PreenFM > preenfm2 and preenfm3

115k resistors

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6581punk:
I'm building my Preen 2 from just the PCB and I forgot to order the 115k resistors. My local store only does 110k or 120k.

Will either of those values do? the tolerance of 5% means a 115k could be 109.25k or 120.75k anyway.

Xavier:
You should go for 1% tolerance resistors for the filter : 1.8K, 8.2K, 115K. (220 and 10K are much less value sensitive).
1.8K & 8.2K define with some capacitors the cutoff frequency of the antialiasing filter.. So you don't want it to be too low not to remove high frequencies. It's set at 20Khz.
The 115K adds a 6 bits dac output to the other DAC that comes from the 1.8K, so you want 115K/1.8K to be as close as possible to 64 (2^6). So that your 18 bits DAC is as linear as possible.
120/1.8 = 66.6... Should work.
I would go for 120K. Buy several and select the 2 that are closer to 115K.  ;)

Xavier

6581punk:
There was me forgetting the tolerances of the various resistor types :)

I'll just use some 120k for now then, i'll solder them in with long leads so I can pull them out and replace with 115k when they arrive.

Thanks :)

6581punk:
In the end my DAC chipped arrived and is the surface mount version :( pretty sure it looked like a DIL in the photo. So I can wait for the correct 115k resistors to arrive.

Once you flash the bootloader and firmware is the internal USB cable needed? only the one I made didn't work.

Xavier:

--- Quote from: 6581punk on December 31, 2013, 06:05:25 PM ---Once you flash the bootloader and firmware is the internal USB cable needed? only the one I made didn't work.

--- End quote ---

Other than flashing firmware the Internal USB cable is needed to :
. have Midi over USB working
. seeing and managing your USB Stick from your computer (Bootloader 1.10+ needed)

Xavier

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