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 Forum index » DIY Hardware and Software
Buchla VCO
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Tasmanian Alkaloid



Joined: Jun 29, 2008
Posts: 116
Location: Isle De Mort

PostPosted: Mon Mar 16, 2009 2:02 am    Post subject: Reply with quote  Mark this post and the followings unread

What value pots did you guys use for this? I find the schematic a bit cryptic, but maybe i'm not reading it right.
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akrearke



Joined: Sep 08, 2008
Posts: 48
Location: US

PostPosted: Tue Mar 31, 2009 11:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just finished two boards. one for saw, one for square. I'm using these as development boards for further study of the wave shaping circuit. the pin placement for the ssm2220 is incorrect. there are good expo circuits out there for sure... the potentiometer values are on the original (buchla brand) schematic.
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Wed Apr 01, 2009 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

akrearke wrote:
Just finished two boards. one for saw, one for square. I'm using these as development boards for further study of the wave shaping circuit. the pin placement for the ssm2220 is incorrect. there are good expo circuits out there for sure... the potentiometer values are on the original (buchla brand) schematic.


Great news! I'm gonna be building a few of these myself soon; Could you post some pictures of your build?
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akrearke



Joined: Sep 08, 2008
Posts: 48
Location: US

PostPosted: Wed Apr 01, 2009 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Still waiting to post pics of the TKB stuff, don't own a digi-cam. will try soon to post pictures
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forbin



Joined: Jan 29, 2009
Posts: 117
Location: Fremantle, Australia

PostPosted: Thu Jun 04, 2009 9:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well it's been a bit of a saga, which now I'm at the end of it all seems a bit unnecessary. I was probably thrown a bit by some of my SPICE modelling which took me off at a tangent. Anyway sourced some 2N4339's -- as recommended by Don -- and it now flies!

Thanks again to Mark Verbos for the layout!

For photos and comparison see my blog: http://forbinthesynthesizer.blogspot.com/
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Thu Jun 04, 2009 10:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

forbin wrote:
Anyway sourced some 2N4339's -- as recommended by Don -- and it now flies!


Had you tried the 3819 first--with less success? Just curious. As usual, inspiring, informative website; Anxious to see how your SOU Romeo-Board 4 comes out!
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forbin



Joined: Jan 29, 2009
Posts: 117
Location: Fremantle, Australia

PostPosted: Thu Jun 04, 2009 10:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

The 3819 problem was that the behavior of the sine generator "flips over" for want of some real understanding of what is going on. Some "interesting" bias issues i think. This results in quite a nice sinewave shape but at a greatly reduced amplitude. I became more preoccupied with the shape and less so with the amplitude. When you come to mixing in the flat topped sawtooth it produced rubbish really.

SoU board #1 (my 3rd board) is running very well and i am now embarking on the last one -- waiting from some LF398's -- I am also working on a board 5 which is an AVR digital/analog noise source and a Grey filter
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Thu Jun 04, 2009 10:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

forbin wrote:
The 3819 problem was that the behavior of the sine generator "flips over" for want of some real understanding of what is going on.


Good to know, thanks. Is there a reliable source for the 2N4339 that you can mention?

forbin wrote:

i am now embarking on the last one -- waiting from some LF398's


I believe this is the one I'm particularly interested to hear about, board#4. Mostly because I wasn't able to get mine working!
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forbin



Joined: Jan 29, 2009
Posts: 117
Location: Fremantle, Australia

PostPosted: Fri Jun 05, 2009 1:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I bought mine from Farnell, in the US they are Newark I think. They were fairly expensive though... but since it was only two parts and it was for my sanity! I did find a document that said that the J201 is exactly the same just a plastic package instead of a metal one. They were cheaper but not available Sad

I must admit to having a number of S&H and was tempted to not bother with #4 of SoU but for completeness why not...
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Luka



Joined: Jun 29, 2007
Posts: 1002
Location: Melb.

PostPosted: Fri Jun 05, 2009 3:49 am    Post subject: Reply with quote  Mark this post and the followings unread

thats good info i have some j201s
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Fri Jun 05, 2009 12:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

forbin wrote:
I bought mine from Farnell, in the US they are Newark I think.


Thanks, I´ll take a look for them.

There is a 2N4339-ES available from Mouser also, if anyone else is looking.

forbin wrote:

I must admit to having a number of S&H and was tempted to not bother with #4 of SoU but for completeness why not...


Understandable, but there´s also the VC Lag and switching pulse outputs. Seems pretty neat to me. I wish I could get back to work on mine; am very far away from projects presently. Crying or Very sad
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Sat Jun 06, 2009 10:28 am    Post subject: Reply with quote  Mark this post and the followings unread

I've made a fpd for this module that I think is getting pretty close to the original panel. I thought I'd share it here. I actually have a scan of an original 258 front panel that I used to compare to this re-creation-- but obviously it's not an exact replica. Note, there are no holes for PCB stand-offs, as I haven't figured out where to put them yet. Anyway, it's still in progress.


258 Dual VCO.fpd
 Description:

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 Filename:  258 Dual VCO.fpd
 Filesize:  2.47 KB
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Peake



Joined: Jun 29, 2007
Posts: 1109
Location: Loss Angeles
Audio files: 3

PostPosted: Mon Jun 08, 2009 2:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://www.flickr.com/photos/11165691@N03/1459599639/
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"IC 741. Sometimes you don't want fidelity." -Small Bear Electronics Catalog
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Mon Jun 08, 2009 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake:

Have you made progress with your 258b clone? I was reading about it with much interest for long while.

