Current status of support for RN-52 chip:

Have managed to get the ground loop noise fixed by being more careful about power and grouding in my breadboard layout, and also by specifically grounding the "Mic -" connections.

There is still a problem with the gain settings on the chip. The empeg line level outputs are way overdriving the RN-52 inputs and making them clip by a large amount.

Trying to solve the gain problem:

- Turning down the Empeg's volume helps, but not completely. Can't turn it down quiet enough to stop it from clipping.

- There is discussion of the mic/line gain here: http://www.microchip.com/forums/m770128.aspx which says "The microphone gain can be changed from -3dB to 42dB in linear steps. If the gain is set to less than 24dB using the ‘SM’ command the line in mode is automatically entered."

- There is indeed an "SM,xxxxxxxx" command which is supposed to adjust the microphone gain, but it does nothing, no matter what I set it to the gain never changes. I can set it to all zeroes and reboot the unit and... still the same volume, gain still clipping.

- Datasheet on the chip says "MIC_BIAS requires a minimum load to maintain regulation. MIC_BIAS maintains regulation within 0.199 and 1.229 mA. Therefore, if you use a microphone with specifications below these limits, the microphone output must be pre-loaded with a large value resistor to ground." - I tried a 10k ohm resistor from Mic_Bias to ground, no change.

- This page: http://www.microchip.com/forums/m843896.aspx hints that there is an "SL" command to set line level to go with that "SM" command but I cannot get it to work, even based on the information that the person in that thread said to set it to. I try to do a "GL" command and it just says "ERR", and all variants of the "SL" command that I try give me "ERR".

- There is also at that same page http://www.microchip.com/forums/m843896.aspx a schematic for converting speaker level to line level using a couple of resistors. I may try that. But I feel like I shouldn't have to if the chip is supposed to support it directly.