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 Forum index » DIY Hardware and Software
SH101 VCF QUESTION
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haxster



Joined: Feb 01, 2006
Posts: 244
Location: MONTEREY PARK, CA 91754
G2 patch files: 2

PostPosted: Tue Jun 23, 2009 2:50 am    Post subject: SH101 VCF QUESTION Reply with quote  Mark this post and the followings unread

Would it be possible to use an LM13700 for the Transc. op-amps and some kind of transistor pair for the Exponential function converter? I am trying to breadboard this filter but I am stuck on the converter.

Does any one know a simple Anti log function generator circuit?
I found this(see pic) but I am not sure if this one is the correct one to use here. I think the one in the picture is a Lin/log converter. I think I need a log/lin converter. I am not sure how to do that.


Moog Exponential converter.png
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Moog Exponential converter.png



sh-101_vcf_schematic.jpg
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beep



Joined: May 05, 2013
Posts: 84
Location: Germany

PostPosted: Mon Oct 28, 2013 4:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

P U S H

This man made a great post and I'll need some advice, cause I'm about
to try this circuit.

_________________
Is the future obsolete?
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haxster



Joined: Feb 01, 2006
Posts: 244
Location: MONTEREY PARK, CA 91754
G2 patch files: 2

PostPosted: Mon Oct 28, 2013 5:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here is an update to help you build a roland sh101 type of filter. These guys did the hard part of figuring out what the resistor values are to replace the BA obsolete chip with Discrete components: http://mutable-instruments.net/shruthi1/build/smr4mkII. There is a schematic at there website.
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jackdamery



Joined: Apr 26, 2010
Posts: 72
Location: UK

PostPosted: Mon Nov 04, 2013 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey not sure if you're on the SDIY facebook group. But I have done it and yes, it is totally possible.

I have some real IR3109s and with advice from guys on the SDIY mailing list I figured out the internal resistor values between the gain cells non-inverting inputs and ground as 432 ohms.

I used one LM13700 to make a 12db version of this filter
For the expo converter I used the standard Thomas Henry current source type. The thing I haven't figured out is the buffers between the gain cells. I used a TL072 in my circuit but next im going to try a FET as it's what Roland preffered to use.

Here's a recording.

https://soundcloud.com/dot/ir3109-12db-ota-build
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jackdamery



Joined: Apr 26, 2010
Posts: 72
Location: UK

PostPosted: Mon Nov 04, 2013 6:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Also check out page 22 of this pdf

http://www.synfo.nl/servicemanuals/Roland/JP-4_SERVICE_NOTES.pdf

it shows the filter of the JP4. It was discrete originally and then in later versions they used the ir3109.
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roglok



Joined: Aug 28, 2010
Posts: 159
Location: uptown

PostPosted: Mon Nov 04, 2013 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Rick from Frequency Central created a LM13700 version of the System 100m filter - http://www.frequencycentral.co.uk/wp-content/uploads/2012/05/Roland-121-VCF-Build-Doc.pdf

It's extremely similar to the JP-4 VCF... Sounds and performs great.
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