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Scott Stites/Buchla 291 adaptation
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mph



Joined: Aug 25, 2007
Posts: 86
Location: France

PostPosted: Wed May 18, 2011 2:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

brother303 wrote:

Which 082 exactly? The lower one (next to the lp/bp/hp-outs) on the left side on Lucas´ v3-pcb?


Nope, it's the 82 which is on the middle of the left side of the pcb (U4 on the corrected schemo). The one which has three 200K resistors connected to its pin 3 on the pcb. That's the mix input section of the circuit and not the output.

You can compare to the wiring of the other 82 in the LP/BP/HP output section which is correctly connected (U5 on the corrected schematic): pin 3 should be connected to ground.
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brother303



Joined: Nov 02, 2010
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PostPosted: Wed May 18, 2011 4:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

thanks mph,that`s what I needed to know.

thumright

Cheers!

Wink

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Luka



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PostPosted: Fri May 20, 2011 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

fixing the layout now

i didn't use the processor
should i replace it with another mixer / buffer arrangement?
it means if you use 2 or more boards you can run in parallel mode

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Luka



Joined: Jun 29, 2007
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PostPosted: Fri May 20, 2011 3:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

here you go
v4

fixed the mixer section - didn't change anything else

it would be nice to completely redesign this pcb so it doesn't have all the wire links. i tried to maintain mark's filter section and it made it hard to add lots of extra circuitry without wasting space.


291_rev4.pdf
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291 with mods

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 Filename:  291_rev4.pdf
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brother303



Joined: Nov 02, 2010
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PostPosted: Sat May 21, 2011 8:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

thanks for offering this update,cool!

No more bugs and kludges now?

Thank god,I didn´t etch the older version ´til now... Wink

Cheers.

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Peake



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PostPosted: Sat May 21, 2011 11:19 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd love to see a dual version like Verbos' but with the multiple output types, perhaps using a single buffer with switching for the Type. Of course, it's always nice to have independent outputs...
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Luka



Joined: Jun 29, 2007
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PostPosted: Sat May 21, 2011 3:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

brother303 wrote:
Hi,

thanks for offering this update,cool!

No more bugs and kludges now?

Thank god,I didn´t etch the older version ´til now... Wink

Cheers.


cant be sure - i haven't tested it and wont have time until 2013 as i'm about to travel overseas for a few years - my studio is all packed up.

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Peake



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PostPosted: Wed Jun 29, 2011 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Danger! Don't etch this! Am having slight size alterations occur when going from photoshop to pdf, and ICs won't fit correctly. Huge apologies to anyone who might have done so; from now on I'll etch and confirm everything prior to posting. Embarassed

Needing ideas please...

I'm working on revising Mark Verbos' 291 filter dual layout because it's sized for Buchla systems (4" x nearly 6"). I like the idea of a single board, or even stacking two boards for a quad setup on a single width panel.

I've built and enjoyed the Stites/Luka/etc. modified versions of Mark's board, with the buffers for LP and HP, and had wanted that and a mixer either per filter or available in a quad concept for summing, or for merely adding LP and BP for variable notch response in any single filter, then summing, etc.

So, I've added Luka's adaptation of Ken Stone's DC mixer, as well as individual buffers for this particular board size, then went a little nuts and changed the mixer in the first filter to a slightly modified MXR distortion +. It would be nice to have something like a RAT per filter, but that's a 308 opamp, and I've just used the sections of a TL084 instead.

Now, the Distortion + uses a 741 with a 9V battery, and 4.5V into a 1M to the input. The 084 is of course using 15V bipolar rails and has several times the slew rate of the 741, meaning a crisper sound (not necessarily desirable here). I'm asking what proportion is required for the 4.5V section, with the main voltage nearly twice that of the original design. Just double it to 9V and it should be well? I wanted to ask before etching, although I'll likely just have to etch and tweak anyhoo.

Also, I have one unused opamp section in the one filter and wanted to see if anyone had any sweet ideas for it (HF boost/cut, etc.) in the available space. I can see how to further tighten the distortion layout to allow a little more room for that open opamp. "What would you do?"

