buchla 295 comb filter / filter bank

Luka · Post by **Luka** » Sat Mar 06, 2010 7:01 pm

Just posting it to see if anyone wants to help verify the layout

It was super stormy yesterday in my home town, huge hail and lightning.
I disconnected my studio in fear of power spikes and entertained myself inside. While my girl was out getting her hair cut i made a pnp layout for the buchla 295 comb filter

i used a serge pcb layout and substituted the opamps for 5532s but i guess TL072s would work. There is also a quad opamp package for the input buffers and output mixer section, based from tl074.

I did this layout as functionally it resembles the serge resonant eq and i planned on making my own serge panel soon in which it would be included

each stage is a 6db filter with trimmable freq, Q and mix level pot. i think 20k trimmers boost the Q so you could bring that out to the panel (untested)
but on the buchla panel there was just a mix level pot and indivual out jacks

i heard it is meant to be a good filter bank with a metalic sound

if you look at the schematic you can see there is a 220ohm resistor before each stage ouput, this needs to be wired off board. the summing line (along with resistors also needs to be mounted off board and then brought back to the mix input)

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schem found here
http://rubidium.dyndns.org/~magnus/synt ... 50_200.jpg

pcb is 2" x 6" and is designed viewing from above

gaslampmusehog · Post by **gaslampmusehog** » Sat Mar 06, 2010 7:58 pm

I can't really help, but that's a very nice looking layout!

DGTom · Post by **DGTom** » Sat Mar 06, 2010 10:14 pm

seeing the seperated views answers a few questions I had from just seeing the combination

Luka · Post by **Luka** » Sat Mar 06, 2010 10:43 pm

haha yeah it was a bit crazy when all combined but it saves so much time designing them like that in illustrator

i just noticed there is a missing link in the component view up the top left

daverj · Post by **daverj** » Sun Mar 07, 2010 12:14 am

You could eliminate a bunch of jumpers by running the traces between the leads of the resistors.

The top part is your current diagram and the lower one is a suggested change.

Luka · Post by **Luka** » Sun Mar 07, 2010 12:47 am

thanks

i might just do that

are links all that bad to signal flow?

Luka · Post by **Luka** » Sun Mar 07, 2010 2:21 am

this is from the storm that hit yesterday, this is a video taken in the middie of melbourne city, pretty wild

[video][/video]

sandyb · Post by **sandyb** » Sun Mar 07, 2010 4:22 am

that is a mad amount of rain Luka!

daverj · Post by **daverj** » Sun Mar 07, 2010 11:33 am

Luka wrote:thanks
i might just do that

are links all that bad to signal flow?

Not really. Just extra "parts" in a sense, and more holes.

You're already running a trace between resistor leads that if you moved it over by one resistor you wouldn't need the jumper. And moving that one over frees up the gap between the original resistor leads to be able to run that other trace, eliminating another jumper.

And then you repeat the same thing a number of times around the board. So those simple changes, repeated a bunch of times, eliminate a lot of jumpers.

Peake · Post by **Peake** » Sun Mar 07, 2010 5:01 pm

I don't/didn't know that there were trimmers in the 295 to adjust the resonance- make sure that they aren't just Fc trimmers.

The 295 is a good FFB but it's not "all that". I'd use on if it came in a system, but can't say that I'd spend much money chasing one down if not.

Good luck on the project, I might add it to my want list if it turns out well!

vladosh · Post by **vladosh** » Wed Oct 16, 2013 12:34 pm

greetings folks ,thanks Luka for sharing the pcb layout ,been thinking this module is not something i'd do on a stripboard , gonna make a board and try to build one ,has anyone verified the layout i was wondering ? i went thru few channels and it seemed all according to the schematic , thanks
vlad

vladosh · Post by **vladosh** » Sat Dec 21, 2013 12:14 pm

I just finished this and plugged it in ..and i can't get the input to the filters , i trimmed it a bit hoping it may do something but i got only oscillation that is harmonic kind of ,each pot acts in ''that'' frequency ..just oscillating instead of filtering, switched a few TL074 and tried LM324 , no change ,gonna wait for monday to buy new TL074 as maybe mine are burned out , any suggestions where and what to look ? is the buchla 295 schematic correct , is the 470K capacitor 470nF ?

wanna get this to work .. hopefully ,anyone ,thanks .

snaper · Post by **snaper** » Sat Aug 22, 2015 1:15 pm

vladosh wrote:I just finished this and plugged it in ..and i can't get the input to the filters , i trimmed it a bit hoping it may do something but i got only oscillation that is harmonic kind of ,each pot acts in ''that'' frequency ..just oscillating instead of filtering, switched a few TL074 and tried LM324 , no change ,gonna wait for monday to buy new TL074 as maybe mine are burned out , any suggestions where and what to look ? is the buchla 295 schematic correct , is the 470K capacitor 470nF ? wanna get this to work .. hopefully ,anyone ,thanks .

