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-   -   Yamaha AX-390 (http://www.diyaudio.com/forums/solid-state/119109-yamaha-ax-390-a.html)

Predator864 9th March 2008 10:56 PM

Yamaha AX-390
 
Well, this amp was built in `96.
Nicely built, with 2 transformers, some Elnas and mostly ceramic caps.

I like how this amp sounds, but i think it can do better.

My first and obvious ideea is to change the 2 large reservoir caps. They`re 6800uF at 56V, a small to fair value I guess. Even my CDP has a larger reservoir cap ( 10.000 uF :D ). I have 2 Russian 15.000uF/80V caps next to me, doing nothing. But this is this enough ?

In the next part, I will remove those 2 ceramic caps at the CD-P input.
And afterwards, I dont know.

That`s we`re you guys come in. Help me improve this little beast.

http://aycu12.webshots.com/image/483...8384225_th.jpg
http://aycu05.webshots.com/image/458...0721264_th.jpg
http://aycu28.webshots.com/image/464...2110932_th.jpg
http://aycu30.webshots.com/image/465...0647575_th.jpg
http://aycu09.webshots.com/image/448...1730563_th.jpg
http://aycu26.webshots.com/image/454...7020230_th.jpg
http://aycu35.webshots.com/image/459...8918840_th.jpg

Predator864 10th March 2008 05:48 PM

Good news:

Purchased 2x31000uF Sprague capacitors.

http://i26.tinypic.com/otho8y.jpg
http://i30.tinypic.com/10d5xms.jpg

Predator864 10th March 2008 07:22 PM

Damn, cannot edit.
Measured the main transformer voltages.
~35,5V in IDLE
~35V in LOAD

And this gives us a theoretical voltage in VDc
~50,055V in IDLE
~49,35V in LOAD

If we include the diodes dropout (which i didnt calculate) i think (theoretical) we will have ~ 48V in LOAD.
Pretty close to my 2 Sprague capacitors.

What do you think ?

Leolabs 11th March 2008 03:28 AM

You need something like 63V but i don't think changing something 6800uF to 31000uF will improve so much on the sound.Get yourself a pair of 10000uF/63V are enough.Better spend some $$$ on replacing the ceramic caps with something better.

Predator864 11th March 2008 06:12 AM

Well the ceramic caps are Toshiba. I`m thinking not to change them. Only where that is necessary.

Gladly, my 2 31000uF we`re a bargain ( 10 Euros ).

Predator864 24th March 2008 07:59 PM

Hi,

A small "choosing" problem.

1. 10000uF/63Vx2 Korea Chemi-Con. 10$ both.
2. 12000uF/63Vx2 Nippon Chemi-Con. 12$ both.
3. 10000uF/63Vx2 ROE. 10$ both .

Leolabs 25th March 2008 03:21 AM

Any pic on the ROE???:D

Predator864 25th March 2008 06:07 AM

http://i32.tinypic.com/2rfpiqe.jpg - number 19
and those 2 chemis:
http://i26.tinypic.com/1sb6gk.jpg
number 14 and 15.

Predator864 3rd April 2008 06:13 PM

I`ve searched for parts that might be changed to gain some improvements.

The first thing, is the bridge rectifier. I might change this to four Schottkys and bypass them with 0,1uF ceramic. Before the bridge I`m thinking about putting some coils and 1Ohm resistors.

Next to the Power Transistors I`ve spotted some resistors that might be changed: 2x47O, 2x560, 2x47K, 2x100K, 2x6,8K, 4x5,6K. There are no pots. The collector-emitter Voltage might be changed by using another fixed resistor.

The Power Transistors are made by Sanken : 2SA1695/2SC4468.

The final Reservoir Caps are 2 Siemens AL-ELKO 17,000uF 75V.

Predator864 21st May 2008 11:34 AM

OK, I received the caps yesterday. They are pretty heavy and bulky.
I focused my attention on the Amplifier CD Player Input.

2 Ceramic caps, 6 resistors, 2 electrolytics and one OPAMP (NJM2068).
The NJM is in SIL Package. Some Browndogs adaptors will fix this.
I am interested in changing this OPAMP.

I have the following at hand: OPA132, OPA2132, THS4032.
The CD Player is equipped with LT1361 which has a pretty high slew rate. :D

The CDP DC offset is low, 2-3mV, while the amplifier offset is 15mV (peak)

Here is the input PCB : http://www.uploadgeek.com/uploads456/0/P3106818.JPG


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