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Old 19th October 2005, 11:53 AM   #1
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Default replacing op-amps in mixer

Hey,
I have just aquired a mm electronics 12 channel mixer and am going to replace the op amps on the output boards as at some point in its history one of the boards have been rebuilt and the op amps are noi longer the same on both channels (and one channel seems to be slightly noisier) they are all versions of the 741 that are being used but i want to replace them with somethign a little better and am wondering what would be best? mabey the LF351 or NE5534?
Any help would be apreciated,
Owen
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Old 19th October 2005, 01:35 PM   #2
tlf9999 is offline tlf9999  United States
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Default Re: replacing op-amps in mixer

Quote:
Originally posted by DoomPixie
they are all versions of the 741 that are being used but i want to replace them with somethign a little better and am wondering what would be best? mabey the LF351 or NE5534?

having seen the inside of quite a few "high-end" mixers, I can assure you that either the lf or ne would absolutely constitude "high-end" for this application. Popular "high-end" opamps for this kind of applications are actually those TL0xx series opamps.

It is not surprising that you see the 741, or sometimes 324s in those mixers. And think all the people who argue about how much differrence they hear in those modern opamps when the signal has gone through a few 741s.
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Old 19th October 2005, 06:42 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
do not use tl07* series on the outputs. They do not like cable capacitance.
If 741s work, well sort of, then 5534 will give good output capability, but check for pin compatability regarding offset and compensation. You will also need to check the output gain since the 5534 must be more than times 3 or +5db from memory.
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Old 19th October 2005, 07:58 PM   #4
macboy is offline macboy  Canada
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Quote:
You will also need to check the output gain since the 5534 must be more than times 3 or +5db from memory.
Actually, it is stable only with a voltage gain of 5 or more, not 5 dB or more. A voltage gain of 5 is approximately 14 dB. The 5534 can be compensated for lower gains, but even then it can be finicky and you should have a high speed scope to help ensure that the final circuit is stable. A lower speed, unity-gain-stable opamp would be a better idea.
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Old 19th October 2005, 08:05 PM   #5
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A 5532 might be a good choice. They have good drive capability and they perform well at unity gain.
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Old 20th October 2005, 02:58 AM   #6
jcx is offline jcx  United States
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Default the pricier options:

opa27(bb/ti), op27(ad) and lt1007 are bipolars designed in part with audio in mind

they will match/silightly better the 5532/4 on noise

opa134, opa604 are fet input and slightly noisier than good bipolars but better than 741

ad743 is the lowest noise fet op amp I know of

faster op amps may all have trouble with large cap load from long cables, 50-100 ohm series r or ferrite bead should cure any problems
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Old 20th October 2005, 09:08 AM   #7
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I use opa227 in a mic preamp, it's low noise and easy to wrk with.. but the 5534 is hard to beat...
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Old 20th October 2005, 12:39 PM   #8
tlf9999 is offline tlf9999  United States
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Default Re: the pricier options:

Quote:
Originally posted by jcx
faster op amps may all have trouble with large cap load from long cables,

it depends. those current opamps used for adsl line drivers are very fast and excellent driving capacitive loads.
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Old 20th October 2005, 04:43 PM   #9
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jcx is right that many of those ADSL opamps are poor in driving capacitive loads unless you don't read the datasheet first....
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