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OPA1656: High-Performance CMOS Audio Op Amp
OPA1656: High-Performance CMOS Audio Op Amp
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Old 16th March 2020, 02:46 PM   #261
BrianL is offline BrianL  United States
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OPA1656: High-Performance CMOS Audio Op Amp
Also note, that for TI and many other manufacturers, at one time it was in vogue to release the same IC in multiple temperature ranges -- 0->70C, -40->85C, -40->125C, etc., as different orderable items. Often the only thing in the specs that was different was the temperature. Maybe sometimes some DC specs were different (like DC offset or offset drift). Almost universally, the actual die in the package was the same. So, you'll see multiple versions with ancient op-amps like the TL071.

It took years, but someone finally figured that the cost of doing this (separate devices with just slightly differing manufacturing flows, separate inventory, etc.) for essentially the same product was expensive. Now, as John says, you'll see just one item specified over it's maximum recommended range, though you may see the same chip released separately automotive-qualified and commercial versions. The automotive likely has differences due to higher testing/qualification requirements, but ultimately still the same piece of silicon inside and either version will work the same for DIY audio.
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Old 19th March 2020, 06:41 PM   #262
ClaudeG is offline ClaudeG
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Couldn’t leave things as they were…

In particular there were these 2 excellent Op amps, having a lot of common but offering a slightly different music representation, perhaps the ADA4627-1 small additional airyness/lightness being a tad more seductive (while the OPA1656 groove can be addictive)… but which one is truer ?

I let the 2 op amps burn-in an additional 20h and decided to use my Ipod as source. Hardly HIFI, but the purpose was solely to be able to monitor things. The Ipod can just drive my Beyer to the right volume level, being the souce direct option. Then I can introduce the simple HP amp, adjust the volume on it, so any change to the music presentation comes from that test rig which is mainly a double op amp per channel.

After another 20h of burn-in sound is settled. TBH I can’t tell if it really improved after the initial 5h, as direct comparison is impossible, but my feeling is negligeable if anything . It used to burn-in initialy though, the first hour mainly and then slightly so.

This test revealed again how excellent both op amps are and that they have more similarities than differences. However, the ADA4627-1 sounded still a tad more open up, airy and with a higher tonality balance. But in comparison to the direct source it turned out it lightens and brightens things a tad. Ads sparkling, takes off weight. Sounds fun though, but less true to the source.

On the other hand, the OPA1656 turned out to be very very close to the source, neutral in fact. Its tonality and balance are true, details are what they are and its massive punch weight are the real ones. In fact it hasn’t really a dark balance : it has a neutral one and the ADA4627-1 chip is in fact a tad brighter, sparkles and shines a tad (and the ADA4625-1 I turned down becomes though quite bright in return).

This gives us options to adjust the tonal balance. If you want pure HIFI and an excellent component that is neutral and incredibly fun, then the OPA1656 is simply an amazing chip, probably state of the art. If you feel on the other hand your output stage needs a bit of extra sparkling, then the ADA4627-1 is a very valuable option… to help adjusting the tonal balance.

I am not sure one can do much better in terms of HIFI than the OPA1656, integrated chip or not (how the world has changed !) as long as it is correctly implemented and used, but let’s see if it reacts to Class A and gets even better, well bearing in mind that air for improvement is very very thin now, at least to my ears.



Claude
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Old 19th March 2020, 09:53 PM   #263
rsavas is offline rsavas  Canada
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Big difference in price but not necessarily sound quality using your ears, as the test bed
Factor in that the ADA4627-1 is a single & OPA1656 is a dual
Good info none the less, thanks, JohnC and the the TI/BB team should be very proud of their accomplishments.
1) ADA4627-1ARZ = $7.81 each
2) OPA1656IDR = $2.72 each

What gain are you running in your testing? Power Amp? Beyer = beyerdynamic, what model? headphones driven directly?

Read through the thread a bit, seems you have a few different test setups you are evaluating these devices in.
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Old 19th March 2020, 10:55 PM   #264
ClaudeG is offline ClaudeG
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Hi

If my understanding of the schematic of the Classic 47 is right then gain is 3.1, so quite lowish. Well, just had a quick look at it, didn't play with that anyway, you to check if you want... and yes, driven directly in this 'test rig'.

