[devouringone3]

I will consider and keep you informed.

 

[speedking]

Today I bought an HPA-2 from Japan! Think will have it in my hands at about 2 weeks!

 

[ECM]

Outstanding Speedking!
 
I still have the parts laying around for my clone...never did get around to putting it together.
 
devouringone3, Please keep me in mind should you decide to sell your amplifier.

 

[devouringone3]

 
devouringone3, Please keep me in mind should you decide to sell your amplifier.

 
I will, and proceed to tell you!

 

[speedking]

 
My HPA-1 and -2 have subtle but annoying hiss with all my Grados, and Head-Fier PCF's too.

 
Today I my HPA-2 arrived!
Have a look here :

 
...and yes it does hiss but is more noticeable when using the GS1000,
First impression is that is more powerful & more detailed than the RA-1.
Professionally built , far better than the RA-1!

 

[devouringone3]

Japanese sure know how to take care of their stuff; used and over 20 years old come out as brand new.
 
HP-2 is 40 ohm and less sensitive hence less hiss; you will like it. For a period I did purchase and use a 122 ohms adding headphone jack adapter which eliminated 90% of the hiss... until I realized that my DAC's amplified jack sounded better through complete silence.

 

[speedking]

  HP-2 is 40 ohm and less sensitive hence less hiss;

I thought already  
If its true that HPA1/2 use the same 4556 opamp as the RA1 then the hiss is caused of the bit more gain setting that the HPA has..
At the moment i'm more impressed at the internal/external construction of the amp , in the meantime i enjoy it more with my HF-2 and my RS1 phones!

 

[parbaked]

I believe the switch is a three way that charges the batteries when in standby.

The HPA amps do not have a charging circuit.
There is a switch on the rear to choose between batteries and the PSU.
This switch bypasses the battery supply so they batteries do not drain when using the PSU.
I would think the amp pre-dates rechargeable batteries...

 

  My HPA-1 and -2 have subtle but annoying hiss with all my Grados, and Head-Fier PCF's too.

My HPA-1 was dead quiet with HP1000 and all my SR cans.
This was with batteries or my H/P PS1 power supply.

 

[speedking]

 
The HPA amps do not have a charging circuit.
There is a switch on the rear to choose between batteries and the PSU.
This switch bypasses the battery supply so they batteries do not drain when using the PSU.
I would think the amp pre-dates rechargeable batteries...

 
My HPA-1 was dead quiet with HP1000 and all my SR cans.
This was with batteries or my H/P PS1 power supply.

Yes indeed,
The Rear switch if for choosing Battery or PSU power!
The Front switch has Off ---> Stanby (amp is on but phones are out) ---> Phones (amp is on and phones are on too!)
The hiss is due to High-Gain of the amp, Is more noticable when using GS1000, Less noticable when use the RS1,HF2... in few days will try with my HP2 but I think will be less than the RS1 etc..

 

[ECM]

Nice grab speedking!  devouringone3, let's make something happen on that amp dude!

 

[devouringone3]

 
My HPA-1 was dead quiet with HP1000 and all my SR cans.
This was with batteries or my H/P PS1 power supply.

 
*Batteries*; I'm desperate for an HPA PSU.
 
 

  Nice grab speedking!  devouringone3, let's make something happen on that amp dude!

 
I will seek to it, but please be patient.

 

[speedking]

   
*Batteries*; I'm desperate for an HPA PSU.

I like more the battery use but since I have a spare RA1 PSU i'm thinking to make it fit on the HPA amp!

 

[ECM]

  I like more the battery use but since I have a spare RA1 PSU i'm thinking to make it fit on the HPA amp!

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 since it has better regulation (the wall wart has none), and will work on world wide voltage.  Check mouser or digikey for the HPA connector.
 
Alternatively, you can always build your own with regulation, extra capacitance, etc.  And it's very affordable since the amp does not draw massive amounts of power.  If I remember correctly, the RA-1 wall wart was rated at 100mA of current.  That's miniscule.  An op amp is very efficient.

 

[speedking]

 
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 since it has better regulation (the wall wart has none), and will work on world wide voltage.  Check mouser or digikey for the HPA connector.
 
Alternatively, you can always build your own with regulation, extra capacitance, etc.  And it's very affordable since the amp does not draw massive amounts of power.  If I remember correctly, the RA-1 wall wart was rated at 100mA of current.  That's miniscule.  An op amp is very efficient.

They were many types i think, The early ones were compact, one of the first was a motorola, the 2 last are like bricks! The middle was making an annoying external noise, I own the last one and is totally quite.
 

 

 

 

 

[speedking]

I'm in thinking to mod my HPA-2....
According to the following chart, these are measurments on an 4556 at 0db gain (as RA1) vs the 13db gain (just abit less than HPA).
 

 
This mod will lower the output level , make it really dead quiet and also will make it more clean.
One thing that is more important to me is make sure that I will not destroy my phones even if the volume control is on max!
Since that Grado drivers (both 32 & 40 ohm) are rated at 150mW I prefer to keep my amp power less that
 
*Thanks to NwAvGuy for the measurments! ..more info can be found http://nwavguy.blogspot.gr/2011/07/cmoy-with-gain.html