Improve the Sound of your Parasound HCA3500

R-44 is actually about half way back and the third component from the top of the board on each side as I recall, but it is marked...........Posted this a few years ago on AA and this will make for a much better amp.....Lots more to do, but the main feedback resistors and getting the AC polarity right are steps in the right direction......Lethal voltages in the amp so unplug it before doing anything.......

Why were so many of these amps built with the wrong AC Polarity?

Why were all the Sony SCD-1s built with the wrong AC polarity? Nobody checked it at Sony and nobody checked it at Parasound's contractor until Parasound instituted a procedure almost two years ago.....

Does changing the AC Polarity of the Sony SCD-1 make any sonic differences and/or improvements to its sound?

Think about it.......All the components are hooked together with interconnects that hook all the ground potentials together.......Just having one piece with the wrong AC polarity will destroy proper imaging of the entire system.....

What's the best way to check AC polarity? And what's the best way to change it if needed?

Get a voltimeter first.Unhook all interconnects and speaker cables from the amp.Get a 'cheater plug'[a plug which you plug your 3-prong plug into,but only has 2 plugs on the end of it that plugs into the electrical outlet].Ground down the end of the biggest prong on the 'cheater plug' so that you can reverse it around 180 degrees and plug it in the opposite way in electrical outlet.
Plug the amp power cord, one channel at a time, into the cheater plug.Plug the cheater plug into the electrical outlet the normal way it would go in if it had 3 prongs.Turn the unit on.Place the black lead of the voltimeter to an earth ground or very good ground, then touch the red lead from the voltimeter to a chassis screw on te amp or to the outside of the RCA input on the back of the amp.Note the voltimeter reading and write it down.Now turn the unit off, unplug the cheater plug from the electrical outlet and plug it in the opposite way,180 degrees.Do the same things I named above:Turn the unit back on, use the leads from the voltimeter in the same way, and note the reading. THE LOWEST READING IS THE CORRECT POLARITY.If the polarity is reversed, the lowest reading will be obtained with the cheater plug reversed 180 degrees.
If it is reversed,MAKE SURE THE UNIT IS OFF AND UNPLUGGED FROM THE OUTLET, take the top cover off.You will see the input screws that holds the wires down from the main-input sockets on the back of the amp.You will see that there are two red wires from the input socket on the amp.One goes to the fuse, then from the fuse is a white wire.The white wire goes to a screw labeled 'IN'.The other red wire goes to a screw labeled 'OUT'.Remove the screws and switch the red and the white wires around then put the screws back in.This is one channel.Now do the other one the same way.After, you do this replace the cover, plug the unit back in to the cheater plug and do the same test again just to be sure its right.Do not remove or replace the Green Ground wire inside the amp!PLEASE BE VERY, VERY CAREFUL WHEN DOING ALL THIS AS DANGEROUS OR DEADLY ELECTRICAL SHOCK CAN OCCUR!!Hope this helps.

Drubin: Here's a post i did about this subject about a year and a half ago. Hope this helps. Sean
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Noise, hum and AC polarity

Do these tweaks work for the HCA2200mkII as well?

Socrates,
Ask Bob Crump this question.I have no idea, myself.Thanks.

Never been inside a HCA2200 .....Might be a good idea to check the AC polarity as it is with any piece of gear inserted into your system......

Other than AC polarity, most all gear responds quite noticeably to swapping better quality parts for lower quality parts. Sean
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Hello all,
Sorry to resurrect such an old thread, but I cannot contain my enthusiasm for the Parasound HCA-3500.
I owned one in the past and sold it, but decided to buy another used one a few weeks back.
Out of the box it was sort of harsh, forward, etched, and grainy. I thought BIG MISTAKE!
But,
Five EASY and CHEAP things that I have done have dramatically improved my HCA-3500:

1. Using a Parasound P/LD-2000 preamp. [Theres a synergy there, after the mods are done].
2. Installed dedicated outlets with 20 amp breakers, one for each channel, on the amp. My other equipment goes into seperate outlets from these.
3. Changed out the R-44 resistors, [one on each side of the amp], from the stock Vishay 47K to Holco 47K. I got the Holco's at Michael Percy Audio.
4. The AC polarity on my HCA-3500 was reversed, just like the first one I owned, so I changed the wires around in my dedicated outlets.
5. Floated the earth grounds on both channels of the amps.
[The preamp is still connected to an earth ground]

Floating the earth grounds on both channels of the amp was the final thing I tried, and turned out to be the icing on the cake! After I floated the grounds, the sound became quite a bit cleaner, with much less grain and hash, a wider soundstage, and a more relaxed and somewhat more laidback sound, which is a plus with this amp.
Now the harshness, etch, and grain is almost completely gone, and I like the 3500 better than the JC-1's that I did own. The modded HCA-3500 is more lively, clear, dynamic, and has better treble dynamics, and depth than the JC-1's.
The JC-1's sound slightly muddy and vague in the mids and highs, and less dynamic in the highs, compared to my HCA-3500 believe it or not.
My HCA-3500 now has crystalline clarity, transparency, tons of detail, depth, a wide soundstage, and punchy dynamics
I am now going to experiment with aftermarket power cords.
Wow, what an improvement!