Paralled 4570 boards questions/help

[drfrink24]

Posted for AR2, to generate a new thread:

I am finishing my BPA (400W ?) not sure on what power.
It is built out of 8 Brian's 4570 boards - 4 boards for each side. Each board is paralleled internally with two 0.1 ohms and than I paralleled two of them. I am supplying balanced signal and each pole of the balanced signal is driving these two paralleled boards, and than they are bridged in the output.
First i taught that I do not need any extra resistors to parallel two boards, since they already have two 0.1 ohms on them, but that didn't work. I tried with another 0.1 for each board and that didn't work ether - the amp oscillate. So I ended up with 0.5 ohm for each paralleled board, and that works fine. I do not understand why is that, and any advise is appreciated.
The heat is tremendous. I have to redo the whole cooling concept. I had 4 boards on big 12 x 8 x 1 inch heat sink, and that wasn't enough. Now I am changing it to two of the same sinks for 4 boards.
In my tests the sound was really awesome. Very powerful and base was very low. It outperforms my 2 x 200 W Mosfet class AB amp, particularly in bass region.
This amp is intended to drive bass speakers that are difficult to drive - 4 ohms and 87 dB sensitivity. I still have to finish and redo my amp to give you better answer, but so far just as a test it is very promising.

[AR2]

This tread is continuation from here
http://www.diyaudio.com/forums/showt...460#post610460

[AR2]

Hello Jackinnj
I am little bit confused about inverting another set. I checked with Brian GT on this issue. Replies I got was that I could run GC as they are in non-inverting mode, if fed by balanced signal and than bridged in output.
I originally felt that I should do as you are suggesting. If I need to change from Brian's boards to inverted mode, would I need to change to different resistor values or just reverse input polarity?

[AR2]

Hello Jackinnj,
The schematic is the Brian GT's schematic and multiplied in the way I posted. Here is Brian's schematic where you could see the details better. I cannot post bigger image of my modifications but I could email it to you.