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Buchla VCO
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Luka



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

PostPosted: Sun Feb 08, 2009 12:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

i believe mark's new 258 is not the design posted on his website
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Sun Feb 08, 2009 4:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
i believe mark's new 258 is not the design posted on his website


Oh yes, because of this ?

http://www.simple-answer.com/DIY.html

Quote:
I made an evil crossbreed of the 258 and the Electronotes Option 2 VCO. Unfortunately that means a PNP based exponential converter.



Buchla Tech talks about 258v...

http://buchlatech.blogspot.com/2009/02/gentlemen-i-give-you-258v.html
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TekniK



Joined: Aug 10, 2008
Posts: 1062

PostPosted: Sun Feb 08, 2009 4:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

'verbos & associates'

!!

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ericcoleridge



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

PostPosted: Mon Feb 16, 2009 4:10 am    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:
I built mark's version.
at the time, it was the biggest p'n'p board i had tried and it took 3 goes before i got a working VCO. I still have the 2 stillborn PCBs in a box somewhere.
My plan had been to build two, a square and a saw version, as you can see on the panel. but, in the end there was just one.

That being said, this VCO is well worth having. its character is very different from anything else i have tried


Andrew, Topp, or anyone,

After a long while, I'm coming back around to the idea of trying out this Verbos 258 PCB.

But, looking at the Schematic and PCB, I don't perfectly understand how one implements the Saw VCO Vs. Square VCO option. Can anyone help me here?

It looks like you would insert either saw or sqaure into the PCB's "variable in" pad. But there are at least 3 square wave versions pointed out on the schematic, and no saw wave (just what looks to be a triangle). Is one of these the point(s) where you extract your initial waveforms? Am I on the right track here?

Any guidance will be much appreciated.
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Mon Feb 16, 2009 4:43 am    Post subject: Reply with quote  Mark this post and the followings unread

funkyfarm wrote:
Luka wrote:
i believe mark's new 258 is not the design posted on his website


Oh yes, because of this ?

http://www.simple-answer.com/DIY.html

Quote:
I made an evil crossbreed of the 258 and the Electronotes Option 2 VCO. Unfortunately that means a PNP based exponential converter.


I thinnk it is a new design; he says this on his blog:
Quote:
Although I did a couple 258 clones a few years back using a CA3080 instead of the discrete transistors in the core, I found the triangle symmetry to be imperfect and the whole exponential converter had to be changed to use a PNP pair, hence this module will be true to the original design using discrete transistors.


I hope he publishes the layout for his new PCB...
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forbin



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

PostPosted: Mon Feb 16, 2009 6:07 am    Post subject: Reply with quote  Mark this post and the followings unread

I have built the Verbos version of the 258 VCO and had a reasonable amount of success. You are correct about the two variants of the output stages. The schematics have a variant block at the bottom for which resistor values need to be fitted for each of the two modes, square or sawtooth. Mark's design updates the original design of Don's, by using an integrated OTA instead of the discrete version. I personally thought that it was well conceived, as the part of the design, that I think is unique, is the waveshaper, which is as per the original. I had a fair bit of grief getting it to work well as i found that it is VERY sensitive to the transistor & FET types. Based upon that, I was pleased that I didn't have to build it as a completely discrete module! I did quite comprehensive SPICE modeling of the design and it is quite a unique design, especially the sine shaper!
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andrewF



Joined: Dec 29, 2006
Posts: 1174
Location: australia
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PostPosted: Mon Feb 16, 2009 6:51 am    Post subject: Reply with quote  Mark this post and the followings unread

ericcoleridge wrote:



It looks like you would insert either saw or sqaure into the PCB's "variable in" pad. But there are at least 3 square wave versions pointed out on the schematic, and no saw wave (just what looks to be a triangle). Is one of these the point(s) where you extract your initial waveforms? Am I on the right track here?



