Would this perhaps be an apt description of the LM318? It has a VERY high slew rate (~80v/µSec) and no THD spec on its datasheet.
Hi John,
Currently kind of assessing the OPA1656 following your excellent thread(s) - very modestly in some line output stages of my HIFI.
I will have a listen to various op amps, old favourites and newer ones, from AD, LT and yours because your triggered my curiousity and all your efforts deserve it for sure.
Question...Some op amps can benefit from a Class A bias at their output stage. I was wondering about the OPA1656. I will of course have a proper listen without any 'extra help' first, but do you thing it could possibly benefit from a 2.4mA output bias pulled by a transistor from its negative supply? That would be on only one of its internal op amps (the B op amp).
I take it there is no danger trying, but ask you first and as you designed it you know how it works best... and I wouldn't want not to make optimal use of the few I got
Many thanks for your help and also for all your very informative posts
Claude
PS: had only a brief listening during burning in (couldn't resist- and I liked it
Defo a step forward from the old TI sound I used to know, well done
Currently kind of assessing the OPA1656 following your excellent thread(s) - very modestly in some line output stages of my HIFI.
I will have a listen to various op amps, old favourites and newer ones, from AD, LT and yours because your triggered my curiousity and all your efforts deserve it for sure.
Question...Some op amps can benefit from a Class A bias at their output stage. I was wondering about the OPA1656. I will of course have a proper listen without any 'extra help' first, but do you thing it could possibly benefit from a 2.4mA output bias pulled by a transistor from its negative supply? That would be on only one of its internal op amps (the B op amp).
I take it there is no danger trying, but ask you first and as you designed it you know how it works best... and I wouldn't want not to make optimal use of the few I got
Many thanks for your help and also for all your very informative posts
Claude
PS: had only a brief listening during burning in (couldn't resist- and I liked it
Defo a step forward from the old TI sound I used to know, well done
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OK, Class A biasing being less forward nowadays than in the past for me, I decided make a final point on the evaluation of the FET op amps for my Chipomatic. For details about the shootout and other op amps, please refer to the Chipomatic thread in the Analog Source section. Please no sterile discussion here on the process I went through nor philosophical debate on subjective findings/earings!
I am solely pointing it out here as I tried the OPA1656 mainly because of... John's posts. And it shone, one of the very best op amps I heard so far. I should mention I am not affiliated to TI, these were early examples (perhaps things have improved down the line, pity I can't get current free samples from TI as I can easily from AD) and last but not least I wasn't a fan of the TI sound so far at all. It had 3h of burn in, as the others, and then some listening time, wonder also if it could open up further with time?
Here is a copy paste of the result for OPA1656
OPA1656
In the past I have to say I prefered widely the AD precise sound vs the softer traditional TI sound. I used though the better TIs in output stages of middle class DACs as these benefitted from a more round /warm presentation with less details, as that masked their weaknesses and in fact improved the situation. It did not to my ears when having higher quality stuff and there AD’s speed, airiness, transparency shone, provided you avoided the bright ones. I tried this TI though because it was recommended here. And I must say that it differs from past TIs ! While not having that traditional « what people call old good tube sound », it is still a bit on the warm and musical side while being more more « open » than the TIs I knew. I found it had weight, impact, some airiness, a very good 3D soundstage, lot of details, noise is really very low, body of the instruments so enjoyable, an open treble that though tends a very small tad to the metalic side. This is also a keeper, probably one of the very best high quality all rounder provided you like it a tad warm. This one is also a potential final choice for the Chipo IMHO. There is not much not to like ! I feel it is though still a bit on the dark side, I tend to miss some bass tone differenciations and also the diabolical overall speed/agility from the top AD op amps. That one plays more to the ground, which could be a plus depending on your records and tastes. It is a tad less refined though than the ADA4627-1. Can it improve (mainly open up a bit) if biased in class A ? That is an unkown to be checked…
And finaly after having reviewed all options I had picked up...
Final choice so far is ADA4627-1 and OPA1656, 2 excellent OP amps with a lot of positive in common while proposing opposite flavours… and possibly the AD825 biased in Class A. I also wish to assess how these 2 modern contenders can improve / or not, once biased in Class A.
Just as a side note, I rank this op amp among the very very best... so well done John
Claude
I am solely pointing it out here as I tried the OPA1656 mainly because of... John's posts. And it shone, one of the very best op amps I heard so far. I should mention I am not affiliated to TI, these were early examples (perhaps things have improved down the line, pity I can't get current free samples from TI as I can easily from AD) and last but not least I wasn't a fan of the TI sound so far at all. It had 3h of burn in, as the others, and then some listening time, wonder also if it could open up further with time?
