[sdiy] OT: TL07x Friend or Foe?

mike ruberto somnium7 at gmail.com
Thu Sep 30 02:04:33 CEST 2010

 This may be of interest if you haven't already found it -

Of particular interest to me is the ability to compare results for the
TL071 and TLE2072. It is clear to see the TLE2072 is quite well off
compared to the older brother. Based on more ad-hoc testing with my
JBL/Urei project, the depth of my wallet and these excellent
measurement results from Mr. Groner it looks like the TLE2072 is the
winner in my search for the ideal TL07x replacement. I also like that
this device can run on 19 volt rails considering my compressor and
some other equipment in my setup has 18V rails and the 07X devices
tend to run pretty warm. Perhaps this has something to do with the
poor performance of these devices in the 7110.

Out of curiosity I checked out Groner's results for the LT1358 since I
really enjoyed the sound of the 1359. It seems this expensive little
chunk of silicon isn't worth it's cost for the performance it
provides. Yet I love the sound of it. Interestingly the THD plots show
a particularly rounded performance curve and I wonder about that.
While it has nice figures for noise levels it has fairly high THD.
Maybe my ears like the manner in which the device becomes distorted.

As for the other fairly exotic opamps I will be holding them for
special projects like microphone preamps or sound card upgrades. The
7110 has always been known for having a strong character to its sound
and I don't want that to change. It is more important to reduce the
hiss to reasonable levels and the TLE2074 does that handsomely and for
pocket change at that. The TL074s in the sidechain pathways will
remain as they obviously have the DC precision necessary to achieve
outstanding control of the VCA and compression levels.

The remainder of the audio path consists of a VCA and another opamp
with transistor buffer for driving the transformer. This opamp is the
NE5534 which is an oldie but goody. For kicks I swapped it for an
LT1468 and also an AD843. No discernible difference in sound and the
AD843 became too hot to touch after a few minutes. Very high quiescent
current and heavy load at high gains isn't a good combination. The
5534 stays.

Overall I am pleased with the compressor now. With one exception - it
is really hard to make the two compress the same even with stereo
linking. And I thought an LM13700 VCO took a lot of knob twiddling to
get right. Wow!

On Tue, Sep 28, 2010 at 1:04 AM, David G. Dixon
<dixon at interchange.ubc.ca> wrote:
> Did you just try one specimen of TL074?  Are they all the same, or did you
> get a bum one?  I've used dozens of the little beasties, and my system is
> virtually noise-free and I don't notice any loss of high frequencies, but
> then again I'm processing VCO-derived waveforms and not audio (and my
> hearing peters out at about 13kHz owing to aural self-abuse).  I'd really
> like to know WHY your compressor sounds this way.
> Here is the list of opamps tried, reordered from best sound to worst sound,
> with slew rates (in V/us), gain-bandwidth products (in MHz) and noise at 1
> kHz (in nV/Hz^0.5) tabulated (all numbers rounded to nearest integer):
> LT1359 - Hiss very low. Sounds very good.         SR = 600   GBW = 25   N =
> 8
> TLE2144 - Hiss very low. Sounds good.     SR =  45   GBW =  6   N = 11
> TLE2074 - Hiss very low. Sounds good.     SR =  35   GBW =  9   N = 12
> OPA404 - Hiss very low. Sounds good.      SR =  35   GBW =  6   N = 15
> OPA4131 - Hiss low. Sounds OK.            SR =  10   GBW =  4   N = 15
> TL074 - Hiss loud. Sounds poor.           SR =  13   GBW =  3   N = 18
> The LT1359 is obviously a really high-quality op-amp (and it costs about 10
> times what TL074 costs as well).  There are piles of other specs one could
> look at, but I would guess that these are the important ones for audio.
> Still, even with a GBW of only 3 MHz, there should still be tons of
> frequency headroom for audio at unity gain.   The noise numbers don't look
> terribly different -- certainly not enough to give audible hiss in the
> TL074.  The low slew rates could perhaps cause a bit of third-harmonic
> distortion at high frequencies in signals with large amplitudes.  However, I
> can't imagine that the effect of any of these numbers would even be
> noticeable for audio signals.
> I'd really like to hear what the gurus have to say about this issue.

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