4558d op amp or 4558dd ?

[plexi12000]

anyone ever try the 4558dd?  suppose to be a "high gain" 4558?

[R.G.]

High gain 4558d???

Opamps routinely have monstrous gains inside, even the "tame" ones. Sounds like an advertising claim to me at first blush.

[UKToecutter]

I think you're being 'led up the garden path' as we say.

Have a look at the following link;

http://archive.ampage.org/threads/5/fxdc/238771/Re_Difference_between_JRC4558D_and_JRC4558DD-1.html

[plexi12000]

haha!!  ok...youre prolly right.  i just hapened to see them (dd) for sale at mojotone........who are overpriced to begin with!  never knew they existed.

thanks for the link UKToecutter!  i'll take a look at it--

[Mark Hammer]

The "open-loop gain" or "gain-bandwidth product" is often shown in datasheets.  It shows you approximately how much gain you can expect the chip to be able to provide at any given frequency.  The chip does not provide that automatically; it must be configured to have that amount of gain via external components.  OPen-loop gain (AKA gain-bandwidth product) is related to, but not the same as, slew rate.

Where an op-amp has greater open-loop gain, that means it is capable of providing considerable gain even at higher frequencies.  If you were building a single-stage mic-preamp for field recordings or sampling nature, you would probably want that high-frequency capability, since that is part of what "fidelity" means.  However, in the world of rock and roll, our bandwidth needs often tend to peak at around 6khz, simply because that's where our speakers tend to run out of steam.  Moreover, if your application is some sort of 9V-based overdrive, not only will you not want to be able to beable to amplify 8khz 1000x, but the limitations imposed by using a 9v supply will also mean that the difference between greater and lesser open-loop gain may well be negligible.

After all, if you are playing basketball on an indoor court with a 7ft ceiling, does it really matter how tall the players are on each team?

[plexi12000]

mark hammer-- awesome man!  yeah....i can understand how you put it. thank you.  it's CAPABLE..if other components MAKE it perform that way. just because you pop in your circuit doesnt mean you "get" anything different.  or at least i think thats what you mean! lol   thanks for taking the time to explain-

[PRR]

For reasons which you can find in feedback theory, op-amp gain falls with frequency, to unity-gain at a specified "GBW" frequency.

For older opamps this was 1MHz. Limited by the maximum speed of classic PNP devices in classic processes.

From this fact we can write-down the gain of an op-amp:

1MHz ------- 1
100KHz ---- 10
10KHz ---- 100
1KHz --- 1,000
100Hz - 10,000
10Hz - 100,000

All opamps with 1MHz GBW will have gain about 1,000 at 1KHz.

In very low frequency work (pH meters, critical temperature gauges, analog computers worked very precision), we may worry if the gain below 100hz really keeps rising to 1,000,000 at 1Hz, or if it levels-out at say 50,000 or 100,000. But in audio, who cares?

(More elaborate "compensations" with steeper slopes are possible, but super un-common.)

Increased GBW has been the perpetual quest of opamp makers. Some of the '558 types may be 1.5MHz. But any significant change of GBW requires a fairly complete overhaul of the circuit and the process, making a completely different opamp.

Also a huge GBW makes a layout much more prone to supersonic oscillation.

The JFET-input TL072 series is 3MHz GBW, and thus has "more gain" over the audio band. It is "drop-in for" '4558 in "many circuits". But the whacko things we build, sometimes a '072 will be "better" (at least technically, less bias-sag), and in some '4558 abuses the '072 just won't do the tricks that a '4558 does.

The '4558 was a low-cost part with wide specs so every part made could be sold. It is possible someone could sort-out the parts that fall near the high end of the spec and sell them at a premium. Such differences are sure to be small. Most of them would have no real effect in small audio circuits.

And as Mark said so well-- if your head is already banging the ceiling (clipping), you don't really need taller shoes.