Hello,
I would like to do some mods on a Parasound HCA3500, any suggestions would be appreciated. I have read that upgrading the main feedback resistors and checking the polarity is a good place to start, the amp sounds good but can be a bit etchy on the top end. Where might I find schematics for the amp?
Thanks for any help,
Matt
I would like to do some mods on a Parasound HCA3500, any suggestions would be appreciated. I have read that upgrading the main feedback resistors and checking the polarity is a good place to start, the amp sounds good but can be a bit etchy on the top end. Where might I find schematics for the amp?
Thanks for any help,
Matt
Thanks, I'll email them tomorrow. I understand that John Curl did a splendid job designing this amp but Parasound used some parts that weren't quite what he would have wanted, and it can be an outstanding amp with a little work.
I wish I could get John to elaborate but he must be bored with this one.
I wish I could get John to elaborate but he must be bored with this one.
Matt --
You touched on the immediate tweaks -- replace the feedback R's with 1/2W Holco's and check the AC phasing. Most of the hundred or so of bypass caps in that amp can be cut-out. Replace the bridge rectifiers with Harris Hyperfast diodes. These hints and many others are over in the diy section of Audio Asylum. Bob Crump posted several tweaks there.
Phil
You touched on the immediate tweaks -- replace the feedback R's with 1/2W Holco's and check the AC phasing. Most of the hundred or so of bypass caps in that amp can be cut-out. Replace the bridge rectifiers with Harris Hyperfast diodes. These hints and many others are over in the diy section of Audio Asylum. Bob Crump posted several tweaks there.
Phil
Matt -- Somewhere I have a list of posted mods for the HCA-3500's plus some of my own (like removing that auto-bias thing). I'll dig them out and post. Also, if you aren't using the balanced input, you can remove that little input board.
But do the feedback resistors and AC polarity first. The change is pretty dramatic.
Phil
But do the feedback resistors and AC polarity first. The change is pretty dramatic.
Phil
Bob Crump and I modified the HCA-3500 about 10 years ago, after listening to it was not what we first expected. The 47Kohm feedback resistor should be changed to a Resista or an OLD Holco resistor. There ARE too many bypass caps in the power lines. They were not part of the original schematic that I submitted, and the feedback resistor brand was changed as well, to my dismay. In the end, we got a very nice product, that we resold for $5000, and it was considered one of the best in its time, before the JC-1, which is better yet. However, what we learned from modifying the HCA-3500 proved to Parasound that there is more to good sound than just measurement, because the first HCA-3500 that we modified, (my own personal unit) was tested by me extensively, before modification, and I thought is was virtually perfect, UNTIL we listened to it. This is what separates audio from industrial designs. If many here would just try some to the changes that we have suggested over the years, almost any product could be made to sound better, even if it did not necessarily measure better.
I don't think that I have met Tony more than once or twice, but he is a very good repair tech, and he knows more about the individual products, outside the JC-1 and JC-2 than I do.
I don't think that I have met Tony more than once or twice, but he is a very good repair tech, and he knows more about the individual products, outside the JC-1 and JC-2 than I do.
Hi Matt -- Here is most of it. I would need to dig further for my notes on more mods (which are a bit more complicated) but these should keep you busy........... The first 6 were mostly taken from Bob Crump's comments in DIY Asylum. Changes and mistakes are my own.
1. Replace R44 with Holco resistors. I bought my Holco's before Holco changed the construction so use OLD Holco's or Resista's as John Curl says. I also replaced R28, R82, and R40 with old Holco's.
2. Replace diode bridges D8 and D16 with IR HFA08TB60 diodes or Fairchild Hyperfast.
3. Remove C25 – C32.
4. Remove C55-C60 and C49-C54 and replace with 0.1µF polystyrene RT RelCaps.
5. Remove C19/C20/C21 and C22/C23/C24 and replace with a 100µF/100V electrolytic and a 0.1µF polystyrene RT RelCap on each rail. I think Bob Crump mentioned the Nichicon KZ here. I used Elna Cerafines.
