Experimenting a lot with dividers. Playing with 4046 VCO

Things like the CGS01 sub octave

I really recommend at least a basic divider for your synth.

In easy to build, bang for your buck, add huge depth to a single VCO sound.
You can't beat a simple 2 octave divider.

I have the Roland filter clone that lead to this thread on my to do list. However there are a lot of things in front of it.

Have a half done divider, 4 channel sequencer, and a 6 Chanel mixer I need to finish. Got to build 2 ADSRs 2 VCAs for my current rack of modules

[alanwilder81]

Cfish,

nice to hear about your progresses !

[StephenGiles]

https://www.dropbox.com/s/mfkb8roi281s2ty/Spacedrum%2013600.png?dl=0

Here is an adaptation of the Electroharmonix Space Drum from CA3094 to LM13600, with a very clever peak follower/AR generator!

https://www.dropbox.com/s/mfkb8roi281s2ty/Spacedrum%2013600.png?dl=0

[wackelpeter]

Did the System 100 VCF with LM13700 and also posted a stripboard layout for that somewhere in this forum...

Mostly all design for the Roland filters are the same basic topology some OTA (also a few different types) different buffers then... but basically they look very close...

There's also a site with a summary of most VCF's Roland ever made with schematics... don't have the link right here but it shouldn't be hard to find.

[alanwilder81]

thanks wackelpeter

i kind of guess the schematics collection you mean.Trouble is,they employ rare and obsolete components,and what s worse,some of those diagrams are hard to decipher, at least to me

[alanwilder81]

so i'd like to find modern Roland VCF reissue schematics easy to understand. like the thousands minimoog or ms20 filters,to name a few,that have been faithfully recreated with readily available components, and the schematics are foolproof sadly, there's no lots of Roland VCF material around.

[Cynosure]

I don't have my schematic ready yet, but here is one that I referenced a lot: http://www.sinneb.net/?cat=9

And here is the complete list of Roland filters that was mentioned: http://fa.utfs.org/diy/roland_filters/

[Cfish]

I have been studying the Roland OTA filter schematics a lot lately. They intrigue me a lot.

Beyond the basics of filters, I don't know much. I have played with the single pole low pass and butterworth low pass in the LM13700 application sheet.

Can anyone point out some good basic reading on multi pole filter designs like these?

Schematics look pretty similar to a 4 pole phase shifter.

[alanwilder81]

thanks Cynosure,very much appreciated !
is the Juno 60 schematics related to the project you mentioned you've been working on? It's in fact 4 OTA s in a row,but i cant see the feedback loop,nor the cutoff and resonance pots. is the schematic sorta incomplete?
cheers!

[alanwilder81]

hello Cfish,



here's the link to this wonderful Mutable Instrument 4-pole OTA LPF .
It absolutely nails the Roland sound were after.

http://mutable-instruments.net/static/schematics/Shruthi-Analog-SMR4-mkII-v01.pdf

and here, the topology and the circuit analysis.Lots of math and obscure formulas
http://mutable-instruments.net/static/documentation/smr4mkII_analysis.pdf

the 4 OTA in a row are said to impart that classic Roland sound

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[Cfish]

This is an EFM version of an oberhime filter, not Roland but it has that sound.

It's only 2 pole but it sounds really nice

[alanwilder81]

hello Cfish,
thanks for the suggestion.

I believe that there are many excellent schematics to implement within that website. I also built a fantastic MS 20 filter replica that sounds spot on to my ears.Sure it's a 12 db oct, but nevertheless very gritty and aggressive

[ringroad]

Just for you, alanwilder81, (but tbh also for my curiosity too) I whipped the CA3080s out of my Roland filter clone and wired it up to three LM13700s in a breadboard, as the below terrible photo indicates.

It works, there's a rather out-of-tune demo attached to this, with attendant huge clicks from my noisy System 100 keyboard when I transpose. Haven't quite got the scaling right on the clone oscillator yet. You get the idea, anyway.

Assuming I've wired it up correctly, I'm still not sure if it sounds quite as good as the 3080 version. Hard to tell cos my other demo is straight out of the 703e clone rather than going back into the System 100.

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[Cfish]

Nice experiment ringroad.

[Cynosure]

[alanwilder81]

hey ringroad. nice beast there ! any chanche to provide me with the schematics ?cheers