[email protected] wrote:
...
> With this in mind, I would like to find a better-sounding opamp to replace
> the Analog Devices AD712 (a JFET input design nominally compatible with
> TI's TL072/082) used in the Sony's I/V and output stages.
>
> Are there any specific opamps that could be sonically superior drop-in
> replacements for the AD712? My short list for high-confidence
> consideration includes the JRC NJM2082 (although this is almost identical
> in specifications, offering only a marginal improvement in noise), and the
> A.D. OP-249 for sure. Could anyone describe how these are sonically in
> comparison with the 712?

Yes, lots of choices for the replacement of the AD-712!  First a
description of what I think the AD-712 sounds like (compared to
neutrality of course):
The AD-712 ha very hi-fi sort of sound, the highs and lows seem
empasized relative to the midrange, and neither the lows or highs seem
completely clear and clean.  The bass sounds a bit wooly or out of
control, and the highs a touch brittle.

The JRC NJM2082 is NOT agood choice as far as I am concerned, to me,
they sound very dry and dull.  So much apparent HF roll-off, I checked
for flat
frequency response to be sure something wasn't broken!  I do not believe
it is a case of less HF distortion sounding less bright either, as the
chip had no bloom or air compared to others.  Leave the AD-712 in
compared to this one!

The OP-249 is a nice chip, sounds more neutral than the AD-712, with a
clear, clean presentation.  A little dry in the high end, but not
brittle.  The bass is better in character than the AD-712, but still not
totally accurate.

> Moving down towards some more promising but less certain choices, I have
> located the A.D. OP-275P and OP-285P, which use a bipolar/JFET "Butler"
> front-end. As I am not familiar with this topology, I am not entirely
> certain if the 275/285 are indeed possible replacements for the AD712.
> Again, if anyone has tried these ICs, I would like to know what they
> generally sound like.

I do not like the sound of the OP-275 at all.  It almost sounds as
though the FET and transistor were "fighting" one another, very
indistinct and a loss of low level details.  Very lifeless and
uninvolving.  Not as bad as the JRC though.

> Can some of the Burr-Brown designs also be used as shoe-in subs for the
> AD712? OPA-2604, OPA-2627, OPA-2637, OPA-2134 etc. Again, sonic
> impressions of these ICs would be most helpful.

My top choice for neutrality, and the best sounding IC for audio is the
Burr-Brown OPA-2604/604.  It "sounds" like the best of the tube and
solid state worlds combined.  Smooth, effortless, tight bass, airy
extended highs with no grain, it does few things wrong.  It could have
less noise, but what noise is there intrudes to a lesser extent than the
spec would tend to indicate, has a decently low noise corner.

The other BB chips you mention also sound very good, maybe even better
than the 2604, but they are also VERY much more expensive.  The OPA-2604
definitely
has the best bang for the buck.

> Finally, if there are any other AD712 subs available from other makers, I
> would appreciate the information.

Realize that the AD-712 is just a souped up LF-353/412.  The AD-746
might be another candidate, but it is prone to oscillation in some
drop-in applications, and it is also more expensive than the OPA-2604.
When it's not oscillating, it sounds fairly neutral, but lacks some of
the air and bloom of the OPA-2604 (is the 2604 being euphonic here?  If
it is, I like the slight euphony!), and it does sound like it's high end
goes on forever, no transient signature at all.

Forget the NE-5532, it was a workhorse in it's day, but has been
significantly bettered by almost all the above mentioned chips.  The
OPA-2604 has the same (or better) low Z drive capability as the 5532,
and sounds a lot better doing it.

Note that the BB chips are available from Digi-Key, who now has a
website,
http://www.digikey.com   I believe.

Jon Risch
 

Subject:
            Re: Which Audio op amp?
       Date:
            Wed, 16 Apr 1997 00:27:48 -0700
       From:
            "Jon M. Risch" <[email protected]>
Organization:
            N/A
         To:
            john pucovsky <[email protected]>
 Newsgroups:
            sci.electronics.components
 References:
            1
 

john pucovsky wrote:
>
> Hi. I am going over the skematics of several guitar effects,
> mixers,etc. and was wondering if there is any AUDIBLE difference
> between the various high grade op amps. ie, LF 351,TL 071, TL 081, NE
> 5553 (I think),the OP x type,etc.Also is the 741 type good for non
> audio stuff like control voltage effects ,etc. ? Thank you very much.

John,

Guitar effects , by definition, are aiming at a different purpose than
faithfully amplifying an audio signal.  They are deliberately trying to
generate desirable (in the ears of the guitarist) distortions/effects
that have little to do with accuracy.  On the other hand, devices that
add "nasties" to the desired effect are not as usefull.

Op-amps good for guitar effects circuits:  LF 351,  (soft, warm, an
almost tube-like sound, then TLO-71, then TLO-81 in order of
preference.  The only problem with these bi-fet input chips is that when
their common mode range is exceeded, usually by overdriving the inputs,
they polarity reverse until the signal comes back within the common mode
range.  This generates a violent and unprdictable "fuzz" sound when it
occurs.  One solution is to double-up on the batteries, either two 9
volts in series, or +/- 9V to help avoid this from occuring.

Other good options are the so-called micropower/lowpower op-amps, which
help prevent dead batteries.  The problem with these is that they
typically are noisy and have limited slew and drive capability (which
adds undesirable and uncontrolled distortion).  A good example of these
that work well for audio/guitar use is the Texas Instruments TLE-2061
(single), 2062 (dual), and 2064 (quad).  The current draw at idle of the
quad part is less than 1/3 the draw of the afore mentioned bi-fet single
op-amps!  These sound a little crisper than the LF351, but certainly
better than a 741, etc.

As for op-amps for use in linear amplification or filtering stages, (and
possibly effects, it wouldn't hurt to listen), my personal favorite is
the Burr-Brown OPA-2604 (dual), OPA-604 (single) IC.  What little sound
it has sounds like a really tight accurate tube amp with no boom or
screech to the lows or highs.  Quite possibly THE best op-amp for
accurate audio use.  Other good sounding/accurate op-amps are (in
descending order, my opinion), PMI(AD) OP-249 (dual, I don't think this
one is available in a single package), Analog Devices OP-275,  and in a
pinch the NE5532 (you could do worse).  Be aware that all these like
lots of current, and will suck a battery dry quickly (overnight), so
they are more appropriate for AC supplied gear.

Hope this helps,

Jon Risch

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