Here is a copy paste of the result for OPA1656
OPA1656
In the past I have to say I prefered widely the AD precise sound vs the softer traditional TI sound. I used though the better TIs in output stages of middle class DACs as these benefitted from a more round /warm presentation with less details, as that masked their weaknesses and in fact improved the situation. It did not to my ears when having higher quality stuff and there AD’s speed, airiness, transparency shone, provided you avoided the bright ones. I tried this TI though because it was recommended here. And I must say that it differs from past TIs ! While not having that traditional « what people call old good tube sound », it is still a bit on the warm and musical side while being more more « open » than the TIs I knew. I found it had weight, impact, some airiness, a very good 3D soundstage, lot of details, noise is really very low, body of the instruments so enjoyable, an open treble that though tends a very small tad to the metalic side. This is also a keeper, probably one of the very best high quality all rounder provided you like it a tad warm. This one is also a potential final choice for the Chipo IMHO. There is not much not to like ! I feel it is though still a bit on the dark side, I tend to miss some bass tone differenciations and also the diabolical overall speed/agility from the top AD op amps. That one plays more to the ground, which could be a plus depending on your records and tastes. It is a tad less refined though than the ADA4627-1. Can it improve (mainly open up a bit) if biased in class A ? That is an unkown to be checked…
And finaly after having reviewed all options I had picked up...
Final choice so far is ADA4627-1 and OPA1656, 2 excellent OP amps with a lot of positive in common while proposing opposite flavours… and possibly the AD825 biased in Class A. I also wish to assess how these 2 modern contenders can improve / or not, once biased in Class A.
Just as a side note, I rank this op amp among the very very best... so well done John
Claude
Yes, indeed, it is a very good op amp... and at a very competitive price.
This being DIY, in my specific case I did not care at all about the price, just the sound.. TBH honest, the most expensive bit in that hobby is me / my time, by far
But for other projects or production, that would be a very different story.
Having said that I would love to improve these 2 options even further as I believe they do already stand a chance vs discrete set ups. The world is changing...
Need a few more OPA1656 to play with (Class A, burn in, decoupling etc.), and time, argh...
Claude
This being DIY, in my specific case I did not care at all about the price, just the sound.. TBH honest, the most expensive bit in that hobby is me / my time, by far
But for other projects or production, that would be a very different story.
Having said that I would love to improve these 2 options even further as I believe they do already stand a chance vs discrete set ups. The world is changing...
Need a few more OPA1656 to play with (Class A, burn in, decoupling etc.), and time, argh...
Claude
Claude,
Thanks for posting your opinion on the opa1656. I'm planning to use it in future products, and your postings confirm it's a good decision to use it.
While you're at it, take a look at the opa1678, seems to be same family, just even lower cost and a little lower performance, would love some opinion on that one too as I'm also planning to use that one in entry level products....
Btw, have you tried some of Linear Tech's hybrid voltage mode / current mode feedback opamps, like the lt1363/lt1364, would love some opinions on those too.... They might be a little trickier to use, they're fast....
Thanks for posting your opinion on the opa1656. I'm planning to use it in future products, and your postings confirm it's a good decision to use it.
While you're at it, take a look at the opa1678, seems to be same family, just even lower cost and a little lower performance, would love some opinion on that one too as I'm also planning to use that one in entry level products....
Btw, have you tried some of Linear Tech's hybrid voltage mode / current mode feedback opamps, like the lt1363/lt1364, would love some opinions on those too.... They might be a little trickier to use, they're fast....
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Hi Soekris
Nope, I haven't tried OPA1678 and indeed being FET input it could have been a contender for my intented Chipo use. My "test rig" though accepts any kind of op amp as HP amp.
So sad TI doesn't give me access to free samples, in which case I wouldn't mind building them on small boards and try them...
LT1363/1364, no I haven't tried them. Indeed very fast and higher noise... are these FET inputs?
Claude
Nope, I haven't tried OPA1678 and indeed being FET input it could have been a contender for my intented Chipo use. My "test rig" though accepts any kind of op amp as HP amp.
So sad TI doesn't give me access to free samples, in which case I wouldn't mind building them on small boards and try them...
LT1363/1364, no I haven't tried them. Indeed very fast and higher noise... are these FET inputs?
Claude
Hi Cdsgame
Short : I/V stage and gain=1 output buffer.
Long : Test rig was the Classic 47 HP amp, but in case of the intented final Chipomatic RIAA amp installation it will be output buffer with gain and DC offset control (eg one half for the second/final stage after the passive RIAA filter, the other half is DC offset control, probably a bit odd I know)
Claude
Short : I/V stage and gain=1 output buffer.
Long : Test rig was the Classic 47 HP amp, but in case of the intented final Chipomatic RIAA amp installation it will be output buffer with gain and DC offset control (eg one half for the second/final stage after the passive RIAA filter, the other half is DC offset control, probably a bit odd I know)
Claude
Not usually. I had some scrap wafers that I gave to Jan and SY who I had invited to come see our facility.
OK, Class A biasing being less forward nowadays than in the past for me, I decided make a final point on the evaluation of the FET op amps for my Chipomatic. For details about the shootout and other op amps, please refer to the Chipomatic thread in the Analog Source section. Please no sterile discussion here on the process I went through nor philosophical debate on subjective findings/earings!
