I do have the HCA3500 and I don't think any of the mods have been done on it. I have no one in area (Phoenix area) that gives me confidence it could be done right. If you are close enough I would be very interested once I see what the whole lot of different parts adds up to! Thanks for response!
I live in Miami area, so can't meet with you. I can send you a complete list of parts, but some things you will have to buy from ebay (pcb)/aliexpress (silver plated wires,heat sinks,plastic holders for the pcbs,etc.)/a store that sells prp+zfoil (for the feedback resistors), and more. You also need to know how to adjust the bias once all done. Do you know how so remove and solder all parts back in?
This is not an easy job....
This is not an easy job....
definitely live too far from here. Shoot. I have minimal tech experience-in fact I just successfully learned to properly solder when I upgraded the crossovers of my old CA1 Dahlquist Preludes thru the help of GR Research. With the HCA 3500 I am interested in doing the least amount of upgrading to get max improvement. First-I don't want to break anything. Second, I do NOT have the skill level to start cutting out capacitors or the unlimited budget to take this amp to the absolute max of its potential as you seemed to have accomplished. Congrats BTW! When looking over the forums that mention the possible mods they almost all universally mention at a minimum swapping out for the NOS Holco 47.5 k resistors( I have those) and double check for correct AC phasing. I proved I can solder so #1 is doable. Would just these 2 steps be enough to squeeze a worthwhile improvement in your opinion? Or is there a few more of the EASIER incremental mods worth the trouble from your own experience and listening? And again I realize there are LOTS of areas that COULD be improved as in your case.
Yes! I would appreciate ANY help on those 3 things. Where to source-What part, how many, ect. Finally The Steps to take. ect..Worst case if I get stumped-I do have a local guy to call on as long as I can explain in tech terms what I need done. But I would like to at least try. As for the Holcos I have -I think I have the correct NOS part that I purchased last year from West Florida Components.
(1/2W 47.5K Ohm 1.0% Holco Metal Film Resistor Audio Holsworthy 4447K5ED)
I have the schematics from a Youtuber that did a short video where he actually compared side by side the HCA 3500 and JC-1 amp of today.He also explained the great return on investment of that often talked about feedback resistor. Everyone mentions replacing it results in less etched highs.
So again, anything you would be willing to provide for guidance would be welcome.
BY chance-Do you have a "simple" trick to easily determine if AC phasing is correct?
PS-I attached pics of my Holcos for reference.
Thanks
(1/2W 47.5K Ohm 1.0% Holco Metal Film Resistor Audio Holsworthy 4447K5ED)
I have the schematics from a Youtuber that did a short video where he actually compared side by side the HCA 3500 and JC-1 amp of today.He also explained the great return on investment of that often talked about feedback resistor. Everyone mentions replacing it results in less etched highs.
So again, anything you would be willing to provide for guidance would be welcome.
BY chance-Do you have a "simple" trick to easily determine if AC phasing is correct?
PS-I attached pics of my Holcos for reference.
Thanks
Attachments
The Harris mosfets are available from 2 suppliers,choose any.
You will need to remove both right and left sides of the amp, i.e. the heatsinks, and disconnect all their cabling (I suggest marking each male/female connector with a different color, or simply take good photos of all connections to the side boards before you disconnect them...). Also, pay attention not to unscrew the 8 screws at middle hight, and there is also no need to disconnect the top row of screews (besides the far right/left ones) because the just hold a bar that can stay intact.
By disconnecting the side heatsinks with side boards, you would get good access to the middle main board (the one with the big "soda can" caps). In order that there is no need to take it apart from the chassis, simply cut what need to be cut with a small cutter, as close to the board as possible.
Remove as described in the paper attached here by. That is,all white little blocks, including the small yellow ones underneath them.
