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 Forum index » DIY Hardware and Software
Mark Verbos/Buchla 292 LPG adaptation
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Tue Feb 13, 2007 9:02 am    Post subject: Mark Verbos/Buchla 292 LPG adaptation
Subject description: Quad Lo Pass gate on one PCB
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After almost two years, it's working !

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


I was sold 1000pF MKP caps for 1000nF ones !? didn't realise they were too small for this value...

Nasty little red caps...(now some big big big 1000nF orange ones fitted the other side)


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


original here:
http://www.simple-answer.com/DIY.html
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Tue Feb 13, 2007 9:44 am    Post subject: Upgrades ? Reply with quote  Mark this post and the followings unread

As for the 291, I'm wondering if there's any simple improvements to achieve. Very Happy

I've tryied last night to emphasize CV sens. by lowering the input 100K resistor (the one called "may have to be 10K" on Buzzclick's schem)
Maybe with a 91k would be a little more "receptive", while still cutting output when pot is on full CCW.

Or maybe it would be more efficient to play with the "- INPUT" 10K resistor of IC 9 ?

Original schematic

What is the "professional" procedure to trim it ?
I've done calibration by ear with sweet triangle =/-5V LFO...mainly in BOTH and VCA modes ; they sound lovely but who knows ?

And what about Grenader's note ? intentionally using different cap types (or surely "value") which affects the timbral characteristics of each four modules.


Those caps are the one associated with the vactrol (still an RC network, no ?)
So we have 220pf for one and 4n7 for the other.
Is there any simple theory in order to change these values ?
keeping the ratio ?

No use to have four "perfectly tuned" LoPass Gates ?



http://www.buzzclick-music.com/
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mono-poly



Joined: Jul 07, 2004
Posts: 936
Location: Rotterdam, Netherlands
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PostPosted: Tue Feb 13, 2007 10:49 am    Post subject:   Reply with quote  Mark this post and the followings unread

I really like the looks of the module!
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Fernando



Joined: Dec 30, 2006
Posts: 207
Location: Barcelona, Spain

PostPosted: Tue Feb 13, 2007 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey it looks great!
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CJ Miller



Joined: Jan 07, 2007
Posts: 371
Location: 127.0.0.1

PostPosted: Fri Feb 16, 2007 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

How did you handle the switching? I've been looking at Mark's schematic and PCB layout... I'm not very knowledgable and his use of the CMOS switch and that special toggle has me a bit confused.

How is the panel labelling done? It all looks great!
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Funky40



Joined: Sep 24, 2005
Posts: 875
Location: Swiss
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PostPosted: Fri Feb 16, 2007 9:55 am    Post subject: Reply with quote  Mark this post and the followings unread

yeah, looks great.
And i'm also very interested to know how the Panel labeling is done.
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Fri Feb 16, 2007 11:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Funky40 wrote:
yeah, looks great.
And i'm also very interested to know how the Panel labeling is done.


FORGET ABOUT IT !

this is (unfortunably) real shit.
(sticker from "Canson", here in france)

only a temporary solution...

I'm real sorry that nowadays digital camera make the world seems smoother than it is.

[edit]Here is a better coloured attempt with "Filmolux"[/edit]
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CJ Miller



Joined: Jan 07, 2007
Posts: 371
Location: 127.0.0.1

PostPosted: Sat Feb 17, 2007 12:20 am    Post subject: Reply with quote  Mark this post and the followings unread

How about that mode switching? Are you using that particular C&K 7211 switch or doing something else? Looking at the LPG version B it doesn't even use a CMOS switch on the board at all. Mark's appears to based on the C version. Anyway, I keep wondering whether I need to shell out for those 7211 switches - which I can't afford now - or if regular DPDT will work. Some 4.7M resistors are due to arrive this week so I'll try on perf soon anyway.
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funkyfarm



Joined: Jan 21, 2007
Posts: 583
Location: France
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PostPosted: Mon Feb 19, 2007 6:01 am    Post subject: Reply with quote  Mark this post and the followings unread

CJ Miller wrote:
How about that mode switching?



According to MV, I'm using "normal" switch STDP
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funkyfarm



Joined: Jan 21, 2007
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Location: France
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PostPosted: Mon Feb 19, 2007 8:54 am    Post subject: Reply with quote  Mark this post and the followings unread

the four modules seem to draw an important amount of current...On the same PSU rails, my VCO are slightly detuned when changing the GAIN pot position.

