Replacement for TL074 seeked
Norbert Hahn
I want to replace all TL084's im my reverb (Alesis Microverb III) to
get rid of the noise. Although it claimes to use 16 bit ADCs and DACs
the reverb has more noise than my cassettes (TDK MA 90). Replacing
the originals by TL074 was of no help and as some of the circuitry
seems to use high impedance I can only use JFET type quad opamps,
but these seem to be rare.
Norbert Hahn
Monte P McGuire
Quad op amps that sound good are indeed pretty rare, and the number of
JFET quads is even smaller. You can use the Analog Devices AD713 or
the Burr Brown OPA404, but both of these have more noise than the
TL074. They do have far less distortion and much better DC specs.
I've used the 713 a lot and while it's not perfect, it does sound more
pleasant than a TL074.
A person on the net (sax...@liberty.com) has made up some little
modules using a pair of surface mounted Burr Brown OPA2604 that work
really well in every TL074 socket I've tried them in. The 2604 also
has very low voltage noise for a JFET (1/2 of a TL074), low current
noise and greatly improved output drive. Plus, the 2604 sounds
excellent, easily better than anything else I've mentioned. Send him
some mail and order a few to try out.
A big disclaimer: although swapping op amps can improve the sound of a
device, there are lots of reasons why a digital reverb is noisy and
some of them won't be affected by a chip swap. The first reason is
that the signal you feed it can be noisy. When I use my Microverb III
on tracks cut straight to 16 bit digital, I find that there's very
little noise on the output of the reverb; the track is quiet and thus
the effected noise is also low. If you're using a narrow gauge analog
recorder, this will not be the case and the effected noise may be too
obnoxious regardless of what you do to the reverb.
Second, a better than 16 bit noise floor isn't all that hard to get
with a TL074. I'd imagine that most of the real noise from a digital
reverb is effected quantization noise from the ADC. You can get
higher spec converter chips and this may also help, but they're not
cheap and sometimes hard to get quickly. I think the chip you want is
the Burr Brown PCM56PK, which costs about $27 over here in small
quantities. You get about 10dB less distortion compared to the stock
PCM56P chip, and this will probably help more than an op amp swap, at
least spec-wise.
Again, these measures will all improve the reverb, which already
sounds pretty amazing for its price, but you have to think of the
whole system to solve a noise problem... Do some experiments with a
clean mike feed first and see if your reverb is still noisy. Also
point a finger at the console and / or mike preamps or your keyboards.
Happy hacking,
Monte McGuire - N1TBL
mcg...@world.std.com
Alan Gore
>
>Hi,
>
>I want to replace all TL084's im my reverb (Alesis Microverb III) to
>get rid of the noise. Although it claimes to use 16 bit ADCs and DACs
>the reverb has more noise than my cassettes (TDK MA 90). Replacing
>the originals by TL074 was of no help and as some of the circuitry
>seems to use high impedance I can only use JFET type quad opamps,
>but these seem to be rare.
>
>
>
try the Analog Devices AD713, which is the quad version of their AD711.
this device is pin compatible with the TL074, offers improved performance,
and doesn't cost the earth.
cheers. alan
KevinA2597
have very little dsp head room. If the unit is quiter with a simple delay
program or E to E then chances are the problem is the math.
kla
Saxman
NH-> Hi,
NH->
NH-> I want to replace all TL084's im my reverb (Alesis Microverb III)
NH-> to get rid of the noise. Although it claimes to use 16 bit ADCs
NH-> and DACs the reverb has more noise than my cassettes (TDK MA 90).
NH-> Replacing the originals by TL074 was of no help and as some of
NH-> the circuitry seems to use high impedance I can only use JFET
NH-> type quad opamps, but these seem to be rare.
NH->
NH-> Norbert Hahn
Hi Norbert!
Well, if your unit it that noisy, I doubt it is the noise
figure of the opamps that is the problem. In a proper design, you
shouldn't run into noise levels competing with cassette tape
noise, assuming your gains are all optimized and such.
However, overall performance can be improved by going to a
better quality part. I'm including some info on a quad audio
opamp assembly I build, which improves upon the TLO series opamps
in almost every parameter, and should have a lower input voltage
noise by approximately 3 to 6 Db.
