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Old 1st November 2011, 03:10 AM   #1
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Default dual opamp recommendations for active X-over?

Greetings,

I'm building the Elliot Sound Product's active X-over kit. It calls for 7 8-pin dual op amps. The instructions say that the TL072 is the most economical option, but doesn't make any other suggestions. They cost from $0.47 to $1.72 at Mouser, so I'm willing to spend a few more $$ if it means I may get better sound. I've been perusing National's web site and Mouser, and I realize that I don't even know what would make an op-amp sound better. Common Mode Rejection Ratio (whatever that is)? slew rate? Input offset voltage?

The kit supplies it with +/- 15V. My X-over frequency is ~200Hz. Any advice?

-Byron
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Old 1st November 2011, 04:02 AM   #2
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I believe you are working with line-level signals (you didn't post either a schematic or a link, and I didn't take the time to hunt down that particular project) so the TL07x family will probably give moderate performance at rock-bottom parts cost.

The offset parameters are probably of no concern, as long as they aren't obscene. CMRR may be of interest, depending on the filter circuit topology. I'd pay attention to slew rate and unity-gain bandwidth, followed closely by THD at moderately high signal levels. (If you can find THD spec'd for a 1 or 2 volt RMS output level, that's a good one to compare.) I doubt that noise will be a problem for any self-respecting opamp that has adequate speed.

As I recall, some active filter topologies put more severe demands on opamp performance OUTSIDE the filter's passband than you may guess at first glance. With a little effort you should be able to find an article or App Note talking about that. (Grad students have been analyzing every possible aspect of the Sallen & Key architectures for about half a century.)

As an alternative to the TL07x family at only slightly greater cost, consider the NE5532/NE5534A devices. Yeah, they have been around for over 30 years now, but overall they have excellent cost/performance tradeoffs - it looks like the engineers at Signetics got it right the first time when they designed those chips.

Dale
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Old 1st November 2011, 04:02 AM   #3
Davey is offline Davey  United States
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Byron,

You might get various answers regarding the subjective sound quality of op-amps, but for fairly tried and true dual op-amp that will work without oscillation in most circuits try these:

Digi-Key - OPA2134PA-ND (Manufacturer - OPA2134PA)

Dave.
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Old 1st November 2011, 04:29 AM   #4
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The only Opamp I think is ok need +/-12 VDC , guess wich ! Then there is discret opamps at a much higher cost.
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Old 1st November 2011, 05:26 AM   #5
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Included is the diagram. This is from the part of the public part of the site, so I guess it's OK to post. Values are for a 310Hz X-over point.

Erlend, I have +/- VDC, but, no, I can't guess which in the only Opamp you think is OK.

Hi Byron, I'm pretty sure Rod is very strict about people not reproducing any graphics off his site elsewhere so I have removed the attachment. I assume this is project 09 Linkwitz-Riley Electronic Crossover anyone who wants to see the circuit diagram please follow the link

Last edited by wintermute; 1st November 2011 at 07:08 AM. Reason: remove attachment
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Old 2nd November 2011, 01:06 PM   #6
Mooly is offline Mooly  United Kingdom
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The TL072 is a very decent performer when used within it's loading limits although I notice more and more that it seems to be fashionable to criticise its performance.

The bipolar 5532 is OK as a straightforward amplifier but it does have a much higher power consumption than the TLO72 and also much higher (due to being bjt) DC offsets.

The OPA2134 mentioned earlier is a good choice.
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