Were you able to see the internal active components of the amp?  My understanding is that the original Grado amp was merely a 4556 op-amp with some big capacitors, and I felt it was horribly overpriced if that was the case.

This is very interresting, and well written John. As the proud owner of a mint Grado HPA-2, RA1, and BSG C-Moy. 
 
I thought I knew the HPA-1 and 2 very well, but you have actually thought me one or two hundred things that I didn't know.
 
Regarding the previous comment. I can see why jnorris could percieve the HPA-1 and 2 as overpriced, however, if, for whatever reason, Grado was losing money with the HPAs, That being said, I don't think that Grado was overcharging, (is that even a word!), their customers for their amp.
 
Again, nice work John, as always!.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

Very nice and detailed review! I was always under the impression that Grado amps (the RA1 and the HPA1) are overpriced and only pair well with Grados. It's nice to see it's completely the opposite. But it's gonna be a very long time for me to own a RA1 of my own...

Oh and I think after selling the company to John, Joseph builds the HP1 and the HPA1 on his own, in another separate business?

Is there a chance of a comparo with other amps like those of Fiio for example? Just curious.

@lehoang15tuoi, yes indeed, the company that Joseph Grado had was Joseph Grado Signature a products, run out of his home in Westfiled, NJ (where head-fier doctorjazz is), rather than the GradoLabs factory in Brooklyn.

@Onix, I used to have, but do not now, have a FiiO E12.

@jnorris, no way to see the top side of that board without breaking off that black shield that is epoxied on top.

To all, I can play Chopin's Fantasie Impromptu on the piano. So can Vladimir Horowitz. Same notes, same music. Same cost of components. But no one would EVER think my rendition was any good, or that Horowitz's was anything other than stellar. The difference in the three amps (HPA-1, RA1, and C-MOY), even if they had the same electrical schematic, is in the quality of their component "notes," as evidenced by their sound in my comparison. Furthermore, one of them (C-MOY) distorted the sub bass on one of my test songs, which the other two did not do.

Nice review after the short chat we had about the HPA! Thanks for all the pics you sent me!

John, great review!  Enjoyed the read.

I own both the items under review and love both, didn't pay near that much for the amp, Papa Joe hadn't left us yet (it was a few years back)..... I just wish I had the DC supply for it. I can redo the plug and fashion some of my existing supplies, but that would deface the amp and disrespect Papa Joe (IMO). Love the amp also with the HF-2's/PS-500's. The combo's get up and walk about a-bit.

Nice review, John. You adoration for all things Grado is legendary!