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Old 17th April 2014, 12:33 PM   #1
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Default Suggestions for single bipolar input op amp?

As part of a preamplifier project for my home audio system I am seeking a single bipolar op amp to use in a non-inverting configuration. I hope to find one that is not too difficult to use, especially since I plan to build the preamp point-to-point (no pcb).

This is my list of requirements:

Single amplifier
Bipolar input
8-pin inline package (not surface mount)
Output voltage in the 12V range for 15V supply
Output current in the 35ma range into a 2kohm load
Unity-gain stable
Slew rate not too low (about 15 or above)
Gain bandwidth not too high (about 50 or below)

I have some flexibility in the individual parameters, but these guidelines give a good idea of what I am seeking. To give an example, a single version of National Semiconductor LM4562 (or LME49720/49860) would be ideal. I have performed various searches, but the op amps I have found don't meet my needs in regard to one or more requirements.

Can anyone offer suggestions?
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Old 17th April 2014, 09:02 PM   #2
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The LME49710 is the single version of LME49720/4562. I got a bunch of the to99 cans and they're great. Need sensible decoupling as usual, GBW ~55MHz, great sound and quality.

The to99 are expensive compared to DIPs but the lead length may make p-p wiring alot simpler.
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Old 17th April 2014, 09:22 PM   #3
jcx is online now jcx  United States
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that LME fails on the output current - many op amps will not manage 35 mA or perform well if used at even 1/2 the data sheet current limit #

some dual op amps (still in 8 pin DIP) with the extra op amp used as a paralleled buffer to double output current may give more choices, requires a couple of small value current summing R between outputs

but common mode input V may limit unity buffer range more than output stage saturation too - another spec to check

http://nwavguy.blogspot.com/2011/08/...surements.html is a possibly useful summary

Last edited by jcx; 17th April 2014 at 09:50 PM.
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Old 17th April 2014, 09:52 PM   #4
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Quote:
Originally Posted by majerjack View Post
. . . . Output current in the 35ma range into a 2kohm load . . .
Is this a typo, or do I misunderstand the intent? Basic Ohm's Law says this opamp is putting over 2 watts into the 2K ohm load, and would require rail voltages in excess of 70 volts.

Dale
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Old 17th April 2014, 10:13 PM   #5
jcx is online now jcx  United States
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good catch - since one of my interests is headphones we do have to deal with current into much lower impedance - some do need >2 W into 30-50 Ohms for dynamic headroom
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Old 17th April 2014, 10:15 PM   #6
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+1 exactly....

26mA isn't too bad anyway... Id just parallel a few up for phones myself. Or use something like a BUF634 (Since I'm not keen on the new packages)
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Old 18th April 2014, 12:12 AM   #7
juma is offline juma  Serbia
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Quote:
Originally Posted by dchisholm View Post
Is this a typo, or do I misunderstand the intent? Basic Ohm's Law says this opamp is putting over 2 watts into the 2K ohm load, and would require rail voltages in excess of 70 volts.

Dale
Yes, that's right. Let's wait for majerjack to explain what he meant...

Last edited by juma; 18th April 2014 at 12:16 AM.
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Old 18th April 2014, 07:24 AM   #8
AndrewT is offline AndrewT  Scotland
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If the I see an output short circuit current for an opamp, it seems sensible to me to never use more than half that hard limit for "normal" operation.

This would limit most opamps to a maximum operational current of 15mA to 20mA.

Similarly I would set myself an output voltage limit of 2 to 3 volts below the supply rail voltage.

I can usually see this by looking at the plots and seeing where the curves start to become excessive.

Eg,
running a 5534 on +-18Vdc I would expect <15Vpk and <20mA into all loads. BUT NOT AT THE SAME INSTANT.
I would not expect 15Vpk into a 600ohm load.
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Old 18th April 2014, 10:19 AM   #9
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Apologies for the confusion. I blame it on a hurried posting while preparing to go bring home the bacon.

The op amp will not have to produce 12V nor sink 35mA. Actual numbers will be closer to 6V and 6mA. The previous numbers were shown to give an idea of the output capabilities that I am seeking (quoted from op amp data sheets). I want drive characteristics that will give me headroom to spare.

Thanks to all for the replies and tips.

P.S. Does anyone have experience with the Linear Technology LT1028? It looks promising, but I can't find a maximum output current rating in the data sheet.
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Old 18th April 2014, 10:32 AM   #10
Mooly is offline Mooly  United Kingdom
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The LT1028 is specified to drive 600 ohms at a guaranteed level of -/+9.5 volts, and typically -/+11 volts.

Never used any LT opamps for audio apart from experiments with their CFB devices.
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