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Pseudo .5 291 Bandpass Filter Board
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Author Pseudo .5 291 Bandpass Filter Board
J3RK
Super Deluxe Wiggler


Joined: 22 Dec 2009
Last Visit: 01 Oct 2014

Posts: 3674
Location: Seattle

PostPosted: Thu Sep 29, 2011 11:41 am    Post subject: Pseudo .5 291 Bandpass Filter Board Reply with quote Add User to Ignore List

Hello,

Just thought I'd move discussion of this to a new thread. I've got a board around 75% laid out now. (first pass, so there will need to be some optimization, fixes, and I'm planning some additions/mod-space) I plan to order prototypes within the next couple of weeks.

Basically it's a single 291 bandpass filter. I'm looking into tapping/mixing other responses now too.

I've decided to do one filter per board using a smaller board. They'll be stackable with thru-power header like the .5 258 boards. This should also help with putting multiple boards into smaller formats. I'm planning a quad-board module myself that can be used as a resonant eq, or formant filter.

Anyway, I'll start updating this thread with any major progress, and hope to have a final design ready within a month or so.

Here's the basic BOM:

Code:
Bill Of Materials
=================


QTY  PART-REFS           VALUE                         
---  ---------           -----                                       
Resistors
---------
2    R1,R45              47k                                               
1    R2                  2.2M                                             
4    R3,R8,R12,R31       6.8k                                             
2    R4,R13              33k                                               
4    R5,R15,R25,R32      10k                                               
1    R6                  5.6k                                             
2    R9,R14              10M                                               
2    R18,R19             4.7k                                             
4    R20,R21,R28,R29     1.5k                                             
1    R22                 1M                                               
2    R23,R26             15K                                               
1    R24                 68R                                           
5    R27,R33,R34,R48,R49 1k                                               
1    R30                 4.7M                                             
1    R35                 100k                                             
1    R36                 220R                                             
2    R38,R39             62K                                               
2    R42,R43             68K

***MODS***
R24=33R
R27=100R
                           
Capacitors
----------
1    C1                  1000pf                                           
2    C2,C5               .022                                             
1    C3                  220pF                                             
1    C4                  15uF                                             
1    C6                  470pF                                             
1    C7                  47pF                                             
1    C8                  .47

***MODS***
C2,C5=.047                                               

Integrated Circuits
-------------------
1    U1                  TL071                                             
1    U2                  TL074                                             
1    U3                  TL072                                             

Transistors
-----------                           
2    Q1,Q2               2N3904

***MODS***
Q1,Q2=2N5089 (sounds a little nicer to me anyway)
                                           

Diodes
------
1    D1                  DIODE-ZEN 3.9V                                       
1    D2                  1N4148                                           

Miscellaneous
-------------
1    Q                   100k UI
4    CF,CF CV,WIDTH,     10k                                               
1    FM                  50K                                                                                                                                   
4    VT1-VT4             OptoCoupler                                               
1    WIDTH TRIM          5k   


2 10uF or higher electrolytic caps for power filtering.
4 .01uF bypass capacitors (labeled BP1-BP4) *


***Errors***

There are two small silk-screen errors on the board unfortunately. On the left side of the board where the controls attach, there are two resistors labeled R21. The top one should actually be R43.

* There seems to be a "bonus" bypass cap on the board. You can populate it or not. (it's an unlabeled cap) Just drop a .01 in there if you feel like it. The original layout didn't have bypass caps at all, so they are optional.

** This is a silly one, but basically the "Q" header at the top-left of the board, is more or less useless. This was on the schematics that I was working from, so I included it. The real resonance/Q trim is the 5K WTrim pot, which will adjust the resonance for the Width control. This is really something that I feel is best left to a trim-pot. Just set it the way you like it, and you're good. I'm actually not sure what the original intent of the 100K pot on the input is. While it does make very slight changes to the signal, it's definitely not audible, so it's entirely optional.

Also, here is the schematic for those interested:

http://home.comcast.net/~r3cogniz3r/291j.pdf


Last edited by J3RK on Wed Feb 19, 2014 11:51 am; edited 11 times in total
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giorgio
NITE MIND


Joined: 24 Oct 2009
Last Visit: 27 Sep 2014

Posts: 2543
Location: BRAND NEW YORK

PostPosted: Thu Sep 29, 2011 11:46 am    Post subject: Reply with quote Add User to Ignore List

cool. this may be the extra filter I'm looking for for my DIY synth, especially if a highpass output could be tapped.
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Last edited by giorgio on Thu Sep 29, 2011 8:23 pm; edited 1 time in total
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PF
Veteran Wiggler


Joined: 02 Jan 2010
Last Visit: 30 Sep 2014

Posts: 639
Location: Sweden/Stockholm

PostPosted: Thu Sep 29, 2011 1:24 pm    Post subject: Reply with quote Add User to Ignore List

yes, yes, yes....... please.

4 boards.


Last edited by PF on Sat Oct 15, 2011 3:02 am; edited 2 times in total
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rico loverde
Super Deluxe Wiggler


Joined: 06 Aug 2010
Last Visit: 01 Oct 2014

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PostPosted: Thu Sep 29, 2011 1:31 pm    Post subject: Reply with quote Add User to Ignore List

applause
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Luka
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Joined: 15 Jul 2008
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Location: melbourne

PostPosted: Thu Sep 29, 2011 1:32 pm    Post subject: Reply with quote Add User to Ignore List

great - i really like my 291s
i would like to have a bank of them

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KNYST
hiding in the forest


Joined: 26 Jan 2009
Last Visit: 24 Sep 2014

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PostPosted: Thu Sep 29, 2011 1:58 pm    Post subject: Reply with quote Add User to Ignore List

Thank you J3RK! I'm in: 2 please.
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Last edited by KNYST on Sat Oct 08, 2011 10:41 am; edited 1 time in total
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kdub
Learning to Wiggle


Joined: 12 Jan 2011
Last Visit: 06 Oct 2013

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PostPosted: Thu Sep 29, 2011 2:03 pm    Post subject: Reply with quote Add User to Ignore List

yes! x4 sounds good to me. I was thinking about building a cgs serge resonant equalizer, but I think a j3rk pseudo 291 is first in order.
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boothnavy
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Joined: 29 Mar 2010
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PostPosted: Thu Sep 29, 2011 3:22 pm    Post subject: Reply with quote Add User to Ignore List

Uh huh, yup.
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negativspace
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PostPosted: Thu Sep 29, 2011 3:38 pm    Post subject: Reply with quote Add User to Ignore List

screaming goo yo
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Junk Rhythm
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PostPosted: Thu Sep 29, 2011 7:18 pm    Post subject: Reply with quote Add User to Ignore List

You can count me in for 4 PCBs.
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