Regards,
Everett Carroll
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
--------------------------------------------------
QOP1 High Performance Quad Audio OpAmp Assembly
--------------------------------------------------
This is a quad opamp assembly designed to be a drop-in
performance upgrade for such standard quad parts as the
TLO-84 TLO-74 LF-347 OPA-404 AD-713
and other pin compatible devices. The assembly uses current
generation dual opamp parts which are much lower in distortion
(especially at high frequency), have outstanding output drive
current, and are stable in almost any reasonable circuit
topology. Those and other qualities make this the ideal all-
around drop-in upgrade. It works well as a standard gain-block,
in active filters, as an output line driver, D/A I-V converter,
virtual earth summing amp, etcetera.
Some selected specs :
* THD .0003 % (f=1Khz Av=1, Rl=1K)
* THD .0006 % (f=10Khz Av=1, Rl=1K)
* Output Current 40+ mA (typ., Ta=25 C )
* NOISE 11 nv/sqr-rt hz (f=1khz)
* CMRR 80 dB (minimum)
* SLEW RATE 25V/us (full comp. unity stable)
* GBP 20 MHZ
* Vs +/- 4.5 to 24V
* Zin 10*12 ohms
The device has a FET front-end (BiFet actually, based on
the Burr Brown OPA2604, and just plain sounds good.
=================================================================
1-4 $10.93
5-19 $10.17 Shipping via UPS ground
20-99 $ 9.69 within the continental U.S.
100-499 $ 9.23 is $5.00 for any qty.
sales tax is applicable for California sales.
prices subject to change without notice.
=================================================================
If you are interested in trying some of these, upgrading your
Alesis stuff, consoles, etcetera, let me know.
For now I can only process orders on a pre-paid basis
(check, money order, etc), but this could change if I find enough
interest in the product.
----------------------------------------------------------------------
** Hi-performance UPGRADES for quad audio opamps (ie TLO-84 pinout) **
EMC Music Services.................sax & flute perf, record eng/prod
EMC Engineering Services...........audio/video electronics consulting
sax...@Liberty.com (Everett Carroll) Garden Grove CA USA 714.539.7887
----------------------------------------------------------------------
Randall Bradley
but kinda "big" and a bit "fat" on the bottom. For that reason,
I find that they are actually a bit colored sounding, despite
the fine steady state distortion specs. I prefer other devices
in the single and dual packs, because of this sonic effect. But,
in the typical recording chain, full of nasty electrolytics and
icky op-amps, it might be a good "flavor" to add.
The caveat to this is that if you are monitoring on mini-monitors,
standard big studio monitors, etc., characterized by not much
output below 40Hz. you might never notice it, since your bass is
either really over damped now, or booms before it drops off. (notice
how that kick drum sounds?). Of course, no one has these problems in
their studios, silly me.
-_-_randy bradley_-_
BEAR Labs
"Single Ended Mosfet Amps? I make 'em"
[ these are not rpi's opinions, they're mine ]
David L. Rick
>
>In article <4bc6an$18...@rs18.hrz.th-darmstadt.de>,
ha...@hrz.th-darmstadt.de (Nor
>bert Hahn) says:
>>
>>Hi,
>>
>>get rid of the noise. Although it claimes to use 16 bit ADCs and DACs
>>the reverb has more noise than my cassettes (TDK MA 90). Replacing
>>the originals by TL074 was of no help and as some of the circuitry
>>seems to use high impedance I can only use JFET type quad opamps,
>>but these seem to be rare.
>>
>>
>>
>
>try the Analog Devices AD713, which is the quad version of their AD711.
>this device is pin compatible with the TL074, offers improved
performance,
>and doesn't cost the earth.
>
>cheers. alan
I'm not sure putting in a better opamp will make much difference.
In a lot of equipment, the noise is primarily determined by the
resistance values used in the associated circuitry. Particularly
in cost-sensitive designs, the manufacturer may use larger-than-
optimal resistors in order to save money on capacitors.
In the case of a reverb, there's another issue: reverb algorithms
(being strongly related to IIR filters) are inherently noisy. Even
if the reverb algorithm is carefully designed for noise performance,
reverb itself amplifies what noise is present in the input signal.
This is true even if your "reverb unit" consists of a room in the
basement. Sometimes gating the reverb send can help.
David L. Rick
dr...@hach.com