OPAMPS - Aliexpress vs the real thing, need an explanation

[cornleader]

We should talk about the use of "Chinese" as a synonym for "cheap and low quality". That's a popular reference, but it is not necessarily so.

A huge fraction of every manufactured goods is Chinese, both high and low quality. I've been dealing with Chinese manufacturing for over 20 years now, and the fact is that the Chinese manufacturers are businessmen. They will sell you what you want to buy. Historically, Western businessmen went to China for cheaper labor and lower costs, and demanded the lowest possible costs above all else. The Chinese responded with "OK, if that's what you want." It was a good fit for the labor available in China and their level of technical advancement. This spawned a whole generation of Chinese factories noticing that the cheapest stuff sold best and moving toward their customers' wishes. It also spawned super cheaply made knockoffs and counterfeiting.

I lived through the time of anything Japanese being thought of as inherently cheap; then through the era of American made cars and most other stuff being thought of as cheaply made and poor quality as compared to Japanese goods, especially cars. I had to sit through classes on quality manufacturing and "how the Japanese do it". Originally just a source of cheap labor, Japan worked its way into a major technical and manufacturing nation.

The bottom line is that buying from aliexpress amounts to buying from the cheapest possible source. Full stop. You get what you pay for.
You can get quality goods from China. You do it the same way you get quality goods from the USA, or anywhere else. You do a quality design, specify materials and processes and a finished goods quality testing program; then you keep on working with the manufacturer on a continuous basis to ensure quality stays up.
As an interesting note, the standard of living and wages have risen in China to the point that Chinese businessmen are off-shoring - moving manufacturing jobs and facilities to even lower-cost places to take advantage of the cheaper labor there.

This was my first post here and it went off track rather quickly. I'm going to try to get things back on track here. My post has two images. A chip from digikey and a fake chinese version. I want to know what technical aspect is taking place. The correct terminology. No need to explain aliexpress business model or the moral outcome of using or selling fake components.

Again. are my origional images slew rate? freq responce? What spec do they relate to on the datasheet?

[marcelomd]

Again. are my origional images slew rate? freq responce? What spec do they relate to on the datasheet?

Yup. Looks like the Chinese one has a lower slew rate - "the maximum rate of change of an opamp's output voltage".

There's an opportunity here: I've heard the secret sauce to the original Proco Rat is the low slew rate...

[cornleader]

Again. are my origional images slew rate? freq responce? What spec do they relate to on the datasheet?

Yup. Looks like the Chinese one has a lower slew rate - "the maximum rate of change of an opamp's output voltage".

There's an opportunity here: I've heard the secret sauce to the original Proco Rat is the low slew rate...

Thanks!! Yea some one mentioned the Rat comparison earlier. I have a legit LM308 I will hook up to the scope for a comparison. I am sure there are other specs on my fake chips that would prevent this working in a Rat.

I strongly believe setting up your own experiments to "see" what is happening on a data sheet can be very helpful.

[Mark Hammer]

Slew rate is a measure of "how quickly can the device reach THIS output voltage?".  It can matter for musicians, sometimes, but in a great many cases, "better" slew rates are moot.  The vast majority of op-amps will easily accommodate/achieve plenty of gain at frequencies <8-10khz.  It only starts to matter when the objective is reproducing/processing LOTS of bandwidth with very busy signals.

Probably the best known case of slew rate being central is the Proco Rat, whose "accidental" design (resulting from a mistaken resistor value, according to Art Thompson's history of distortions) pushed the LM308 well past its ability to reproduce upper midrange and higher frequencies.

Of course, how quickly a given chip can provide gain of X amount for this or that frequency, is separate from what may happen when they hit maximum voltage swing.  A chip may well have FAR greater slew rate than is really needed for the task, but clip in a pleasing way when it hits its headroom limits.

[cornleader]

Slew rate is a measure of "how quickly can the device reach THIS output voltage?".  It can matter for musicians, sometimes, but in a great many cases, "better" slew rates are moot.  The vast majority of op-amps will easily accommodate/achieve plenty of gain at frequencies <8-10khz.  It only starts to matter when the objective is reproducing/processing LOTS of bandwidth with very busy signals.

Probably the best known case of slew rate being central is the Proco Rat, whose "accidental" design (resulting from a mistaken resistor value, according to Art Thompson's history of distortions) pushed the LM308 well past its ability to reproduce upper midrange and higher frequencies.

Of course, how quickly a given chip can provide gain of X amount for this or that frequency, is separate from what may happen when they hit maximum voltage swing.  A chip may well have FAR greater slew rate than is really needed for the task, but clip in a pleasing way when it hits its headroom limits.

This is why I'm hooking "good vs bad" components to the scope to see whats going on. Once I start pushing my signal generator past 15kHz everything changes. It's very cool to see. I'm watching RC tone circuits work, putting high frequencies into caps, chips my cat lol. The visual representation of whats going on at the component level is my goal here. Having fake parts to test against the real thing is actually encouraging me to scope everything! I don't really know how to work my cheapest finest scope very well but that's not stopping me.

[m4268588]

You may be get something a little more.