Grado HPA-1 & GS1000i
Mar 6, 2016 at 7:14 PM
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?

Mar 8, 2016 at 2:25 PM
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?

The standard RA1 has x1 gain (actually is not an amp but a buffer) ,the RA1-HG has x4.8 gain ..

Mar 8, 2016 at 8:09 PM

The standard RA1 has x1 gain (actually is not an amp but a buffer) ,the RA1-HG has x4.8 gain ..

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?

Mar 10, 2016 at 1:38 AM

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?

My RA1 has 464/121k with x1, i never had an HG version but googling around found that the RA1HG has 464k/121k with x4.8 gain

Mar 12, 2016 at 10:44 AM
My RA1 has 464/121k with x1, i never had an HG version but googling around found that the RA1HG has 464k/121k with x4.8 gain

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

Mar 12, 2016 at 11:27 AM

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

I know..
This is the internal of my RA1,I made this shot before I replaced the internal wiring with Grado UHPLC copper wires.
Please have a look at the resistors..

Did you ever used your GS1000 with an RA1? If you can notice any hiss  then is a HG version, Mine is totally quiet

Mar 13, 2016 at 8:28 PM
I know..
This is the internal of my RA1,I made this shot before I replaced the internal wiring with Grado UHPLC copper wires.
Please have a look at the resistors..

Did you ever used your GS1000 with an RA1? If you can notice any hiss  then is a HG version, Mine is totally quiet

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.

Mar 14, 2016 at 2:29 AM
They are both quiet with my GS1000 or SR-125.

Then you probably have the standard RA1 with 464/121k!
Here is a picture...

The last mod i would like to do is to replace the volume pot with an ALPS Blue Velvet but it has not enough space and i'm not willing to mod the wooden housing!

Mar 14, 2016 at 5:54 AM
Does that amp sound any good at all? Just by the looks of it, it seems to be a massive rip off, even in a business where lots of snake oil stuff is sold all over the place.

Mar 14, 2016 at 2:01 PM
Then you probably have the standard RA1 with 464/121k!
Here is a picture...

The last mod i would like to do is to replace the volume pot with an ALPS Blue Velvet but it has not enough space and i'm not willing to mod the wooden housing!

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?

Mar 14, 2016 at 2:12 PM
Does that amp sound any good at all? Just by the looks of it, it seems to be a massive rip off, even in a business where lots of snake oil stuff is sold all over the place.

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.

The amplifier sounds great with Grado headphones.  Is it the ultimate in resolution or soundstage or whatever?  No it isn't.  But it's a fun headphone amp to listen thru.

I've made an exact clone of an RA-1 using the exact resistor values, same caps, same pot, down to the same power switch and it didn't sound the same.  It wasn't awful, it just didn't sound the same as an RA-1.  There's something about the RA-1 that I like.

My DAC is a Benchmark DAC2 HDR, but I often find myself listening thru the RA-1 with the outputs of the DAC2.

Mar 14, 2016 at 4:24 PM
Originally Posted by ECM /img/forum/go_quote.gif

Is the cable taken from a stock pair of headphones?

I had to replace a broken cable on my old HF2 so I took the wire from it!

Dec 12, 2017 at 3:06 PM
Did you got any already??...a friend of mine recently got an HPA1 for \$280!!

Dec 12, 2017 at 9:27 PM
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.