RC4558 and TL072 question

[Christopher Berry]

Here's my first post - a friend recomended that I ask this question here and
said that you were very friendly and responsive.
I've got a fairly old preamp ('86 ASHLY BP41) that I've fixed up (It works
properly now) and I'd like to rejuvenate it a little.
There are 14 RC4558's performing various functions from tone networks to
active crossovers and headphone amplification. There's one TL072 in the
input gain control.
I looked around and the best DIP8 replacements I could find were the OPA2604
and OPA2134's for the RC4558's and the OP249 for the TL072.
I know that the information I usually find is almost always a little dated
so I thought that this might be a good place to ask.
I have the schematic I could send anyone if it makes sense.
Thanks,
Chris Berry (cb)

[Uwe Zimmermann]

Why would you want to replace those opamps? WHat do you expect to
improve?
Both the 4558 and the TL071 are still active device from their
respective manufacturers (SGS Thomson and TI).
These are not top-end operational amplifiers and most probably any
pin-compatible replacement with similar bandwidth, noise figure and
supply voltage range will do...

Uwe.

[Christopher Berry]

Lower noise and distortion would really help me (I'm not satisfied with the
headphone output and tone network noise thresholds and this is a 60db gain
unit!)
Better slew rates would help reduce the overall compression I experience
with the preamp no?
cb

"Uwe Zimmermann" <u...@imit.kth.se> wrote in message
news:3DD977E6...@imit.kth.se...

[Bob Weigel]

You will, especially in circuits where the signal passes through many
stages, see improvement in treble clarity by using higher slew rate
circuits. The headphone circuit...you may want to redesign that part and
use a TDA2822 or some other amp with a watt headroom to avoid loading
distortion there. But it is true that sometimes you wont' notice a lot of
difference putting the best op amp in. It all depends on

1) how many stages and how much gain per stage (eg an amp wired as at unity
gain won't require low noise specs.
And if the signal at that point is fairly low, it won't require very
high slew rate either. )
2) how much drive is required of it at the output. 5332 has a little more
drive than 4558 and lower noise but higher idle power for examples. Often a
lot of trade offs you have to weigh out to really find the best op amp.
Technology today though if you are willing to pay for it minimizes the need
for weighing those things in most applications as heavily.

-Bob
Christopher Berry <christofo...@hotmail.com> wrote in message
news:arbtcc$g68$01$1...@news.t-online.com...

[Christopher Berry]

Thanks Bob.
With 60db overall gain, a presence control, 3 band eq, 1 band parametric EQ,
active fx loops etc, I think I'd be seeing some improvement.
Overall drive at the moment is max 1V as used but the unit . Stated is
+20dBv.
cb

"Bob Weigel" <soundd...@montanadsl.net> wrote in message
news:arcer4$4c9$1...@news.tamerica.net...

[Christopher Berry]

I forgot to add - there's really too much gain for the headphone out and I
really would like to avoid redesigning the headphone out.
It is the least critical application and is next to the transformer and
power switch anyway.
cb

"Bob Weigel" <soundd...@montanadsl.net> wrote in message
news:arcer4$4c9$1...@news.tamerica.net...

[Lizard Blizzard]

So, what's your question?

--
----------------(from OED Mini-Dictionary)-----------------
PUNCTUATION - Apostrophe
Incorrect uses: (i) the apostrophe must not be used with a plural
where there is no possessive sense, as in ~tea's are served here~;
(ii) there is no such word as ~her's, our's, their's, your's~.

Confusions: it's = it is or it has (not 'belonging to it'); correct
uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone);
but ~the dog wagged its tail~ (no apostrophe).
----------------(For the Apostrophe challenged)----------------
From a fully deputized officer of the Apostrophe Police!

[Christopher Berry]

Question: Are these the best replacements to rejuvenate the somewhat dated
preamp?
cb

"Lizard Blizzard" <NOS...@rsccd.org> wrote in message
news:ardmsb$13sgo$5...@hades.csu.net...

[Christopher Berry]

A more precise question would be: are these used as direct replacements
appropriate and likely to give me a noticeable improvement? If you suggest
any alternatives please include your reasoning.
Thanks.
cb

"Lizard Blizzard" <NOS...@rsccd.org> wrote in message
news:ardmsb$13sgo$5...@hades.csu.net...

[Bob Weigel]

Ok, yeah I'd just ID the amp section that is doing most of the gain at least
and replace it with one of those opa numbers optimized for low noise and
you'll possibly hear a little increase in definition as well, at least. The
remaining improvement will probably be very slight but your call. -Bob

Christopher Berry <christofo...@hotmail.com> wrote in message

news:ard1rt$iai$07$1...@news.t-online.com...

[Christopher Berry]

Any ideas for better replacements? I'm thinking especially for the TL072
(the main gain chip).
cb

"Bob Weigel" <soundd...@montanadsl.net> wrote in message

news:ardrr5$77v$1...@news.tamerica.net...

[Bob Weigel]

I thought you'd already gotten opa prefixed Burr brown recommendations. I
don't know them off hand. I know they're all better than the 072 in every
way though pretty much. I'd say if you got a recommendation it's probably a
good one. If you didn't then look through their specs for a jfet input dual
op amp of that pinout. Get the lowest noise one you want to spend the
dollars on that has a bandwidth better than the 072's. -Bob

Christopher Berry <christofo...@hotmail.com> wrote in message

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