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Old 15th July 2010, 07:36 AM   #761
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in addition ? thats what Im thinking now. A-n-y b-o-d-y-o-u-t-t-h-e-r-e ?
Im presuming only a few people have made the jx...
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Old 15th July 2010, 09:54 AM   #762
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Measure the Idss of the JFET in the CCS, with that number you'll find the corrresponding transconductance in the datasheet of the J74.
1 divided by that mS number is the apparant resistance of the JFET.
Adding a resistor value at the Source of the JFET will lower the drain current to the level you want, Id is reduced from the Idss value by the total series resistance of Rs and the virtual resistance value of the JFET.
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Old 15th July 2010, 10:41 AM   #763
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Bah, Cheers Jacco measured the wrong part. That'll be cause I dont know wtf Im doing. Think I know how to work it out now. Soooooooo just add a 100r to ground on the outputs and Im done I guess....
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Old 15th July 2010, 02:48 PM   #764
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The J-X is a balanced version, your J109 is 5% Off.
No itch to fiddle wih the drain resistor values ?
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Old 15th July 2010, 02:58 PM   #765
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too much off ? what would you advise ?
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Old 19th July 2010, 12:46 PM   #766
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Default Inrush Current Limiter & Capacitor Ripple Specification

Quote:
Originally Posted by BobEllis View Post
I'm not sure about the current capacity of the Super Q- perhaps the Erse data sheets will help. But, given 500W into 8R is almost 7A I suspect that you will be saturating the cores. You might want to consider air core coils, but see if you can find the data sheets. You can probably use the Farnell common mode chokes with one leg in each rail. referring to the drawing in post 742, the caps will be two caps in series, with the junction being ground. That makes the DC saturating currents cancel.

Caps are a bit of a personal choice, but I think high ripple current capacity and high temperature rating is important. If the heat sinks will be 55C, how hot will it be inside? It may not exceed 85C, but you'll get better life out of 105C caps. I don't think you'll hear much of a difference, but there may be a reliability difference.

There is a free tool called PSUD2. Use it to model the ripple current expected in your caps. It might surprise you, especially if you model your transformer a bit too ideally.

I'm not quite sure what computer grade means, other than the implication of high quality. Look at the data sheets to see if you need the ripple current capacity. Note that you get 50% more ripple capacity with 3 x 33,000uf than a single 100,000 uf. Also the Panasonic caps are rated at higher ripple current than the U36D at the same capacitance/voltage rating. Seems that they are a better value.
With Respect To(WRT) capacitor ripple capacity, is it a specification
to maximize or is there a limit with dimminishing returns, because I was told a long time ago that it is better to have many capacitors to make up the required capacitance insted of just one or two, I dont know the logic in the statement though and it may have been marketing for a David Hafler DH100 retrofit kit from a third party, the DIY'r selling statement was those big can capacitors in the DH100 are no good compared to many smaller capacitors making up the same capacitance.
I dont know how to read the Capacitor Ripple Specification from the Data Sheets, is a higher number good or a smaller number good ? I know that all capacitors do not give out this specification, I suspect because the number is bad WRT the competition capacitors ?
So, insted of me useing three 33KmicroFerrid capacitors I should use ten 10KmicroFerrid in parallel making up the four places I will use in the 100KmicroFerrid +/-20% capacitance in the CLCRCRC Power Supply ?
WRT the inductor I found out that the 16gage Erse Super Q is 16amps I belieive but I could be wrong, it was used in the Aleph 3 amplifier succsessfully, so I will purchase the 14gage Erse Super Q someware insted of the 16gage one at Parts Express Erse Super Q 2.0mH 16 AWG 500W Inductor | Parts-Express.com Parts Express dose not stock the 14gage inductor, I believe that it should have better amps power specification, I will find this out if it is public information before purchasing.
Finally I am down to the last question for this message. Can I use just a AMETHERM MEGAsurge part#MS35-10018(see attachment Data Sheet) Ametherm's new Inrush Current Limiter insted of all of the parts on the "PowerSwitch-CurrentLimiter" schematic attached to this message ?
Thank You again for your help, all comments are usefull and I hope that some of the questions I have had solutions for helps others as well in the construction your own Aleph J-X amplifier.
Attached Files
File Type: pdf MegaSurge DS 2003.pdf (71.3 KB, 55 views)
File Type: pdf PowerSwitch.pdf (7.2 KB, 67 views)
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Old 19th July 2010, 01:46 PM   #767
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Ripple current capability must exceed the in circuit ripple current. Beyond a small margin, increasing ripple capability buys some extended lifetime. There are many ways of looking at using multiple caps. As noted earlier, in the same type you will likely have more ripple current capability with two smaller caps than a single of equal total capacity. You will also lower the effective ESR with multiple caps, as the ESR of each is in parallel. Lower ESR means increased ripple current and in the back of my head I remember reading something about potential resonances.

