These differences correspond to those, which I have in mind from the 80s - by a listening test between Raytheon's OP27 and OP37 in the TO outline - go to
OP-37* datasheet and application note, data sheet, circuit, pdf, cross reference, pinout | Datasheet Archive
and
OP-27 OP-27 Noise Operational Amplifier Very noise Spec | Datasheet Archive
for download the associated datasheet.
BTW I am still looking for the internal schematic of ADA4627/4637.
ADA4627 designed as a 100% drop-in replacement of OPA627 ?
I just recently ran over the ADA4627/37 again for a different purpose than Audio (optoelectronics frontend), but when I saw the large signal step response of the ADA4627 I had a deja vu.
I know that only a very few OPAs do this very strong "snap" during negative slew. One of the very few types with this behavior is the .... OPA627 ! See apended picture. With the very similar performance characteristics on top of that, I would think, that the ADA4627 was planned as a 100% drop-in replacement, otherwise ADIs engineers certainly had eliminated this old fashioned misbehaviour.
From the engineering point of view, really good drop-in replacements use the same circuit as the "original", so I would expect that the ADA4627 is based on the same basic circuit as the OPA627, with some minor improvements, which don't influence drop in compatibility, like better clipping response etc.
Hopefully they didn't introduce additional substrate diodes into the inputs. In this case the OPA4627 could be as "perfect" in common mode distortion with high source impedances as the "original" (See Samuel Groner's OPA paper on this), with some very nice niche applications like buffer for high impedance volume pots etc.
This beast is certainly worthwhile a little bit of measurements to find out, what it's real strengths are (Not alone listening, because ears are often an inappropriate means to differentiate the subtle differences of modern OPAs).
I just recently ran over the ADA4627/37 again for a different purpose than Audio (optoelectronics frontend), but when I saw the large signal step response of the ADA4627 I had a deja vu.
I know that only a very few OPAs do this very strong "snap" during negative slew. One of the very few types with this behavior is the .... OPA627 ! See apended picture. With the very similar performance characteristics on top of that, I would think, that the ADA4627 was planned as a 100% drop-in replacement, otherwise ADIs engineers certainly had eliminated this old fashioned misbehaviour.
From the engineering point of view, really good drop-in replacements use the same circuit as the "original", so I would expect that the ADA4627 is based on the same basic circuit as the OPA627, with some minor improvements, which don't influence drop in compatibility, like better clipping response etc.
Hopefully they didn't introduce additional substrate diodes into the inputs. In this case the OPA4627 could be as "perfect" in common mode distortion with high source impedances as the "original" (See Samuel Groner's OPA paper on this), with some very nice niche applications like buffer for high impedance volume pots etc.
This beast is certainly worthwhile a little bit of measurements to find out, what it's real strengths are (Not alone listening, because ears are often an inappropriate means to differentiate the subtle differences of modern OPAs).
Attachments
I've used ADA-4627 for 1 year, I used it to replace old type Motorolla opamp in MSB link III. Before that, for short time I use LM4562 in that MSB (standard parts).
From Motorolla to LM4652, I hear increase of detail, sounds more natural and bit thinner bass but more punchy and faster than motorolla.
From LM4652 to ADA-4627, I hear more warm vocal, detailed sound especially in midbass and vocal (I don't know how to describe it, more thicker??). But when I compared it to my Musical Fidelity A324 - heavily modified components with LM4652HA (tin casing), the sounds of MSB almost close enough with MF but modified MF sounds more refine, smoother (less grain), and wider soundstage but MSB bit more punchy.
I haven't have time to use ADA4627 in MF, I'm too tired enough when I upgrade in trial error MF almost 1.5 years (sigh...) but I will someday
From Motorolla to LM4652, I hear increase of detail, sounds more natural and bit thinner bass but more punchy and faster than motorolla.
From LM4652 to ADA-4627, I hear more warm vocal, detailed sound especially in midbass and vocal (I don't know how to describe it, more thicker??). But when I compared it to my Musical Fidelity A324 - heavily modified components with LM4652HA (tin casing), the sounds of MSB almost close enough with MF but modified MF sounds more refine, smoother (less grain), and wider soundstage but MSB bit more punchy.