As for the KORG PS 3100 RES and Buchla 291, there is no hurt putting in parallel three or six 10KA potentiometers (a small value) between +15 and ground ?

This could help ?

MFOS Control Voltage Distributor

Or maybe a separate PSU ?
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Scott Stites
Janitor
Janitor


Joined: Dec 23, 2005
Posts: 4121
Location: Mount Hope, KS USA
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PostPosted: Mon Feb 19, 2007 1:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

3 10K pots will have a parallel resistance of 3.33K, which will draw 4.5 mA from 15V.

6 10K pots in parallel = 1.67k, which will draw 9 mA from 15V.

I wouldn't cnsider either figure excessive. What is the current rating on the power supply you're using?

Cheers,
Scott
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funkyfarm



Joined: Jan 21, 2007
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PostPosted: Mon Feb 19, 2007 2:17 pm    Post subject:
Subject description: Too hot in here
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Here, the 291 MMF draws 35mA on +15volts and 20mA on -15 volt

while the QUAD 292 is 57mA on +15 volts and 50 mA on negative rail ?!?

Absolutly nothing is hot in here ! Wink


...

PS : formant PSU

[edit] All four LPG owns a separate 22ohm/22uF RC network for both rails... [/edit]
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synth_ollie



Joined: Sep 11, 2006
Posts: 149
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PostPosted: Tue Feb 27, 2007 9:11 am    Post subject: Reply with quote  Mark this post and the followings unread

wouldn´t it be nice with a resonance control
as on the doepfer lpg ? any ideas of how to do it ?
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funkyfarm



Joined: Jan 21, 2007
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PostPosted: Mon May 14, 2007 12:47 pm    Post subject:
Subject description: After few weeks in use, I can say this quad module is way cool !
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After few weeks in use, I can say this quad module is way cool !

I've own about seven VCA but was still feeling I need one or two more ; those particular but quite versatile modules I was the solution.

However, as vactrols are fun as you can do music with gates (?!), attenuator-potentiometers have to be added at cv ins. (voltage divider)

It's way more cool if you can offset a bit the incoming controls.


Fonik's CVP is a good add ; it has glide circuitry as bonus !

http://www.modular.fonik.de/Page15.html

I really wish my panel twice big and lookin like that :

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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vtl5c3



Joined: Sep 08, 2006
Posts: 423
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PostPosted: Mon May 14, 2007 7:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I like the lopass gate a lot too. It doesn't do fast transitions, which is too bad, but the sound makes up for it. It's like switching from a metal and plastic cd player (normal VCA) to a wood and leather victrola. In lopass mode it has a nice brassy effect on the sound.

Idea Idea Idea Idea Idea
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funkyfarm



Joined: Jan 21, 2007
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PostPosted: Mon May 21, 2007 10:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

if you own more than two :

Quote:
And what about Grenader's note ? intentionally using different cap types (or surely "value") which affects the timbral characteristics of each four modules.


yes ! what about ?
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Funky40



Joined: Sep 24, 2005
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PostPosted: Tue May 22, 2007 10:14 am    Post subject:
Subject description: After few weeks in use, I can say this quad module is way cool !
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funkyfarm wrote:
After few weeks in use, I can say this quad module is way cool !

I've own about seven VCA but was still feeling I need one or two more ; those particular but quite versatile modules I was the solution.

However, as vactrols are fun as you can do music with gates (?!), attenuator-potentiometers have to be added at cv ins. (voltage divider)

It's way more cool if you can offset a bit the incoming controls.


Fonik's CVP is a good add ; it has glide circuitry as bonus !

http://www.modular.fonik.de/Page15.html


I really wish my panel twice big and lookin like that :

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


sounds and looks great.
how about a PCB run for this one ?
fonik has also a LPG adaption, but i don't know the difference
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vtl5c3



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PostPosted: Tue May 22, 2007 12:01 pm    Post subject:
Subject description: After few weeks in use, I can say this quad module is way cool !
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Funky40 wrote:


sounds and looks great.
how about a PCB run for this one ?
fonik has also a LPG adaption, but i don't know the difference


My vote is for Fonik's version, which I think was based on Peter Grenader's revision. No analog switch IC required, just one that's mechanical. If I were to build another one, that's the way I would go.

