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 Forum index » DIY Hardware and Software » YuSynth
yusynth surface mount VCO?
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Tue Nov 20, 2012 8:48 pm    Post subject: yusynth surface mount VCO?
Subject description: want to build an all SMT VCO
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I'm currently laying out a PCB for an SMT-based yusynth VCO. My experience is mainly limited to digital stuff, so this is my first real analogue project. I want to make an SMT version of the VCO with the eventual goal of building a DIY polysynth with 2XVCO, VCF and VCA (envelopes and LFOs will be software generated). Huge project, so I just want to start with the VCO and see how its goes.

After reading on Matrixsynth about how Arturia translated Yves' modular prototypes to SMT for mass production for the Minibrute, I was wondering if there are any specific pitfalls/challenges I should worry about? For instance, how crucial is PCB layout to the quality/performance of a VCO?
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Wed Nov 28, 2012 8:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, after doing some research and meeting with an EE who does layouts for MHz+ RF design, my mind has been mostly put at ease. The consensus seems to be that component layout becomes more critical at higher frequencies (starting in the 10s to 100s of Khz), so a VCO operating roughly in the 20Hz-20KHz range shouldn't be too sensitive to non-optimal layout (which, because of my tiny board size, is decidedly non-optimal!). Ditto for keeping external interference to a minimum, which can be held at bay with a sufficient ground plane. In my case, I've got more than 80% ground plane coverage on both top and bottom layers.

This is a gross oversimplification for the experts, but hopefully enough of an understanding so that if my VCO doesn't work, non-optimal layout won't be the first thing I blame...
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Wed Dec 12, 2012 7:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, boards for VCO, VCF and VCA ordered. The VCO and VCF are 5cm x 5cm and the VCA is 2.5 cm x 5 cm - very small, so the parts are crowded. Will hopefully arrive shortly after xmas to give me a holiday soldering project. Fingers crossed!

VCO pcb layout attached. Trimmers and pol caps on bottom side.


vco.png
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LFLab



Joined: Dec 17, 2009
Posts: 191
Location: Rosmalen, Netherlands

PostPosted: Sun Dec 16, 2012 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks pretty good! Nice one.

Are you going to hand solder or reflow?

Part spacing doesn't look too tight, but it is hard to judge without having the thing in front of you. Will need to take care in the order of soldering I suppose.

Keen on hearing how it turns out!
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Wed Jan 16, 2013 11:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Finished hand soldering the smt VCO and tested it. Waveforms look good. Still need to try v/octave tracking. Hopefully all is OK and I'll move on the VCF and VCA!


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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Thu Jan 31, 2013 4:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

VCO and 4072 VCF are done. VCO tracks well from C3 to C8+ but C0 to C2 are out of whack. No amount of tinkering with the tracking trimmer seems to be able to remedy this but I have a couple of things to try still. Eventually I'll use a digital tuning algorithm to correct scaling problems. VCF seems to be working well but I did have the bleed-through problem which was remedied by removing R43 (at the expense of compensation at high resonance). A little demo I wanted to share: https://soundcloud.com/minisystem/yu

So far I'm very pleased with this experiment. Smile

I compared the VCF to the Modcan 4075 VCF clone and to the filter in my black/orange Arp Odyssey. The Yusynth design is so close to the original Arp filter as to be almost indistinguishable to my ears. The Modcan sounds nice, but it is a little different sounding - more precise I think.


Posted Image, might have been reduced in size. Click Image to view fullscreen.

Yves said he doesn't mind if I release the Eagle CAD files for these surface mount versions in case anyone else might find them useful. The advantage is that all the parts can be sourced from one supplier (Digikey) and none are obsolete. Also, the 5cm x 5cm boards only cost $1 each to fabricate ($2 with 100% E-testing). Once I get the VCA tested and working I'll post a link to the Eagle projects.
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roglok



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

PostPosted: Sat Feb 02, 2013 2:48 am    Post subject: Reply with quote  Mark this post and the followings unread

great work, looks awesome!
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yusynth



Joined: Nov 24, 2005
Posts: 1224
Location: France

PostPosted: Sat Feb 02, 2013 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

good work indeed.
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Yves
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gdavis



Joined: Feb 27, 2013
Posts: 155
Location: San Diego

PostPosted: Wed Feb 27, 2013 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just saw this post and just had to sign up and reply because I'm working on a similar project, building a polysynth based on some yusynth modules. I've been prototyping the individual modules etching the pcb's myself straight from the layout on the website and sloppily connecting them together, but just started the layout for a single board that integrates all the modules together.

I'm using SMT IC's but the cost of SMT resistors seemed so much higher than regular resistors I was reluctant to use them. Maybe I should rethink that choice considering the space savings.

I built the yusynth VCA, but thinking of going with a OTA VCA (lm13700 based) instead to save space and component count. Not sure what the drawbacks might be though.

I started a blog for it also http://gndsynth.blogspot.com/

Anyway, looks like you're off to a real nice start, I hope to follow along with your progress.

And a big thank you to Yves for all the great circuits!
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Mon Mar 04, 2013 7:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool project and nice blog! What matched pair did you wind up using in your Yusynth VCO?
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gdavis



Joined: Feb 27, 2013
Posts: 155
Location: San Diego

PostPosted: Mon Mar 04, 2013 11:51 am    Post subject: Reply with quote  Mark this post and the followings unread

minisystem wrote:
Cool project and nice blog! What matched pair did you wind up using in your Yusynth VCO?


