[sdiy] OT: TL07x Friend or Foe?
David G. Dixon
dixon at interchange.ubc.ca
Tue Sep 28 07:04:46 CEST 2010
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 =
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.
More information about the Synth-diy