Muff's Modules & More

moogah · Posted: Tue Apr 09, 2013 10:03 am Post subject: [BUILD] SEM VCF

For the moment I'm just getting this thread together as a placeholder, look for more detailed info soon!

Link to BOM:
https://docs.google.com/file/d/0Byb1hJRK5lw6OU9ZRmpGVy1yM1U/edit?pli=1

Link to Synthcube site for ordering:
http://synthcube.com/cart/index.php?route=product/product&product_id=1 77

Link to original thread:
http://www.muffwiggler.com/forum/viewtopic.php?t=69431

The PCB with component values:

The original schematics (page 6), all components not marked with a '$' are the exactly the same as the original with this layout.

http://www.synthfool.com/docs/Oberheim/Oberheim_SEM1A/Oberheim_SEM_1A_ Schematics.pdf

My schematics:

There are 3 100n SMT caps mounted on the bottom of the board. If you really don't want to deal with SMT, the filter will still work without them.

The components marked with a $ are for the version with VC Resonance.

The components marked with a * are for the original version, but they are left off on the vc res build.

the FET buffer transistors (2N4302 on the original) are the two in the middle of the board in this picture. The silkscreen shows the correct orientation for the 4302, but there are two additional pins which make it easier to use a substitute without having to bed pins.

The 2n3904 and 2n3906 pair are poorly labeled (not labeled...). They are the two without any markings and the 2n3906 is the one with a trace connected to its middle pin.

you will probably need to stretch the pins of the 5pF capacitor above the LM301. To be sure, just don't let it's leads touch the board directly.

There are 3 150K resistors on the board, all three will be 120K instead for a 12V version. However, one of the 150K is only needed for vc-res, so you can ignore that one.

The inputs are on the bottom left and the pins are: Input, Ground.

The outputs are on the bottom right and the pins are: Ground, LP, HP, BP, Variable.

The pots mount on the component side of the board.

If you're building to use a Clarke68 Panel, the Frequency pot will be off board!

moogah · Posted: Tue Apr 09, 2013 10:04 am Post subject:

Stuff to take note of:

The pots mounted on the board are:
Frequency
Resonance (with the *)
Variable response

If you're building this for the clarke68 panel the frequency pot is mounted off board!

The 100n SMT caps can be left off if you really just don't want to deal with it.

The .150nF caps listed on some of the BOMs are actually .150uF! These values were correct on the last one of synthcube's Mouser orders that I saw.

The TL074 is marked with a '$' BUT it needs to be installed for all versions of the build!

Some info on wiring, for those who can't wait for a nice diagram smile

OK, using this image as a reference: http://www.baud-rate.com/sem_vcf.jpg

The pins on the inputs are (left to right) signal, gnd

The pins on the outputs are as labeled

The topmost 3 pin header on the right side is for the attenuverted frequency cv. The middle pin connects to the wiper, the topmost pin connects to the full ccw side of the pot and the cw side of the pot is where the signal coming in from the jack also connects, so that lug of the pot will have one wire coming from the jack and another wire going to the bottom pin of the header.

The next one down is a 2 pin header for 1v/oct resonance tracking. We're not using that one.

And nestled in between the two resonance cv pots is the un attenuated CV input. If you first wire the cv input jack so that the ground wire connects to the ccw side of the pot and the signal wire connects to the wiper, the connect the ground wire to the top pin of the header and the wiper to the bottom pin

qfactor · Posted: Tue Apr 09, 2013 10:14 am Post subject:

Awaitin'

moogah · Posted: Fri Apr 26, 2013 9:08 am Post subject:

DERP. Bump for updating the first post (last night).

More/better docs to come.

raisinbag · Posted: Fri Apr 26, 2013 11:54 am Post subject:

Hey, so do pots mount on component side? It looks like it from diagram, just double checking.

moogah · Posted: Fri Apr 26, 2013 12:23 pm Post subject:

Good question! The pots are mounted to the component side of the board.

HOWEVER, if you're building for a Clarke68 panel the Frequency pot (on the top) is left off.

raisinbag · Posted: Fri Apr 26, 2013 7:46 pm Post subject:

Ok one more question, Well two more. 1- How important are the IC suffixes? (ie can we use subs (or should avoid certain suffixes or should we stick to the BOM like gospel) and 2- are there component options for 12v vs 15v? gota watch dem SemSqanches in this neck of the woods!!!!!! Rasta-nana

Dego · Posted: Sat Apr 27, 2013 10:43 am Post subject:

Suffix not important

moogah · Posted: Sat Apr 27, 2013 10:51 am Post subject:

Ah, I am forgetful!

There are 3 150K resistors on the board, all three will be 120K instead for a 12V version. However, one of the 150K is only needed for vc-res, so you can ignore that one.

raisinbag · Posted: Sat Apr 27, 2013 11:40 am Post subject:

Great, that's all good news. Looks like I have all parts EXCEPT 4302. I know SB has a workaround for it, anyone know what that part number is actually called? They may have one at my favorite store full of crazy old stuff.

LED-man · Posted: Sat Apr 27, 2013 1:12 pm Post subject:

raisinbag · Posted: Sat Apr 27, 2013 1:23 pm Post subject:

Right on! I have some 202s in bin, woo hoo. Thanks missed that paragraph.

logicgate · Posted: Sat Apr 27, 2013 1:39 pm Post subject:

LM3080 is CA3080???

EDIT:

yes it is... lol

raisinbag · Posted: Sat Apr 27, 2013 1:43 pm Post subject:

I use them interchangeably often. I'm sure it will work to use ca.

logicgate · Posted: Sat Apr 27, 2013 1:44 pm Post subject:

logicgate · Posted: Sat Apr 27, 2013 1:53 pm Post subject:

Are the pots 50K linear? It doesn't say on the BOM.

And I never seen pots with 5 lugs!

raisinbag · Posted: Sat Apr 27, 2013 1:55 pm Post subject:

Pretty sure they are Lin. And I'm also pretty sure the five holes are so that you can use 9mm or 16mm pots.

moogah · Posted: Sat Apr 27, 2013 3:02 pm Post subject:

All of the pots are 50K linear.

The 5 pin footprint is so that you can use pots with either a .100" or .200" spacing (typical for 9mm and 16mm pots).

Barcode · Posted: Wed May 01, 2013 10:32 pm Post subject:

Couple questions. I built the original version of the VCF.... Is it correct to leave off the $ stuff?

Does this look correct? (I know that the top pot is Freq but what are the others.) I built mine this exact way (excluding the 2 bottom trannies from the $ build) and I get no sound...

raisinbag · Posted: Thu May 02, 2013 7:27 am Post subject:

I'm still a bit in the dark as well, but only thing I noticed (which made me MY ASS IS BLEEDING

For a second) was you have a 4305 in place of 4302. No biggy but I just thought I finally had all I need and d'oh!

Some other rare tranny.