Very Happy

Thanks to all who have brought this design to this point!! I haven't added a wiring diagram as the core is still unproven. Here is the Distortion +:

http://www.premierguitar.com/Magazine/Issue/2008/Dec/MXR_Distortion_Plus_Mods.aspx


291 Dual 2.pdf
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 Filename:  291 Dual 2.pdf
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numbernone



Joined: Aug 16, 2006
Posts: 477
Location: new york city

PostPosted: Tue Aug 09, 2011 6:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Assembled the third from my original 3 boards of 2007, has it really been so long?? WOW

So this one is again different from the other 2. Probably the most straitforward sounding of them the 3. HOWEVER this guy just wont go to the bottom like the other 2. I tend to the HP output and love to sweep the bass frequencies away and have them come rushing back with a WHOOMP. This one just. almost makes it but not quite. Mind you it will pass low frequencies, it just doenst not emphasize them like the other 2 will. Not really sure where to proceed to try and get some additional bottom.
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xi-boy



Joined: Dec 16, 2008
Posts: 18
Location: germany

PostPosted: Mon Aug 22, 2011 5:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
here you go
v4

fixed the mixer section - didn't change anything else

it would be nice to completely redesign this pcb so it doesn't have all the wire links. i tried to maintain mark's filter section and it made it hard to add lots of extra circuitry without wasting space.


hi

i am a little bit confused about the potiometer values of the current version

its still
r47 100k lin
r7 resonance 5k
r47 fm level 50k lin
r37 initial cent freq 10k lin
r40 center freq 10k lin
r41 initial bandw 10k lin
r44 band mod level 10k lin
?

thanks a lot
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thermionicjunky



Joined: Dec 07, 2006
Posts: 90
Location: san francisco

PostPosted: Tue Aug 23, 2011 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

xi-boy wrote:

hi

i am a little bit confused about the potiometer values of the current version

its still
r47 100k lin
r7 resonance 5k
r47 fm level 50k lin
r37 initial cent freq 10k lin
r40 center freq 10k lin
r41 initial bandw 10k lin
r44 band mod level 10k lin
?

thanks a lot


Those values work for me.
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xi-boy



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PostPosted: Tue Aug 23, 2011 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

great. thanks
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L´Andratté



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PostPosted: Sun Mar 02, 2014 6:25 am    Post subject: Reply with quote  Mark this post and the followings unread

I have just breadboarded the circuit from the Scott Stites schematic and am positivly blown away by the beautiful sounds of it, I´m totally in resonance! cyclops

Now being a analog freak, I have to understand how it works, but altough I thought I had knowledge of the vc filter topologys, I´m kind of clueless with this one, it looks a bit like a heavily modified state variable...

Please is there anyone willing to Idea me?
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Snaper



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PostPosted: Thu Oct 09, 2014 3:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
here you go
v4

fixed the mixer section - didn't change anything else

it would be nice to completely redesign this pcb so it doesn't have all the wire links. i tried to maintain mark's filter section and it made it hard to add lots of extra circuitry without wasting space.

Have somebody wiring diagram for this one?
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fuji



Joined: Mar 08, 2017
Posts: 11
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PostPosted: Thu Jun 28, 2018 3:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! Smile
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Fernando



Joined: Dec 30, 2006
Posts: 256
Location: Barcelona & Emporda, Spain

PostPosted: Thu Jun 28, 2018 3:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! :)


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs

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fuji



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PostPosted: Sat Jun 30, 2018 4:55 am    Post subject: Reply with quote  Mark this post and the followings unread

hi thanks for reply!! Very Happy so whit this basic layout it should work?

Fernando wrote:
fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! Smile


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs



wiring 291.jpg
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Fernando



Joined: Dec 30, 2006
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PostPosted: Sat Jun 30, 2018 11:36 am    Post subject: Reply with quote  Mark this post and the followings unread

fuji wrote:
hi thanks for reply!! :D so whit this basic layout it should work?

Fernando wrote:
fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! :)


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs


You are using Mark Verbos pcb, which reflects Verbos schematic (= Buchla schematic with the dual FET erased and substituted by an op amp twice)
Scott's one is a modern redrawn of Verbos schem, aditionally showing the LP and HP taps and a buffer for each, plus an input mixer. It looks clearer to me.
Compare both schematics.
It is really enriching to look at both schematics plus the Buchla original.

Also check Ebolatone's blog for CV input resistor values, etc: http://ebolatone.blogspot.com/2013/06/j3rks-291-clone-build.html
he is using J3RK pcb, but refered to same circuit/schematic

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Last edited by Fernando on Sat Jun 30, 2018 3:07 pm; edited 17 times in total
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Fernando



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PostPosted: Sat Jun 30, 2018 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

FM-input pot wiring is wrong in your drawing - compare with schematics:
you should exchange conections on the pot (the two not being ground). Center leg (wiper) is what should connect to the circuit and the banana to one side of the pot.
The rest looks good to me (to me : )


BTW, you could implement the 100k trimmer at the main audio input as a 100k panel pot, "in-trim" in your Verbos pcb drawing.
(looking at the Buchla and Verbos schematics; Verbos pcb in your drawing is based on that. Scott schematic has an input mixer, so input is slightly different)
And the 5k "Q" trimmer as a panel pot too ("res" in your Verbos pcb drawing) See below.