i think the square/tri waves drawn on the schematic indicate what you should expect to see on a scope. Maybe just to help you set it up once it has passed the smoke test.
In the bottom right corner of the schematic there is a list of resistors to leave out, change or install for whichever version you desire. This is all you need to do to set up for each version.
..with a multi-pole switch and a bit of planning you may even be able to have both versions and switch back'n'forth....maybe just getting it working 1st Smile

fwiw - i used the same old generic japanese transistors that I have used on nearly every synth module I have built - C1815 and A1015, a A798 for the dual. The fet was probably a K30.
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Mon Feb 16, 2009 10:22 am    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:


I thinnk it is a new design

Quote:
Although I did a couple 258 clones a few years back using a CA3080 instead of the discrete transistors in the core, I found the triangle symmetry to be imperfect and the whole exponential converter had to be changed to use a PNP pair, hence this module will be true to the original design using discrete transistors.


You're right !
I've missed that...

I wait and see... Very Happy
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ericcoleridge



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

PostPosted: Mon Feb 16, 2009 5:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:

In the bottom right corner of the schematic there is a list of resistors to leave out, change or install for whichever version you desire. This is all you need to do to set up for each version.


Ah! As ususal, I'm not looking close enough! So then, the little infinity symbols in the Saw Vs. Square table mean that this resistor is left out, yeah?

But, what then is the "Variable In" Pad for? I already see pads for the Waveshape Manual, and Waveshape CV. Perhaps this is an external input to the Waveshaper?

andrewF wrote:

fwiw - i used the same old generic japanese transistors that I have used on nearly every synth module I have built - C1815 and A1015, a A798 for the dual. The fet was probably a K30.


Ok, cool I have C1815s and A798s.

The PCB obviously needs to be reversed before etched, and then the Parts Placement PDF is shown from the bottom view. But then, if you can recall, the dual transistor you used had the correct pinout as represented?

Thanks a bunch!
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andrewF



Joined: Dec 29, 2006
Posts: 1174
Location: australia
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PostPosted: Mon Feb 16, 2009 5:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

ericcoleridge wrote:

Ah! As ususal, I'm not looking close enough! So then, the little infinity symbols in the Saw Vs. Square table mean that this resistor is left out, yeah?

yes

ericcoleridge wrote:

But, what then is the "Variable In" Pad for? I already see pads for the Waveshape Manual, and Waveshape CV. Perhaps this is an external input to the Waveshaper?

this is labelled on the schematic as 'control in' (top left). Two are shown on the schematic but only one is implemented on the PCB
ericcoleridge wrote:

The PCB obviously needs to be reversed before etched, and then the Parts Placement PDF is shown from the bottom view. But then, if you can recall, the dual transistor you used had the correct pinout as represented?

from memory the A798s pins had to endure some artful bending, nothing too difficult.
i guess you know - but remember the Japanese trannies have a different pinout - ecb rather than the usual ebc.
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ericcoleridge



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

PostPosted: Mon Feb 16, 2009 6:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:

this is labelled on the schematic as 'control in' (top left). Two are shown on the schematic but only one is implemented on the PCB


Yes, I thought it was strange that it connected to the freq CV inputs, but then he calls it "variable in", so wasn't sure. Thank you for clarifying this for me.

andrewF wrote:

from memory the A798s pins had to endure some artful bending, nothing too difficult.
i guess you know - but remember the Japanese trannies have a different pinout - ecb rather than the usual ebc.


OK, great. Think I've got it now. I'll be very careful with the trannie placement. Thanks for all your assistance!
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Wed Feb 18, 2009 1:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

funkyfarm wrote:
LetterBeacon wrote:


I thinnk it is a new design

Quote:
Although I did a couple 258 clones a few years back using a CA3080 instead of the discrete transistors in the core, I found the triangle symmetry to be imperfect and the whole exponential converter had to be changed to use a PNP pair, hence this module will be true to the original design using discrete transistors.


You're right !
I've missed that...

I wait and see... Very Happy


Just had a message from Mark and he said the new discrete design is custom work for Buchla users.

He did say that he's had success replacing the expensive UA726 with a Linear Systems LS311 and a tempco. So maybe some clever soul can design a clone using that?
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ericcoleridge



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

PostPosted: Thu Feb 19, 2009 1:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Other's here have reported good results from the PCB already posted. I'm definitely gonna give it a try.

