DIY progress report

[Manu]

Recently, a member of an another forum (froggy) ebayed some mosfets (IRf 240 and 9240) in order to build an UGS UP (Cheff de Gaar).
According to the seller they were matched Vth and Ids at this point (around 1 - 2mA for the most), with a so called Fet analyzer ...
Anyway, surprisingly it appeared that the fets offer not a bad match also at 100mA bias (measured in situ) .
Is it just chance? or is there a correlation between those Vth numbers and matching at any bias current ...

Manu

[luvdunhill]

I have decided to build a new speaker. I'm going to try my hand at the Lowther TP-1 Isis using DX4 drivers. I'm curious what amplifier would NP recommend to power these? I'm looking for a range of ideas I guess. I'd love a gen-u-ine (with a Texas accent) INT-30A, and might be able to pull that off, but perhaps there is a better choice? a more realistic choice?

[jimbo51]

Manu,

Measuring IRFP240, IRFP9240, FQA12P20 & FQA19N20C at 200mA @ 25 deg C and 1A @ 50 deg C I found a relatively strong consistency in the matching.

[philbyx]

Hi,

I put here my own experience about matching mosfets.
The method :
On a thermostated table home made, regulated at 35°C +/-0.3°C :



I measure the Vgs when Gate and drain are connected, and Ids injected by a regulated source of current.
The Ids are 100ma and 200ma

Two full batches of Irfp240 and Irfp9240 (2x1000 mosfets).

Here the results for the two batches :
Vgs of the Irfp240 and 9240
Magenta : Batch 1, 200ma / Dark Blue : Batch 1 100 ma
Cyan : Batch 2, 200ma / Yellow : Batch 2, 100ma

You can see that the batches of 240 are better than the 9240 ones.
These batches permit to have a good sextet matching (1mv for 240 and 2mv for 9240).

[philbyx]

I also made a comparison between some Vgs mosfets at 100ma, 200ma, 400ma, 700ma 1A, and 2A.
The mosfets :
Irfp 240, Irfp 9240, 12p20, 19n20

[Variac]

Originally Posted by luvdunhill

I have decided to build a new speaker. I'm going to try my hand at the Lowther TP-1 Isis using DX4 drivers. I'm curious what amplifier would NP recommend to power these? I'm looking for a range of ideas I guess. I'd love a gen-u-ine (with a Texas accent) INT-30A, and might be able to pull that off, but perhaps there is a better choice? a more realistic choice?

Check out the last newsletter with the article about Burning Amp. It discusses the amps Papa used and a filter to make it work..

[Manu]

Originally Posted by jimbo51

Manu,

Measuring IRFP240, IRFP9240, FQA12P20 & FQA19N20C at 200mA @ 25 deg C and 1A @ 50 deg C I found a relatively strong consistency in the matching.

Thanks for your feedback ...

Originally Posted by philbyx

Hi,

Hi Philippe,

Nice setup and interesting results
Thanks for sharing ...

Manu

[luvdunhill]

Originally Posted by Variac

Check out the last newsletter with the article about Burning Amp. It discusses the amps Papa used and a filter to make it work..

Hm, I see the F2J mentioned and a network to integrate it with a Seas driver, but perhaps I missed something? Thanks for that though, it was a great read, even a second time

[Tea-Bag]

Originally Posted by luvdunhill

Hm, I see the F2J mentioned and a network to integrate it with a Seas driver, but perhaps I missed something? Thanks for that though, it was a great read, even a second time

Luvdunhill -
I use a F2J clone,
with a lowther PM5A, a 10R-10uf across the terminal sounds good to me. (running OB)
next choice was 10R across the terminals. I left out the 3x47R resistors in F2J.

I wonder what Papa or Jon ver Halen use in OB with PM5 or 6A.
I have not experimented around too much. it sounds really laid back, with a sweet mid and really nice top end.

[Variac]

Originally Posted by luvdunhill

Hm, I see the F2J mentioned and a network to integrate it with a Seas driver, but perhaps I missed something? Thanks for that though, it was a great read, even a second time

Sorry, you're right, the info was for the Seas driver. Still, clearly the F-2J is a contender!

Papa has a lot going on at the moment so can't post much, but maybe later..