Where does the point of diminishing returns hit? Your call. Is the additional labor and hardware required to mount multiple caps worth the increased current capability and lower ESR?

An inductor that won't saturate its core at 16A should be fine at 10A. The 14 gauge will likely be built on the same core, the only advantage being the lower DCR.

The MegaSurge is a negative temperature coefficient thermistor, another version of the CL60 used in so many Pass amps and clones. You won't get the DC blocking shown in the switch circuit, if you think that you need it.
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Old 19th July 2010, 02:29 PM   #768
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Quote:
Originally Posted by BobEllis View Post
Ripple current capability must exceed the in circuit ripple current. Beyond a small margin, increasing ripple capability buys some extended lifetime. There are many ways of looking at using multiple caps. As noted earlier, in the same type you will likely have more ripple current capability with two smaller caps than a single of equal total capacity. You will also lower the effective ESR with multiple caps, as the ESR of each is in parallel. Lower ESR means increased ripple current and in the back of my head I remember reading something about potential resonances.

Where does the point of diminishing returns hit? Your call. Is the additional labor and hardware required to mount multiple caps worth the increased current capability and lower ESR?

An inductor that won't saturate its core at 16A should be fine at 10A. The 14 gauge will likely be built on the same core, the only advantage being the lower DCR.

The MegaSurge is a negative temperature coefficient thermistor, another version of the CL60 used in so many Pass amps and clones. You won't get the DC blocking shown in the switch circuit, if you think that you need it.
WRT the CL60 it is only rated to pass a max of 5Amps, which will be fine with the other amps it was used in, I felt that the 5 amps max continuas current will be to low for this project, so I chose the AMETHERM MEGAsurge #MS35-10018 because it is rated at 18amps max continuas current while rated at 25degree 10ohms, same as the CL60. Have I analysed this properly ??

the specification I need to know how to read is the Capacitor Data Sheet is the "Ripple Current Multiplier" and the "Ripple Current Ambient Temperature Factors", again are higher values or lower values better so I can do some valuable analyses between Capacitors.

I am now thinking of useing nineteen 6.8KmicroFerrid in paralell totaling 129.2KmicroFerrid for each group required by the CLCRCRC Power Supply for a total of 304 capacitors for two monoblock Aleph J-X amplifiers. What do you think, is this going to far, it will not cost much more because the price drops significantly over 300 units ordered, that is why I came up with 19 paralell capacitors per bank ?

Thank You, I am almost ready to order parts, but I am scared of making a mistake, not that the amp will not work but I may need to upgrade it next year because knowing that other parts may have been better choice, so I will try and do all of the research I can now, but I realy need to have this amp working in my stereo now because I have just finnished speakers I have been researching for years that sound amazing but I need another amp for above 100Hz, what do I do now, buy or research?

Thank You For Your Help

Last edited by SCAIFF001; 19th July 2010 at 02:40 PM.
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Old 19th July 2010, 03:03 PM   #769
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IIRC, You'll be running at around 500W, which is ~4A @120V. Your calculations for the NTC are correct as far as they go. The other side is how low the resistance drops at the operating point. The CL-60 will be within its limits but much lower hot resistance. The Mega Surge MS35 20010 might be a good choice - higher cold resistance (lower inrush current) and lower hot resistance than the -0018.

Without seeing the data sheets in question, I'll guess that those are derating factors. The smaller the number the shorter the life. There is usually an example of how to use them in the data sheet.

15 caps per position seems like an awful lot of assembly work for potentially a marginal gain. Will you make PCBs to mount them? Use heavy copper and wide traces.

It sounds like analysis paralysis is setting in. No matter how long you study, there will always be some idea that might sound better that would require a redesign to incorporate once you start your build. Build, enjoy, and if you really think you need to upgrade in a year or so, go ahead.

Edit: You can also use lower rated NTCs by using one in each leg of the transformer primary (assuming you have a dual primary transformer)
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Old 19th July 2010, 05:00 PM   #770
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Someone asked a few posts back if Peter had built one of the XJ amps. Has anyone else got one up and running.
I purchased four of these boards several months back and have been trying to decide if just constructing the stock J would not in itself be a great amp. Nelson thought enough of this design to reengineer the earlier Aleph 3 and incorporate into the First Watt lineup.
I would like to see a progress report on the completed XJ before plunging into this with huge heatsinks and the like.

Bob, I like the analysis paralysis nice one. Most of the DIY efforts at perfection will hardly be audible anyway. The real meat in this amp is the decades of experience this designer has given us.

Tad
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