Last edited by ericcoleridge on Mon Sep 07, 2009 2:45 am; edited 2 times in total
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TekniK



Joined: Aug 10, 2008
Posts: 1062

PostPosted: Tue Jun 09, 2009 2:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
http://www.flickr.com/photos/11165691@N03/1459599639/


thumb up thanks!
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Peake



Joined: Jun 29, 2007
Posts: 1109
Location: Loss Angeles
Audio files: 3

PostPosted: Fri Jun 12, 2009 3:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

ericcoleridge wrote:
Have you made progress with your 258b clone? I was reading about it with much interest for long while.


All it requires is a bit of time and effort (currently not possible). Remember, Don did not give me permission to publish the PCB artwork.

I have a Moog 901a/b direct PCB trace copy artwork ready to post, excepting wiring diagrams and the technical work required to select the critical transistors; however, like the Buchla, it's in storage and not easily avaialble! Shrug..

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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Mon Sep 07, 2009 2:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Tasmanian Alkaloid wrote:
What value pots did you guys use for this? I find the schematic a bit cryptic, but maybe i'm not reading it right.


Based on the two online schematics (for the 258, and 258c), I've found the following pot values:

CV +/- : 10k
FM Input: 50k Audio
Waveshape Control: 10k
Frequency Control: 10k

However, I noticed that there are only pads for 4 pots on the Verbos layout, but 5 pots on the original module. Does anyone know what the other pot does? It's between 'FM' and 'Waveshape' and it's a +/- input. I thought at first it could be a +/- index for the FM? But looking at the schematic (top left hand corner), it seems to be a second +/- CV input. Am I looking at this right?


258-large.jpg
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258-large.jpg



Buchla_258c schematic.jpg
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Buchla_258c schematic.jpg


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Luka



Joined: Jun 29, 2007
Posts: 1002
Location: Melb.

PostPosted: Mon Sep 07, 2009 3:57 am    Post subject: Reply with quote  Mark this post and the followings unread

perhaps

fm w/ attenuation
fm w/ processor
waveshape cv w/offset
waveshape cv w/ processor
frequency

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zthee



Joined: Feb 20, 2008
Posts: 413
Location: Stockholm

PostPosted: Mon Sep 07, 2009 5:11 am    Post subject: Reply with quote  Mark this post and the followings unread

I think you're right, it looks like a second CV in.

So it's:
Exp CV in
FM in
Exp CV in
Waveshape in

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Tasmanian Alkaloid



Joined: Jun 29, 2008
Posts: 116
Location: Isle De Mort

PostPosted: Mon Sep 07, 2009 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

ericcoleridge wrote:
Tasmanian Alkaloid wrote:
What value pots did you guys use for this? I find the schematic a bit cryptic, but maybe i'm not reading it right.


Based on the two online schematics (for the 258, and 258c), I've found the following pot values:

CV +/- : 10k
FM Input: 50k Audio
Waveshape Control: 10k
Frequency Control: 10k


Thanks Smile
I also spoke to forbin, & he told me he used 100k Linear pots for all of them, & that they worked ok. I still haven't gotten round to building mine yet, but i have the parts now...just gotta focus & get it done
Smile
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mono-poly



Joined: Jul 07, 2004
Posts: 935
Location: Rotterdam, Netherlands
Audio files: 2

PostPosted: Mon Sep 07, 2009 3:54 pm    Post subject:   Reply with quote  Mark this post and the followings unread

zthee wrote:
I think you're right, it looks like a second CV in.

So it's:
Exp CV in
FM in
Exp CV in
Waveshape in


Bingo!
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Mon Sep 07, 2009 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Does anyone have any close-up photos of a populated Verbos 258 PCB? I'm specifically interested in the 4339 orientation on the PCB. It's difficult for me to understand exactly what the pin-out of the 4339 looks like just based on the datasheet.

Also, it would be helpful to see the 3565 orientation, as well as the trimpot orientations. This is a partial photo from the Forbin Synth website that allows one to see the SSM2220, but most everything else is cut off.


DSC_3282.JPG
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DSC_3282.JPG


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zthee



Joined: Feb 20, 2008
Posts: 413
Location: Stockholm

PostPosted: Mon Sep 07, 2009 11:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
http://www.flickr.com/photos/11165691@N03/1459599639/


Is that a real panel, or you made it yourself? Smile

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forbin



Joined: Jan 29, 2009
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Location: Fremantle, Australia

PostPosted: Mon Sep 07, 2009 11:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

To try and help I have put some more pictures on my Blog site... The whole VCO project has started to grow a second head -- since i am not really that interested in creating a perfect clone I have made a second wave shaper that is fed from the same control voltage and I have also picked out the triangle signal. My panel no has fine/coarse frequency, two frequency modulations (linear and log) with CV amounts, and the waveshape control with a CV amount (+ and -) and an offset and the three outputs, triangle, saw and square. I have made a small PCB that buffers the three outputs and also has a summer and gain and offset control for the waveshaper. Currently waiting for more cliff sockets to finish the panel!

Blog: http://forbinthesynthesizer.blogspot.com/
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ericcoleridge



Joined: Jan 16, 2007
Posts: 885
Location: NYC

PostPosted: Tue Sep 08, 2009 12:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Forbin,

Thank you for the photo!

Did you have to bend your 4339 leads to get it into this footprint? My 4339s are definitely in a different orientation. Mine are more like the ones on the second PCB in your picture, although I had to bend the 'G' lead a bit underneath...

On the datasheet I have, the 'D' seems to be to the left of 'S'. But in your photo, 'D' is on the right of 'S' (?).

I'm very confused.

What transistors did you use for the NPNs? They look like 3904s? I have 3565s, but again, I'm not 100% sure about the orientation.


4339.pdf
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 Filename:  4339.pdf
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Last edited by ericcoleridge on Tue Sep 08, 2009 3:00 am; edited 1 time in total
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