I'm going to build Aussieamplifiers 200W@8ohms symmetrical amp. Construction notes says MOSFETs are recommended to match. I understand why but I would like to know how big can the difference be in current sharing without matching. In other words what will happen if I don't match the output devices.
I'm going to build stereo power amp. So I have to buy eight 2SK1530 and eight 2sj201. Is it enough if I match with those eight devices, taking four as similar as possible ? I don't have money to buy extra FETs 🙁
Link to the schematic:
http://www.aussieamplifiers.com/sym-sch.htm
I'm going to build stereo power amp. So I have to buy eight 2SK1530 and eight 2sj201. Is it enough if I match with those eight devices, taking four as similar as possible ? I don't have money to buy extra FETs 🙁
Link to the schematic:
http://www.aussieamplifiers.com/sym-sch.htm
Naula,
it depends a bit on how (un)lucky you are🙂 If not very lucky (different batches) you can have differences of 20-50%. What you can do is build the thing and then switch fets between left and right channel (this is what I did with my crescendo) until you get a reasonable spread.
The other possibility is to measure Vgs for a given bias (see "matching" in numerous threads) for the 16 fets, match them as good as possible, put them in the circuit and then decide if you have to buy a few more.......
I think current differences of 20% (highest to lowest) are acceptable.
william
it depends a bit on how (un)lucky you are🙂 If not very lucky (different batches) you can have differences of 20-50%. What you can do is build the thing and then switch fets between left and right channel (this is what I did with my crescendo) until you get a reasonable spread.
The other possibility is to measure Vgs for a given bias (see "matching" in numerous threads) for the 16 fets, match them as good as possible, put them in the circuit and then decide if you have to buy a few more.......
I think current differences of 20% (highest to lowest) are acceptable.
william
Insofar as Anthony is using low values (.22 ohm) of
Source resistance, matching becomes more critical to
insure that the devices share current in such a powerful
circuit.
Best to get some extras and match them as close as
possible; I would suggest .1 volt Vgs variation or smaller.
Source resistance, matching becomes more critical to
insure that the devices share current in such a powerful
circuit.
Best to get some extras and match them as close as
possible; I would suggest .1 volt Vgs variation or smaller.
if you purchase a "sleeve"
of Toshiba, IRF or ST Micro devices, they usually match very closely. For Toshiba (lateral MOSFET's) there are 30 in a sleeve. For ST Micro there are 50.
of Toshiba, IRF or ST Micro devices, they usually match very closely. For Toshiba (lateral MOSFET's) there are 30 in a sleeve. For ST Micro there are 50.
You might also check my posts here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5713&postid=62126
/UrSv
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5713&postid=62126
/UrSv
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