Nice! I’ve been looking from time to time but haven’t found one yet! I’ve kinda given up on the idea and just rock the RA-1.

I used polyurethane on another Grado project and it went on nicely, but this one I will leave as is.

From what I have seen, all the schematics show 5.1uF, however, those are a bit bigger than what fits in the cavity, hence having to insert them sideways. The previous owner had installed 2uF, but those were not the stock units and poorly done. I've seen the DIY PH-1...he did a fantastic job of...

And the final product!  Looks great and sounds the same as my battery powered RA-1.   Most of the dents on the face came out with a bit of steam.   New screws for the bottom plate.  

Once I cleaned everything up, it was time to put it all back together.  I installed new Solen 5.1uF caps and all new wiring.  The caps required me to install the circuit board sideways due to their size...which leads me to believe the original caps might not be 5.1uF but maybe 3.9uF.    ...

That's exactly what I did to the wood...I used a damp paper towel and an iron to get the dents out.       I did end up buying new input caps and reused the rest.  I touched up some of the solder joints and then cleaned it all up with alcohol before sealing it all in.

First, was to remove the circuit and clean it up.                          

I picked up an AC powered RA-1 on Audiogon which was rated a 9/10.  The pictures looked ok and there was no mention that the unit had been altered.  I received the amp and it wasn't packed properly so the AC adapter prongs left some gouges on the face of the amp.  Upon inspecting the amp, I...

We've been down this road before derbigpr.  Some people claim it's a massive rip off due to only having a few dollars worth of parts, plus the wooden case.  Others feel it offers good synergy between Grado products and is worth it's asking price.  It's up to you to decide if it's worth it.  ...

  Good work dude.  Looks good.  I too have toyed with the idea of installing an ALPS pot, but the shaft is too long, even when trimmed down.  You'd have to carve out a spot and I'm unwilling to do that as well.   Is the cable taken from a stock pair of headphones?

  Do you have any "after" pictures with the new internal wiring?  Where did you pick up the wire? I have a couple RA1's.  A battery powered one and an AC powered one.  They are both quiet with my GS1000 or SR-125.

  Speedking, the 464k/121k resistors are what set the gain.   The formula is: gain = 1 + (R2/R1)   For an RA1 it is: gain = 1 + (464K/121k) gain = 1 + 3.8 gain = 4.8

Not sure what the gain is on an RA1HG, but I'm pretty sure the gain on a regular RA-1 is 4.8, not 1.     I had three RA-1's at one point and opened one of them up.  It had 464k/121k feedback resistors, gain 4.8.   Either way, is the metal plate removable on the HPA circuit board? 

What's the gain on the HPA-2?  The Grado RA-1 has a gain of around 5.   How will you modify the amp if it has the metal cover on the circuit board?  Is it removable?

It's possible to change the connector on the power supply to fit the HPA.  Which RA-1 power supply do you have?  They made two different models, one used a wall wart and the newer version used a switched mode power supply and looked like a brick.     I'd look for the switched mode power supply...