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Old 16th June 2008, 09:15 PM   #1
trodas is offline trodas  Czech Republic
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Red face JRC4558 - anyone know, where to get em?

I looking for 4pcs of DIP8 versions of JRC4558 (JRC4558D?) opamps.

I know they are the "worst opamps ever" JRC4558, worst op amp EVER.... ), however when I replace them into my speakers with LM4562 (I know, I know, waiting for the AD8599 SOIC samples to be soldered on DIP8 socket and inserted into the sockets...) then oscilation happen.
Opamps stage design questions

A big one. Noise to signal is like 1:1 (if the noise is not stronger, lol) ...

Regardless, I wonder if I can obtain them somewhere to test out if was my modifications that caused the oscilation, or if the circuit need to be changed for the LM4562 or other sensitive and fast opamp...
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Old 16th June 2008, 09:21 PM   #2
anatech is offline anatech  Canada
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Hi trodas,
They aren't that bad. Check out the early 741 types (Yes, I know this is a dual 741 - but it's newer! ). You can pick these up from almost anywhere. Possibly try 4559 or 4460, TL072, TL082 ... the list goes on. I doubt these will oscillate.

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Old 17th June 2008, 03:24 AM   #3
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as long as you don't drive a load less than 5k, the TL072 will make for a nice, less noisy drop-in replacement. if you want actual specs, look up RC4558 or LM1458 at www.datasheetarchive.com
then look up TL072. another good fet input replacement would be LF353. all dual opamps are pinned out the same.
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Old 19th June 2008, 09:43 PM   #4
trodas is offline trodas  Czech Republic
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anatech -
Quote:
They aren't that bad.
Agreed. The amplifier played reltively nicely with them onboard too, so... They are not great, but they will do for most of the low-end applications.

Quote:
Possibly try 4559 or 4460, TL072, TL082 ... the list goes on. I doubt these will oscillate.
Thanks for suggestions. What about NE5532 then? I just tested them and believe or not, again oscilations, even in the default scheme...
http://s232.photobucket.com/albums/e...-51_HT_mod.gif

Now it is possible that these more modern opamps just does not handle ZERO gain, as the circuit seems to have?!


unclejed613 - less that 5k? That should not be the case, as the input resistance of TDA amplifiers are around 20k or so...

Quote:
look up TL072. another good fet input replacement would be LF353
Thanks. But can they handle zero gain?
I think I will change the R9 to 12k or 15k, witch should introduce some gain and stabilize (fingers crossed?) the opamps... What do you think?
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Old 19th June 2008, 11:41 PM   #5
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Hi

Your schematic doesn't have zero gain, but unity gain (1), so any unity stable op amp will work....
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Old 20th June 2008, 10:25 AM   #6
trodas is offline trodas  Czech Republic
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Okay, point taken. But both LM4562 and NE5532 produce in the schematic very nasty oscilations that is producing a strong audio noise/brum...

Witch is why I looking for the JRC4558 opamps to get at least noise-free output back
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Old 21st June 2008, 09:04 AM   #7
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RC4580

JRC version ---> NJM4580
http://semicon.njr.co.jp/njr/hp/file...o?_mediaId=152

TI version ---> RC4580
http://www.ti.com/lit/gpn/rc4580

 Operating Voltage . . . 2 V to 18 V
 Low Noise Voltage . . . 0.8 μVrms (TYP)
 Wide GBW . . . 12 MHz (TYP)
 Low THD . . . 0.0005% (TYP)
 Slew Rate . . . 5 V/μs (TYP)
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Old 21st June 2008, 09:13 AM   #8
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Have you tried to take out C117 and/or C7 when using the 4562?

Jan Didden
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Old 21st June 2008, 10:57 PM   #9
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Hi trodas,
The NE5532 is unity gain stable. Therefore, your decoupling caps are not sufficient, or defective. Something is fishy there, poor PCB design? I say this because I've never had an NE5532 oscillate when dropping into a spot occupied with a 4558, 1458 or anything like those.

You may be stuck with the 4558 as the manufacturer may have "fixed" a bad design with a slow op amp. Hard to say. You could install 1 uF ceramic caps across to power supply pins. Avoid using signal ground as the return. That might actually be your problem.

-Chris
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Old 21st June 2008, 11:01 PM   #10
trodas is offline trodas  Czech Republic
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abbacat66 - thank you, this is interesting. However I would preffer the original 4558 anyway, because the noise I hearing now is TERRIBLY ANNOYING, and I did not fully believe in the "compatibility" anymore

The Japan site is nice and informative (there is the NJM4558D infos: http://semicon.njr.co.jp/njr/hp/prod...TAIL_MOVE_SPEC ) but no sample order?
Where I can obtain these then?



janneman - Yes. I run it like that right now.
Noisy as hell

Even with the C7 present it seems to me (but I could remember it wrong, of course) was the noise a bit smaller...

Suggestions what to do to stop the oscilations are more that welcome.
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