Modfying M-Audio Bx8a

[darkdream]

I want to modify my Bx8a but, i've some important questions.

Can someone try to specify the which one is crossover unit? Here is the schematic of Bx8a:
http://music-electronics-forum.com/t24913/

Also i saw 2 big caps which are "50V 4700uf" and "35V 2200uF" in below of schematics(behind the "power in"), what is the job of them? Why does is so high value? Does is for amp or crossover unit or something?

[Jazz P Bass]

Modify it in which way?
Looking at the schematic you will see in the upper right corner HP & LP.
These are the high pass & low pass outputs to the TDA power IC's.
High pass is UH1 & Low pass is UL1.
The crossover is active. It is comprised of the IC's directly before the HP & LP outputs.
The high capacity caps are for the power supply of each power IC.
They are high value to reduce the ripple voltage & provide 'capacity' as the power IC's are consuming power.

[darkdream]

Modify it in which way?
Looking at the schematic you will see in the upper right corner HP & LP.
These are the high pass & low pass outputs to the TDA power IC's.
High pass is UH1 & Low pass is UL1.
The crossover is active. It is comprised of the IC's directly before the HP & LP outputs.
The high capacity caps are for the power supply of each power IC.
They are high value to reduce the ripple voltage & provide 'capacity' as the power IC's are consuming power.

You're the great. Thank you very much.
It is nearlly as i think. I modify the caps of crossover unit. Also i want to change my high-value caps. My high value caps which are "50V 4700uF" and "35V 2200uF", unfortunately buckling.

If i change my high high value caps with elna sismic 2, does it affect sound quallity? Because it is just related with power? I'm not sure. you know high value caps are very costly, if it doesn't affact sound quallity, i'll change it with reliable and cheaper one.

[Steve Conner]

There is no need to buy "audiophile grade" electrolytic capacitors. The ordinary cheap ones work fine.

[darkdream]

There is no need to buy "audiophile grade" electrolytic capacitors. The ordinary cheap ones work fine.

Thanks. Did you say it for power or crossover? I also change all caps of crossover.

[Steve Conner]

Power. The active crossover circuit shouldn't contain any electrolytic caps: they should all be plastic film.

[Jazz P Bass]

Question for the OP: why are wanting to 'change' the crossover?
New power capacitors I can see as justified.
But the crossover....?

[darkdream]

Power. The active crossover circuit shouldn't contain any electrolytic caps: they should all be plastic film.

Nope, It has, 22uF/16V as you see in the schematic. If i know something wrong, you can explain it.

[darkdream]

Question for the OP: why are wanting to 'change' the crossover?
New power capacitors I can see as justified.
But the crossover....?

I don't understand why you try to say.

Because high quality caps improve frequency response?

[Steve Conner]

These 22uF/16V caps are just for DC blocking. They don't determine the frequency response of the crossover. So, no AC voltage appears across them, and therefore they shouldn't affect the sound quality unless they are actually faulty.

And to be fair, they might well be faulty if they have been stuck inside a hot speaker enclosure for several years.

If you find any large value ceramic capacitors in the filter circuitry, you could replace those for plastic film. High-K ceramic capacitors generate a lot of distortion and should never be used in audio filter networks, but I have seen them used in cheap products.

[darkdream]

These 22uF/16V caps are just for DC blocking. They don't determine the frequency response of the crossover. So, no AC voltage appears across them, and therefore they shouldn't affect the sound quality unless they are actually faulty.

And to be fair, they might well be faulty if they have been stuck inside a hot speaker enclosure for several years.

If you find any large value ceramic capacitors in the filter circuitry, you could replace those for plastic film. High-K ceramic capacitors generate a lot of distortion and should never be used in audio filter networks, but I have seen them used in cheap products.

Thank your very much. But it confused me. I read many articles about modfying. They said: If the crossover contain any caps, they'll definetly affect sound quallity of the speakers. Bacause of their tolerance, fast and true response. They hold and release some current so that it affects quality of sound.

Most of audio grade caps is available because of it. Also most of low cost caps don't have the real value as it is written on it.

Can you see any high-k ceramic caps on this schematic which i should change?

[Steve Conner]

The articles you've read probably relate to hi-fi speakers with passive crossovers. These need high grade capacitors to handle the high voltage and current from the amplifier.

Your speakers are active, the crossover comes before the amplifiers and handles a small high impedance signal, much easier for even cheap capacitors to deal with.

I can't tell from the schematic whether there are any high-k ceramic caps.

[darkdream]

The articles you've read probably relate to hi-fi speakers with passive crossovers. These need high grade capacitors to handle the high voltage and current from the amplifier.

Your speakers are active, the crossover comes before the amplifiers and handles a small high impedance signal, much easier for even cheap capacitors to deal with.

I can't tell from the schematic whether there are any high-k ceramic caps.

I understand, you're right, i don't change the caps which are related with crossover.

It also thinking me:
if i change caps which is 50v-4700uF near power, it affacts my sound, because it handle very high-voltage?

[Steve Conner]

Like most solid-state amps, the amplifier chips in these speakers use negative feedback to reduce distortion. The negative feedback also helps to correct distortion caused by the power supply filter capacitors, the 50V 4700uF ones you are talking about.

So they shouldn't affect the sound unless they are actually faulty. Dried up, bulging, or the like. In audiophile speak, they are "not in the signal path". Upgrading to "audio grade" capacitors probably won't make much difference to the sound quality.

[darkdream]

I really appreciate for your answers. Thank you.