Blackmer Synth Module Board

First Posted March 11, 2012
Changed Completely on July 18,2014
Updated September 2, 2014

Who rocks the scene with sound that's clean
It has the bass to shake your face
Filters so lean they really scream
Everybody knows its Noota

The best synth yet to give or get
The DJs will all want to try
The hit of the day when you are ready to play
Everybody knows its Noota

Its Noota, Its Noota
For fun the best of the synths
Its Noota, Its Noota
The favorite of girls and boys.

Everybody wants a Noota
Get Yourself a Noota
(sung to the slinky song tune)

September 2, 2014

Well, I have had a minor setback.  And it has to do with the VCO.  I am not sure why, but, the tempco of the gain of a Blackmer VCO changes with gain.  So, as it turns out, you need to figure out what control voltage is required in order to exactly compensate for the tempco of the VCO.  The changes to the circuit are rather minor.  I was originally changing the scale factor by adjusting the gain of the BMVCA that provides the  temperature compensation.  This, of course, just won't work.  The  gain of the BMVCA must remain fixed.  So, I moved the tuning pot over to the base of the transistor in the exponential circuit..

Another setback which is related, has to do with ORCAD.  I need to revise the schematic.  I always keep a copy of past mistakes, because you never know when you are going to need it.  This is really the first schematic I have done, that became a PC board that uses the Synth Blocks library I created.  These are little circuit blocks that are handy for making synthesizer modules.  Well, as it turns out, when I make a copy of a schematic that uses these blocks, all of the reference designators of the components  in those blocks gets reset.  Not good.  I will either have to re lay out the board, or pains takenly manual fix all of the reference designators by hand.  Neither option apeelling to me.  So, I am working a bit with orcad to see if I can figure out how to correct this problem.  Otherwise, I will go back to doing schematics the boring way.
August 2, 2014

did some checking on prices today.  The NOOTA board  would probably sell for the neighborhood of $30 (bare) and the 100-1071 quad pot board would probably sell for about $35 -> $40 for a set of six boards.  But this is getting just a head of myself a bit.  Before any orders can be taken, I need to get the thing to work first.

August 1, 2014

am just about ready to start making CAM files.  But here is what I need to do first.

1.  Sell a bunch of stuff on EBAY.  I am liguidating my model railroad stuff since it is sort of useless to me now.  This will raise the necessary funds needed to get the PC boards fabricated.

2. Before I send the artwork out, I would like to test the VCA circuit.  This means I need to build a breadboard.  Not something that is easy for me to do.

3.  Do a panel layout.

After I do get boards back and build up the first one I will decide if any of this had any merit, or was it just a big waste of time.  

And as soon as possible, I will get all the files posted.  After all, this is supposed to be an open source project.
July 31, 2014

So, as of today, the board has been completely routed.  There are still a couple of minor things I need to do to the artwork before it is ready for CAM generation.  I also want to verify the performance of the Blackmer Cell that I am using.  Control feed through, of course, is a major concern..  I also need to go through and calculate the values of the unknown parts as well.  Here is a photo of the PC Board as it stands today.  Also, the schematic PDF has been updated as well.  See Below.

    Now as it turns out, this is not all I did today.  I designed this board to use some auxiliary boards that hold the control pots.  These are not needed, but, for those of us who are challenged doing popint to point wiring, these will help make the assembly a lot faster and easier.  If you look on the schematic, you will notice that many of the connectors are labled with the part number 500-1071.  This is a quad pot board that also has the option for 4 LEDs as well.  Here is a picture of the board.

And this schematic can be found here.

I can't remember how many of these will be needed, but it is several, OK, well, I just checked, it is 6.  There are 8 connectors labled with 500-1071, but the two boards for the Envelope generators have two cables going to them, one for the pots, and one for the LEDs..

The other board has 5 pots on it for the 5:1 mixer.  Only one of these is needed, although, you could also use one with the 3:1 mix at the VCA.

And the schematic can be found here.

July 23, 2014

Well, ran into a little bad luck.  As I was placing the parts on the board, I discovered a serious problem with the netlist.  Try as I might, I was not able to fix it in a way that would preserve what I had done.  In  order to find the problems, I had to re-annotate, which ruined what I had done.  On the good side, this will give me a fresh start on placing parts, and hopefully I will be able to squeeze them in a bit tighter.  At the density I was placing them, they would have never all fit on the 6x9 board.  Anyway, I have at least updated the schematic PDF file to reflect recent changes.

July 19, 2014

Schematic is STILL not done, but it has been updated considerably, and is also two more pages long.  See below to download the PDF of the schematic.  However, I have gotten it to netlist and  as well as load the netlist into Protel without any errors.  So that is something at elast.  There are currently about 480 components on the board.  Man, that is a lot to have to place on a PC board.  And even worse, to solder.  Not really sure how, but I vow I will get this one to a OPC board.;  It is just so different, I have to do it.

July 18, 2014
   When I first started this project back in 2012, my foals were a lot different.  Well, not too different, actually, but I was willing to include a couple of OTAs that were used in the VCOs for temperature compensation.  But, I continue to learn.  And I decided that why not try and also use the Blackmer Cell to temperature compensate the VCOs as well.  So, thus the NOOTA (No OTA) Synth Module Board was born.  So, in this project, you will not find a single OTA, anywhere.  So, this is a complete redesign.  The structure of the synth is fairly cliche.  And it is also fairly simple.  I like to think of it as a NOOTA'd version of the ASM-1 synth board.

So what do you need to build this circuit?   The only expensive chip is the MAX551 DAC chip.  It comes in at about $13.  The next most expensive chip is the ATmega328 micro controller,  Everything else is pretty run of the mill, TL052, DG201, some HC logic, and a bunch of 2N3904 and 2N3906 transistors.

I chose the ATmega328 partly because of the fact that it is an popular Arduino processor.  Even though I am not going to use it that way, if you are enterprising enough I am sure you can figure out how to get it into that environment.

This is an open source project.  So, as files become ready, I will post them.  The schematic is still not done yet, it needs to be gone over and all the little details filled in, and then I can lay it out.  I suspect this will be about 8" x 6".

Another thing I have to work out is a block to put the transistors into for the BM cell and Expo transistors (a total of 7) as all of these need to thermally track each other in order for the temperature compensation to work.

PDF of above schematic.

Orcad 9.2 Library of Circuit Modules.  I sort of think of this as being a Synth BLOCKS library.

Features of this synthesizer include:

1. Microprocessor controlled envelope generators.  The core of the envelope generators is basically the same as the glide circuit.  The micro controller supplies a voltage level and a time constant control to the glide circuit depending on the current GATE and the past history of the envelope output.  The control voltages are supplied by having the micro controller read a set of four pots which set the Attack time, Decay Time, Sustain Level and the Release Time.

2.  All of the transconductance functions are done by Blackmer Log-Antilog multipliers.  I decided to use a semi discrete version rather than using something like the THAT Blackmer VCA.  I am trying to get away from using the odd specialized chip here and there.  I really miss the CA3280. And learning to do without will make me stronger.  Some chips you just have to use.  For instance, if the ATmega2561 goes obsolete, it is not too big a deal.  There will always be some other type of micro controller to take its place.

Creative Commons License
Noota Blackmer Synth Module Board by James Patchell is licensed under a Creative Commons Attribution 4.0 International License.