This trimmer (5k) is intended to be set this way (as per original Buchla schematic):
"trim for no oscillation at 2kHz with 2kHz signal input and minimum bandwidth"
One could implement it as a panel pot and mark on the panel the point where this setting is right, to have a reference mark for the "originally intended" response.

fuji wrote:
hi thanks for reply!! :D so whit this basic layout it should work?

Fernando wrote:
fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! :)


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs

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Fer

.
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fuji



Joined: Mar 08, 2017
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PostPosted: Sun Jul 01, 2018 3:02 am    Post subject: Reply with quote  Mark this post and the followings unread

yes Fernando I agree everything you said... btw I checked all the schematics and pcbs and made this new layout (last one has few errors)...the only missing part is the optional cv processor section


Fernando wrote:
FM-input pot wiring is wrong in your drawing - compare with schematics:
you should exchange conections on the pot (the two not being ground). Center leg (wiper) is what should connect to the circuit and the banana to one side of the pot.
The rest looks good to me (to me : )


BTW, you could implement the 100k trimmer at the main audio input as a 100k panel pot, "in-trim" in your Verbos pcb drawing.
(looking at the Buchla and Verbos schematics; Verbos pcb in your drawing is based on that. Scott schematic has an input mixer, so input is slightly different)
And the 5k "Q" trimmer as a panel pot too ("res" in your Verbos pcb drawing) See below.

This trimmer (5k) is intended to be set this way (as per original Buchla schematic):
"trim for no oscillation at 2kHz with 2kHz signal input and minimum bandwidth"
One could implement it as a panel pot and mark on the panel the point where this setting is right, to have a reference mark for the "originally intended" response.

fuji wrote:
hi thanks for reply!! Very Happy so whit this basic layout it should work?

Fernando wrote:
fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! Smile


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs



wiring 291_2.jpg
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Fernando



Joined: Dec 30, 2006
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Location: Barcelona & Emporda, Spain

PostPosted: Sun Jul 01, 2018 4:49 am    Post subject: Reply with quote  Mark this post and the followings unread

- I would let alone the FM input, same as the original. It was intended for audio signals (*) to modulate the cf in addition to a CV on the cf CV input, which already has attenuator/inverter and offset controls. Of course you can modulate it with an AC control voltage too or a very low freq audio signal. So I (I : ) would not add anything to this input.
You could tweak the values of C8 and R45 to achieve the response you like for this input.
* (take a look to a Buchla 291 original panel: FM input is a jack, not a banana)

- I preffer the input of this filter as per the original (100k trimmer or 100k pot) So I would not implement (again, I : ) the input mixer as per Scott schematic.
I'd rather build a mixer on the same panel with inverting capability (to be able to have VC resonance using an VCA, among other things) and a bit of gain. Two or three channels that can go from -1.5 to +1.5, it's just a dual op amp, same as a Serge processor/mixer, as in here:
https://www.cgs.synth.net/modules/cgs04_mix.html
but choosing the resistors for 1.5 gain instead of unity (so it will go from -1.5 to +1.5) and using the "processor" inputs (in red), not the normal ones.
Gain of 1.5 is just an idea, it could be just unity; the filter is by itself very hot (it can go to 20Vpp output for 3Vpp input with certain settings/signals)
Again, this mixer/inverter being a separate circuit and leaving the 291 input as per the original.

- I don't understand why you connect the BP out to the input of the filter??? (the red line in your drawing)

- Problems were reported here http://ebolatone.blogspot.com/2013/06/j3rks-291-clone-build.html
when using a dual op amp to implement the two buffers for LP and HP outs.
You better use two single op amps now that you will etch your own pcb.

- You better use 07x instead of 08x


fuji wrote:
yes Fernando I agree everything you said... btw I checked all the schematics and pcbs and made this new layout (last one has few errors)...the only missing part is the optional cv processor section


Fernando wrote:
FM-input pot wiring is wrong in your drawing - compare with schematics:
you should exchange conections on the pot (the two not being ground). Center leg (wiper) is what should connect to the circuit and the banana to one side of the pot.
The rest looks good to me (to me : )


BTW, you could implement the 100k trimmer at the main audio input as a 100k panel pot, "in-trim" in your Verbos pcb drawing.
(looking at the Buchla and Verbos schematics; Verbos pcb in your drawing is based on that. Scott schematic has an input mixer, so input is slightly different)
And the 5k "Q" trimmer as a panel pot too ("res" in your Verbos pcb drawing) See below.

