This is a pretty interesting utility module with loads of functionalities to explore!
About the Module
The Smooth & Stepped Generator (SSG) consists of two sections wich are linked together by a comperator. With the smooth section you are able to add a positive and negative slew to an incoming signal. This can be used to produce lag effects, voltage controlled portamento or as a filter for low frequencies. By applying a high signal (>4.5V) into its hold input it works as a track and hold with voltage controllable slew rate. It is also an oscillator in CV and audio rate – usally by patching the cycle output to the input. I thought it would be usefull to pre-route this patch, so I just connected the switch terminals of these two sockets together. If a cable is patched into one of them, it is disconnected. If you want to build it true-Serge by using banana sockets, you can add a cycle switch (SPST or SPDT) to add this function. I also added this to the stepped section.
The stepped section can be used as a sample and hold with voltage controlled slew rate limiting. To generate complex staircase functions (in cycle mode), feed the hold input with a square signal.
With the coupler you are able to generate random voltages or complex controll voltages. It compares the output signals of the smooth and stepped section.
My Build
First of all, you can download my stripboard layout, the BOM and schematic with the following link. I used it for my own build.
It took me a little effort to get this module going. At first I messed up the power connections of the LM3900’s. From previous builds and from the datasheet I was used to tie pin 7 to ground. In this module it has to be connected to V- instead. As this was solved I discovered that there need to be some modifications applied to make it properly work with a LM13700 instead of two CA3080. The CA3080 is no longer in production and hard to find. It is possible to get but relatively pricy. The two 82k resistors need to be swapped out by 150k’s and there need to be two additional 150k resistors to be added to each of the LM3900’s. Also one of the 1nF caps should be increased to 2.2nF. I added these modifications to the schematic to make this clear. After this was solved too, the smooth section worked like a charme. The stepped on the other hand… So back to the bench. I discovered a missplaced resistor and boom! It was working!
Also the J201 JFETs aren’t that easy to find as through hole components. I was lucky to have a retailer here in Berlin that got those in stock. On the original source it’s mentioned that most general propose JFETs should work, same with the PNP transistors. So try whatever you already got or can get easily. Just make sure the pinouts fit by comparing it with the schematic.
Here are some pictures of the finished product:
Calibration
You got one trimmer for each section of the SSG. The left one on my layout is for the smooth and the right one for the stepped section. An oscilloscope can be handy but you can also calibrate it by ear – so did I. To calibrate the smooth side it needs to be set in cycle mode, which is already pre-patched in my layout. Now turn the the rate pannel potentiometer to maximum. You will get triangle signal in audio rate. The trimmer changes the frequency of this signal. From a certain point you wont notice a change anymore. This is the point where it’s calibrated.
The stepped side needs also to be set up in cycle mode. In addition, you need to put a high frequency square wave into the sample input – otherwise it won’t cycle! Now it’s the same procedure as before. Turn the rate potentiometer to the maximum and find the spot from where the trimmer has no influence on the frequency anymore.
Now you are done and ready to role!
Patching Techniques
This module can be a little overwhelming at first and it is definitely not self-explanatory. I found this threat on Wiggler where someone cited an old yahoo-post. As you can see, the SSG offers loads off functionalities to explore and has lots of hidden secrets!
If you like what you see or got any feedback just leave a comment below or come over to my Facebook group. Thanks for tuning in!
Moebius Synths 