Are there some fundamental differences between OPA627 and OPA637 ICs (excluding SR and stability for gain=1)? Because one of experienced audio designer has told that OPA627 is a completely misunderstanding in sonic quality terms, while OPA637 is quite qood.
There are some coincidence between increasing an A class biasing current for opamps like AD847, AD825 and LT1362 and its "musicality" (information from the web). From the same source - the compensating current for AD825 should be 2.4 mA.
There are some coincidence between increasing an A class biasing current for opamps like AD847, AD825 and LT1362 and its "musicality" (information from the web). From the same source - the compensating current for AD825 should be 2.4 mA.
Well - I have simulated the OPA627 - an output stage and preceding BJT LTP with current mirror and current source. I did not include input cascode. I agree that my simulation will be quite far from the real circuit.
But one thing can be seen clearly. Loading the output against -Vs by resistor changes the mode of operation of the output stage. Now only the upper transistor is working, the lower one having negligible current. The output stage works as an SE class A one transistor output stage with emitter load resistor. The conditions of the output stage are changed and an investigation of the new output stage drive capability should be done.
But one thing can be seen clearly. Loading the output against -Vs by resistor changes the mode of operation of the output stage. Now only the upper transistor is working, the lower one having negligible current. The output stage works as an SE class A one transistor output stage with emitter load resistor. The conditions of the output stage are changed and an investigation of the new output stage drive capability should be done.
Upupa Epops said:How I see, by meaning most of yours, manufacturers of audio integrated amps are idiots. Whatabout to make any public inquiry and by results let to make an realy " musical " one ? This neverending discussions are still rather tedious.
These opamps are not optimized for audio use, but for instrumentation and measuring purposes.
We post our opinions of certain opamps, in certain circuits, in certain pieces of equipment, here and on other forums.
At best we can hope to give others a suggestion of something to try for themselves but we can never give a definitive recommendation of which will be the best opamp for somebody else.
Most opamps are not too expensive and by using a socket, it is not too difficult to try different types (and different circuits). What is pointless is arguing that one opamps is better than another, or one circuit is better than another.
As Carlos says about his class A resistor mod - try it and see for yourself and I would add that goes for opamp make and model as well.
Even describing an opamp as musical is open to interpretation as 'musical' means different things to different people. I am a little worried that newbies who read threads like this one try to decide on which opamp to use based on what is written, rather than on what they could hear if they tried the opamp for themselves.
Fashions abound in this game but the wise hi-fi builder will not be swayed by them. Never discount an opamp because it is either cheap or because it has been around a long time. You may be ruling out your 'perfect opamp!
We all know (or should know) about system matching by now. I am sure that the same rules apply to choosing an opamp. Much will depend on all the other factors in the system.
Finally, let's not forget that many opamps were never designed for the purpose of reproducing music (although some may do that job well) Having said that, some of those that make that claim don't seem to do a very good job, in my experience.
At best we can hope to give others a suggestion of something to try for themselves but we can never give a definitive recommendation of which will be the best opamp for somebody else.
Most opamps are not too expensive and by using a socket, it is not too difficult to try different types (and different circuits). What is pointless is arguing that one opamps is better than another, or one circuit is better than another.
As Carlos says about his class A resistor mod - try it and see for yourself and I would add that goes for opamp make and model as well.
Even describing an opamp as musical is open to interpretation as 'musical' means different things to different people. I am a little worried that newbies who read threads like this one try to decide on which opamp to use based on what is written, rather than on what they could hear if they tried the opamp for themselves.
Fashions abound in this game but the wise hi-fi builder will not be swayed by them. Never discount an opamp because it is either cheap or because it has been around a long time. You may be ruling out your 'perfect opamp!
We all know (or should know) about system matching by now. I am sure that the same rules apply to choosing an opamp. Much will depend on all the other factors in the system.
Finally, let's not forget that many opamps were never designed for the purpose of reproducing music (although some may do that job well) Having said that, some of those that make that claim don't seem to do a very good job, in my experience.
Guys,
I opened this thread to share with you all a trick that I always use on the OPA627.
Yes, this thread is about the OPA627.
The op-amp I love, the one I always use, when possible.
The trick is very easy to try, I just wished that all the tweaks were so easy as throwing a resistor into a circuit.
This is, I think, valuable information for who uses the 627, and even those that don't, with a socket they can easily test the 627 again, with the resistor, and listen .
Even those who tried to bias the 627 into class-A with other methods and/or values can try again, with the method I describe here.
Sometimes I also ask myself why is it so complicated to open a thread here and share information.
It usually degenerates into a nonsense and endless discussion.
Just try it if you want, listen and tell us what you think.
Like Pavel did.
I opened this thread to share with you all a trick that I always use on the OPA627.
Yes, this thread is about the OPA627.
The op-amp I love, the one I always use, when possible.
The trick is very easy to try, I just wished that all the tweaks were so easy as throwing a resistor into a circuit.
This is, I think, valuable information for who uses the 627, and even those that don't, with a socket they can easily test the 627 again, with the resistor, and listen .
Even those who tried to bias the 627 into class-A with other methods and/or values can try again, with the method I describe here.
Sometimes I also ask myself why is it so complicated to open a thread here and share information.
It usually degenerates into a nonsense and endless discussion.
Just try it if you want, listen and tell us what you think.
Like Pavel did.