This trimmer (5k) is intended to be set this way (as per original Buchla schematic):
"trim for no oscillation at 2kHz with 2kHz signal input and minimum bandwidth"
One could implement it as a panel pot and mark on the panel the point where this setting is right, to have a reference mark for the "originally intended" response.

fuji wrote:
hi thanks for reply!! :D so whit this basic layout it should work?

Fernando wrote:
fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! :)


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs

_________________
Fer

.

Last edited by Fernando on Sun Jul 01, 2018 10:11 am; edited 5 times in total
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fuji



Joined: Mar 08, 2017
Posts: 11
Location: milan
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PostPosted: Sun Jul 01, 2018 5:29 am    Post subject: Reply with quote  Mark this post and the followings unread

hi Fernando Laughing , the out pin on the top of the pcb is the simply out of the input mixer/buffer (it is not the out of the 291)... so you can connect it or not to the input of 291 (i think i will bypass it using only a 100 trimmer as you said - and bypass also the cv fm in section)..the real bp filtered out is the one on the left

Fernando wrote:
- I would let alone the FM input as it is. It was intended for audio signals to modulate the cf in addition to a CV on the cf CV input, which has attenuator/inverter and offset controls already (take a look to a Buchla 291 original panel: FM input is a jack, not a banana) Of course you can modulate it with an AC control voltage too or a very low freq audio signal. But I (I : ) would not add anything to this input.

- I preffer the input of this filter as per the original (100k trimmer or 100k pot) So I would not implement (again, I : ) the input mixer as per Scott schematic.
I'd rather build a mixer on the same panel with inverting capability (to be able to have VC resonance using an VCA, among other things) and a bit of gain. Two or three channels that can go from -1.5 to +1.5, using a dual op amp, same as a Serge processor/mixer, as in here:
https://www.cgs.synth.net/modules/cgs04_mix.html
but choosing the resistors for 1.5 gain instead of unity (so it will go from -1.5 to +1.5) and using the "processor" inputs (in red), not the normal ones.
Again, this mixer/inverter being a separate circuit and leaving the 291 input as per the original.

- I don't understand why you connect the BP out to the input of the filter??? (the red line in your drawing)

- Someone reported problems (read this thread carefully) using a dual op amp to implement the two buffers for LP and HP outs. You better use two single op amps now that you will etch your own pcb.

- You better use 07x instead of 08x


fuji wrote:
yes Fernando I agree everything you said... btw I checked all the schematics and pcbs and made this new layout (last one has few errors)...the only missing part is the optional cv processor section


Fernando wrote:
FM-input pot wiring is wrong in your drawing - compare with schematics:
you should exchange conections on the pot (the two not being ground). Center leg (wiper) is what should connect to the circuit and the banana to one side of the pot.
The rest looks good to me (to me : )


BTW, you could implement the 100k trimmer at the main audio input as a 100k panel pot, "in-trim" in your Verbos pcb drawing.
(looking at the Buchla and Verbos schematics; Verbos pcb in your drawing is based on that. Scott schematic has an input mixer, so input is slightly different)
And the 5k "Q" trimmer as a panel pot too ("res" in your Verbos pcb drawing) See below.

This trimmer (5k) is intended to be set this way (as per original Buchla schematic):
"trim for no oscillation at 2kHz with 2kHz signal input and minimum bandwidth"
One could implement it as a panel pot and mark on the panel the point where this setting is right, to have a reference mark for the "originally intended" response.

fuji wrote:
hi thanks for reply!! Very Happy so whit this basic layout it should work?

Fernando wrote:
fuji wrote:
Hi anyone can help please ?? Do I should connect bp, lp, and hp to the 3 mix in points?? thanks!! Smile


This filter is a BP one. The main output is the BP.
The LP and HP outputs are tapped from two points of the circuit and each one uses a buffer both to avoid influence on the filter and to adapt the level.

I don't see the mixer you mean.

The only mixer in Scotts schematic is for the input, not the outputs
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Fernando



Joined: Dec 30, 2006
Posts: 256
Location: Barcelona & Emporda, Spain

PostPosted: Sun Jul 01, 2018 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

fuji wrote:
hi Fernando :lol: , the out pin on the top of the pcb is the simply out of the input mixer/buffer (it is not the out of the 291)...


oh ok :D

But if you implement Scott's mixer then you have to build the input as per his schematic. Note it is not the same as the Buchla/Verbos schem.
It has a pull-down 100k resistor and not the 100k trimmer, etc.

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eurocrack



Joined: Nov 28, 2020
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PostPosted: Sat Nov 28, 2020 4:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, sorry for necro-ing this post a bit.
I was wondering if one can get this vcf to ping?
cheers
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