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fake opa627's in the wild.
May 23, 2008 at 9:25 PM Post #76 of 184
Quote:

Originally Posted by Beefy /img/forum/go_quote.gif
I just measured my OPA627BP and 637AP that were bought from eBay seller Parts and Audio. All four measured 48-56k ohm between pins 1 and 5.


You might be just lucky to get a OPA627AP remarked to BP. Also remember to measure resistance in both positive/negative directions, I see some fakes measures different resistance from different directions. For me, the 4 0018WM155 opa627bp got from ebay seller trigeminal05, one has no read, the other three has around 18K. I guess the ones have 18K resistance are remarked AD711, and the one without resistance could be anything from junk JRC to opa132/134.
 
May 24, 2008 at 12:24 AM Post #79 of 184
Quote:

Originally Posted by eboy2003 /img/forum/go_quote.gif
Also remember to measure resistance in both positive/negative directions, I see some fakes measures different resistance from different directions.


Yes, same resistance in both directions, as per the schematic.

Quote:

Originally Posted by naamanf /img/forum/go_quote.gif
I have some legit 637s that read about 50k.


Interesting. More confirmation anyone?
 
May 24, 2008 at 2:08 AM Post #80 of 184
I bought the OPA627AP from Digikey and the OPA627BP off ebay.

The BPs read at 52k and 54k
The APs read at 64k and 60k

One very noticeable difference between the two is the volume level. If I have the knob at 9:00 for the AP, I need to turn it to 11:00 for BP to reach the same volume.

In my opinion the APs sound better. They have more separation and clarity. The BPs sound slightly veiled by comparison. I realise these two aren't the same model so perhaps the comparison is flawed.
 
May 24, 2008 at 2:15 AM Post #81 of 184
Ok, I gave into pressure, and got out my trusty meter. Here are the results with info:

OPA627BP's bought from Tube_Buyer on eBay. #0045WM3805. Notch and no circle dimple thingy. Lettering in two colors like the other photos. Circle on bottom with TAIWAN and L01 in center. Pin 1+5 check, both directions = 53K

OPA627AU's from Lawrence. I can only read the model number, they are so small. One on top and one underneath the adapter. Pin 1+5 check, both directions = 52K

So, I have two "good" sources with these. Like I posted in the Zero review thread, I can't tell the difference between the BP's and AU's, now I know why.
smily_headphones1.gif


If someone could check Tube_Buyers other numbered BP's, then we would know if his current batch is good. EDIT: Coredump (over in the Zero thread) pin checked his BP's from Tube_Buyer, they are the same as mine, but the number is 0036WM8420, and he got in the 50's for a reading as well.
smily_headphones1.gif

Lawrence has more AU's already on an adapter ready to go.
smily_headphones1.gif
 
May 24, 2008 at 2:45 AM Post #84 of 184
Quote:

Originally Posted by Henmyr /img/forum/go_quote.gif
Which pin 1 and which is pin 5, and what is your serial number on them and what reading did you get?

EDIT: This is all really strange as I find my 0018WM155 to actually sound very good. I A-B between those 0018WM155 and LT1028 just now, and with this short A-B I prefer the 0018WM155. If these are not OPA627BP then what are they?


x2.
 
May 24, 2008 at 3:33 AM Post #88 of 184
Quote:

Originally Posted by AudioCats /img/forum/go_quote.gif
now, are we sure the pin1/5 resistance measurement is a reliable way to check these chips?
Is it possible that other BB chips might have similar resistor network built in?


Well, it is looking like it is the only reasonable method at the moment. Your seller claims his are verified, and you get good readings from them, so that is a good sign I would think. I've felt that my BP's from Tube_Buyer were good all along, but once measured, I feel far more certain now.

Many folks are coming up with wrong readings, from chips bought from certain sellers, that do not sound good, so this also adds a small amount of validity to the measurement idea.

The more confirmation we get, that the good sounding ones read correctly, the better this will get.
smily_headphones1.gif
The notch vs circle, printing, shape and bottom, all seem to vary too much for a "overall" rule. Or I have missed something.
smily_headphones1.gif
 
May 24, 2008 at 5:45 AM Post #89 of 184
Another tip, if you buy opa627 metal can, AM, BM, SM, make sure pin 4 is connected to the can. Combine with pin 1, 5 resistance check, it pretty much guarantees to detect the fake.
 
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