Convert Pre-Amp Output to Headphone out. Or how to "lower" 75 ohm output impedance.

[ursdiego]

Erik: I was actually thinking about looking for a kit with a similar board as designed by Wakibaki. I guess I basically would have to leave away the potentiometer, and just bridge it, if the rest is equivalent. However, also the headphone amp kits need a decent power supply etc. About the purity thing: I am not religious about that, but as long as it does not get even more complicated, I still believe that less is usually more when it is about hifi. At least in my experience it has proven to be true (which does - unfortunately - not mean less expensive, but less circuits...).

 

[wakibaki]

Quote:

Back to electronics: you suggested as an opamp the NJM4556. In another thread, a fellow here wrote in a quite convincing manner, that he uses the " LM49720HA TO-99 (metal can version) because they are simply the best opamps I have heard to date ". However, what I look for is just the one that does the job at the most next-to-source way possible... So, I guess, I should stick to your suggestion of the NJM4556?
 
Cheers!

 
The LME49720HA TO-99 is indeed a very highly specified opamp, but personally I doubt that it provides any audible difference over a common NE5532, which is used everywhere in professional mixing desks, and which most recorded music will have already passed through. You will have to make up your own mind about this.
 
In this application, however, you would need to use perhaps 8 or 16 of the LME's to achieve the same output current and impedance that the 2 MJE's have, and again, I doubt that you would hear any difference. Of course many people would dispute this, particularly those who have bought and used LME49720HA TO-99 opamps, but about the output current and impedance there can be no dispute.
 
I am an engineer, and besides being a photographer, I am a musician (click the logo on the main page of my website). I feel that much that is written about audio is written by people who are poorly qualified to judge and who seek to discover in their equipment some satisfaction which would be better pursued by learning to play an instrument. An amplifier's reproduction cannot exceed perfection and modern electronics in many instances in my opinion outperforms the ear's capacity to discriminate, but there will always be those who insist on the superiority of some equipment, very often costing thousands of dollars, and there will always be those prepared to supply such equipment, very often at a profit of thousands of dollars, and a profit of thousands of percent.
 
I have advised you to the best of my knowledge. I don't seek to become embroiled in an argument with no greater likelihood of resolution than a discussion about the existence of God. My advice is not to take too seriously the electronics where music is concerned, but simply to listen past it and marvel more at the performance itself.
 
w
 
 

 

[nikongod]

 
Quote:

The LME49720HA TO-99 is indeed a very highly specified opamp, but personally I doubt that it provides any audible difference over a common NE5532, which is used everywhere in professional mixing desks, and which most recorded music will have already passed through. You will have to make up your own mind about this.
 

There is an amusing story about why many DAC datasheets specify the NE5532... 
 
Link and laugh, see the post by Allen Wright April 2 2010
 
If there is any truth to the story its reasonable to assume the same wisdom applies to the op amp selection in other gear.

 

[ursdiego]

Quote:

Originally Posted by wakibaki /img/forum/go_quote.gif
 
...

I feel that much that is written about audio is written by people who are poorly qualified to judge and who seek to discover in their equipment some satisfaction which would be better pursued by learning to play an instrument. An amplifier's reproduction cannot exceed perfection and modern electronics in many instances in my opinion outperforms the ear's capacity to discriminate, but there will always be those who insist on the superiority of some equipment, very often costing thousands of dollars, and there will always be those prepared to supply such equipment, very often at a profit of thousands of dollars, and a profit of thousands of percent.
 
I have advised you to the best of my knowledge. I don't seek to become embroiled in an argument with no greater likelihood of resolution than a discussion about the existence of God. My advice is not to take too seriously the electronics where music is concerned, but simply to listen past it and marvel more at the performance itself.
 
w
 
 

 
Good morning, Wakibaki
 
Wow now you wrote quite a bit about live principles…

I am not an engineer, but as well a musician, and I agree with every word you say about electronics and music. At least with almost every word. I am convinced that electronic, it does matter - but there is no doubt that you agree on that too. However, there is a limit of what makes sense and what does not. And I am very thankful indeed for your advise. However I am a bit surprised, as it seems, that you take my question about what opamp to use somehow like if I was putting into doubt your competence? Or do I get that wrong? I was just asking about an opamp of which I read nice things, and asking, if it might fit into the design, and if you would suggest using it with a big question mark behind it… as you wrote in some place, that the choice of opamp is very important.

So short version: I was just asking... - and I really don't understand what I have done wrong by doing so? I really appreciate enormously your help! The other thing was what you have cited, that I am thinking of looking for a pre-printed board - well I will just look what I find, as it would make me feel more comfortable, less I have to solder and to layout the board myself. I intend to stick strictly to your diagram, but try to find a suitable printed board, where I can implement your design. This way my possibilities to mess something up would be a bit more limited. And if I don't find a board, I will do it soldering anyway.

So now I think it's the moment to start with the argument about the existence of god
 

 

[wakibaki]

Ah, no, urs. I don't feel you are calling my competence into doubt.
 
I have designed many circuits, some using LME49xxx series opamps. I can probably build a circuit with these parts that measures better than a circuit using NE5532s, at least in some respects, and I love to have equipment that is as good technically as can be achieved, but I doubt that I, or anybody, can hear a difference between amplifiers with, for example, 0.01% THD and 0.001% THD. Blind testing (where the listener does not know which system they are listening to) supports this. 
 
So when I make a recommendation to somebody, perhaps an inexperienced builder, on how to achieve a particular result, I tell them to use a $0.29 NE5532 instead of a $10.78 (ebay prices) metal can LME49720, and I don't bother mentioning the LME, because I truly believe that people who think the LME sounds better are mistaken.
 
If you want to know a high current chip whose performance, on paper, exceeds that of the NJM4556, then you could look at the TPA6120A (dual) from Texas Instruments, or the LME497600 (single) from Nat. Semi., but both of these chips are surface mount (not DIL08) and are much harder to use successfully. They require a proper PCB, and really need soldering by reflow in an oven, and there are other considerations besides. I still believe anyway that you will not hear an improvement with these chips over the NJM.
 
The LME49720 is admittedly not surface mount, but as I said before, it does not offer the current drive of the NJM, and several would be required to match the output.
 
Of course you may be one of those who are convinced that you can always get a better sounding system by spending more money. If you look at the thread linked to above, you will see that there are people who hate the NE5532 and who want to ridicule anyone who doesn't. I am happy to discuss technical matters matters with you, or even photography, until the cows come home, but I don't really want to argue about beliefs which I don't think are based on reality. I've been involved in many such arguments in the past, I don't really enjoy them. What I enjoy is passing on my technical knowledge.
 
Despite my attempts to limit this to a technical discussion, you have succeeded in extracting more from me than I really intended.
 

 
w
 
200dpi bitmap
 

 

 

 

[ursdiego]

Just leaving right now, but before I leave: Thank you, looks great and quite a bit more understandable to me! Cheers!