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Old 28th January 2004, 08:31 PM   #1
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Default Analog active xover

Hi all,

This is my first post in the speaker forum. I tried to get some answers about my active xover in the solid state forum, but no one replied.

What would be best, SMD resistors or normal ones that need drilling?

SMD gives a smaller layout, but are difficult for most DIY folks to get. Normal resistors are alot bigger and more easy to come by.

Is there any difference in sound?

Are PP caps ok for sound?

What about OPamps, what do you prefer?

Please look at my plan too and comment on it.

Thanks

\Jens
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Old 29th January 2004, 12:29 AM   #2
maylar is offline maylar  United States
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There's no advantage to SMD except size. Most people chose metal film resistors because of low thermal noise, low temperature coefficients, good stability and they're available with 1% tolerances if you need it.

What's a PP cap?

Everyone has their own favorite opamps. Check web sites for Linear Technology, Burr Brown (TI), and Maxim. Low noise and unity gain stability are things to look for. Also be aware that some are only available in SMT packages nowadays.

Nice block diagram. Looks like a big project.
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Old 29th January 2004, 07:04 AM   #3
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PP probably means PolyPropylene.

Just a guess.
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Old 29th January 2004, 08:51 AM   #4
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All I can say with regards to surface mount is, if you can avoid using it then do, its just more of a faff to use SMT, also if something goes wrong with thru hole its easier to repair or fault find.

My active xovers use polystyrene layer caps with 1% metal films and they sound very very good. The op amps used are OPA627's from BB and AD6010's? surface mounts from Analog Devices. These all sound fantastic. Others to consider are the OPA2134 from BB, the AD 6020 from AD the AD's are surface mount.

The OPA627's are always priased as one of the best but only use them if you can get them for free, otherwise they are too expensive.
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Old 29th January 2004, 09:21 AM   #5
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Default xover

Hi,

Sorry I schould be more precise, PP means PolyPropylene.

I'd like to use dual opamps due to the layout.

I'm making a PCB at the moment, two layers all leaded components.

I plan to use LM833N (ON semi) for the prototype, these are cheap and are good enough to check that the circuit is ok.

Thanks

\Jens
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Old 29th January 2004, 09:34 AM   #6
UrSv is offline UrSv  Sweden
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SMD makes for a compact layout and today I think they are just as easy to come by as normal through-hole resistors. Building however is a bit more complicated.
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Old 29th January 2004, 12:14 PM   #7
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Id deffo agree with regards to size, much more compact, if you are sure that everything is as you want it in the original design and you know the design will work then by all means go for SMT. But if you intend to tweak till you get the xover perfect or you dont know if the PCB is flawless then go with thru hole.
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Old 29th January 2004, 12:23 PM   #8
Fuling is offline Fuling  Sweden
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You might want to have a look at emitter followers instead of OPamps (as long as the filter doesn´t need gain).
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Old 29th January 2004, 04:42 PM   #9
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Regarding op amps:

It appears that the OPA2134 is hard to beat for sound quality and specs (for audio). It seems to be the standard people measure against. Main disadvantage is price.

The LM833 appears to be a fine alternative. The LM833 gets good personal testimonials in diy crossovers and is quite cost effective. Since it is a "faster" op amp it can require some small capacitors across resistors to stop oscillation occuring from higher frequencies. Beware this oscillation can cause your amp to heat up fast even though it is not in the audio range!

I built 2 crossovers from an identical circuit. One had OPA2134 and the other LM833s. The LM833s version needed 22pF caps at a few of the resistors to stop oscillation. A phono preamp I made also needed them.

I used Dayton Film and Foil Polypropylene Crossover Capacitors
in the input and output side of the OPA1234 crossover. The LM833 version has polyester on board capacitors.

Both versions of the crossover are very clear and detailed without any descernable (by me) added noise. I cannot hear the difference between the two and I am pretty fussy.

Since the OPA2134 version was a gift to someone it was nice to know I had gone all out for good sound. The one I am using now in my setup has the LM833s.

The NE5532 also has it's supporters and like the LM833 and OPA2134 is a low noise choice very suitable for audio range and active crossovers. It does not seem to have the oscillation issues. People express that they get suprisingly warm but this does not seem to cause any failure issues.

It could be that the NE5532 would be better to work with for a prototype than the LM833 because you can avoid dealing with oscillation issues since it's behavior in this respect is more similar to the OPA2134.
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Old 29th January 2004, 08:01 PM   #10
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Default One filter section

Hi,

I have one section of the filter for you to look at.

The jumpers across each EQ section is to bypass it if/when it's not needed.

Please comment.

thanks

\Jens
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