All,
I just finished doing a quick test between a STOCK AK100 with 1.33 and STOCK AK100 with the Russian SW. Using a 16/44.1 WAV file of a 1kHz test tone (0dBm), setting the volume to max (75), EQ OFF, and measuring the RMS voltage at the output jack with NO load connected, I get:
STOCK AK100 with 1.33 = 1.02 Vrms
STOCK AK100 with the Russian SW = 1.52 Vrms.
So we are looking at a approx. 3.5dB difference output between the two.... which can definitely be heard.
I know that the "de-emphasis mode ON" takes away around 3dB of signal in the dac before the d/a conversion takes place - so it is possible that whoever came out with this patch also turned OFF de-emphasis in the software (as the WM8740 dac in the AK100 is ran in "software mode" - not "hardware mode").
I have a prototype modded RWAK100 with a WM8741 dac (dac configured in hardware mode and using a 'minimal phase' digital filter setting that has been hardware configured for the dac. Digital volume control
is completely bypassed from the chain - so no digital attenuation used for the data. When I measure the output voltage of the same file above (in the same configuration) with SW 1.33, I get 1.8Vrms. When I load the Russian SW, I still get 1.8Vrms.... so running in HW mode and completely bypassing the digital volume control is proven to give true MAX line-out capability (I believe the 0.2Vrms difference to the datasheet's 2Vrms is because I was still using the headphone output stage, which will be bypassed. The headphone output stage is a voltage follower and topology and seems to drop about 0.2Vrms, but provides the current required to drive headphones).
That's it for now... I hope this helps,
Vinnie