6. Replace diode bridges D53 and D57 with Harris RURG3060 diodes. Remove all film caps from the power supply board.
And here are a few more ......
Replace RCAs and Speaker Binding posts. I also made some changes to the Zobel on the output but that's in my notes that I can't find. If I remember right, R1 and C1 were mounted on a little PC board or on the main PCB. I replaced these with a 10 ohm Caddock MP-820 and an 0.1µF polystyrene RT RelCap soldered directly to the binding posts. I used Cardas wire for the input wiring. You can remove the input PCBs if you are using the RCA jacks and just ignore the XLR input. I'm using the XLR and still removed the input PCB board but my preamp can drive a lo-Z load.
Replace C11/C12 and C13/C16 with 100µF/25V BlackGate and 0.01µF polystyrene capacitors.
Replace R43, R46, R47, and R48 with Caddock MK-132 resistors of same value. Resistas would be fine here also.
Replace C62 and C9 with 10pF mica capacitors.
Other mods I did include removing the auto-bias thing and re-biasing the output stage; more resistor and capacitor changes; upgrading the servo and the +/- 15VDC supplies; upgrading wire; and replacing surgistors with soft-start circuits.
Phil
1. Replace R44 with Holco resistors. I bought my Holco's before Holco changed the construction so use OLD Holco's or Resista's as John Curl says. I also replaced R28, R82, and R40 with old Holco's.
2. Replace diode bridges D8 and D16 with IR HFA08TB60 diodes or Fairchild Hyperfast.
3. Remove C25 – C32.
4. Remove C55-C60 and C49-C54 and replace with 0.1µF polystyrene RT RelCaps.
5. Remove C19/C20/C21 and C22/C23/C24 and replace with a 100µF/100V electrolytic and a 0.1µF polystyrene RT RelCap on each rail. I think Bob Crump mentioned the Nichicon KZ here. I used Elna Cerafines.
6. Replace diode bridges D53 and D57 with Harris RURG3060 diodes. Remove all film caps from the power supply board.
And here are a few more ......
Replace RCAs and Speaker Binding posts. I also made some changes to the Zobel on the output but that's in my notes that I can't find. If I remember right, R1 and C1 were mounted on a little PC board or on the main PCB. I replaced these with a 10 ohm Caddock MP-820 and an 0.1µF polystyrene RT RelCap soldered directly to the binding posts. I used Cardas wire for the input wiring. You can remove the input PCBs if you are using the RCA jacks and just ignore the XLR input. I'm using the XLR and still removed the input PCB board but my preamp can drive a lo-Z load.
Replace C11/C12 and C13/C16 with 100µF/25V BlackGate and 0.01µF polystyrene capacitors.
Replace R43, R46, R47, and R48 with Caddock MK-132 resistors of same value. Resistas would be fine here also.
Replace C62 and C9 with 10pF mica capacitors.
Other mods I did include removing the auto-bias thing and re-biasing the output stage; more resistor and capacitor changes; upgrading the servo and the +/- 15VDC supplies; upgrading wire; and replacing surgistors with soft-start circuits.
Phil
Hey Matt --
You're welcome! I forgot to mention that the output protection relays sometimes fail. One of the relays on my amps (I have two HCA-3500's to biamp my speakers) ended with fused contacts just through normal use. I don't think the originals are available anymore so I replaced mine with a bigger & better relay and mounted them off the main PCB.
Good luck with the mods and I look forward to hearing your opinions.
Phil
You're welcome! I forgot to mention that the output protection relays sometimes fail. One of the relays on my amps (I have two HCA-3500's to biamp my speakers) ended with fused contacts just through normal use. I don't think the originals are available anymore so I replaced mine with a bigger & better relay and mounted them off the main PCB.
Good luck with the mods and I look forward to hearing your opinions.
Phil
hca3500 mods
Got the hca3500 and planning some mods.
Looked into some list of changes appearing here, have a few questions, if anyone might answer
1. The issue with q5 is 2nd harmonic distortion from the InternationalRectifiers irf96210 installed, right? Will Vishay ifr9620 do fine or only Harris?
2. why change only q5 to Harris ifr9620 and not also q6 (they are symetrical, aren't they?)
