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Old 9th March 2008, 09:56 PM   #1
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Default 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 ). 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.

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Old 10th March 2008, 04:48 PM   #2
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Good news:

Purchased 2x31000uF Sprague capacitors.

http://i26.tinypic.com/otho8y.jpg
http://i30.tinypic.com/10d5xms.jpg
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Old 10th March 2008, 06:22 PM   #3
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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 ?
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Old 11th March 2008, 02:28 AM   #4
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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.
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Old 11th March 2008, 05:12 AM   #5
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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 ).
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Old 24th March 2008, 06:59 PM   #6
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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 .
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Old 25th March 2008, 02:21 AM   #7
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Any pic on the ROE???
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Old 25th March 2008, 05:07 AM   #8
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http://i32.tinypic.com/2rfpiqe.jpg - number 19
and those 2 chemis:
http://i26.tinypic.com/1sb6gk.jpg
number 14 and 15.
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Old 3rd April 2008, 05:13 PM   #9
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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.
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Old 21st May 2008, 10:34 AM   #10
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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.

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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