whether or not increase current of front-end of alephx

john-china · 15th December 2003, 06:12 AM

i want to build 200w aleph-x. i collect a lot of irfp250 and irf9610.
i worry about too high input capacitance of irfp250 which will affect high frequency. so i want to increase the current of 9610 to 50ma ( how much is enough?). but i dont know whether or not
the modification of original sch is correct. my aleph-x will parallel
6 banks of irfp250 for each side.
if i increase the current , the volt of 392OHM resistor will not be about 4v , so i must resolve this problem , but i dont like capacitor-decouple. then i must keep the joint of 392OHM and irfp250 stay about -26v because rail to rail of my aleph-x is +30v to -30v. so negative supply of 9610 will be -26v-50ma*392OHM=
-45v. then i must separate power supply of 9610 from irfp250.
finally my aleph-x will use +-45v for front-end(irf9610) and +-30v for back-end(irfp250). can i do it so? will this aleph-x work?

i dont know if above modification is correct. pls tell me how to do.
maybe some simple way i dont know. give me more suggestion. thanks

Nelson Pass · 15th December 2003, 08:54 PM

You can crank up the front bias all you want in the front end.

Just adjust the resistors on the bias and off the Drains of the
diff pairs.

john-china · 16th December 2003, 02:05 AM

this is really a good way to resolve my question.
so i will adjust 392(OHM) resistor to 80(OHM) for 50ma current of front-end. but i have another question. is 80(OHM) too low ?,
will this affect gain of diff pair of irf9610?

Nelson Pass · 16th December 2003, 02:21 AM

Yes, it will lower it.

15th December 2003, 06:12 AM	#1
john-china diyAudio Member Join Date: Feb 2001 Location: where fair living	whether or not increase current of front-end of alephx i want to build 200w aleph-x. i collect a lot of irfp250 and irf9610. i worry about too high input capacitance of irfp250 which will affect high frequency. so i want to increase the current of 9610 to 50ma ( how much is enough?). but i dont know whether or not the modification of original sch is correct. my aleph-x will parallel 6 banks of irfp250 for each side. if i increase the current , the volt of 392OHM resistor will not be about 4v , so i must resolve this problem , but i dont like capacitor-decouple. then i must keep the joint of 392OHM and irfp250 stay about -26v because rail to rail of my aleph-x is +30v to -30v. so negative supply of 9610 will be -26v-50ma*392OHM= -45v. then i must separate power supply of 9610 from irfp250. finally my aleph-x will use +-45v for front-end(irf9610) and +-30v for back-end(irfp250). can i do it so? will this aleph-x work? i dont know if above modification is correct. pls tell me how to do. maybe some simple way i dont know. give me more suggestion. thanks __________________ Maybe i should not be lazy again

16th December 2003, 02:05 AM	#3
john-china diyAudio Member Join Date: Feb 2001 Location: where fair living	thank you Mr. Pass this is really a good way to resolve my question. so i will adjust 392(OHM) resistor to 80(OHM) for 50ma current of front-end. but i have another question. is 80(OHM) too low ?, will this affect gain of diff pair of irf9610? __________________ Maybe i should not be lazy again

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15th December 2003, 08:54 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	You can crank up the front bias all you want in the front end. Just adjust the resistors on the bias and off the Drains of the diff pairs.

16th December 2003, 02:21 AM	#4
Nelson Pass The one and only Join Date: Mar 2001	Yes, it will lower it.