arcam fmj a32 dim display noise

dazzz

Member
2013-04-07 3:01 pm
ashdod
This is my 2 project I worked about a year
arcam fmj a32
and
denon dvd 2900

I still have a little problem amplifier
When the display to dim mode
There is a little noise from the speakers. High frequency
When the display is turned off or in full light
Quiet.
I tested the amplifier ground.
All the star ground
All chassis connections.
5V voltage display clean.
From what I know from other products SMD capacitors
Can introduce oscillations to the display circuit.

Again little problem that everyone arcam amplifiers have
If someone has a tip how to solve it, I'd love to hear

I shot this video of the noise
Link to the video on YouTube
https://www.youtube.com/watch?v=96Q8uRQ1yxw&nohtml5=False
 
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dazzz

Member
2013-04-07 3:01 pm
ashdod

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dazzz

Member
2013-04-07 3:01 pm
ashdod
Did the fault appear after you "worked" on this project?

The problem was always before I started working on the project.
This amp burned two years ago
I started
Repair Project
Then I did it so is the project comprehensively improve it
It sounds amazing
Even 70 percent of power is at room temperature.
Before the project he was heats a lot.
Then burned in flames.
Darlington transistors 15 SAP burned
and a lot smd resistor and diode burn .
I switched to SAP 16
This amp mostly SMD components
Many protection circuits
No one at the time could not believe that I could fix it
Because I fixed it with just a multimeter
And capacitor tester
Paper and pencil
And 20 pages of circuit analysis
Until I solved all its problems.

All amplifiers ARCAM
Have this problem
The noise is only a dim display on.
I was able to significantly bring down the noise level
By addressing circuit 5 volts.
But the noise still exists, though weaker
I guess it has to do SMD capacitors
In the display circuit

This thread i opened two years ago wan started the repair project. And improvement
http://www.diyaudio.com/forums/solid-state/248632-my-diy-arcam-fmj-32-amp-mod.html
 
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dazzz

Member
2013-04-07 3:01 pm
ashdod
I was able to resolve the shrill noise
Almost completely
By replacing the op amp from LT072 to OPA1662
Z111
Z113

At the input of the pre-amplifier
Shrill intensity Reduced About 50 percent .
The most important problem of Small clicks sounded from the speakers when I up and down the volume completely disappeared :)
I later Also replace the op amps
Z112
Z114

to OPA1662
I only had two units at the moment
I will order another couple and see
If the problem is completely solved.
(Usually I really like the sound tone of the op amps JFET-based But they are much more noisy )

Input Bias Current of the OPA1662 bigger 600nA
Compared to the LT072.... 65na
But because of the resistor values in this part circuit
low
So I was not to worried About offset error.
 

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