Rev 2.0 instructions are up

[tpryan]

Updated BOM, schematics, and assembly instructions for rev 2.0 of the C84 are now available on the site. If you find discrepancies between the BOM, schematic, and assembly instructions, please post them to this thread.

Rev 2.0 replaces the now-obsolete and unobtainable LM394 with the new MAT14 quad matched NPN transistor. A second MAT14 is used as a matched current source for the input pair. These are SOIC-14 surface mount packages with 50 mil pin spacing. If you doubt your soldering abilities at all, do everyone a favor and order an assembled module.

This latest revision boasts a measured EIN of better than -131dBu (50 ohm source), THD+N as low as 0.0007%, maximum output level greater than +31dBu, and a usable S/N of as much as 132dB.

Some background on the circuit can now be found here: http://www.leonaudio.com.au/cohen.htm

[donks]

Just started working on my first of two C84 kits and have come across a couple of discrepancies.
1) Conn4 and Conn5 are highlighted in yellow on my BoM and not present in either of the 2 kits;
2) J1 and J2 (step 15 on the assembly doc) are not on the pcb (or I just can't find them) - Conn4 is where J1 and J2 are pictured on the assembly doc
3) The parts kit includes two 2-pin headers (Item 17) along with jumpers (Item 20) that should go in J1 and J2

[brettyc]

I got a board that shows Rev 2.1 and I got BOM and Schematic for Rev 2.0. I have the same question about J1 and J2. Also, the BOM shows these as 3 pin headers but they are 2. Where do I put each of the 2 pin headers?

[brettyc]

I think I figured this out. The picture of the C84 board on the website is Rev 2.1 and shows these jumpers installed at P1+ to M+ and P2- to M-.

[noysie]

I'm wondering whether the P1+ to M+ and P2- to M- was the correct placement for the headers and shorter jumpers ?
Another issue with BOM rev 2.0 and Rev 2.1 circuit board is there is no mention of C42,C43,C44 and C45 in the BOM but these are on the circuit board.
Does anyone know what type of ceramic Caps go in these positions?

[brettyc]

C42-46 are contained in BOM Item 3. It says "C41 - C46". They're 0.1uF, marked 104K.

I put my jumpers there and my preamp is functioning great, phantom power and all. Now, that may still not be the right place to put them but I seem to be safe for now.