Not sure how doepfer did the feedback mod. If I had money to spend, I would buy one and analyze it.
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verbos



Joined: May 09, 2007
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PostPosted: Wed May 30, 2007 4:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

CJ Miller wrote:
How about that mode switching? Are you using that particular C&K 7211 switch or doing something else? Looking at the LPG version B it doesn't even use a CMOS switch on the board at all. Mark's appears to based on the C version. Anyway, I keep wondering whether I need to shell out for those 7211 switches - which I can't afford now - or if regular DPDT will work. Some 4.7M resistors are due to arrive this week so I'll try on perf soon anyway.


I got into an argument with Peter about this on SDIY a while back. I explained that the gain of the input stage has to be changed between modes to keep the level constant when the switch is flipped. There is a gain stage on the input, that switches in and out 3 dB of gain.

In the B version the op amp is normally in the high gain mode and the switch adds a resistor to ground to bring down the gain of the signal going in. The C version is normally in low gain mode and the switch adds a resistor to ground in the the opamp feedback loop, making the gain go up.

To get constant gain in all three modes, you need the higher gain in the "gate" and "both" modes and the lower gain in the "lopass" mode. You need a 7211 to do that. If a 292B was built with a 7203, the "both" mode would be 3dB lower than the other two modes.

Peter's claim was that Buchla Tech J.L. told him that 292Bs don't use a 7211.

I have since acquired a 292B of my own and have a picture of the C&K 7211 in it. I hope this puts this debate to bed.


Mark


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verbos



Joined: May 09, 2007
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PostPosted: Wed May 30, 2007 5:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

synth_ollie wrote:
wouldn´t it be nice with a resonance control
as on the doepfer lpg ? any ideas of how to do it ?


If you increase the gain going through the .0047 uF feedback capacitor, you will get resonance. In practice, this can be done by adding an opamp gain stage between the ouput opamp and that capacitor. Just intercept the line between the switch and the .0047uF cap. Send the switch side into the + input and put a 50k pot with the wiper to the - input, the CCW end to the ouput and the CW side thru a 50k resistor to ground. Send the output of that opamp through the .0047uF cap.

The funny thing is how this control is useless in 2 out of the three modes. You could do it like Wiard Borg II.... insted of a 3 position switch, just use a pot with a switch at the CCW end. Then you have a lopass filter with resonance until you turn the resonance all the way down and switch in the gate for a "both" mode. You then lose the "gate" mode, but you probably just wanted the filter anyway.

mark
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synth_ollie



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PostPosted: Thu May 31, 2007 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you for this Smile


cheers

OLLIE
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CJ Miller



Joined: Jan 07, 2007
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PostPosted: Sun Jun 03, 2007 12:21 am    Post subject: Reply with quote  Mark this post and the followings unread

verbos wrote:

I got into an argument with Peter about this on SDIY a while back...
I have since acquired a 292B of my own and have a picture of the C&K 7211 in it. I hope this puts this debate to bed.



Hi Mark! I remember reading a thread between you two when I was determined to read all of the LPG stuff in the SDIY archives. No debate with me! My guess is that Peter was just going by what was remembered from the Buchla service schems. The 292B doesn't *say* that it uses the 7211, but as we can all see - this is not to say that it in fact doesn't.

My main concerns are that 1. I still can't afford the switches 2. I feel uncertain how to connect them. I'll figure it out one of these days. I'm still doing flood damage control in my basement from weeks ago. Relatively soon I'll hopefully have finished my PSU/breadboard/testing rig I've been dreaming about for exactly this kind of thing.

Anyway, thank you for showing us! You've got some really wonderful kit to play with.
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Snaper



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PostPosted: Wed Apr 29, 2015 7:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry about renew this old thread, but im still wondering : 3 modes (gate, lopas, both) with a simple spdt switch?
How?
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LFLab



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PostPosted: Thu Apr 30, 2015 3:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Not a simple SPDT switch, but a SPDT with center "off"

CMOS switching is involved.
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Snaper



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PostPosted: Thu Apr 30, 2015 4:35 am    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
Not a simple SPDT switch, but a SPDT with center "off"

CMOS switching is involved.

Aaaaah, yes. Just checked the scmo again Very Happy
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