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Hoffman Amps Forum image Author Topic: Source Follower After PI and Before PPIMV - Will it act as hoped ?  (Read 445 times)

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Offline kagliostro

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I was thinking to us a pair of LND150 as Source Followers in that position but someone explained me that the available current to drive the Power Section will be too low and also in the first approach I put the couplign caps before the PPIMV and that was told me is not a good choice

This is the first approach


and this is the new version with moved coupling capacitors and new MOSFET, a DN2540


I've never seen something like this arrangement with a SF that follows the exit of a Cathodyne PI and feed a PPIMV

Why I've think to this solution ?

The reason is because I don't want to load too much the PI and alter the tone when the Frondelli PPIMV has the shaft rotated near ground and the PPIMV is used because the gm of the 6N6P is near 3 times the gm of the 12BH7 tube that is originally used on the Wangs Mini 5, so it is there to enlarge the possibilities of use of the amp

Need really help to evaluate if this thing will be useful or not

MANY THANKS

Franco
« Last Edit: November 29, 2025, 07:12:15 am by kagliostro »
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Offline Merlin

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Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
« Reply #1 on: November 29, 2025, 09:02:22 am »
Someone gave you bad advice. Your first schematic makes more sense, and it doesn't even need LND150s, it could use ordinary enhancement MOSFETs. The second schematic will not work at all; it has DC on the pots and positive bias on the output tube grids!
« Last Edit: November 29, 2025, 03:02:28 pm by Merlin »

Offline pdf64

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Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
« Reply #2 on: November 29, 2025, 09:16:55 am »
first schematic makes more sense,
Sorry for a derail, but how are you viewing imgur stuff?
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Offline Merlin

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Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
« Reply #3 on: November 29, 2025, 09:27:56 am »
Sorry for a derail, but how are you viewing imgur stuff?
VPN

Offline kagliostro

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Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
« Reply #4 on: November 29, 2025, 11:38:42 am »
Many thanks Merlin

I surely misunderstand the council it was given to me

I can see what you say

So, I'll maintain the first arrangement and use on it a DN2540, will this MOSFET be adequate or it will be better to use one other one ?

Many Thanks

Franco
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Offline Merlin

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Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
« Reply #5 on: November 29, 2025, 03:02:06 pm »
So, I'll maintain the first arrangement and use on it a DN2540, will this MOSFET be adequate or it will be better to use one other one ?
DN2540 will work, even a classic like the IRF820 will work in that scenario

Offline kagliostro

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Re: Source Follower After PI and Before PPIMV - Will it act as hoped ?
« Reply #6 on: November 29, 2025, 03:14:43 pm »
Many thanks

Franco
The world is a nice place if there is health and there are friends

 


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