Did you fixed it?

marcn · Post by **marcn** » Sat Aug 22, 2015 2:36 pm

I built one of these on breadboard recently sticking to Luka's layout for starters. I think there's a slight mistake around IC 2 (sticking to the original schematic for reference) involving R5 R6 and C4. The connection between R5 and R6 isn't there or at least on the wrong end of that R6 56k, that's at least what I see but I might be wrong.
Mine works fine as in it passes sound and all individual filters are more or less in the ballpark of where they should be. I used NE5532's for it but will try other IC's some time as all my filters on the right side (IC 8-12) have a slightly different sound and behaviour in regards to tweaking their Q's.
Then again there might be mistakes on the schematic and I'm really not too handy with circuits to point em out.
The copy of the circuit isn't exactly high res either and for some reason a lot of 3's seem to look like 9's (f.ex. R69 reads as 330 ohms and R68 as 390ohms but it might be indeed a 330 there too, all the resistors on the outputs that are wired off-board are either 33k or 39k too, I mixed em up and you get different output levels on the individual outs).

fragletrollet · Post by **fragletrollet** » Sun Aug 23, 2015 7:42 am

how does this sound compared to the serge resonant eq? Is it basically the same circuit?

Post by **Paranormal Patroler** » Fri Jan 18, 2019 10:23 am

I would also like to know whether this can be used as a replacement to Serge Resonant EQ. Is this resonant?

MMI Modular · Post by **MMI Modular** » Mon Jan 28, 2019 2:51 pm

For those who are looking for a verified functional Model 295 clone, here you go!

Here is a short sound demo of Rings being processed by a 295 and a couple VCAs:
https://www.soundcloud.com/about_blank_ ... 295-demo-3

Looks like the embedded soundcloud player isn't working for me so here's a direct link if it doesn't work for you.

There's a few more demos on my soundcloud if you are wondering how it sounds in other contexts. If there's something in particular you'd like to hear, let me know.
_____________________________________________________________

Two Nine Five is a direct adaptation of the schematic that is floating around online. The only changes I have made are replacing the obsolete op amps with TL07x series op amps, adding filter caps to the supply rails, and putting some LEDs on it so your eurorack looks a little bit cooler. It rolls in at a cool 14hp. Not small, but not too big either.
_____________________________________________________________

I had 30 of these assembled by a PCB house and so far they have all worked just fine. There's also some DIY ones floating around from other builders that seem to work as well.

If you'd like to build one, PCBs are available on Modular Addict and Pusherman.
____________________________________________________________

For more info and a calibration guide, pay a visit to my Github. I have tried to document this module as best as possible. If there is anything missing let me know and I'll add it!

Hopefully you all are as jazzed about this module as I am. I'll be hovering around to respond to any questions or comments you guys might have.

-little mod edit. Joe.
-little mo edit. sduck

Jarno · Post by **Jarno** » Tue Jan 29, 2019 3:32 am

Looks great!
I might give this a spin myself, would be cool to break out the Q control, and perhaps the frequency as well.

MMI Modular · Post by **MMI Modular** » Tue Jan 29, 2019 9:50 am

Jarno wrote:Looks great!
I might give this a spin myself, would be cool to break out the Q control, and perhaps the frequency as well.

Thanks!
I've noticed when tuning these that the Q control has a LOT of control over the gain where as the frequency control has a relatively small influence on the center frequency. Breaking them out is something I haven't tried, but I have cranked the Q before and it is pretty wild. Lots of clipping but some filters of the filters self oscillate and the filters become very resonant. If you attenuate the input a bunch you might be able to avoid the clipping and get a decent sound out of it.

Jarno · Post by **Jarno** » Tue Jan 29, 2019 11:28 am

Add distortion diodes and call it a feature?

Maybe even the LEDs in the sliders, for extra blinken lights.

av500 · Post by **av500** » Tue Jan 29, 2019 12:59 pm

and VCAs!

MMI Modular · Post by **MMI Modular** » Tue Jan 29, 2019 1:23 pm

av500 wrote:and VCAs!

I'm working on it Vlad gimme a break!

wackelpeter · Post by **wackelpeter** » Sun Jan 10, 2021 5:09 pm

Have build this one some time ago myself on stripboard and it worked and still works... No i'm wondering if there's a good way to tune/calibrate this bank... what i exeperienced is that i can bring certain bands to self oscillation when patching mix out to signal in hook my scope on the individual output and turn the corresponding pot into the mix.
Curiously only one half seems to oscillate. These are all that are on the 200hz to 7khz bands in the schematic, the others won't. My idea to trim them was to push the q and fc so that it self oscillates at exactly that frequency and thus settings it's fc and also have them all in the same amplitude range. Q also affects fc so you have a bit to fiddle. Would this be the best way to set the center frequency?
Do any of your own builds self resonate or is it just a coincidence that mine does?

MUFF WIGGLER

MUFF WIGGLER

buchla 295 comb filter / filter bank

buchla 295 comb filter / filter bank

Re: buchla 295 comb filter / filter bank