To remove caps/resistors/mosfet from the side boards, you will need to separate the board from the black metal heatsink. For that, unscrew the 8 screws at more or less the middle hight of the heatsink. Then, remove the white paste with cotton and alcohol. At the end of the journey, you will need to put new paste so that heat goes from the power transistors to the heatsink. Will send you a link to that paste.
Now you can decide what parts to take out, I would go with the list in the paper, without the Electrolytic caps, and go with vishay caps as described. The prp resistor in r28 can be purchased from Michael Percy, look him in google.
Remember you need twice the number of each type of part you decide to remove according to the list, since there are 2 side boards....sending you the schematics too.
Good luck, anf feel free to ask me questions
You will need to remove both right and left sides of the amp, i.e. the heatsinks, and disconnect all their cabling (I suggest marking each male/female connector with a different color, or simply take good photos of all connections to the side boards before you disconnect them...). Also, pay attention not to unscrew the 8 screws at middle hight, and there is also no need to disconnect the top row of screews (besides the far right/left ones) because the just hold a bar that can stay intact.
By disconnecting the side heatsinks with side boards, you would get good access to the middle main board (the one with the big "soda can" caps). In order that there is no need to take it apart from the chassis, simply cut what need to be cut with a small cutter, as close to the board as possible.
Remove as described in the paper attached here by. That is,all white little blocks, including the small yellow ones underneath them.
To remove caps/resistors/mosfet from the side boards, you will need to separate the board from the black metal heatsink. For that, unscrew the 8 screws at more or less the middle hight of the heatsink. Then, remove the white paste with cotton and alcohol. At the end of the journey, you will need to put new paste so that heat goes from the power transistors to the heatsink. Will send you a link to that paste.
Now you can decide what parts to take out, I would go with the list in the paper, without the Electrolytic caps, and go with vishay caps as described. The prp resistor in r28 can be purchased from Michael Percy, look him in google.
Remember you need twice the number of each type of part you decide to remove according to the list, since there are 2 side boards....sending you the schematics too.
Good luck, anf feel free to ask me questions
Attachments
Forgot, all small Electrolytic caps (given you are going to replace them) ,the Roederstein (now Vishay) 0.1uf 160v film caps and the Wima mkp10 0.1uf 250v caps (these come in different legs spacing, so measure the space on the board where they should be soldered and order accordingly), can be ordered from Mouser.com or digikey.com
Things come into my memory. So that you do not need to disassemble the middle main board in order to solder new caps, just leave it with all parts cut as described. Instead of soldering new parts on that board, what you should do is order (Mouse/digikey), 4 Vishay/roederstein mkp1839, 0.22uf, 160/250v and solder them instead of 0.1uf at locations c21 and c24 (instead of 0.1uf as in the paper). That is 2 on each side.
Vishay mkp1839 0.1uf 160/250v, you will need a total of 12, 6 for each side.
Wima mkp10, need 8 in total.
Q5- Harris irf9620 - 2 in total.
R44 - holco h4 47k - 2 in total
Vishay mkp1839 0.1uf 160/250v, you will need a total of 12, 6 for each side.
Wima mkp10, need 8 in total.
Q5- Harris irf9620 - 2 in total.
R44 - holco h4 47k - 2 in total
Thanks for the wealth of information to guide me. Did you by chance see the pics of my NOS HOLCO 47.5s and determine that they look like the correct resistor?
I want to be sure to get this critical starting point correct.
Hi, it looks like old holco h4 series. Do not know what 47.5 instead of 47 would do. If I were you,I would call Michael Percy and consult with him. His catalog states they are slowly replacing old Resista and Holco for prp, same quality and highly praised for high end audio. You will need to order 2 prp9372 2.2k ohm for r28, so not a big issue to add prp9372 47k ohm if your 47.5 will not do the job by his opinon
Hey my man
I know u were replying to OP in regards to parts list
Do u have this handy still ?
I've inherited the hca 3500 I mentioned a year or 2 ago
So would like to start making moves modding this amp
It has an issue with over current [random] on right channel which I will need to address also
Cheers