I haven't have time to use ADA4627 in MF, I'm too tired enough when I upgrade in trial error MF almost 1.5 years (sigh...) but I will someday
What I must cosider by the use of such OP-Amps in parametric equalizers like this one from UREI - go to
Urei 545 Parametric Equalizer Schematic
The Musician's Room: What's New?
Thank you for advices.
Urei 545 Parametric Equalizer Schematic
The Musician's Room: What's New?
Thank you for advices.
Hi Guys
Just for fun. I'm putting up a link of my latest studio recording effort.
It's not a perfect mix but the drums, vox, lead guitar, djembe and ac guitar all used Trident Fleximix mic pre's loaded with 4627-1 BRZ in the first stage and LM6171 in the second stage.
Unfortunately, I had the 70Hz filters on the two drum mics.
Bass going in direct through a 12AX7 smooth plate loaded Demeter VTBP-1.
I am going to put them in my mastering stereo compressor/limiter and see if that doesn't thicken things up a bit.
Hope you like.
https://app.box.com/s/qqgmzqpeu8ck39lb9eop
Just for fun. I'm putting up a link of my latest studio recording effort.
It's not a perfect mix but the drums, vox, lead guitar, djembe and ac guitar all used Trident Fleximix mic pre's loaded with 4627-1 BRZ in the first stage and LM6171 in the second stage.
Unfortunately, I had the 70Hz filters on the two drum mics.
Bass going in direct through a 12AX7 smooth plate loaded Demeter VTBP-1.
I am going to put them in my mastering stereo compressor/limiter and see if that doesn't thicken things up a bit.
Hope you like.
https://app.box.com/s/qqgmzqpeu8ck39lb9eop
In comparing the spec sheets of OPA627B and ADA4627B-1, the current noise specs are identical (1.6fA @100 Hz), and the voltage noise favors the 627 only slightly (4.5nv/6.1nv). The 4627 is faster the the 627 (82v/uSec vs. 55), but in inverting mode only. The common-mode rejection is identical at -116 db, and the THD specs are also quite similar, with the 627 having a -3db advantage. But the BIGGEST difference is the $$$$---checking Mouser prices, the OPA627s are $34.65 EACH; the 4627s are $10.76 apiece. As the specifications are quite close to one another, methinks the better than 3x price difference makes the 4627 the clear winner.
4627 vs 4562
Now, I understand the advantage of using a JFET opamp (ADA4627) as opposed to a bi-polar(LM4562) when the source is high impedance, such as a guitar pickup----lower current noise. But, what about AFTER the original input gain stage? Does the 4562's superior THD trump the 4627 in all remaining circuit applications? Such as equalization, buffering, gain control, et cetera?
Now, I understand the advantage of using a JFET opamp (ADA4627) as opposed to a bi-polar(LM4562) when the source is high impedance, such as a guitar pickup----lower current noise. But, what about AFTER the original input gain stage? Does the 4562's superior THD trump the 4627 in all remaining circuit applications? Such as equalization, buffering, gain control, et cetera?
I've used the ADA4627-1 in several applications and it has yet to disappoint me. Thus far, it is my favorite sounding op amp, and I've tried many, including LM4562, AD825, OPA275, OPA2604, OPA2132, OPA2134, OPA211/2211, OPA1612, OPA1642, OPA2107, OPA249, NE5532, LM6171, TL072, LME49990, AD797, OPA827, etc....
Roughly speaking, I'd say it sounds fuller in the lows and more "alive" than something like the LM4562, AD797, or OPA211, yet still with nice detail, and not boring or "clinical". The OPA827 also sounds nice, but not quite as good as the ADA4627-1, IMO. The LME49990 might be better in some applications... but sadly, no longer available. Have never heard the OPA627... too expensive.
Roughly speaking, I'd say it sounds fuller in the lows and more "alive" than something like the LM4562, AD797, or OPA211, yet still with nice detail, and not boring or "clinical". The OPA827 also sounds nice, but not quite as good as the ADA4627-1, IMO. The LME49990 might be better in some applications... but sadly, no longer available. Have never heard the OPA627... too expensive.
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