Hi Audioguru.
1) The first voltage divider is made to make the OPAMP work with non symetric supply, as you suggest me at the time to do it (R12/13 C5). The main problem that i've faced with this is the cross talking effect when, if, i dont use the other dividers (R17/18 & R32/33) maybe because the R5 (100K) at the pin 3 of the OPAMP, if i remove R5 the circuit doesn't work and if i join all at the same point i get this strange effect. So the idea was to isolate and avoid this effect.
2)Hahaha ;D
No Audioguru, in fact, this is the same program from the same audio source, this is the main propose of the circuit, to use the OPAMP and make a calculation and reproduce only R - L as surround channel and R + L as center channel, this configuration is also know as Hafler Effect. It took me a long time to get to this configuration because the effect is not perfect, you get some "garbage" as a result if you play a bad MP3 audio for example, you can hear the compression artefacts mixed with what you want to hear.
If you heard the sample, you will noticed that the vocal is almost gone and the background is almost intact and very clear, using some acoustic technics when used inside the car you will only hear the back ground and the vocal is completly removed making a very impressive effect.
The configuration here with the CD4053 is made only to bypass the surround circuit since i have only one source of audio (my car head unit) and on power amp.
But, thank you for the comment, if you told me that i was changing from two different sources i guess i'm doing a good job
3) We will have to solve how to make only one bias point, if i bias the output using the same configuration will do the trick??
The 10uF capacitors play a important role at this circuit and i can explain why:
a) My car audio system was build with focus on quality, so i use a pair of component speaker with a pair of passive cross over each component, a total of 4 passive crossover and a pair os 12' JL subwoofer.
b) The signal is digitaly crossovered to not allow 120Hz frequency and below (my head unit is Pioneer DEH-9880BT), tests made with capacitors from 1uF to 4.7uF do a strange "buzz" when i turn the circuit off.
c) Since i have subwoofer in the car is not interesting to me to make the surround channel reproduce low bass, and the second point is that part of the solution to remove part of the garbage from the surround channel is to not allow too many bass in the channel, including thouse 30Hz frequency.
d) As part of the design, when the surround circuit is turned on it will not kill all the bass but also will not remove all, maybe allowing to pass from midle to high frequency (200Hz and up, sorry can't precise that information), this is good for voice, guitar, symphony orchestra or what ever you hear at the car. You will notice in that sample that the backgroung is pushed forward, mixing that with the full configuration of the car you will hear the voice on the front and that beat song at the rear. Fading away that little voice echo and pushing forward the background, since is playing midle range frequency and up you can pin point exacly that the backgroung music is coming from the back and the voice is coming at the front.
There is another problem that i thought for a long, long time. The bias resistors are in a indirect way "mixing" the signals ( L + R ), when i say indirect is because is not my intention to mix the signal channels but also i can't make it without it. If a 1M bias resistor makes the 10uF charge 10 times slower, if i down the value from 1M to someting about 530K it will make the same capacitor charge 5 times faster, but also will also mix the channels evem more, correct?
Thank you.
