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Old 8th October 2008, 08:29 PM   #1
paba is offline paba  Canada
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Default TL071 and TL072 upgrades

Hi all,

I hope this is the right place to post this.

the stock circuit has TL071 which I since replaced with OPA134 and TL072 which I replaced with OPA2604. Straight drop in for both cases. It is much better now.

I wondering if there is something better still today to try for each of these positions.

I would prefer similar dip package but I guess I could use some conversion sockets for some of the newer chip packages.

Thanks
paba
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Old 8th October 2008, 08:46 PM   #2
DcibeL is offline DcibeL  Canada
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Please use the search function, op-amp swapping has been beaten to death on this forum.

That said, the op-amps everyone is raving about these days are the LM4562 and maybe AD797. Keep in mind that while op-amps are pin compatible, this does not necessarily mean drop-in replacement. You must always look at the surrounding circuit to determine that the op-amp will be stable and operating to it's full potential.
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Old 8th October 2008, 08:55 PM   #3
paba is offline paba  Canada
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Thanks for your response,

I guess I wasnt clear. TL071 and TL072 are JFET op amps with certain specs and sound and output Z. I'm asking for actual experience in replacing TL071 and TL072 specifcally and sucessfully with something else. Not op amp swaping in general.

But I'll check out the datasheets of your suggestions to see if there is an electrical fit.

Thanks
Paul
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Old 8th October 2008, 10:00 PM   #4
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These are often overlooked as upgrade drop in replacements for the TL071 and TL072:

TLE2071
TLE2072

ZAP
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Old 8th October 2008, 10:42 PM   #5
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I use LF412's everywhere I need a JFET. I get them dirt cheap from a surplus house and their specs are great. I searched for that link on opamp noise measurements (a National paper written by Bob Pease or Bob Cordell?) where the LF411 and LF412 fare very well but could not find it.
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Old 9th October 2008, 05:29 PM   #6
wg_ski is offline wg_ski  United States
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LF412 is a low-drift version of the LF353. They should sound exactly the same. They're good for most purposes, but don't like driving cables - output stage gets marginally stable with 300pF load. OPA2604 is the next step up - similar characteristics in the input stage and still unity gain stable for applications where that is needed.
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Old 10th October 2008, 03:07 PM   #7
Bonsai is offline Bonsai  Taiwan
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The LF412 is probably not the best choice for audio. I used the 356 (a distant cousin of the 353) in a preamp I designed in . . . 1979 (my first solo audio effort). Yes, my hair is gray, I like red wine and jazz. These op-amps do not behave well when overdriven. Their strength at the time was low bias curents (at ROOM TEMPERATURE) and relatively high slew rates. So, this was a major step up from the 741 (which was still being used in audio then . . .e.g. the 'Texan' amp that was published in England) and the LM301 (which Bob Dobkin used in a natsemi ap note to demonstrate feedforward compensation). A great advantage with the LF3xx devices was you could feed them straight from the volume pot with no decoupling cap because the bias currents were very low. (The 308 input bias current performance was better over temperature, but it really was designed for DC applications - great T/C amp choice in the 70's and early 80's until LT introduced a slew of great devices for DC applications - I never fell for the IC chopper stabilized op-amps that also came into vogue around te same time)

If you are looking for a real step up now days, ADI's AD797 has to be at the top of the list along with natsemi's LME49713 (CFA) and LME4562 (VFB). The AD797 is not a drop in replacement and requires some RC comp networks on the inputs.

Keep a few key points in mind when using op-amps for audio:-

1. isolate the op-amp output from capacitive loads with a 50 ohm resistor in series with the output (but take the feedback network directly off the op-amp output. This will stop oscillations due to cable capacitance.
2. Place the feedback resistors and the upper and lower leg connections as close as possible to th e inverting input - this is a very important point
3. Check when experimenting that you do not violate the 'unity gain stable' rule.
4. Take care with decoupling


Buck for buck, modern IC op-amps are an engineering marvel and get you into the top league in audio without having to spend silly money. It might be that some esoteric discrete high end designs just pip them but on an 80/20 rule its a no contest win to the op-amps every time.
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Old 10th October 2008, 03:23 PM   #8
wg_ski is offline wg_ski  United States
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Quote:
Originally posted by Bonsai

1. isolate the op-amp output from capacitive loads with a 50 ohm resistor in series with the output (but take the feedback network directly off the op-amp output. This will stop oscillations due to cable capacitance.
This practice, unfortunately is why cables sound different. Depnding on the intentional source resistance or lack thereof interacting with load capacitance, the op-amp's behavior at high frequency changes. Use an op amp that doens't get pi*** with capacitance, or put a high-current buffer inside the feedback loop with it, you'll get a preamp that doensn't care what cable you've got hanging off it. Much like a top-notch discrete design.....
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