General > General Technical Chat
Fake MC12080 prescalers and LM4562 op amps from eBay (China)
floobydust:
It can be worse. I bought OPA627 for use in audio DACs, off eBay and Aliexpress. The IC's have very low distortion and work fine, although they will RF oscillate if you go near the offset trim pins, which I think strange. Non-vanilla op-amp prices are just obscene.
OP627 $25 Digikey
OP627 $4 eBay
AD744 $8 Digikey
AD744 $2 eBay
AD797 $11 Digikey
AD797 $3 eBay
Apparently one possibility with OPA627 knockoffs are some other Burr Brown part or AD744 according to Zeptobars die shots. So I purchased legit AD744 but no RF oscillations at the offset pins, but they do have different sound, a different IC.
So I have no idea what IC's I've actually got :-//
wraper:
--- Quote from: floobydust on August 07, 2020, 09:34:05 pm ---OP627 $25 Digikey
OP627 $4 eBay
AD744 $8 Digikey
AD744 $2 eBay
AD797 $11 Digikey
AD797 $3 eBay
--- End quote ---
None of them are even possibly genuine so savings are non-existent.
OPA627 for $13-16 depending on quantity. https://lcsc.com/product-detail/Precision-OpAmps_Texas-Instruments_OPA627AU-2K5_Texas-Instruments-Texas-Instruments-OPA627AU-2K5_C22061.html
Ebay and aliexpress are not worth even trying for any opamps.
magic:
--- Quote from: floobydust on August 07, 2020, 09:34:05 pm ---So I have no idea what IC's I've actually got :-//
--- End quote ---
Test things like quiescent current, offset voltage, noise, input bias current (is it FET or BJT to begin with?), GBW (shows up as a knee on noise measurements at high gain), slew rate...
Even if you can't identify them, at least you will have some clue if they are any good.
What if they are real 627 :scared:
floobydust:
They could be genuine, we have no idea where the silicon fab is done for these parts. Packaging, font etc. looks like the usual low grade though. I would expect them to be rejects, overruns or untrimmed.
USD $25 for a single op-amp, $50 for a stereo pair from Digikey, OUCH! $37 for DIP-8.
Fake audiophile opamps: OPA627 (AD744?!)
Red Squirrel:
I don't bother at all with Ebay, Amazon etc for parts anymore. Digikey is cheap enough in general and at least I get genuine parts. Basically I feel the piece of mind is worth whatever extra it may cost compared to some deal on Ebay. I have some Amazon parts in my bins like resistors and capacitors but those you can go less wrong, if you don't care too much about specific ratings. (ex: non production stuff and just playing around) Typically that stuff is just to pad an order to get free shipping.
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