Thanks! You know, for the first two VCO's I gave up on matching and just threw in two BC547's. Works fine as far as I can tell dunno

For the SMD version, I'm looking at the FMB2222A. Just a general purpose dual BJT. As far as the matching, I figure it can't be much worse than two random BC547's. In terms of the transistor characteristics, I'm hoping it's close enough, I don't really know much about selecting transistors.

After working on my SMD layout for a few days, I'm amazed at how small and organized yours looks compared to mine. I've only done a few layouts so I'm pretty new to this. So tedious.
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LFLab



Joined: Dec 17, 2009
Posts: 191
Location: Rosmalen, Netherlands

PostPosted: Mon Mar 04, 2013 2:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

There's a matched dual 2n3904 available in SMT, but I don't recall the partnumber. If you can get "european" transistors, BCM847bs is a matched dual NPN and there's even a PNP version (BCM857bs).
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gdavis



Joined: Feb 27, 2013
Posts: 155
Location: San Diego

PostPosted: Mon Mar 04, 2013 5:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
There's a matched dual 2n3904 available in SMT, but I don't recall the partnumber. If you can get "european" transistors, BCM847bs is a matched dual NPN and there's even a PNP version (BCM857bs).


Ya, I just noticed that minisystem had mentioned he was using the BCM847 in another thread. I'll have to think about using one of those. But as well as the two BC547's seemed to work for me I wasn't too worried about getting a dual matched IC, but if I can make these work without much hassle I may as well. The tracking issues he mentioned worry me a little, though I haven't done and accurate measurement like he did, just sounded OK to my ears from a little noodling around. But if I wanted absolute perfection, I'd be building a digital synth Wink

I can find several choices searching dual matched bjt on mouser, but sorting through them all to find out the differences and which is the best choice for me is quite daunting.
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Mon Mar 04, 2013 8:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, if you don't feel like reinventing the wheel, here's a link to my Eagle CAD project: http://minisystem.ca/yusynth_smt_vco.zip

I also have a Digkey BOM, I just have to figure out how to share it.

[edit] Ok, here's a link to a .xls that you should be able to upload to the Digikey site. I've double checked it, but it could use triple checking!
http://minisystem.ca/yusynth_smt_vco_bom.xls
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gdavis



Joined: Feb 27, 2013
Posts: 155
Location: San Diego

PostPosted: Tue Mar 05, 2013 12:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

minisystem wrote:
Well, if you don't feel like reinventing the wheel, here's a link to my Eagle CAD project: http://minisystem.ca/yusynth_smt_vco.zip

I also have a Digkey BOM, I just have to figure out how to share it.

[edit] Ok, here's a link to a .xls that you should be able to upload to the Digikey site. I've double checked it, but it could use triple checking!
http://minisystem.ca/yusynth_smt_vco_bom.xls


Thanks for sharing. Glad to see I picked the same package for the resistors and caps, almost makes me feel like I know what I'm doing...

You mentioned that this is your first real analog (or analogue :p) project but that you have some digital experience. Did you just develop your component selection and layout skills from working on those projects over time? I'm wondering if there's some resources that would help guide my learning or do I just need to keep doing it with help from the friendly forum people?
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Tue Mar 05, 2013 2:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

PCB layout seems like a bit of a black art to me. I find it a slow and agonizing process. For my Yusynth project, I limited the board size to 5 x 5 cm to keep fabrication costs as low as possible. I try to position my components within the board perimeter as best I can, route what I consider important (and I'm often not sure what is) and let the autorouter take care of the rest, after setting appropriate net class properties like trace width, clearance and vias. I then try to have as much of a contiguous ground pour on both top and bottom layers as possible and hope for the best. If the autorouter takes some ridiculously circuitous route for a particular trace then I'll route that by hand or start shifting components until the autorouter generates better results.

I'm under the impression that skilled designers don't rely on the autorouter at all for simple designs. I doubt I'll ever be that good. :/

When it comes to mixing analogue and digital signals I've been referring to this document: http://www.sparkfun.com/datasheets/BreakoutBoards/mixed_signal_design.pdf

Last edited by minisystem on Tue Mar 05, 2013 2:42 pm; edited 1 time in total
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minisystem



Joined: Nov 16, 2012
Posts: 35
Location: Toronto

PostPosted: Tue Mar 05, 2013 2:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Also, I've recently made the switch to Kicad to avoid the size limitations of the freeware version fo EagleCAD. I've laid out the Yusynth VCO schematic in Kicad, but haven't designed a PCB.
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gdavis



Joined: Feb 27, 2013
Posts: 155
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PostPosted: Tue Mar 05, 2013 4:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info. Glad I'm not the only one that finds it slow and agonizing. I was surprised by some of your placement choices (particularly the voltage regulators) which just didn't seem obvious to my naive layout sensibilities but it looks like it worked out.

I rotated the resistors and caps in my layout 90 degrees to match your orientation and it seemed like things started falling together better. Almost down to the same size as yours but I think I'll do things a little differently since I'm planning to integrate VCF, VCA and control switches on the same board and have to be mindful of that routing. I don't want connectors scattered all over Wink

Man, I just switched to DesignSpark for the same reason (size limitations). Maybe I should look at Kicad if that's what more people are using (was just starting to get used to DS though).

I've pretty much given up on the autorouter too, though depending on the design it seems if you guide it well through placement, design rules and manually routing key signals it can work.

You really got the board made for only $1?
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