3. What about all other ifr9610, will it make a difference replacing all with irf9620?
4. Big Sky Audio mentioned 0.5w Vishay dale rn60 series for r46 r48 390 ohm and r43 r47 2.2K resistors. sure 0.5w is needed? first thing is rn60 is 0.25w, second thing is the schematics do not call for 0.5w resistor there, third-will TE Connectivity/Holsworthy H8 series do better? (0.1% 0.25W 15ppm), or the precision line from Yageo? fourth, will H4 0.5w 1% be best choice? (caddocks mk132 are out of reach and very expensive)
5. r28 - 2.21k prp9372/ they are sold only at 2.2k..dramatic difference?
6. r44 47k Holco - Michael Percy wrote me that nowadays a tx2575 zfoil would be superior, what is your opinion ?
7. No need to replace D8 D16? (maybe only D8?) I can build a small pcb with 4 hyper fast rectifiers + c330c104 across each and wire connect them to the original holes where the D8 D16 are installed, that way not having a problem with tight space. Is it worth the hassle?
7. the late Bob Crump mentioned somewhere that to make the hca3500 really good would require replacing the 0.22Ohm emitter resistors. What is your recommendation? How big of a change will it make? I looked at Vishay LVR05 wire wound 0.1% 50ppm 5W, any other recommendation other than the pricy Vishay LVR05? Other options TT Electronics W22-0R22 (5% 7W 75ppm), or Vishay cw005r220 (5w 5% 90ppm)?
8. disconnecting the auto bias circuit (disabling q35 or the r140 resistor)- a good idea?
So many questions...
Hope you find the time to answer
Sincerely
Boaz
Got the hca3500 and planning some mods.
Looked into some list of changes appearing here, have a few questions, if anyone might answer
1. The issue with q5 is 2nd harmonic distortion from the InternationalRectifiers irf96210 installed, right? Will Vishay ifr9620 do fine or only Harris?
2. why change only q5 to Harris ifr9620 and not also q6 (they are symetrical, aren't they?)
3. What about all other ifr9610, will it make a difference replacing all with irf9620?
4. Big Sky Audio mentioned 0.5w Vishay dale rn60 series for r46 r48 390 ohm and r43 r47 2.2K resistors. sure 0.5w is needed? first thing is rn60 is 0.25w, second thing is the schematics do not call for 0.5w resistor there, third-will TE Connectivity/Holsworthy H8 series do better? (0.1% 0.25W 15ppm), or the precision line from Yageo? fourth, will H4 0.5w 1% be best choice? (caddocks mk132 are out of reach and very expensive)
5. r28 - 2.21k prp9372/ they are sold only at 2.2k..dramatic difference?
6. r44 47k Holco - Michael Percy wrote me that nowadays a tx2575 zfoil would be superior, what is your opinion ?
7. No need to replace D8 D16? (maybe only D8?) I can build a small pcb with 4 hyper fast rectifiers + c330c104 across each and wire connect them to the original holes where the D8 D16 are installed, that way not having a problem with tight space. Is it worth the hassle?
7. the late Bob Crump mentioned somewhere that to make the hca3500 really good would require replacing the 0.22Ohm emitter resistors. What is your recommendation? How big of a change will it make? I looked at Vishay LVR05 wire wound 0.1% 50ppm 5W, any other recommendation other than the pricy Vishay LVR05? Other options TT Electronics W22-0R22 (5% 7W 75ppm), or Vishay cw005r220 (5w 5% 90ppm)?
8. disconnecting the auto bias circuit (disabling q35 or the r140 resistor)- a good idea?
So many questions...
Hope you find the time to answer
Sincerely
Boaz
Ok , so got the hca3500 and in the process of making some mods:
1. Main power supply board- removed all yellow and white caps. Replace with two 0.1 polystyrene on each side, c145 c146, c155. C156 (k71-5 Russian polystyrene caps, see chap 5 ).
