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[alfredokiwi]

I was performing some changes on my R3 synth to master its audio quality. I added a LPF antialiasing filter after DAC converter to remove all type of high frequencies noises and unwanted signals that are out of ear audible spectrum.
Also I have compensated the line out stage after filtering with more output level and with an active equalization to follow Fletcher-Munson human ear response theory. This circuit design is much better as in Pa500 circuit changes that I have developed because it has a double EQ compensation network to compensate not only low freq also highs to cancel the filter roll off attenuation. At the same time the custom DAC antialisang filter is much better as in Pa500 because Pa500 original filter freq cut off is set a 40Khz and on my bended Korg R3 I have set it to 12,5 Khz approximately. Has not sense to set a filter at so high band pass response because high freq components are not audible, consumes amplification power wasting efficency and produce ear fatigue and severe damage at very high levels. Also the response on lows freq is improved to because I have increases the DAC overall stages decoupling capacitors values for better bass impulse.

Korg R3 original design don´t use an active DAC antialiasing image filter stage after DAC, sounds strange and the reasons why this is removed from other designs I don´t know. A detailed explanation of this topic is available on my blog

http://www.alfredoblogspage.blogspot.com.ar/2012/11/my-korg-r3-that-shines-in-sound-quality.html

Here some pictures about the circuit changes





I have check the quality before and after, what I can say is that audio quality is superb after changes, with more details. Also I have improved the dynamic range due the low audio output.

Here the audio samples before and after changes

Factory R3 sound


The new sound quality after circuit bend


Some parts from R3 factory demos after changes


I'm very happy with the circuit bend and its final quality
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