Op-amp "upgrade" for TL074 IC
Peter
I am running a car-type 3-way electronic crossover (Alphasonic) that
uses 14-pin DIP 074 op-amps in the circuit. Would it be worthwhile to
replace these with "better" op-amps? REcommendations?
Thanks
Peter
Greg J Szekeres
If you do, its always best to check the opperation
with a scope, etc., to make sure no spurious opperation
exists. I don't know all the brands, but if
you knew what kind of op-amps they put in some of the head units,
you would just forget it all.
greg
cue...@my-dejanews.com
audi...@hotmail.com (Peter) wrote:
> Hi,
> I am running a car-type 3-way electronic crossover (Alphasonic) that
> uses 14-pin DIP 074 op-amps in the circuit. Would it be worthwhile to
> replace these with "better" op-amps? REcommendations?
>
No if you're using it in your car! As it is a line-level application, chances
are that they are not going to "contamine" the signal much and it certainly
won't be noticable in a car. But if you DO decide to replace them, make very
sure you use other BiFET / JFET type opamp. There are probably several other
things you could do to improve the performance - grounding, power supply
decoupling etc.
Mats
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Robert J. Berghammer
I have no Idee.
Peter wrote in message <36ab644...@news.pacific.net.sg>...
>Hi,
>I am running a car-type 3-way electronic crossover (Alphasonic) that
>uses 14-pin DIP 074 op-amps in the circuit. Would it be worthwhile to
>replace these with "better" op-amps? REcommendations?
>
>Thanks
>Peter
>
Bernd Ludwig
>
> Forgot to mention that I am using the car crossover in my home audio.
> At first, I fed it off a 12 volt DC power supply. I then injected sine
> waves of differing freqs, and monitored the signals with a scope. The
> waveforms on the TL074 op-amps that are located near the DC-to-DC
> convertor portion (in the crossover, the 12 volts is converted to +/-
> 12 volts via a switching circuit) was just unbelievably dirty, with
> plenty of HF noise superimposed on the signals. I next used an
> external, linear, +/- 12 V DC and all signals look very clean, very
> nice. I am just curious, at this stage, if upgrading the opamps would
> do any good, or am I just going to waste my time ?
>
You might try BBs OPA4134: Same kind of OP with better overall
performance, better PSR especially. But additional rail-decoupling with
about 1uF tantalum is imperative with these more up-to-date-devices.
Dropping-in some new OP is no big affair, so why not try it.....
maybe that helps.
Bend
Peter
At first, I fed it off a 12 volt DC power supply. I then injected sine
waves of differing freqs, and monitored the signals with a scope. The
waveforms on the TL074 op-amps that are located near the DC-to-DC
convertor portion (in the crossover, the 12 volts is converted to +/-
12 volts via a switching circuit) was just unbelievably dirty, with
plenty of HF noise superimposed on the signals. I next used an
external, linear, +/- 12 V DC and all signals look very clean, very
nice. I am just curious, at this stage, if upgrading the opamps would
do any good, or am I just going to waste my time ?
Peter
On Sun, 24 Jan 1999 13:31:15 GMT, cue...@my-dejanews.com wrote:
>In article <36ab644...@news.pacific.net.sg>,
> audi...@hotmail.com (Peter) wrote:
>> Hi,
>> I am running a car-type 3-way electronic crossover (Alphasonic) that
>> uses 14-pin DIP 074 op-amps in the circuit. Would it be worthwhile to
>> replace these with "better" op-amps? REcommendations?
>>
>
cue...@my-dejanews.com
improve the psu-decoupling quite a bit. Add small (0,1uF) capacitors from
pins 4 and 11 to signal ground VERY close to the op-amp.
For even better performance - use an external PSU. A built in switching
converter so close to audio circuit sounds like bad news to me. As this a
car- type crossover, chances are they didn't spend to much money on it.
Mats
In article <36ac2249...@news.pacific.net.sg>,
audi...@hotmail.com (Peter) wrote:
> Forgot to mention that I am using the car crossover in my home audio.
> At first, I fed it off a 12 volt DC power supply. I then injected sine
> waves of differing freqs, and monitored the signals with a scope. The
> waveforms on the TL074 op-amps that are located near the DC-to-DC
> convertor portion (in the crossover, the 12 volts is converted to +/-
> 12 volts via a switching circuit) was just unbelievably dirty, with
> plenty of HF noise superimposed on the signals. I next used an
> external, linear, +/- 12 V DC and all signals look very clean, very
> nice. I am just curious, at this stage, if upgrading the opamps would
> do any good, or am I just going to waste my time ?
>
> Peter
-----------== Posted via Deja News, The Discussion Network ==----------
Gordon Waters
Peter <audi...@hotmail.com> wrote:
>Hi,
>I am running a car-type 3-way electronic crossover (Alphasonic) that
>uses 14-pin DIP 074 op-amps in the circuit. Would it be worthwhile to
>replace these with "better" op-amps? REcommendations?
