MF Citation12 - MF gate resistor value

NVD33 · 12th September 2010, 02:00 PM

Hi,

I have built recently one channel of MF Citation 12 (quasi complementary version) and it sounds great.

I want to build now the complementary version using IRFP240/IRFP9240 pair. I have seen on many posts overhere that it is recommended to put a 240R resistor on this type of Mosfet. Refering to Mr. Nelson Pass original schematic (see attached pisture) must I change R18 & R19 from 680R to 240R?

Thanks for your help,

Melon Head · 08:51 PM

Quote:

Originally Posted by NVD33

Refering to Mr. Nelson Pass original schematic (see attached pisture) must I change R18 & R19 from 680R to 240R?

Thanks for your help,

It will definitely sound better with the smaller resistor.

If you have a scope you could try even lower.

You could probably try as low as 100 ohms.

The resistors should be as close to the gate as possible (eg soldered directly to it).

NVD33 · 12th September 2010, 09:40 PM

Will the amp oscillate with lower gate resistance value?

Thanks for your reply.

PS: Thanh1973 please see your PM.

Nelson Pass · 12th September 2010, 09:44 PM

Maybe. Not much reason to go below 100 ohms, though.

BTW, you actually don't have to get fancy with placing the
Gate resistors right on the Gate. I have gone a couple
feet on occasion without issues.

NVD33 · 13th September 2010, 07:53 AM

Hi NP,

I am completly "stoned" by the sound produced by this simple, rugged, 7-transistors design. It works like a charm at the first power up. I will try with lower Gate resistance values.

In the quasi complementary version I have implemented Gate resistors in the Gate of IRFP240 (see picture attached).

My question: Must I short R18 or leave it like this?

Thanks for your help,

Tekko · 13th September 2010, 10:40 AM

Im considering building one of these too.

Melon Head · 13th September 2010, 07:32 PM

Quote:

Originally Posted by Nelson Pass

BTW, you actually don't have to get fancy with placing the
Gate resistors right on the Gate. I have gone a couple
feet on occasion without issues.

That is good to know.

Melon Head · 13th September 2010, 07:56 PM

I will be interested to see which one you like better.
quasi vs comp

NVD33 · 13th September 2010, 08:25 PM

Yes Tekko go on.

OK Thanh I will report back after completing and listening to the complementary version. Be patient it can be very quick or it can take time

No answer for my question in post #5?

Tekko · 13th September 2010, 08:31 PM

I'm not nelson passut it looks like you can remove it since you added the other resistor to the left of the mosfet symbol.

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12th September 2010, 09:40 PM	#3
NVD33 diyAudio Member Join Date: Aug 2004 Location: Bordeaux	Will the amp oscillate with lower gate resistance value? Thanks for your reply. PS: Thanh1973 please see your PM.

12th September 2010, 09:44 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	Maybe. Not much reason to go below 100 ohms, though. BTW, you actually don't have to get fancy with placing the Gate resistors right on the Gate. I have gone a couple feet on occasion without issues.

13th September 2010, 10:40 AM	#6
Tekko diyAudio Member Join Date: Jan 2005	Im considering building one of these too.

13th September 2010, 07:56 PM	#8
Melon Head Banned Join Date: Nov 2006	I will be interested to see which one you like better. quasi vs comp

13th September 2010, 08:25 PM	#9
NVD33 diyAudio Member Join Date: Aug 2004 Location: Bordeaux	Yes Tekko go on. OK Thanh I will report back after completing and listening to the complementary version. Be patient it can be very quick or it can take time No answer for my question in post #5?

13th September 2010, 08:31 PM	#10
Tekko diyAudio Member Join Date: Jan 2005	I'm not nelson passut it looks like you can remove it since you added the other resistor to the left of the mosfet symbol.