Removed both bridges from main power supply board. I ordered two small pcb boards designed for bridge rectifiers, + ordered Vishay 60amp 1200v ultrafast doft recovery rectifiers and installed these with heat sinks. Also installed 0.1uF/850V Roederstein MKP1839HQ across the two AC inputs on each of these boards.
I bought a 10awg silver coated wire and soldered the +/- of the rectifier bridge directly to the large 33000u Nichicons (disassembled the main power board so I could reach the big Nichicons +/- at the back of the board).
2. Remove all yellow+white square caps (bypass) from the sideboards (as PH104 mentioned above). Also remove c11 c16 c17 c18 c1.
3. Remove c59 c69 c53 c54 1000u 63v. Get Nichicon lx or lg series and install only 2 470u 250v on each side (c53 c59) , jumpering c60 and c54.
4. C38, C39, C47, C48 = .1uF/250V WIMA MKP10 polypropylene film or evel leave the original 4 white bulk caps .
5. C21 , C24, C28 , C31 , C51, C57, C17, C1 - Now, Rel Rt are hard to find and very expensive. I got some very good recommendations for old Russion polystyrene caps (k71-4 k71-5 polystyrene on Ebay), so ordered:
4* 0.01u to replace C11 C16, and about 20 for the rest.
6. q5 - replaced with Harris ifr9620
7. r44 47k Holco? - Michael Percy wrote me that nowadays a vishay/charcroft tx2575 zfoil would be superior to old Holco H4. Going to try each one on the right and left, watch the difference in sound and then decide.
8. r46 r48 390 ohm and r43 r47 2.2K - my model has Vishay high precision sort of z-foil for resistors. Did not touch these.
9. r28 2.2k, r129 2.2k : prp9372
10. R40-1.8k - I used Charcroft zfoil here. Think it is an overkill, maybe prp9372 are good enough.
11. D8 D16 - hfa08tb60 hyper fast rectifiers
12. Disconnect the auto bias circuit (disabling r94 r140 resistors)
Hoping that helps...
1. Main power supply board- removed all yellow and white caps. Replace with two 0.1 polystyrene on each side, c145 c146, c155. C156 (k71-5 Russian polystyrene caps, see chap 5 ).
Removed both bridges from main power supply board. I ordered two small pcb boards designed for bridge rectifiers, + ordered Vishay 60amp 1200v ultrafast doft recovery rectifiers and installed these with heat sinks. Also installed 0.1uF/850V Roederstein MKP1839HQ across the two AC inputs on each of these boards.
I bought a 10awg silver coated wire and soldered the +/- of the rectifier bridge directly to the large 33000u Nichicons (disassembled the main power board so I could reach the big Nichicons +/- at the back of the board).
2. Remove all yellow+white square caps (bypass) from the sideboards (as PH104 mentioned above). Also remove c11 c16 c17 c18 c1.
3. Remove c59 c69 c53 c54 1000u 63v. Get Nichicon lx or lg series and install only 2 470u 250v on each side (c53 c59) , jumpering c60 and c54.
4. C38, C39, C47, C48 = .1uF/250V WIMA MKP10 polypropylene film or evel leave the original 4 white bulk caps .
5. C21 , C24, C28 , C31 , C51, C57, C17, C1 - Now, Rel Rt are hard to find and very expensive. I got some very good recommendations for old Russion polystyrene caps (k71-4 k71-5 polystyrene on Ebay), so ordered:
4* 0.01u to replace C11 C16, and about 20 for the rest.
6. q5 - replaced with Harris ifr9620
7. r44 47k Holco? - Michael Percy wrote me that nowadays a vishay/charcroft tx2575 zfoil would be superior to old Holco H4. Going to try each one on the right and left, watch the difference in sound and then decide.
8. r46 r48 390 ohm and r43 r47 2.2K - my model has Vishay high precision sort of z-foil for resistors. Did not touch these.
9. r28 2.2k, r129 2.2k : prp9372
10. R40-1.8k - I used Charcroft zfoil here. Think it is an overkill, maybe prp9372 are good enough.
11. D8 D16 - hfa08tb60 hyper fast rectifiers
12. Disconnect the auto bias circuit (disabling r94 r140 resistors)
Hoping that helps...