This is all just for a convenient preselection (to avoid wrecking a delicate board), gain in MY application (eg my Chipo RIAA) will be the one I have chosen for the second stage, and that is at the moment x28 (29dB). No way higher, but I have the possibility to adjust downwards if needed (x15 or even x10). My highish gain didn't affect the noise and it could enable me to drive directly some power amps, in case of...

I understand that different gains (and set ups, not to mention I normaly always listen to loudspeakers) could lead to different findings, hence me just doing my preselection that way, but keeping all parts and trying first the 2 or 3 I retained to hear in what direction the wind blows and if general impressions are indeed confirmed... and what fine tuning might be required. But that's another story, for the other thread preferably, there are other parameters to consider for that RIAA amp

HP are Beyerdynamics DT990, the old and trustfull initial version from the late 80s, made for the pros (not the current DT990 PRO!) - the one with 600R impedance, 1/4" plug and a more linear frequency response than today. Perhaps not the most resolving nowadays but more than enough to assess these differences and still a nice and proven HP for that kind of stuff IMHO. Used it a lot a few decades ago when monitoring opera recordings, another story. Pity they tweaked it later for portable devices and a different market, reducing impedance to 250R and changing some quality bits on the rare 600Rversion, but well...

Sorry, OFF TOPIC!

Claude
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Old 20th March 2020, 04:41 AM   #265
dotneck335 is offline dotneck335  United States
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The OPA1656 is obviously a world-class performer in all aspects. The question is, due to its extremely fast nature (GBW=55 MHz), what's the best way to keep it from oscillating when used as a replacement IC in older designs? The usual 100nF cap across the power pins is a good start, but is that enough? Will a 100pF cap across the feedback resistor tame it sufficiently without sacrificing performance?
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Old 20th March 2020, 04:45 AM   #266
JohnYang1997 is offline JohnYang1997
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Quote:
Originally Posted by dotneck335 View Post
The OPA1656 is obviously a world-class performer in all aspects. The question is, due to its extremely fast nature (GBW=55 MHz), what's the best way to keep it from oscillating when used as a replacement IC in older designs? The usual 100nF cap across the power pins is a good start, but is that enough? Will a 100pF cap across the feedback resistor tame it sufficiently without sacrificing performance?
If the circuit itself is regular it's difficult to make it oscillate. However old designs seem to like using tricks that only works with certain opamps. In that sense, it may oscillate. The 1656 itself is not prone to oscillation.
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Old 24th March 2020, 06:26 PM   #267
Zoji6645 is offline Zoji6645  United States
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Default OPA1656

I just chip rolled a Carver C-2 preamp with all OPA1656 (except the headphone amp which was OPA2156, because I wanted R-R input). Worked fantastically.
I added 0.1uF caps on the back side and had not stability problems. I have a 400MHz scope and saw nothing untoward. Used Browndog adaptors.
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Old 24th March 2020, 07:24 PM   #268
mlloyd1 is offline mlloyd1  United States
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OPA1656: High-Performance CMOS Audio Op Amp
ClaudeG:

I had a pair of the original DT-990, also.
They were indeed VERY nice AND very comfortable as well!
Thanks for reminder of good memories!

mlloyd1

Quote:
Originally Posted by ClaudeG View Post
...
HP are Beyerdynamics DT990, the old and trustfull initial version from the late 80s, made for the pros (not the current DT990 PRO!) - the one with 600R impedance, 1/4" plug and a more linear frequency response than today. Perhaps not the most resolving nowadays but more than enough to assess these differences and still a nice and proven HP for that kind of stuff IMHO. Used it a lot a few decades ago when monitoring opera recordings, another story. Pity they tweaked it later for portable devices and a different market, reducing impedance to 250R and changing some quality bits on the rare 600Rversion, but well...
...
Claude
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Old 24th March 2020, 11:22 PM   #269
ClaudeG is offline ClaudeG
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