Do all OPA2134PA's sound the same? - Page 2 - diyAudio
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Old 10th November 2010, 11:42 PM   #11
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It's very likely that the OPA2134 has been "blessed" with several die shrinks for cost and yield improvement during its lifetime. When the analog IC houses were in their prime, and I was working for a major customer (Harris) I remember receiving notices of pending die shrinks, which detailed changes in non-data-sheet parameters, or shifts in typical values; min-max of course were almost never changed, and then only for the better.

Last edited by Curmudgeon; 10th November 2010 at 11:47 PM.
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Old 3rd July 2011, 09:11 AM   #12
karmik is offline karmik  Italy
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I came to this thread through a google search for "opa2134 counterfeit". I bought 5 2134s from ebay to build a Rod Elliott's P88 on breadboard (i fully intend to buy it as soon as i can afford it). I rebuilt the first stage twice already (no second stage yet, until i can fix the first), the last iteration seems to *work*, meaning it does amplify signal (140mv input, higher output), but the sound is AWFUL!

It sounds like a mistuned FM radio, completely distorted if i raise the volume even a little on the source and whenever there is a voice in the signal it's all "robotic". I'm gonna rebuild it a third time but i don't see how it can do its job if i mis-wired something but do it so badly.

The other components are
  • MKT caps rated for 100V (signal)
  • MKT caps rated for 63v (bypass on the opamp power pins).
  • 1% Resistors, from china as well (standard values for 3db gain)

Also, the opa2134s lack the "dent" between pin 1 and 8 that i saw on every other DIP package i've ever seen (not many, but still dozens of them).

I'm starting to think i ran into a counterfeit batch. This could very well be just a bad case of mis-wiring on my part (i'm very very very much of a newbie) but the weird distortion i'm getting is so fishy!

Anyone has info about this?
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Old 3rd July 2011, 09:53 AM   #13
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you sure you got the pots right?
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Old 3rd July 2011, 09:57 AM   #14
karmik is offline karmik  Italy
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No pot wired by me, the volume i mentioned raising either is the one from the software mixer inside Windows 7 (outputting to either a USB Dac from Xitel based on PCM2704 or a Realtek integrated soundcard, i tried both) or of a pair of active pc speakers (outputting through the headphones out).
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Old 3rd July 2011, 10:52 AM   #15
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Your description sounds worse than what you'd get from a lowly 741 chip. Closely check your work; if it's not that than those OPA2134s aren't counterfeit... they are dud rejects!
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Old 3rd July 2011, 11:07 AM   #16
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I've made a P88 before and it worked fine, nothing spectacular, but functional.
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Old 3rd July 2011, 11:40 AM   #17
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by karmik View Post
I bought 5 2134s from ebay to build a Rod Elliott's P88 on breadboard ...................

It sounds like a mistuned FM radio, completely distorted if i raise the volume even a little on the source and whenever there is a voice in the signal it's all "robotic". I'm gonna rebuild it a third time but i don't see how it can do its job if i mis-wired something but do it so badly.

Anyone has info about this?
You mention a "breadboard layout" and that could (and without seeing its impossible to say) be the problem.

Maybe post a picture of your project
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Old 3rd July 2011, 05:27 PM   #18
karmik is offline karmik  Italy
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I will rebuild it as i don't trust my skills. I have a Szekeres headphone amp made on breadboard a couple years back and it sounds quite fine so i don't think that's the problem

I want to say that i never said the project itself sounds bad. I'm willing to bet my pajamas that it will sound great once i get it right. I was complaining about my board, which is very likely badly soldered and/or has a counterfeit active element.

I will post a pic as soon as i make a third revision, i want to be extra-sure that i didn't get something wrong in this revision. Give me two or three days thanks for your help and sorry for hijacking the thread! :P
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