[ECM]

I'm currently using an RA-1 with my GS1000i headphones and would like some opinions regarding the HPA-1. 
 
From what I have gathered, generally, the HPA-1 has "less grain" than the RA-1.
 
From pictures I have seen of both amps, the HPA-1 appears to be better built even though it contains "the same circuit" as the RA-1.  The HPA-1 seems too use 4 capacitors instead of 2, like the RA-1.  Are the additional caps used to bypass the PS?  I also notice two small caps in parallel with the output.  I'm assuming these form a low pass filter on the output. 
 
Basically, is it worth trying to find an HPA-1 to replace my RA-1?

 

[parbaked]

Yes, the HPA-1/2 is a far superior amplifier.
The RA-1 is good, but it was designed to sell at a reasonable price point and as such does not have the best components.
The HPA-1/2 were designed without limitations and use all the best sounding components that Joe Grado could find.
I am not 100% sure of the circuitry but it seems that the HPA-1/2 has two separate paths, one for 9V batteries and one for the power supply so it is in fact like getting two amps as far as quantity of components. 
The HPA-1 retailed for $795 (+$120 for the P/S-1) 20 years ago and Grado and they were still too expensive to make.
I have an HPA-2 with the P/S-1. It is a fantastic amp. It was also designed to drive the HP-1000 headphones which were not as efficient as today's Grados. As such, it will drive a wider variety of cans than the RA-1.
Well worth finding one, especially as they are not that expensive <$500.
 

 

[lextek]

I had forgotten about these amps.  Beauties..........

 

[devouringone3]

Very little has been said about the HPA-1 and -2 on Head-Fi.
 
It was designed by Sidney Stockton Smith, has a discrete circuit a bit simpler (or equivalent?) to a cMoy.
 
The RK40 potentiometer was the best ALPS made at the time (it's really smooth in its volume progression), they only sold them on mass orders so they weren't available to DIYers.
 
Anyway you can read this if you want:

 
It's definitely better than the HPA-1 in build quality (the metal chassis is really neat [the size of a DVD box, transportable with four 9 volts batteries in the compartment] and solid [feels like its going to last centuries], and it's very well "shielded" inside there); I don't know about the sound, sorry. And Parbaked is right, they can be had used (if you're lucky enough to find one of the 250 [100 HPA-2s, 150 HPA-1s] for sale, a few collectors have already secured theirs and hold on to them for really long) for relatively cheap.
 
I'm trying to make a power supply for mine, maybe the one of the RA-1 will work (with a retermination, I'm still in need of the HPAs' pin-out information) seeing it's also a ±12V and has a third auxiliary +5V pin.

 

[ECM]

I appreciate all the info.  I will definitely start actively searching for an HPA-1 or 2.  I really enjoy the sound of the RA-1/GS1000i combo and would like to stay with the Grado house sound.
 
Parbaked, have you compared an RA-1 to your HPA-2?  What's the biggest improvement?
 
Devouringone3, a PS shouldn't be too difficult to build if you know the voltages.  Power-One makes some nice linear power supplies and I'm pretty sure they have one with +/-12 and 5v outputs.  I recently bought a 12v version to replace the cheap wall wart of my clearaudio turntable.  I boxed it up in a nice aluminum case and it works really well.  Maybe someone on here can supply the pin outs for you.

 

[parbaked]

Quote:

I appreciate all the info.  I will definitely start actively searching for an HPA-1 or 2.  I really enjoy the sound of the RA-1/GS1000i combo and would like to stay with the Grado house sound.
 
Parbaked, have you compared an RA-1 to your HPA-2?  What's the biggest improvement?
 
Devouringone3, a PS shouldn't be too difficult to build if you know the voltages.  Power-One makes some nice linear power supplies and I'm pretty sure they have one with +/-12 and 5v outputs.  I recently bought a 12v version to replace the cheap wall wart of my clearaudio turntable.  I boxed it up in a nice aluminum case and it works really well.  Maybe someone on here can supply the pin outs for you.

