[sdiy] CEM3340 question -- interpolating scanners (again)

Thu Dec 3 23:19:41 CET 2020

Here you go:

https://drive.google.com/drive/folders/1UXyPdM5WwAVK_nq9IqkdBDsSp8csCiQL?usp=sharing

You'll have to pardon the mess that my print to pdf made of an LTSPICE file, but it is legible. The LTSPICE file is in there, too. 

The idea is to set up a series of thresholds where an input ramp will turn around, and offset each output by the threshold of the previous. I'm rectifying the outputs for clarity, but you may not need to depending on where you fed these voltages. Maybe someone here can see an easy way to save an op amp or 4, I tried today to no avail ¯\_(ツ)_/¯  

Cheers, 
Chris 

> On Dec 3, 2020, at 2:31 PM, dk <dk at telcosystems.net> wrote:
> 
> +1 on the scanner schematic interest, yours also Chris. I was just today starting some simulations based on the different approaches I have come across online.
> 
> All the best
> David
> 
> 
> 
> 
>> On 3 Dec 2020, at 20:49, Chris McDowell <declareupdate at gmail.com <mailto:declareupdate at gmail.com>> wrote:
>> 
>> David, I'd love to see these schematics! I have a design for an "n-channel" scanner that makes evenly spaced peaks, I've read your scanner exploits here over the years and have always been curious how went about it :) 
>> 
>> I'm happy to share mine, too, if anyone wants it. 3 op amps and 8 passives per channel, which feels like a lot, but it is very simple and scales to any reasonable number of channels easily. 
>> 
>> Cheers,
>> Chris 
>> 
>>> On Dec 3, 2020, at 12:19 PM, David G Dixon <dixon at mail.ubc.ca <mailto:dixon at mail.ubc.ca>> wrote:
>>> 
>>> I have both 4-channel and 8-channel interpolating scanners that work perfectly and are not terribly parts-intensive.  You can see YouTube demonstrations of them here:
>>> 
>>> My "simple" 8-channel scanner, is shown here:
>>> 
>>> https://www.youtube.com/watch?v=hZGskck31hs <https://www.youtube.com/watch?v=hZGskck31hs>
>>> 
>>> There is also a slightly less parts intensive 4-channel version.  This module works by controlling a single linear crossfader to process two adjacent channels in a group of 8 (or 4) channels.  The scanning is completely seamless and can be done at audio rates with no glitching.
>>> 
>>> My older 4-channel scanner design with variable width and spacing of the control trapezoids, is shown here:
>>> 
>>> https://www.youtube.com/watch?v=Hf_KCZX1fcQ <https://www.youtube.com/watch?v=Hf_KCZX1fcQ>
>>> 
>>> The beauty of this older design (which I've just redesigned and built again in Euro format for a local synth enthusiast here in Vancouver) is that it can be built just as a trapezoid generator, and used to drive any quad-VCA module (such as the Intellijel Quad VCA, or two Intellijel uVCAs).  This option involves very little circuitry.  I've redesigned this circuit to put not only the fader, but also the trapezoid width, under voltage control, and I use an onboard linear VCA to keep the trapezoids perfectly within the fader field regardless of the width control.  This scanner can be adjusted to go from complete overlap of all channels to significant separation (with dead-space in between) of the channels.  Regardless of the width setting, Channel 1 will come on from the bottom of the fader, and Channel 4 will just disappear at the top of the fader.
>>> 
>>> I will happily share schematics for these circuits, or make PCBs for a very reasonable price (through-hole Doc Sketchy specials -- not terribly small, but a real pleasure to stuff and solder).  For a bit more moolah I will happily stuff and test the boards, and for a bit more, I will install them behind 5U panels.  If you are a Eurorack user, I can do that too, but the modules are pretty deep.  Here's a couple pictures of my eurorack 4-channel variable width scanner buddy (for external VCAs) that I just delivered two days ago:
>>> 
>>> <EuroScan1Small.jpg> <EuroScan2Small.jpg>
>>> The top board (the one you can see) is the trapezoid generator -- four identical circuits generating -0.6V to +5.0V trapezoids at different locations on the main CV ramp to turn on a linear VCA (assuming the VCA is at unity gain when the CV is 5V).  The bottom board (which you can't see) is the CV control board, processing the panel controls and CV inputs to generate the voltages to control the position and width of the trapezoids.  These boards are 2.1" wide and 3.5" long, and they plug into each other.  I made this circuit on two boards to accommodate Eurorack.  I could rearrange the various inputs and outputs so that it would actually plug into the panel PCB in true Eurorack style, but I was in a hurry to get this done.
>>>  
>>> So, if you watch the second video, you will notice that the width control (the red knob) alters the width of the fader field such that the CV must be adjusted to put all the voices in the field symmetrically.  I've solved that problem with my new circuit.  To demonstrate, the following plots show the position and width of the control trapezoids across the entire fader range as a function of the Width voltage (which I called "Range" in the video):
>>>  
>>> <Width 0V.png><Width 2V.png><Width 4V5.png><Width 10V.png>
>>>  
>>> Notice how Channels 1 and 4 just appear and disappear at the bottom and top of the fader range, respectively, no matter the Width voltage.  This involved a bit of algebra.
>>>  
>>> Anyway, back to your previously scheduled programming....
>>> 
>>> 
>>> 
>>> 
>>> 
>>> -----Original Message-----
>>> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org <mailto:synth-diy-bounces at synth-diy.org>] On Behalf Of Joel B
>>> Sent: Thursday, December 03, 2020 1:30 AM
>>> To: Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>>> Subject: [sdiy] CEM3340 question
>>> 
>>> [CAUTION: Non-UBC Email]
>>> 
>>> The Behringer Neutron uses two 3340s but it has a feature that I’m not seeing in the CEM3340 data sheet - voltage controlled wave shape - you can sweep between four different shapes. It’s a little glitchy unless you modulate at a fairly low frequency. Yet when I look at what is available otherwise, especially in Eurorack format using this chip, nothing has that feature.
>>> 
>>> How did Behringer implement that?
>>> 
>>> Joel
>>> 
>>> Sent from my iPhone
>>> 
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>>> http://synth-diy.org/mailman/listinfo/synth-diy <http://synth-diy.org/mailman/listinfo/synth-diy>
>>> Selling or trading? Use marketplace at synth-diy.org <mailto:marketplace at synth-diy.org>
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>>> http://synth-diy.org/mailman/listinfo/synth-diy <http://synth-diy.org/mailman/listinfo/synth-diy>
>>> Selling or trading? Use marketplace at synth-diy.org
>> 
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>> http://synth-diy.org/mailman/listinfo/synth-diy
>> Selling or trading? Use marketplace at synth-diy.org
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20201203/1ee53f50/attachment.htm>