In batch #2 there is almost no audible sound left now, here I will try to explain how this is achieved. If you have some experince soldering SMD components it is not that hard to fix yourself.
What we've done is we increased the chopper frequency of the motor`s current regulating circuit so that you will not hear it any more. Also by increasing the frequency the mechanical vibration (thats in fact what you hear) decreases in amplitude.
However the electronic switching losses are a bit increased also resulting in a bit higher temperature of the stepper drivers. I advise you to place some small heatsinks on it (about 50 - 70 K/w). Gen 6 batch #2 has it already preassembled. See picture.
File comment: Gen6 Batch #2 with heatsinks
imgp2765.jpg [ 102.19 KiB | Viewed 2673 times ]
How to change the frequency:
Replace the resistors R36...R43 with 68K ohm resistors. This will change the fixed off time of the drivers.
That`s what we've done in batch #2.
When you want to alter your existing PCB, I suggest you just stack a resistor of 100K (in a 0603 SMD package) on R36...R43 (you`ll need 8 pcs of them) and solder it. This way you don`t have to remove the existing resistors.
(why 100K? 1/(100K^-1+220K^-1)=68,75K ohm)
Now check your board for functionality by trying every axis on your machine to control it by software. If it works, stick/glue on the heatsinks and congratulations: now you have a silent Gen 6 machine!
Please note that this change to your hardware could result in damage to your board, only do it when to feel confident you can do this.
Also note that this change will void your warranty!
Any problems, you can post em here!