The HPA-1/2 is more neutral/flat and has tremendous detail and tonal weight. There is so much detail that it sounds lush, serious and business-like. It's a tool for critical listening.
I remember the RA-1 to be more fun and colored (not in a bad way). more like a toy for enjoyment.

 

[speedking]

I use the same combo (RA-1 & GS1000) and i enjoy alot of it!
I 'm also trying to find info about the HPA-1 and until now i found that they have almost the same circuit design but HPA-1 use better quality components, better cables (not the china cheap ones as the RA-1) , point-to-point circuit construction and is more sophisticated !
I'm still trying to find the values of each component but its really hard..
i only found pictures of the circuit board (thanks to kayandjohn) ...
 

 

[ECM]

Thanks for the pic of the circuit board.  I was expecting a PCB actually!
 
From what I have read, the RA-1 circuit is identical, but like everyone has mentioned, built with better components.  The wiring is the quad wiring used by Grado in their RCA cables.
 
I ordered some precision resistors and PIO caps to try and recreate a HPA1/2 according to what I have seen and read, but I haven't made time to knock it out.  Soon maybe...

 

[speedking]

  I was expecting a PCB actually!

 
Me too and i was disappointed when i saw that...but its an point-to-point circuit and there is no other way  to built it!
Please notice that all in/output connection are soldered directly on the IC pins and not after or in the end of the line!
Also the 2 cables (parallel to the feedback resistor) ,seems like a "hand-made" capacitor!
And last there are 2 impedance resistors in series (2x50k maybe?) on each channel instead of 1x100k!

 

[speedking]

According to this link : http://www.stereophile.com/content/grado-hp-1-headphones
 
"Joe's demonstration focused on the HP 1s' abilities as an analytical tool for evaluating microphones, cables, and other equipment recording engineers normally encounter in the signal path. His headphone amplifier is a portable unit using a dual operational amplifier, powered by a pair of 9V alkaline batteries: the ±9V supply rails are each locally bypassed with a 330µF capacitor. Sid Smith, famous for his classic Marantz designs, developed the circuit topology, while the selection of internal wiring and components was done by Joe using the HP 1s. No expense has been spared in selecting parts for this amplifier. Roederstein metal-film resistors, Grado's own proprietary wire, and the most expensive potentiometer Alps manufactures combine to produce an amplifier with very low sonic coloration. The Grado headphones, used with the HPA-1DC amplifier, are sonically so clean that they reveal subtle differences in electronics and cables in a fraction of the time normally required when using loudspeakers."

 

[ECM]

Nothing wrong with point to point wiring if implemented correctly.  Soldering the output directly on the pin avoids any traces and secondary solder points.
 
Would you have a picture of the top side?  I wonder where the 330uf caps are installed?
 
It seems to me that the two pair of capacitors in the other interior photos are input and bypass caps stacked per channel.  Unless one of those is 330uf.
 
The black beauty isn't available anymore either so there's that too...

 

[ECM]

Actually, a quick eBay search reveals black beauty pots available from $55 to $130!  I'll build mine with a blue pot and go from there.

 

[speedking]

 
Would you have a picture of the top side?  I wonder where the 330uf caps are installed?

I wish i had.... 
There are 2 stacks of big black caps, the top cap is the 330uF and the bottom is the input cap 5.1uF !

 

[ECM]

  I wish i had.... 
There are 2 stacks of big black caps, the top cap is the 330uF and the bottom is the input cap 5.1uF !

I see...but those caps look identical.  
 
Also, I wonder if there's the standard 0.1uF bypass cap on the power supply pins of the opamp along with the 330uF caps.
 
I'll look into the amp a bit more the next couple days; see what I can come up with.  And I'll start laying out the board as well.  Not that difficult point to point.

 

[speedking]

The top cap (330uF) is connected between V+ (or V-)  and Ground so is in the place of the 0.1uF (as the RA-1 has)
 

 
 
I only wish I could find a top view of the circuit board so I can see  the values of each component..
Do you know whats the value of the capacitors on the headphone jack?