Besides the fact that Verbos has stated he will not offer PCBs or PCB designs of his new 258V for DIY, his new design is made for funky Buchla 1.2V/per octave. I for one would rather have the volt/octave response of his original, posted, PCB design.
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Thu Feb 19, 2009 2:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Absolutely, I'm also going to attempt the old PCB too (although I have quite a few modules to build before it), I was just posting the information for the people who didn't like the CA3080 version.
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cbm



Joined: Oct 25, 2005
Posts: 381
Location: San Francisco

PostPosted: Thu Feb 19, 2009 2:52 am    Post subject: Reply with quote  Mark this post and the followings unread

ericcoleridge wrote:
...his new design is made for funky Buchla 1.2V/per octave. I for one would rather have the volt/octave response of his original, posted, PCB design.


Don't you mean that his new design is for the supremely funky 100mV per semitone standard instead of the "popular" 83.333 mV per semitone? Smile

- C

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ericcoleridge



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

PostPosted: Thu Feb 19, 2009 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
Absolutely, I'm also going to attempt the old PCB too (although I have quite a few modules to build before it), I was just posting the information for the people who didn't like the CA3080 version.


Oh, yes. I see. sorry Smile

CBM wrote:

Don't you mean that his new design is for the supremely funky 100mV per semitone standard instead of the "popular" 83.333 mV per semitone? Smile Smile


yes, exactly Laughing
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ericcoleridge



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

PostPosted: Thu Feb 19, 2009 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is there an easy way to reverse this PCB image PDF using acrobat or other common/free imaging software? I don't have Photoshop.

I tried scanning a print-out-- to get it in non-PDF form, but I had a lot of trouble preserving the exact size of the image. My imaging tools here are quite rudimentary.

If someone wouldn't mind sending me a mirrored image pdf or other file type, I'd be very happy to accept it. Very Happy
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TekniK



Joined: Aug 10, 2008
Posts: 1062

PostPosted: Thu Feb 19, 2009 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

knobs..


258pctracersmirror.rar
 Description:

Download
 Filename:  258pctracersmirror.rar
 Filesize:  293.74 KB
 Downloaded:  296 Time(s)

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ericcoleridge



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

PostPosted: Thu Feb 19, 2009 3:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

TekniK wrote:
knobs..


Thanks. What sort of file is this?
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
Location: London, UK

PostPosted: Thu Feb 19, 2009 3:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's a Winrar file. I can post the enclosed jpg for you...


258pctracersmirror.jpg
 Description:
 Filesize:  488.27 KB
 Viewed:  242 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

258pctracersmirror.jpg


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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
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PostPosted: Thu Feb 19, 2009 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here's a pdf version of it reversed...


258Reversed.pdf
 Description:

Download
 Filename:  258Reversed.pdf
 Filesize:  161.15 KB
 Downloaded:  243 Time(s)

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ericcoleridge



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

PostPosted: Thu Feb 19, 2009 7:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool, thanks very much for these!
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andrewF



Joined: Dec 29, 2006
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PostPosted: Thu Feb 19, 2009 10:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
It's a Winrar file.


i am finding a lot of rar files these days. good to have rarzilla (free) to open them.
http://www.philipp-winterberg.de/software/rarzilla_free_unrar.php
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forbin



Joined: Jan 29, 2009
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Location: Fremantle, Australia

PostPosted: Sun Feb 22, 2009 10:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

I was looking at my board the other day and there is a small mistake in the PCB that you might want to fix up before you etch. There should be a link between the junction of R40 & R34 and the 68K resistor. It is easy enough to link across if you have made the board.

The choice of FET's is pretty important to get this going 100% -- I am currently using 2N5458's and the shapes are OK but the levels are a bit low. The 2N3819 that is specified for the original has an NTE equivalent of a NTE133. I had little luck with this though...
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LetterBeacon



Joined: Mar 18, 2008
Posts: 454
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PostPosted: Wed Feb 25, 2009 10:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Just noticed something: On the PCB layout, the resistor between the v/ octave trimmer and ground looks like it's 100K, whereas on the schematic it's 390R, unless I'm reading it entirely wrong...
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