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Old 24th December 2012, 05:32 AM   #1
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Default Modify Bx8a with new condensator/capasitor

Hello to everyone

i want to change my condansators of my old bx8a. Because it has buzzing sound and little humming, also sometimes sound is suddenly gone. I look caps and some of them are bucking. I change most of them but i'm not sure which caps for the crossover unit. I have some important problems.

1) There are high voltage caps, 50V, 4700uF, 105 C for low speaker and 35V, 2200uF, 105C for high speaker near power switch. But i didn't find high temp(105 C) caps which is Elna sismic II, Nichicon KZ/FG/KG(audio series). All of them are for 85 C. this fact thinking me, bx8a stock caps doesn't relate with crossover unit, it just about simple power circuit.
This is shematic of BX8a: http://music-electronics-forum.com/t24913/

What should do? If i buy 85C, are there any problem? Also i'm not sure, this caps is about crossover unit or doesn't affect sound quaillty directly. So i need help.

2) Are there anyone inform me which caps should i change for enhance sound quaility? i don't have knowledge on circuits.

This is circuit photos of Bx8a
http://www.badcaps.net/forum/showthread.php?p=289252
Also:
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Old 24th December 2012, 04:27 PM   #2
JMFahey is offline JMFahey  Argentina
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Quote:
which caps should i change for enhance sound quaility?
Please define "enhance".
Power supply caps are power supply caps, don't mess with them unless broken, in which case replace with similar spec ones.
Now if you want to buy snake oil, go for the most esoteric and expensive you can find.
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Old 24th December 2012, 11:42 PM   #3
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Quote:
Originally Posted by JMFahey View Post
Please define "enhance".
Power supply caps are power supply caps, don't mess with them unless broken, in which case replace with similar spec ones.
Now if you want to buy snake oil, go for the most esoteric and expensive you can find.
If you don't know about electronic, you don't need to write anything. Because i don't ask that you answered. Sorry.

Firstly i said that my caps are broken. I know it should be change with same proporties like Voltage, Farad but Temp. is different. I want to take ideas about the people who are experienced.

What do you think, when i talk about "enhance"? What can it be? Enhance is enhance which means universally better treble, better crossover, better bass.

I don't ask that should i change power supply's caps. I ask that do caps which you can see in schemetics, belong to power supply or not? Also if it belongs, does it effect quality of signal?

Last edited by darkdream; 24th December 2012 at 11:46 PM.
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Old 25th December 2012, 10:36 PM   #4
JMFahey is offline JMFahey  Argentina
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Ok, let's go step by step.

1)
Quote:
What do you think, when i talk about "enhance"? What can it be? Enhance is enhance which means universally better treble, better crossover, better bass.
Enhance means different things to different people.
But now that you defined it, the answer is no.
Replacing
Quote:
There are high voltage caps, 50V, 4700uF, 105 C for low speaker and 35V, 2200uF, 105C for high speaker
with others of a (perceived) "better" brand will not change "treble/crosover/bass".
They are, as you suspect, PSU caps.

2)
Quote:
it has buzzing sound and little humming, also sometimes sound is suddenly gone.
You are describing different unrelated symptoms.
I don't say you don't experience them, but be aware you won't find a "single solution" for all of them.
a) "buzzing/humming"? Maybe, but describe better.
Do you hear hum or buzz with the monitor on but volume on 0? ... or at some other level? ... what if you disconnect input cables?
You *may* have a bad PSU cap problem ... you may have grounding problems ... etc.
b) sound is suddenly gone ??? Looks more like bad cables or connectors or bad connections inside the PCB or bad volume pot or bad speaker flexible wires or .................
As you see, the "maybe" list can become very long.
Be as precise as possible to save time.

3)
Quote:
Also i'm not sure, this caps is about crossover unit or doesn't affect sound quaillty directly.
You are right, it doesn't. Specially because you will replace with same value parts.

4)
Quote:
Are there anyone inform me which caps should i change for enhance sound quaility?
You won't ... but there is people who claim otherwise ... and charge $65 for a $3 part, that's why I warned about "snake oil " salesmen.

5) so, in a nutshell, if you have bad caps (of which I am not sure at all), replace them with fresh new same specs, bought from a reputable vendor.

6) In fact I *do* find design problems in that amp schematic, but since nobody complained about them, who am I to disagree?

7) the "badcaps" site you linked to , well, by definition finds bad caps everywhere, that's their mission on Earth
For example, they make a big fuss about
Quote:
The amount of ooze around my capacitors seems to be much greater than what I've seen in other photos, so I'm wondering if more ooze amounts to more serious problems.
Quote:
Wow, those are really leaking..... surprised the speakers still work !
The electrolyte (that brownish substance) can conduct electricity and short components so you should really replace those capacitors and put new ones AFTER cleaning the boards a bit.
Well, it ain't ooze but contact cement glue, applied liberally to dampen cap vibration.

Now, a "veteran" says (correctly):
Quote:
The two big caps are bulging. However, that would add background noise, not reduce sound quality. You might want to check the voltage across those two caps to make sure they didn't fail from running too close to (or over) their rated voltage.
Well, I can answer that.
From the schematic, C55/56 must stand 32V and are rated 50V; and C53/54 are rated 35V and must stand puny 18V , so the answer is : no, they are not under rated *at all*, quite the contrary.
In fact I don't see any reason for them to fail, nor anything relating them to the problems bothering you.
But if any of them is bulging, go ahead and replace it with a similar one.
And I'd start checking where your other problem comes from.
Good luck and enjoy some ayran or tea in my name, on board some of those beautiful ships that criss cross up and down the Bosphorus.
I have very fond memories of Istanbul.
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