Do LM7x15s sound any different from L7x15CVs?

A review by The Absolute Kilowattski .......

Review Subject: LM7815s 3 Terminal Regulator

Reviewed by Kilowattski


Upon first listening I was sure that the $1.49 price was a misprint. I've had very highly thought of 3 Terminal Regulators retailing for $3.00 to $4.00 that were nowhere as clean, detailed and involving as this little upstart! A quick double-check at the website confirmed the price. Now I was intrigued!

This LM7815s was quiet, every bit as quiet as any regulation device to come through my listening room. This is almost certainly attributable to the balanced operation. Its level of transparency, in my experience, has only been bested by a handful of 3 Terminal Regulators. Soundstaging was precise, with nice illumination to the rear sides of the presentation. Image specificity was very real, both in terms of size, never bloated or miniaturized, and location. Timbre was remarkable, with just the slightest inclination toward the darker side of neutral. Dynamics were it's strong suit, with crushing power on macrodynamic events and the subtlest of shadings offered on intimate and low level occurrences.

Everything I fed it sounded GREAT, be it 12-inch vinyl or 5-inch aluminum! Small, intimate jazz recordings reeked of cigarette smoke. Large orchestral music loomed before me in its full venue. Singer/songwriters sat on a bar stool just between my speakers. Blues players took their cues from one another along the front wall of my listening room. If not for its slight veiling, in terms of ultimate transparency, and just the slightest tinge of a cooler than natural disposition, this could be a giant killer. Even so, it is certainly the best value in 3 Terminal Regulation I can think of. I dare you to find a more open, articulate and evenhanded performer for less.


;) :D
 
One thing I have noticed though: LM regulators definitely tend to oscillate more easily than their STM counterparts. They usually require more decoupling. [/B]
"Decoupling" is not right term for voltage regulators. Input and output capacitors both are really need for any chip regulator with feedback topology, for stability reason. Min required value and ESR listed at datasheet. Just read carefully, and stay within layout recommendations - and chip regulator never will go to oscillations.
 
Vidalgo said:

"Decoupling" is not right term for voltage regulators. Input and output capacitors both are really need for any chip regulator with feedback topology, for stability reason. Min required value and ESR listed at datasheet. Just read carefully, and stay within layout recommendations - and chip regulator never will go to oscillations.


Well, actually, I think the 100-220 nF capacitors that you have to put close to the regulator's input and output pins can qualify as "decoupling". They are often necessary, even if you use bigger input and output capacitors too anyway. I guess this could lead to debate whether they are decoupling or not. I think their role as preventing high-frequency oscillation qualifies as decoupling. You're talking about feedback, yes; and isn't the feedback in most logic gates' topology that make them prone to oscillation too? And isn't that why we use decoupling capacitors close to their power pins? Ok, I guess all this could be debatable, but I don't think I was so far off with my "decoupling" stuff.

And in my (admittedly limited) experience, I noticed that the 78xx/79xx series from National were more prone to oscillation than the ones from STM. Now whether this really matters in the end once you have provided the right capacitors is another question... it's just my experience that says STM parts tend to "behave" a bit more under stress conditions.

As to what is mentioned in datasheets, I checked in the National datasheet for the LM78xx series: they talk about "bypass capacitors", which for me is the exact same as "decoupling". Oh, and they say the following:

The bypass capacitors, (2.2μF on the input, 1.0μF on the
output) should be ceramic or solid tantalum which have good
high frequency characteristics. If aluminum electrolytics are
used, their values should be 10μF or larger.

Again in my experience, this can be misleading. Depending on the circumstances, eletrolytics larger than 10 µF might not be enough to prevent RF oscillation. You might still need 100 nF ceramic capacitors in parallel...

Just my thoughts.
 
Ok, Ok, don't start discussion about terminology.
For me, it is strange enough that easy to get oscillations from regular voltage regulator like 78xx, provided with typical "deoscillating" :D capacitors, closed to it's pins. Low-drop regulators - another story.
Hmmm, may be we are both talking about small ringings at load transients? Small ceramics really helps to prevent it.

As for topic question.
78xx from National has a better minimal and typical PSRR, other than 78xx from ST. So it provide more clean from ripples voltage and sonic differences may be in precense, depends of schematics of powered circuits (assuming the circuits is an amplifier).