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29 Sep 2016

Yamaha CDX-750E discrete class A Jfet output the hell inside!!!

Yamaha CDX-750E an average CD Player with some tricks became a real hell......an Audiophile CD Player without compromise.......ok, I don't blame you if you don't believe me , that's why you will have a complete DIY tutorial this time!
Good Luck!





...my first attemt was what I call 1st level mod. , that means an accurate recapping and swapping all components on the signal path , swap the opamp with better ones , mounting them on their sockets, , change some value of resistor on LPF filter, skip the muting resistors, damp the mechanical unit and the game is done.....in this way you will have a very nice sounding player quite over the original......but with discrete JFet  you will have a real audiophile beast capable to challenge with great brand and outstanding devices without deface!..............ok! let's start !

...probably you will need a service manual but I had't any and I found all the paths with my tester..... a long job!...then ..                 1)remove both the jumpers between the 2 couple of blu philips capacitors 2) remove C95 and weld a wire by the opamp side 3) weld another wire by the closest DAC side of the other channel jumper 4) lift the resistor R138 (in this case the sockets are useless) 5) in a second time you can stole the dual power supply from the pin 4 and 8 of the socket setting a cap among them...............

...desolder the solenoid L5 and L6 from their in pin and lift them   to isolate even R166 and R167.......now all the LPF circuit is disconnected from output and from the DAC...even the muting!!!!! ...by the way, I want to aware you ......you will listen to heaven after this mod, but  you will  even can hear some imperceptible hum during the normal operation like open/close the drawer ( don't be afraid) , then better you keep your amplifier volume control very low when charging or descharging disk.....and probably you will need a subfrequencies filter if you don't like the strange loop that gives this DAC in this situation......I had gone for the minimum low filter to obtain the best compromise between the very tight bass and a silent operatin mode t............. believe me ,you will hear the magic , I swear!!!!!



...here you are a class A JFet dedicated output........I used a couple of Faichild BF256B with the following Biasing setup , Id=10mA  Vcc=20V  Vgs=0,5V
If you're able to play with suchs small gem you can achieve great result indeed!!!But you can achieve great result from many of them if you like to play with them ;) (I mean FET)
6)the white wires takes the signal from the DAC                            7)the three tongled others, respectively : white +; black- ;grey ground        8) from the red MKT caps we'll take the output signal to carry to L5 and L6


will follow an accurate schematic of this layout



...I used for decouplig different parallel capacitors and among them I used these outstanding tantalum SMD caps used in such great and expensive devices such as Linn , Krell, and much more




..What Yamaha is hiding inside this curious box????Is it a very nice DAC to be hide?or Yamaha shamed and didn't want to show it .....you'll find out soon!!!! For sure we know that it's a very rare DAC in a quite rare CD player....only CDX550 and 750 adopted this DAC and not others even out of the brand Yamaha.......was it a flop or a masterpiece?! or neither of them?!!! at least you'll have my opinion now! ;)





The sound




Rarely I've heard such beauty in sound!..It is really different by the most of CD player I've heard.......the sound comes much more intimate and less congested than an average cd player .....it's not fadiguin at all, and there's no veil...... a lot of detail, but not too much, not a overload of 3°harmonic, but all comes very natural open and refinite....  great deepness with a tight bass and a respectable soundstage ......It seems to listen at a tube cd player without any dubt !
It's really a great Audiophile CD Player now!!!!! 

....ah, by the way from Vasiltech.Ru the propietary Yamaha DAC YM7141 is rated like a "mediocre" DAC !!!!!!!! :o   ... that makes wonder!!!!! Is it my job so wikedly fantastic????! I gues the answer in any case is "YES" :D but (jokes apart) even this DAC is a hell of component!!! 
In any case I'm quite agree with Vasiltech , just 'cause listening at the only 2 original (not tweacked) players with this DAC , you will listen at two mediocre sounding Players for true so I can't do else than share this opinion with Vasiltech .....they are mediocre but not the inner YM7141 DAC ....not at all!!!!It's an outstanding DAC coupled with a poor LPF filter based on JRC4570 opamp with the result that all the CDX750 owners knows very well!!! If you're skilled enough go for this mod. You will find out the magic!!!!   the schematic will comes soon...............

look at this review!......YM7141 is rated to be an average converter
http://www.soundbsessive.com/information-about-dac-chips
/..........ok! Let's try it after this mod. and let me know!! ;)

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