I inserted this 2k resistors 30 minutes ago, and actually Marla Glen is singing like never before!
It is an interesting hint, Carlos! Would be great, to drive a tube with this OPA627...
As for different opamp types: I tried NE5534AP (maybe 18V is a little bit to high for this chip?), OPA134 and OPA627 in my amp and my favourite is the OPA627.
The NE5534AP, Philips, where second choice for me, OPA134 third and NE5534AP Ti are at the end.
BUT: I am very happy with my NAD Phono Preamp PP 2 and I opened it. What is in there: an NE5532!
So, it depends really on the circuit and other factors, wich opamp you like.
Just try, for every new circuit!
My two cents
Franz
BTW: my OPA627 are still sitting in sockets, but no problem! I bypassed them at the socket with 2x0,1uF foil, 1uF Tantal and 0,15uF foil between +Vs and -Vs.
It is an interesting hint, Carlos! Would be great, to drive a tube with this OPA627...
As for different opamp types: I tried NE5534AP (maybe 18V is a little bit to high for this chip?), OPA134 and OPA627 in my amp and my favourite is the OPA627.
The NE5534AP, Philips, where second choice for me, OPA134 third and NE5534AP Ti are at the end.
BUT: I am very happy with my NAD Phono Preamp PP 2 and I opened it. What is in there: an NE5532!
So, it depends really on the circuit and other factors, wich opamp you like.
Just try, for every new circuit!
My two cents
Franz
BTW: my OPA627 are still sitting in sockets, but no problem! I bypassed them at the socket with 2x0,1uF foil, 1uF Tantal and 0,15uF foil between +Vs and -Vs.
Carlos
The sound is now really good, but I want to see the results on my scope.
What would happen, when we do the same for the LM3875? Just bias to a certain level, so you have class A up to 1 or 2 watt, what is enough for my speakers.
I think one of the bottleneck of all LM38xx amps are the quasi symetrical outputstages. So, you could add the best buffer, but this problem resists.
Franz
The sound is now really good, but I want to see the results on my scope.
What would happen, when we do the same for the LM3875? Just bias to a certain level, so you have class A up to 1 or 2 watt, what is enough for my speakers.
I think one of the bottleneck of all LM38xx amps are the quasi symetrical outputstages. So, you could add the best buffer, but this problem resists.
Franz
Forget class-A with the LM3875 for now and try this first:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39039
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39039
I also would like to share a little 'secret' of mine when it comes to the OPA-627. Especially since on this thread there has been several references re the need for good decoupling etc.
Her is my trick:
What you are seeing here is a little difficult to describe. Essentially this idea applies to all opamp ICs - even LM3875 et al. But this trick works a treat on the OPA-627.
The key here is the signal return. But more importantly, it is the return signal current.
In many opamps only one of the caps shown is needed. In most cases it is the 'neg' one, but not always. If memory serves me right, the OPA-627 requires the positive cap. Best to add both and if using ICs in plug'n'play comparisons, you are covered.
Which cap is necessary actually depends on the internal comp cap, whether it has a neg or positive voltage across it. This indicates whether an IC is referenced to which voltage rail. Think about it, the IC does not have a ground terminal, right? Exactly! So where does it get its signal ground reference.... from one of either rails.
Now it may not become immediately apparent, but think about: Does it not make sense that the signal currents return back to this point via the decoupling cap shown above? It kinda does.
This is a bit simple, it gets rather more complicated as the open loop gain falls with increasing frequency we lose power supply rejection and now unwanted (disturbed) HF signals can appear right across the comp cap. Does it affect the sound? You betcha, and not to mention stability.
So analyse how you are using the 627 (and others too, but I agree the 627 is special IMHO), we know where the signal (and its currents) are going out - but where do the return?
Bring 'em home.
Joe R.
Her is my trick:
An externally hosted image should be here but it was not working when we last tested it.
What you are seeing here is a little difficult to describe. Essentially this idea applies to all opamp ICs - even LM3875 et al. But this trick works a treat on the OPA-627.
The key here is the signal return. But more importantly, it is the return signal current.
In many opamps only one of the caps shown is needed. In most cases it is the 'neg' one, but not always. If memory serves me right, the OPA-627 requires the positive cap. Best to add both and if using ICs in plug'n'play comparisons, you are covered.
Which cap is necessary actually depends on the internal comp cap, whether it has a neg or positive voltage across it. This indicates whether an IC is referenced to which voltage rail. Think about it, the IC does not have a ground terminal, right? Exactly! So where does it get its signal ground reference.... from one of either rails.
Now it may not become immediately apparent, but think about: Does it not make sense that the signal currents return back to this point via the decoupling cap shown above? It kinda does.
This is a bit simple, it gets rather more complicated as the open loop gain falls with increasing frequency we lose power supply rejection and now unwanted (disturbed) HF signals can appear right across the comp cap. Does it affect the sound? You betcha, and not to mention stability.
So analyse how you are using the 627 (and others too, but I agree the 627 is special IMHO), we know where the signal (and its currents) are going out - but where do the return?
Bring 'em home.
Joe R.
Just separate signal return of the input non-inverting input resistor, small stabilizers (LM317L etc.), bypass capacitors etc. to separate PCB traces and connect it into just one point of the PCB - that's my way. No problems with ground induced noise. Left and right channel have separate power supplies, no ground loops.
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