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CEM 3396 Analog Synth from scratch Project
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ru_klo



Joined: Apr 09, 2011
Posts: 7
Location: Argentina
Audio files: 1

PostPosted: Sat Jul 09, 2011 10:45 pm    Post subject: CEM 3396 Analog Synth from scratch Project Reply with quote  Mark this post and the followings unread

I was looking for simple ways to build a synth. After spending some time in the net, I ran into the CEM an SSM synth chips and was hoping to get some to start building something, but they were obsolete, rare and hard to find (and of course expensive).
Then I discover the UTSOURCE page, which sells worldwide (I´m from Argentina) small qtys of chips. And they had this CEM 3396 (one chip synth) which was the answer I was looking for. I bought some (10 pieces = usd 30 – shipping included – real cheap).
So I had this CEM 3396. The next thing was to find info. But (apart from the datasheet and some posts) there is no complete project info (I mean ready to go – with PCB, info, and testings).
So I decided to start my own project.

The project:
The project is divided in 3 parts. The first part is to know and use the analog part of the chip. The second part is to use the 2 DCOs and digitally control the analog part. The third and last part is to make a VOICE CARD for the MIDI BOX (so we can have an analog MIDI BOX synth)

Everything is on the datasheet, Google it.

Currently I´m in the first part of the project, and this is what I found.

CEM 3396 Analog Part.

After reading the datasheet I decided that the best thing to do is to build a “trainer”. This trainer should have :
a) four supply voltages (+12, +5, -5, -12)
b) all the circuits that are on the datasheet to control the chip

So I build this:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

After building the trainer I discovered that some section did not worked as expected (or worked at all)

Building the trainer:
(Please read all before wasting your money and time)
1) The “DCOs buffer and external signal” part do not work – so don’t build them
2) The waveselection part work as expected (I mean the voltages and bit selection are ok) but do not have influence on the wave selection – (maybe if you use the Abalog part only) I only change R37 from 33K to 1K to be in the voltages the chip needs (regarding the datasheet), but If the jumper is removed, the analog part becomes a little unstable. I thing the best thing to do is to connect the WS CV Pin (6) to the -5V supply directly (both converter on). Not tested.
3) After building the PCB and BEFORE inserting any chip:
A) control the supply voltages
B) build the CV part (not shown in the schematic) Almost every input worked with 0 - 5 V. Except the balance -2.5V / +2.5V, and the filter CV (-2.5V / +5V).
Every CV is done with a 100KB pot. (one end to GND and the other to +5V). BUT the filter CV has a 33K resistor and is connected to the -5V supply (-5V / 33k / 100KB pot / +5V) and the Balance is connected to the -5v and +5V supply with a 47K res. (-5V / 47K / 100KB pot / 47K / +5V)
C) connect the CV potentiometers to the PCB
D) check (test) every voltage in the chip socket (first the supply and then the CV – test if they are in the expected range)
E) test the WS selection (if you decided to build it anyway) – If the voltages are not in the expected range, tweak the R37 resistor. Refer to the datasheet

If everything works as expected, disconnect the supply and insert the chips.

First test:
The first test I made, was to produce some noise with the resonance (self oscillation). I power up the thing and did not worked. Then I increased the LIN and LOG VCA CV voltage to the max and ….. ITS ALIVE….
You must turn both VCA CVs to the max (or near to hear something) because they are in a serial fashion).

Second Test:
Was to input some signal in the EXT SIG . The thing did not worked (that’s why I tell you not to build it) I got +12V in the CTA pin and not 0 - 2.5V signal I was looking for.
So I discarded this part, cut the trace from pin 4 and 8 (CTA & CTB) and apply the signal directly. If you read the datasheet (recommended) the signal must be 0 – 2.5 V (offset 1.25V), but the best result (more output) I got from a 0 – 5V signal. I took them from 2 oscillators made from the 40106.

Here is the sound file I got. Its not pretty, but show some noise you can make with this chip. Mainly I played with the filter and resonace, and was all done with pot CVs, no modulation from ADSR, LFO, etc.
It was recorded with an SB live 24, and the cables were long and everything was connected with clamps, so expect no pro sound an a lot of noise.

The sound file:
In the first seconds are the RAW “noises” taken directly from 40106 (this is to test how the chip alters the sound)
At sec. 5 you will hear how the balance CV works (Filter fully open , RES: 0)
At sec. 23 , how the filter works (res: 0)
At 50, playing with res,
At 2:30 no input, only self oscillation (and playing)
At 3:10 no input, self oscillation and playing with the MOD CV.


Well this is it. I think the first part is finished. Here are the PCB and Layout EAGLE files, If someone wants to make a better PCB, take the parts that do not work out, and made a nice Analog module, feel free.

I think that for aprox 10 usd, (if you find the cem 3396 chip for 3 usd) an:
2 input
24 db LP VCF with VC resonance
2 VCA, and some other things
Easy to build,
It´s like a Synth Heaven gift.

The next part is going to be difficult, so any help will be gratefull.

The basic Idea:
8253 / 8254 timer to generate the clock (1 8253 for 1 CEM3396) (8253/8254 are obsolete too)
TLV5630 12 bit 8 output to generate the CV and WS voltages (MidiBox friendly) OR a cheaper 12 bit R-2R ladder with sample and Hold and 4051 multiplexers.


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shematic 2.brd
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cem 3396.mp3
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tomcat



Joined: Oct 14, 2005
Posts: 141
Location: earth

PostPosted: Thu Jul 14, 2011 3:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you do a pcb you should include pinout for narrow and wide body CEM3396! There are two versions (eg matrix 6 uses wide body, matrix 1000 narrow body). Beside the physical dimensions the chips are the same.
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blakeAlbion



Joined: Jun 16, 2020
Posts: 23
Location: Boston, Massachusetts, USA

PostPosted: Sun May 29, 2022 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

How is VCO tuning done? My Six Trak had this terrible tuning procedure.
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