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Old 12th September 2010, 02:00 PM   #1
NVD33 is offline NVD33  France
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Default MF Citation12 - MF gate resistor value

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,
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Old 12th September 2010, 08:44 PM   #2
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Quote:
Originally Posted by NVD33 View Post
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).

Last edited by Melon Head; 12th September 2010 at 08:51 PM.
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Old 12th September 2010, 09:40 PM   #3
NVD33 is offline NVD33  France
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Will the amp oscillate with lower gate resistance value?

Thanks for your reply.

PS: Thanh1973 please see your PM.
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Old 12th September 2010, 09:44 PM   #4
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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.

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Old 13th September 2010, 07:53 AM   #5
NVD33 is offline NVD33  France
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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,
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Old 13th September 2010, 10:40 AM   #6
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Im considering building one of these too.
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Old 13th September 2010, 07:32 PM   #7
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Quote:
Originally Posted by Nelson Pass View Post
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.
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Old 13th September 2010, 07:56 PM   #8
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I will be interested to see which one you like better.
quasi vs comp
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Old 13th September 2010, 08:25 PM   #9
NVD33 is offline NVD33  France
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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?
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Old 13th September 2010, 08:31 PM   #10
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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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