Wow. I'm amazed that the schematic I worked up several years ago is still floating around the web. I should say that the NJM4556A spec is largely a guess, based on the fact that they seemed to be using common parts between the PH and RA-1s. That schematic and my subsequent prototype were based on a series of photographs of the amp, but the markings on most of the parts were either smudged or obscured. The IC used on the PH-1 is most definitely a JRC/NJM part, but I couldn't swear that it is the 4556. I think I tested the prototype with a 4556, but I've always used BB OPA2134PAs in practice as they are widely considered to be a superior part.
Cheers,
-Lee
Just to add to the confusion here is an alternative to consider:
http://www.national.com/ds/LM/LM4562.pdf
The LM4562 is both technically and sonically a great performer - should outperform the JRC part even if used in the Grado circuit.
Note that the data sheet shows a design using passive EQ and a couple of 4562 for stereo.
Interestingly enough it is also available in a metal can because in the Asian high end audio market metal canned op-amps are often preferred. (China in particular..) I have metal canned singles from this family that I have not yet tried.
http://www.national.com/ds/LM/LM4562.pdf
The LM4562 is both technically and sonically a great performer - should outperform the JRC part even if used in the Grado circuit.
Note that the data sheet shows a design using passive EQ and a couple of 4562 for stereo.
Interestingly enough it is also available in a metal can because in the Asian high end audio market metal canned op-amps are often preferred. (China in particular..) I have metal canned singles from this family that I have not yet tried.
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With some care in layout yes, but I would probably try the application circuit recommended by National..
And now I show the wet behind my ears.
They intend for me to use both channels of the chip per signal, dual mono essentially? I suppose I could split it the other way and use half of each chip per channel but that would theoretically offer less isolation right?
Where they say 22nF//4.7nf//500pF what do they intend, is it a choice depending on desired gain, or do they mean me to run them in parallel or series or something? Same with 3.83kOhm + 100Ohm, is that to mean a 3.83k and then a 100 in series? Why not just illustrate it thusly? I find this circuit more difficult to grasp than the other (poor math skills).
EDIT: I see the other phono pre on page 29... this is easier. But which is better?
They intend for me to use both channels of the chip per signal, dual mono essentially? I suppose I could split it the other way and use half of each chip per channel but that would theoretically offer less isolation right?
Where they say 22nF//4.7nf//500pF what do they intend, is it a choice depending on desired gain, or do they mean me to run them in parallel or series or something? Same with 3.83kOhm + 100Ohm, is that to mean a 3.83k and then a 100 in series? Why not just illustrate it thusly? I find this circuit more difficult to grasp than the other (poor math skills).
EDIT: I see the other phono pre on page 29... this is easier. But which is better?
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I just asked this question!
Yes, caps in parallel to arrive at the correct value.
Yes, resistors in series to arrive at correct value.
I ordered my parts yesterday and will be building a phono pre using two LME49720 dual op amps.
Is that a common practice? Writing diagrams like that.
I think I'll build this as shown... cheap and cheerful right? Maybe a nice sappele or bubinga case to class it up a bit...
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