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Old 28th December 2002, 01:53 PM   #1
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Default opa627ap/bp

does anybody know the difference between the A grade opa627ap and the B grade opa627bp?
is this op better than the Analog Devices 825?
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Old 28th December 2002, 03:03 PM   #2
halojoy is offline halojoy  Sweden
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Arrow OPA627

I di search with google using words:
opa627ap opa627bp

This guy says he couldn't hear diff between ap and bp
also about OPA2134 and other OPamps:
http://tangentsoft.net/audio/opamps.html

Here you can download OPA627 PDF datasheet
and read about the differnces yourself:
http://www-s.ti.com/sc/ds/opa627.pdf

It is just a matter of KnowHow - how to search! with google

/halo -the great searcher!
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Old 28th December 2002, 03:55 PM   #3
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I like the opa627, alot better than opa(2)134 (2)604 that i have tried.
AD825 is also a good op, but which one thats better i think depends on the application.

I prefer opa627 over the 825.

/kasra
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Old 28th December 2002, 05:47 PM   #4
Bobken is offline Bobken  United Kingdom
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I swapped out all eight 'A' grade OPA 627's with 'B' grades (about a year ago) in my well-modded Assemblage 'Platinum' DAC 3.1, and was pleased with the result.

It was one of the most expensive 'single' mods I have ever done at $160 US plus carriage to UK and Customs etc., from Digikey.

I wouldn't wish to go back now to the earlier ones, but at this cost, it is hard to say it was necessarily good value as far as a particular mod goes.

However, this DAC is excellent (and, in my opinion, justifies the extravagence) and I have done almost everything else I know of to 'gild the lily' as it were, and I was after the last possible fraction of performance from it.
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Old 28th December 2002, 07:51 PM   #5
Electrons are yellow and more is better!
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I wonder what the benefits really were B vs A type?

B type has slightly better DC-specs (which are rather unimportant in the audio band. It's only important at DC.

The noise is lower but was with the A type lower than the digital noise (98 dB S/N), unimportant

The open-loop gain was slightly higher in a application with heavy feedback, unimportant

I can't see that changing from A to B would really improve the sound qualilty....and....be worth the money. Was it for free I would also do this tweak.
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Old 28th December 2002, 11:33 PM   #6
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I doubt you could hear the difference also.

What would really make an improvement and save you a lot of money is biasing the o/p into class A.
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Old 28th December 2002, 11:58 PM   #7
Bobken is offline Bobken  United Kingdom
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Quote:
Originally posted by CraigBuckingham
I doubt you could hear the difference also.

What would really make an improvement and save you a lot of money is biasing the o/p into class A.
You are entitled to your opinion, but I have done the job, and there *is* an improvement which I am pleased with, as I said.

As I also honestly reported, I am not so sure that for many people it would be considered a cost-effective mod., especially if the rest of their system was not of extremely high quality.

That kind of outlay would probably be better spent elsewhere.

There have been many other mods I have caried out to my systems over the years (some of them being extremely time-consuming and also costly) which have been a complete waste of time, but luckily, this was not one of them, and it was a five minute 'plug in' job.

I won't bother you with the perceived results from replacing the four PCM1704 DACs with 'K' grade versions in the same DAC which was nearly as expensive, but which is a nightmare to carry out as they are 20 lead *small* SOICs, as you seem to know better, anyway!

Regards,
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Old 29th December 2002, 08:15 AM   #8
Electrons are yellow and more is better!
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Quote:
Originally posted by CraigBuckingham
I doubt you could hear the difference also.

What would really make an improvement and save you a lot of money is biasing the o/p into class A.
I have added this class A thing into my RIAA amp and my headphone amp and I can't hear a thing, maybe it's possible to measure a difference.

I gather that the greatest benefit is reached when the load (current) is slightly above the internal current of the op's outputstage. For small signals this tweak doesn't harm but how much good does it make? Don't know. The distortion for the OPA627 is 0.000008%, is it neccessary with lower values...?
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Old 29th December 2002, 11:43 PM   #9
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Bobken,

No need to be so sensitive.

Costiss (who started the thread) was asking for opinions and I was one of many offering one.

It was that simple, nothing more nothing less.

Regards, Craig.
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Old 30th December 2002, 12:20 AM   #10
Wombat is offline Wombat  Germany
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Biasing OP amps into Class A seems a new trend.

I tried it with my DAC and the AD826. A FET delivering
constant source of 2.6 mA.

What can i say...

After listening for some days i kicked it out,
the sound had missing precision here and there.

Maybe i will try it in another circuit.
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