Aleph 2 fet matching question

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Just received my new adjustable supply and I’m in the process of fet matching. I took an initial reading at power up and throughout, let them sit at 15v for 5 minutes each. A few I let sit for 10 minutes, and they barely got warm; granted I was using a large heatsink, thermal grease, and the fets were clamped down with aluminum angle bar. Measured 11v across R1. NP's Mosfet matching article uses 56r for R1, am I off in using 150r? To get the best matched sets, do I need to match in situ? I understand this would be optimal, maybe not necessary. My aleph2: 1500VA Plitron 38v secondaries 49000uf - 2.2mH - 49000uf, around 50-53v unloaded coming off the PSU. In situ fet matching 45-50V?, R1?



11 of 50 fets tested (Irpf244, R1 150 ohm @ 15v)

3.75
3.80
3.80
3.76
3.74
3.83
3.79
3.84
3.90
3.83
3.83

regards,
John H.
 
I am starting to build my Aleph2 clone, and in process of getting parts for it.

Questions (I am a newbie and does not have EE background):
1. Is it absolutely necessary to match the 12 IRF244 mosfets? What will happen if they don't match? What kind of tolerance (in mV)should all these 12 match?
2. Is it necessary to also match the three IRF9610?

Thank you!
 
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It's not absolutely necessary to match the output fets (irf244), but its good practice. Close matching to around 0.01mV will ensure each fet is sharing the load equally else distortion will rise. The input fets (irf9610) should also be matched as closely as possible to keep DC offset as low as possible, 0.01mV is fine, maybe even closer. The 9610 that's in the current source does not need to be matched to the two input fets.

-john
 
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Whew.... matching to 0.01mV will be hard

As far as the output section of the Aleph2, you don't need to match 12 fets within 0.01V of each other. 6 closely matched for the current source, and another 6 closely matched for gain section. Within a batch of 50 fets, this should be feasible. I wouldn't say its hard, maybe tedious.

Lots of reading, including fet matching at the bottom:
passdiy
 
My notes :

I used this (Cheffdegaar) matching schematic :
AppairageMosfets.jpg

Left schematic (IRFP044N) is ok too for IRFP240 or 244.

Matching values:
IRFP9610 +/- 0.01V - Only for Q1/Q2
IRFP240 +/- 0.05V if possible (0,1V max)

With replace R11 (221R) by "100R + Pot200R" for example, it’s possible to adjust offset to 0mV about (at running temp).

Laurent
 
MEGA-amp said:


As far as the output section of the Aleph2, you don't need to match 12 fets within 0.01V of each other. 6 closely matched for the current source, and another 6 closely matched for gain section. Within a batch of 50 fets, this should be feasible. I wouldn't say its hard, maybe tedious.


I have always thought that all 12 IRF244 has to be matched as 1 set.

Just to clarify: So I really only need to match 6 at a time, and the set in current source does not have to match with the set in gain section at all?
 
Buying mosfets for matching.

my own exp to buying IRFP, i used to perchase the same batch number from the same tube. i found its very good matching. when i buy, most of them are very same and some only very close to each other like 0.01 arround there. its probably made from same wafer as the batch number is same. i checked Each tube containg dfrnt batch number and they are not same value too. one tube have 25pcs. i buy all of them together so i get all are purly same value like mine is 4.12, all of them, i used in my aleph-3. all are same value.....very nice.
 
space2000 said:

my own exp to buying IRFP, i used to perchase the same batch number from the same tube.

Where is the best place to buy electronics components in Singapore? Sim Lim or other place?

The biggest challenge in this project is to get (reasonably priced) heatsinks and big Elko (47000 uF and up, 63+V). Are these easily available in Singapore at cheaper price?

I am planning a trip to this part of the world in a few months and would like to shop around for parts if it is cheaper than here in the USA. :D
 
kop89 said:


Where is the best place to buy electronics components in Singapore? Sim Lim or other place?

The biggest challenge in this project is to get (reasonably priced) heatsinks and big Elko (47000 uF and up, 63+V). Are these easily available in Singapore at cheaper price?

I am planning a trip to this part of the world in a few months and would like to shop around for parts if it is cheaper than here in the USA. :D


hi,

yes, all you can buy at sim lim. IRFP is cheap only s$1.50 each. 47000uf 63v will be expensive arround S$40. heat sink is not suitable to buy here. can't get big size.

may i know how much in your country?
 
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