EX3? If so, I've already beat you to trying that. Didn't seem to make
much difference.
However, this WAS back in the late 1980s, so there might be some better
op amps out there now, for the purpose... it's been so long ago, frankly,
that I'd probably have to go crack open the case to see what I actually
did use to replace the original op-amps with... ^_^;
In any case, if you DO find a trick to lower the noise floor on this
unit, I'd be all ears. IMHO, a fantastic sounding unit, but with just a
little too much hiss. However, I've been running mine on a
higher-than-normal preamp voltage (I'm feeding it from an EQ that can do
about 2-4 volts out) and that has seemed to help a lot- it's more than 10
dB quieter that way, compared to an average 500mv-1V typical preamp feed...
Since the rails in the EX3 are at +- 15 volts, I'd guess that you might
even be able to feed an up to 8V preamp into it. With that, you'd
probably be able to get a near-100 dB effective SN out of it, even before
any mods...
Regards,
Gordon.
who's had his EX3 in constant use since 1984, installed in 4 different
cars... never a moment's trouble, either...
--
GALAXY convention --------- Anime Weekend Atlanta 5- October 8-10,1999
/| || //| // /| ,, //~// //~// //~// ----- Marriott Gwinnett Hotel
//|| ||//||// //|| ./ //_// //_// //_// --- http://www.anime.net/~awa
//~~|| |/ |/ //~~|| / ,,_// ,,_// ,,_// Gordon Waters-...@crl.com
Gordon Waters
Peter <audi...@hotmail.com> wrote:
>Forgot to mention that I am using the car crossover in my home audio.
>At first, I fed it off a 12 volt DC power supply. I then injected sine
>waves of differing freqs, and monitored the signals with a scope. The
>waveforms on the TL074 op-amps that are located near the DC-to-DC
>convertor portion (in the crossover, the 12 volts is converted to +/-
>12 volts via a switching circuit) was just unbelievably dirty, with
>plenty of HF noise superimposed on the signals. I next used an
>external, linear, +/- 12 V DC and all signals look very clean, very
>nice. I am just curious, at this stage, if upgrading the opamps would
>do any good, or am I just going to waste my time ?
Ah HA! I didn't have the equipment to test for this type of thing when I
tinkered with mine, (no O-scope handy back in '89!) but this sounds quite
like a reasonable explanation as to why just changing the op-amps didn't
change the noise floor.
However, IIRC, aren't the op-amps near the chopper supply the section for
the sub-bass output? If so, I would think that the superimposed noise on
this section would probably much less noticable, as it would probably be
above the FR capabilities of the subwoofer speakers...
I'd forgotten that the EX3 was +- 12V. For whatever reason, I remembered
it as +-15V. Must have been all those old Orion and PPI amp phantom-power
stuff I used to tinker around with... they actually were +- 15v...
Hmmm... as for the present, it'd be pretty simple to rig up a phantom power
supply for that EX3 from my old Zapco 200a, which has a extra +- 40V
output from it's Energy Storage Module. A couple of regulators, some
good LCR filtering... and with a new crop of high-voltage capable
newer op-amps (+- 18V or more compatible)...
Maybe that ol' codger's got some new life left in it yet. I've always
liked the filter characteristics themselves, and with the little bit of
hiss gone... hmmmm...
Regards,
Gordon.
Gordon Waters
>This has NOTHING to do with the type of op-amp used. Instead, you need to
>improve the psu-decoupling quite a bit. Add small (0,1uF) capacitors from
>pins 4 and 11 to signal ground VERY close to the op-amp.
>For even better performance - use an external PSU. A built in switching
>converter so close to audio circuit sounds like bad news to me. As this a
>car- type crossover, chances are they didn't spend to much money on it.
True, especially when this crossover sold for a list price of only $129,
back in 1984.
However, it was the bang-for-the-buck champion of car stereo crossovers
for many years, in that it was one of only crossovers with a) a true 4th
order LP on the sub b) over/under-lappable sub/midbass crossover points
c) CONTINUOUSLY variable frequencies on ALL crossover points and d)
flexibility in configuration unlike anything else of the time- the
option to run as a 3 way, with 4th order sub LP, 2nd order LP and HP on
the bandpass and 2nd order on the high-freq HP, or as a 2-way with 4th
order LP and 2nd order HP, OR as a symmetric 4th order LP/HP 2-way with
"adjustable" HP Q-factor (you could cascade the 2 HP sections, and since
they had independant freq. adjustments, you could change the shape of
the HP curve knee quite significantly by seperating one from the other
in frequency). Some of those features are STILL not available in many of
even the most exotic currently-available car or home stereo
crossovers/signal processors!
In short, it was probably the best single piece of car stereo equipment
I've ever purchased, and it's the only piece to survive throughout all
the myriad systems I've assembled in various cars of mine over the years.