Tom's Hardware > Forum > Audio > Pro Audio > Monte M, Scott Dorsey? Direct Replacement for LF351 op amp?

Monte M, Scott Dorsey? Direct Replacement for LF351 op amp?

Forum Audio : Pro Audio - Monte M, Scott Dorsey? Direct Replacement for LF351 op amp?

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Anonymous   08-08-2004 at 06:46:03 AM

Archived from groups: rec.audio.pro (More info?)

 

I need a direct pin compatible replacement for the LF351 op amp?
TL072? LT1357? OP275? Is there something better, with low chances of
oscillation? Mainly for line input. Thanks in advance.

Nathan Eldred
http://www.atlasproaudio.com

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Anonymous   08-09-2004 at 12:16:32 AM
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Archived from groups: rec.audio.pro (More info?)

 

"Nathan Eldred"
>
> I need a direct pin compatible replacement for the LF351 op amp?


** Then you need a single op-amp.


> TL072? LT1357? OP275?


** Those are duals - except for the 1357.


Is there something better, with low chances of
> oscillation? Mainly for line input. Thanks in advance.


** The TL071 is equivalent.

The OPA627 has exceptional specs - and price too.




............ Phil

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Anonymous   08-08-2004 at 12:53:09 PM
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Archived from groups: rec.audio.pro (More info?)

 

LF351 is a single channel device. I'd choose a BurrBrown OPA134PA or OPA604PA.

--
Stephen Sank, Owner & Ribbon Mic Restorer
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"Nathan Eldred" <atlasproaudio@hotmail.com> wrote in message
news:b14184ab.0408072346.5b13e26f@posting.google.com...
> I need a direct pin compatible replacement for the LF351 op amp?
> TL072? LT1357? OP275? Is there something better, with low chances of
> oscillation? Mainly for line input. Thanks in advance.
>
> Nathan Eldred
> http://www.atlasproaudio.com

Reply to Anonymous
Anonymous   08-08-2004 at 08:54:08 PM
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Archived from groups: rec.audio.pro (More info?)

 

On 8 Aug 2004 00:46:03 -0700, in rec.audio.pro you wrote:

>I need a direct pin compatible replacement for the LF351 op amp?
>TL072? LT1357? OP275? Is there something better, with low chances of
>oscillation? Mainly for line input. Thanks in advance.
>
>Nathan Eldred
>http://www.atlasproaudio.com


Hi Nathan,

LF351 is an old FET input device with fair drive spec and so-so noise
spec. For a drop-in replacement, try the TI OPA604AP. Much lower
root-Hz noise, much higher slew rate, way more output current, IMO
better sounding (though the 351 wasn't bad for its era), and similarly
unity gain stable. An alternative drop-in might be the OPA132AP --
less expensive, even lower noise.

Ignore JW -- both are good sounding parts :-)

JL

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Anonymous   08-08-2004 at 04:53:19 PM
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Archived from groups: rec.audio.pro (More info?)

 

In article <b14184ab.0408072346.5b13e26f@posting.google.com> atlasproaudio@hotmail.com writes:

> I need a direct pin compatible replacement for the LF351 op amp?

How about another LF351? It's probably perfect for the design in which
it's used. The only reason I can see to replace it is if died.

Of course if you want to design something else around the existing
socket, that's your business. Start plugging in pin-compatible ICs and
start listening. If it sounds OK, put a scope on it and start looking
for oscillations that you can't hear, but which will affect things
that you could hear if you listened hard enough.

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

Reply to Anonymous
Anonymous   08-08-2004 at 10:06:54 PM
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Archived from groups: rec.audio.pro (More info?)

 

In article <b14184ab.0408072346.5b13e26f@posting.google.com>,
atlasproaudio@hotmail.com (Nathan Eldred) wrote:

> I need a direct pin compatible replacement for the LF351 op amp?
> TL072? LT1357? OP275? Is there something better, with low chances of
> oscillation? Mainly for line input. Thanks in advance.

In order from better to worse, the OPA132 is very nice, the OPA604 is a
close second, the AD711 is a slightly souped up replacement for a
generic BiFET that has somewhat less distortion and DC imbalance but
otherwise similar performance, and a TL071 is basically a direct
replacement with marginally different (i.e. better or worse) specs,
depending on who made it.