I am solely pointing it out here as I tried the OPA1656 mainly because of... John's posts. And it shone, one of the very best op amps I heard so far. I should mention I am not affiliated to TI, these were early examples (perhaps things have improved down the line, pity I can't get current free samples from TI as I can easily from AD) and last but not least I wasn't a fan of the TI sound so far at all. It had 3h of burn in, as the others, and then some listening time, wonder also if it could open up further with time?
Here is a copy paste of the result for OPA1656
OPA1656
In the past I have to say I prefered widely the AD precise sound vs the softer traditional TI sound. I used though the better TIs in output stages of middle class DACs as these benefitted from a more round /warm presentation with less details, as that masked their weaknesses and in fact improved the situation. It did not to my ears when having higher quality stuff and there AD’s speed, airiness, transparency shone, provided you avoided the bright ones. I tried this TI though because it was recommended here. And I must say that it differs from past TIs ! While not having that traditional « what people call old good tube sound », it is still a bit on the warm and musical side while being more more « open » than the TIs I knew. I found it had weight, impact, some airiness, a very good 3D soundstage, lot of details, noise is really very low, body of the instruments so enjoyable, an open treble that though tends a very small tad to the metalic side. This is also a keeper, probably one of the very best high quality all rounder provided you like it a tad warm. This one is also a potential final choice for the Chipo IMHO. There is not much not to like ! I feel it is though still a bit on the dark side, I tend to miss some bass tone differenciations and also the diabolical overall speed/agility from the top AD op amps. That one plays more to the ground, which could be a plus depending on your records and tastes. It is a tad less refined though than the ADA4627-1. Can it improve (mainly open up a bit) if biased in class A ? That is an unkown to be checked…
And finaly after having reviewed all options I had picked up...
Final choice so far is ADA4627-1 and OPA1656, 2 excellent OP amps with a lot of positive in common while proposing opposite flavours… and possibly the AD825 biased in Class A. I also wish to assess how these 2 modern contenders can improve / or not, once biased in Class A.
Just as a side note, I rank this op amp among the very very best... so well done John
Claude
Thanks for the excellent review! I'm glad you enjoyed the OPA1656!
Hi John,
I hope you can help me with an elementary level question about opamp. I see a overshoot at around 7-11MHz (G=-1) on the closed loop gain vs frequency plot of various OPAs like OPA1612, OPA828, OPA2156. Does it mean we should be cautious (or avoid) using those OPAs at that gain of -1?
Best regards,
Trung
I hope you can help me with an elementary level question about opamp. I see a overshoot at around 7-11MHz (G=-1) on the closed loop gain vs frequency plot of various OPAs like OPA1612, OPA828, OPA2156. Does it mean we should be cautious (or avoid) using those OPAs at that gain of -1?
Best regards,
Trung
There shouldn't be. But there's one thing to consider is that high feedback resistance and the inverting input capacitance can cause instability.
I think you're referring to the slight peak in frequency response in the closed-loop gain curve. That's pretty normal, and corresponds to a dip in the phase at those frequencies as well. There's no reason to avoid using the op amps you list at a gain of -1, all were designed to operate quite happily at that gain.
Many thanks to you John, it all happened 'because' of you
It is pity about the free samples, but I will try to investigate further during my next part purchase. Do you think this op amp can benefit further from an external Class A bias (say 2.4mA ish), or is it done internaly already, or else etc.?
Oh, and while at it purchasing units, given you had a read at my test... and tastes, are there other recent OP amps from TI I should give a listen to perhaps, of course with audio in mind?
Thanks again John, you triggered interest!
Claude
It is pity about the free samples, but I will try to investigate further during my next part purchase. Do you think this op amp can benefit further from an external Class A bias (say 2.4mA ish), or is it done internaly already, or else etc.?
Oh, and while at it purchasing units, given you had a read at my test... and tastes, are there other recent OP amps from TI I should give a listen to perhaps, of course with audio in mind?
Thanks again John, you triggered interest!
Claude
No, and they're definitely not cherry picked parts since cherry-picking is a no-no for cost efficient mass production.
First, I want to clarify what the recommended temperature range for a device really means. This is the range of temperatures, over which the device is guaranteed to meet the specifications in the electrical characteristics table. Outside of this range of temperatures, we don't guarantee the device will meet its datasheet specs. Note, this doesn't necessarily mean the device will fail outside of those temps, just that it won't meet the datasheet. Also, high temps ALWAYS accelerate the aging mechanisms of semiconductors, so while the device might not fail immediately, it will certainly fail sooner, regardless of the recommended temperature range. At cold, some interesting problems can start to pop up as well, like start-up issues.
I would say >90% of the op amps the Precision Amplifiers team (where most of TI's audio op amps come from) is releasing are guaranteed over the extended industrial temperature range of -40 to 125 degrees C. Beyond those temperature ranges, we have to take more variables into account, like the glass transition temperature of the mold compound and some silicon effects. Even export compliance could potentially become an issue depending on the specs/features of a part.
Some devices are not rated up to 125C because the quiescent power dissipation of the device causes significant self heating of the die. So the temperature range recommended is a calculation of the ambient temperature which will allow the die to stay below a certain temperature.