The smArTT verter is a simple but very effective utility module (known in the modular world as atenuverter) for scaling the level, polarity and DC offset of audio and CV signals.
Why another atenuverter considering that there are several ones in existence? As musicians we used variations on the atenuverter theme and our practical experience showed us that there are some aspects where things can be improved to make it more versatile.
Will try to draw to your attention the aspects where our smArTT verter is different (and in our opinion a better one).
1)- most atenuverters have the signal level pot used to change the level from maximum inverted at CCW (counter clockwise), zero at center to maximum non inverted at CW (clockwise). This solution has three disadvantages. The dynamic range of the inverted and non inverted signal takes the whole mechanical range of the potentiometer so it makes it harder to dial in precisely the level you want in some critical situations. The second disadvantage is that because of the tolerances of pots and parts, your signal zero will not be exactly where the mechanical zero (mid position) should be. The third disadvantage is, the signal zero has a very narrow range and sometime you really need your signal to be reduced in a performance to zero fast, easy and precisely.
We solved the three problems with a switch. In one position the signal has a range from zero to maximum noninverted, associated to the whole angular range of the pot. In the other position the signal has a range from zero to maximum inverted and it is also associated to the whole angular range of the pot. This way we solved all three problems: the whole mechanical range of the pot is used in a much more efficient way and the zero signal is really zero and easy to dial in.
2) - most atenuverters that have a DC offset option use the mechanical range of the pot to cover the range from negative DC (at CCW) to 0V (centre) to positive DC (at CW). The disadvantage is the DC zero is extremely narrow and hard to dial in.
We used a smart little trick to make that centre zero gap a bit larger and easier to dial in.
3) - several times when using an atenuverter we discovered that we had to use multiples to distribute the processed CV/audio signal to various modules . We decided to use three outputs, so you don't need to sacrifice a multi to distribute the processed signal.
The smArTT verter is the result of what we think the best set of features for an atenuverter in Eurorack format.
What our smArTT verter is not. Our smArTT verter can scale audio and CV signals for modulation and audio purposes but it is not recommended for precise 1V/octave pitch control. Of course you can use it to drive oscillators but if you need precise 1V/octave, you need a different circuit. Also our smArTT verter has the build out resistor outside the negative feedback. This is not an error, it was an intentional design decision.
The smArTT verter also has a bicolour LED for visual information about signal level and DC offset.
This is a comprehensive build document for our smArTT verter project and we hope it will make soldering and assembling this project an easy task.
We tried to make the whole experience as easy as possible and give as much information as needed to avoid confusion. We also provide additional documents like BOM lists
(PDF and XLS), images with part values, and photos of the construction in various stages. Feel free to download the whole pack and have fun.
This document assumes that you have a decent knowledge about electronics, soldering, using tools and measurement instruments.
The smArTT verter is an easy project so we recommend it even if you are relatively new to electronics.
We built some modules from this construction manual so we are confident we ironed out any errors, but we are human and if you discover any problem, feel free to give us a feedback.
The module is not a problematic build because it has no rare/vintage parts, everything is available from various electronic parts distributors.
We recommend to check and double check the values of the parts to avoid errors. You spend significantly less time by checking everything in the process of building than the time needed (and frustration generated) if something is wrong. Troubleshooting can be a pain, especially if you are newbie.
Pay attention to polarity. Will say it again PAY ATTENTION TO POLARITY. It is essential to install parts like transistors, diodes, ICs, electrolytic capacitor the correct way not only because the circuit will not work, but there is a big chance parts will be damaged and be unusable.
Also we recommend to build this project in the order described in the manual. If you do everything as described here and the parts you use are the correct ones, you can be sure the circuit will work as it should from first powering. The minimum needed measurement equipment is a digital multimeter but if you have an oscilloscope it is even better.
The circuit is protected from reverse powering error with diodes and it has also RC circuits for better decoupling.
Project is available in 2 KITs :
KIT1 : PCBs + Panel
KIT2 : PCBs + Panel + Pots, miniJacks, knobs, Board to Board connector
Availability and prices :
KIT1 : 20eur (20pcs.)
KIT2 : 30eur (10pcs.)
Shipping to eu : 3eur, non eu : 5eur
For ordering write on the forum, but also pm me, it's hard of keeping track of ordering in two places. Please pay the paypal fee.
KIT1
KIT2
ALTERNATIVE KNOBS. We do not provide this type of knobs. This
photos are for KIT1 purchasers to have an idea how the module is looking with other knobs.
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