The OPA604 is basically in the same league as the OPA132, but it has a
little kink in its open loop response way way up there, making it
probably a bit more fussy (stability wise) than a 351. It also sounds
sort of harsh (and also measures more poorly) for a minute or two until
it warms up, whereas the 132 avoids this problem. The nice thing is
that you could add a single small valued cap from the output (pin 6) to
the inverting input (pin 2) to fix up almost any possible layout induced
stability problem, so just consider this if the feedback path is long or
if there's not already such a cap in the circuit.

In reality, by the time the 351 was common, most designers had their
stuff together with respect to HF stability in their PCB layouts. The
previous generation's stuff was a little dicey, and sometimes you'd need
to add feedback caps to deal with excessively long and inductive
feedback paths. These sloppy layouts aren't a problem with stuff like
the 4558, but anything slightly modern like the TL07x would not work in
some of the layouts that will actually function with a 4558.

By that token, modern chips (like the 711, 132 etc) are not that much
more finicky than a 351, so you should probably not worry about HF
stability if the OEM amp was an LF351. Definitely check the circuit for
stability with a scope, but I wouldn't expect problems automatically
like I would with mid-late 70s era gear.


Regards,

Monte McGuire
monte.mcguire@verizon.net

Reply to Anonymous
Anonymous   08-08-2004 at 11:20:26 PM
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Archived from groups: rec.audio.pro (More info?)

 

Monte McGuire <monte.mcguire@verizon.net> wrote:
> atlasproaudio@hotmail.com (Nathan Eldred) wrote:
>
>> I need a direct pin compatible replacement for the LF351 op amp?
>> TL072? LT1357? OP275? Is there something better, with low chances of
>> oscillation? Mainly for line input. Thanks in advance.
>
>In order from better to worse, the OPA132 is very nice, the OPA604 is a
>close second, the AD711 is a slightly souped up replacement for a
>generic BiFET that has somewhat less distortion and DC imbalance but
>otherwise similar performance, and a TL071 is basically a direct
>replacement with marginally different (i.e. better or worse) specs,
>depending on who made it.

The question is what is the circuit? If it's a low gain circuit that
really needs the high input impedance, the LF351 may be just fine.

The OPA604 is rather my favorite singleton for FET-input amps, and
while it has some odd stability issues in EQ circuits, it should be
fine in most circuits that an LF351 works in, if the bypassing and
board layout are good. But it might not be any better than the LF351.

If it's a high gain stage, or even worse, if it's a stage with a gain
control in the feedback loop, the LF351 is probably something you want
to get rid of fast. But if it's just part of a balancing circuit at
unity gain, I doubt replacing it will do any good.

>The OPA604 is basically in the same league as the OPA132, but it has a
>little kink in its open loop response way way up there, making it
>probably a bit more fussy (stability wise) than a 351. It also sounds
>sort of harsh (and also measures more poorly) for a minute or two until
>it warms up, whereas the 132 avoids this problem. The nice thing is
>that you could add a single small valued cap from the output (pin 6) to
>the inverting input (pin 2) to fix up almost any possible layout induced
>stability problem, so just consider this if the feedback path is long or
>if there's not already such a cap in the circuit.

I can't see this being a big deal in an input stage but it can be a real
issue in an EQ network.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Reply to Anonymous
Anonymous   08-09-2004 at 07:12:16 AM
- 0 +

Archived from groups: rec.audio.pro (More info?)

 

(Nathan Eldred) wrote in message news:<b14184ab.0408072346.5b13e26f@posting.google.com>...
> I need a direct pin compatible replacement for the LF351 op amp?
> TL072? LT1357? OP275? Is there something better, with low chances of
> oscillation? Mainly for line input. Thanks in advance.
>
> Nathan Eldred
> http://www.atlasproaudio.com

Nathan,

Is this by any chance for a Sound Workshop Series 30?

I replaced the LF351s with OPA604s in the line inputs of my Series 30.
They oscillated at minimum gain but that was solved with a small cap
connected as Monte suggests. I don't recall the value right now but I
can check that if you want.

Peter Andersson

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