Several of Q-s about Citation 12 MosFet

argo · 23rd October 2003, 12:43 PM

Hi to all Pass fans

I have been thinking to build a Mr. Pass Citation 12 MosFet version for some time.
Looking at the schematic in the original article I got several questions?
 Why the outputs Fets (Q6, Q7) are not equipped with the Grid stop resistors?
 Are the diodes D1, D2 between Drain and Source really necessary with modern Fets like IRF240, where the Fets already have those diodes installed internally?
 What’s the purpose of R8?
 Why the input cap is excluded?
 I cannot easily source suggested ZTX450; ZTX550 transistors locally so I think to use BC560 for the diff pair (Q1, Q2). Can they be safely used for Q3, Q4, and Q5 as well or should I use some more powerful devices like BD139 and BD140.
 Would adding the rail decoupling caps (like 100uF parallelled with 100nF) improve anything?
 Are there any other improvements to the circuit that could be made?

Cheers,

Argo

Nelson Pass · 23rd October 2003, 05:53 PM

1) They apparently not needed as they are driven by
relatively high impedances.

2) No, they would be superfluous.

3) I recall connection to chassis, which is otherwise isolated.
This might be an error.

4) Why include it?

5) I imagine they will work fine.

6) Maybe

7) No doubt. Norm Thagard wrote an excellent piece for
AudioXpress on the Mosfet 60.

argo · 23rd October 2003, 07:00 PM

Short and sharp
Thanks a bunch Mr. Pass

Argo

Zen Mod · 23rd October 2003, 08:58 PM

Quote:

Originally posted by argo
Short and sharp
Thanks a bunch Mr. Pass

Argo

hehe-old Fox!

Drafance007 · 16th January 2004, 06:40 PM

Well on sugestion by Millwood...i built Mosfet citation 12 and was very satisfied. Well my first Mosfet amp ever but good one. Good Job Mr.Pass.
Pcb was made for about half an hour. Everything elese on about 1 hour. and there is the music. I also did destroy one pair of irf540. Maybe beacouse bias tromier pot was old 1o years like all the other components

Drafance007 · 16th January 2004, 06:41 PM

other side...panic and acid made board...

Nelson Pass · 20th January 2004, 05:43 PM

Very excellent.

Nat Riscica · 22nd January 2004, 08:10 AM

Hello,

I am built the Citation 12 using the MPSA 42 & MPSA 92 for all the transistors used, and the IRFP 240 for the Mosfet.
He work great!

Thank you Mr Pass.

Nat

wputera · 8th December 2006, 12:37 PM

i build citation 12 mosfet using 2sk1058, sounds great but the amp runs very hot, my finger can't hold the output transistor for 10 seconds

Any suggestion Gentlemen? I love the sound of this amp very much.

What should I do if i want to parrallel the output with 10 pieces IRF 450? Are there any changes for the components and its value?

Thank you Gentlemen, especially Mr. Nelson Pass.

Cheers,

Nelson Pass · 8th December 2006, 08:02 PM

Sounds like too much bias. You need to measure the
idle current in the output stage, for starters.

23rd October 2003, 12:43 PM	#1
argo diyAudio Member Join Date: Feb 2001 Location: Estonia	Several of Q-s about Citation 12 MosFet Hi to all Pass fans I have been thinking to build a Mr. Pass Citation 12 MosFet version for some time. Looking at the schematic in the original article I got several questions?  Why the outputs Fets (Q6, Q7) are not equipped with the Grid stop resistors?  Are the diodes D1, D2 between Drain and Source really necessary with modern Fets like IRF240, where the Fets already have those diodes installed internally?  What’s the purpose of R8?  Why the input cap is excluded?  I cannot easily source suggested ZTX450; ZTX550 transistors locally so I think to use BC560 for the diff pair (Q1, Q2). Can they be safely used for Q3, Q4, and Q5 as well or should I use some more powerful devices like BD139 and BD140.  Would adding the rail decoupling caps (like 100uF parallelled with 100nF) improve anything?  Are there any other improvements to the circuit that could be made? Cheers, Argo

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23rd October 2003, 05:53 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	1) They apparently not needed as they are driven by relatively high impedances. 2) No, they would be superfluous. 3) I recall connection to chassis, which is otherwise isolated. This might be an error. 4) Why include it? 5) I imagine they will work fine. 6) Maybe 7) No doubt. Norm Thagard wrote an excellent piece for AudioXpress on the Mosfet 60.

23rd October 2003, 07:00 PM	#3
argo diyAudio Member Join Date: Feb 2001 Location: Estonia	Short and sharp Thanks a bunch Mr. Pass Argo

20th January 2004, 05:43 PM	#7
Nelson Pass The one and only Join Date: Mar 2001	Very excellent.

22nd January 2004, 08:10 AM	#8
Nat Riscica diyAudio Member Join Date: Jan 2004 Location: Sicily	Hello, I am built the Citation 12 using the MPSA 42 & MPSA 92 for all the transistors used, and the IRFP 240 for the Mosfet. He work great! Thank you Mr Pass. Nat

8th December 2006, 12:37 PM	#9
wputera diyAudio Member Join Date: Mar 2006 Location: surabaya	i build citation 12 mosfet using 2sk1058, sounds great but the amp runs very hot, my finger can't hold the output transistor for 10 seconds Any suggestion Gentlemen? I love the sound of this amp very much. What should I do if i want to parrallel the output with 10 pieces IRF 450? Are there any changes for the components and its value? Thank you Gentlemen, especially Mr. Nelson Pass. Cheers,

8th December 2006, 08:02 PM	#10
Nelson Pass The one and only Join Date: Mar 2001	Sounds like too much bias. You need to measure the idle current in the output stage, for starters.

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