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op amps for active crossover
op amps for active crossover
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Old 18th October 2006, 08:44 PM   #1
deriver23 is offline deriver23  United States
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Default op amps for active crossover

i plan on building rod elliots 4th order LR active crossover. What high quality opamp shold i use in the output buffer? What should i use to change the gain?

schematic and inf o here
http://sound.westhost.com/project09.htm
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Old 18th October 2006, 10:54 PM   #2
preiter is offline preiter  United States
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Do a search, there are many threads with people expressing opinions on their favorite crossovers.

To add gain, you could reconfigure the input stage to have gain.
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Old 18th October 2006, 10:59 PM   #3
FastEddy is offline FastEddy  United States
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Analog Devices just released a very interesting book (in pdf format). My sub title would be "everything you ever wanted to know about op-amps ... and then some." ... lots of filter circuits and op-amp recommendations, etc.

I got it by subscribing to their new letters re: op-amps ...
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Old 19th October 2006, 06:15 AM   #4
Calvin is offline Calvin  Germany
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Hi,

I recommend FET-type OPs. Since in filter circuits almost always high impedance values exist, FET-types are imo better to couple out the signal. There are many useful types starting from BB´s OPA604/2604, 132/2132, 134/2134/4134 to AnalogDevices AD711/712, 8510/8512, 8610/8620. Using double and Quad-OPs reduces stray effects and keeps the layout compact. With the suggested OPs sound is rather more a function of proper layout, grounding and power supply than anything else.

As an output buffer with gain, I suggest something like in Fig.3c of the BB OPA604 datasheet. This circuit shows more flexibility and clearly better results in driving capacitive loads than just a simple resistor at the output. With this circuit You can tune in on Your´re load situation. Giving best possible signal behaviour (best rectangular wave). The influence of cabling is minimized vastly and You can use even very highly capacitive and/or very long cables. For critical loads like very long cables You should use a OP thats capable of delivering some mA at the output, or use a additional Buffer like the BB BUF634 or an dicrete Buffer circuit.

jauuu
Calvin
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Old 20th October 2006, 07:06 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
look up WaltJung's site.
He describes (in detail) cascading two opamps to create a composite that has excellent input and precision characteristics of a single opamp combined with the output capability of a true IC buffer for driving any sensible cable & load.

He also has a comprehensive article there, for building a high quality discrete buffer. This would replace the buffer in the composite or could be used on it's own if all you need is impedance conversion and no voltage gain.

If you don't fancy implementing these, at least read the articles for the knowledge and then ask the informed question that you aren't aware of at the moment.
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Old 20th October 2006, 07:53 AM   #6
nilsomat is offline nilsomat  Germany
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Quote:
Originally posted by FastEddy
Analog Devices just released a very interesting book (in pdf format). My sub title would be "everything you ever wanted to know about op-amps ... and then some." ... lots of filter circuits and op-amp recommendations, etc.

Hello! Does anyone have a link?
AD site has loads of information, but can become a bit confusing...
Greetings,
Nils
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Old 30th October 2006, 07:46 PM   #7
dougmorse is offline dougmorse  United States
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Default answer to what kind of op-amp

My short answer is 5532. I use 'em.

I do think there is some advantage to using FET types where there is expectation that there is EMI. FETs have less opportunity to demodulate RF, and thus cause interference problems .

By the time any audio signal get to the user, it's alredy been through 100 5532s in the recording process.

Doug
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Old 30th October 2006, 08:19 PM   #8
Ryssen is offline Ryssen  Sweden
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Quote:
By the time any audio signal get to the user, it's alredy been through 100 5532s in the recording process.
Spare them from one more an use LT1469..
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Old 30th October 2006, 08:45 PM   #9
FastEddy is offline FastEddy  United States
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LT1469 = Yes ... http://www.linear.com/pc/productDeta...09,C1022,P1845

( LT1604 = No, don't bother with 16 bit A to D.)

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Old 30th October 2006, 09:55 PM   #10
deriver23 is offline deriver23  United States
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While were talking about active filters what is are good passbands and stopbands for a two way crossover?
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