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Old 10th October 2012, 12:57 AM   #1
dazed2 is offline dazed2  Canada
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Default Other MOSFETs for the F5?

I have so far tried the toshiba 2sj201 / 2SK1530Y outputs with the F5.
And just Saturday for variety I installed the Fairchild 12P20C/16N25C. I also have a set of IRFP 240/9240 lying around never installed.

Perhaps it will be better after 100 hours or so of burn in, but I find the Fairchilds, although have a little more punch, is lacking the special liquidity and sparkle that the Toshiba's bring. The Fairchilds also seem a little colder in character than the Toshiba's.

Now here is the question, Does toshiba make other similar mosfets that may work with the F5 that retain the smoothness of the 2sj201/2sk1530y combo, but with more punch and perhaps current handling? (ie if you add the diode a la light F5T v2) or perhaps even a fully built F5T v3? The toshibas only have a max current capability of 10A whereas the fairchilds and irfp are 20+A.

Has anyone tried and compared other available mosfets with good results?
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Old 14th October 2012, 06:36 AM   #2
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I have great fun with my Toshiba version, but these are older and larger TO-3 2SK175/2SJ55 FETS. At 6 (8) amp each they make a great device, and can be paralleled (I have 3 parallel now, to go up to 4), and there is a source resistor that you can forgivingly omit (the FET has negative temperature coefficient).
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Old 14th October 2012, 11:06 AM   #3
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by dazed2 View Post
The Fairchilds also seem a little colder in character than the Toshiba's.
did you try 'adjustments' ?

btw, I think the '12' in the fairchild means it a 12A device

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Originally Posted by dazed2 View Post
.... installed the Fairchild 12P20C/16N25C.

..... whereas the fairchilds and irfp are 20+A.
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Old 14th October 2012, 11:27 AM   #4
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If sinlge pair F5, you probably dont have pot across the jfet source resistors. If you do, then you can tweak the harmonic structure of the amp. More pairs sound decidely better, IMO, on the F5.
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Old 15th October 2012, 02:37 AM   #5
dazed2 is offline dazed2  Canada
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Originally Posted by tinitus View Post
did you try 'adjustments' ?

btw, I think the '12' in the fairchild means it a 12A device
You know I just realized that! I was looking at the irfp ones, and forgot about the fairchild replacements being a little lower current .

what "adjustments" do you mean? resistor changes and biasing?
I've biased them to 0.74V at the source resistors.
I have caddocks in the feedback loop, and vishay nudes in the signal path and ground. and the source resistors are fukushimas. Also I removed the current limiting circuit.

I didn't know that there is a pot across the jfets in the turbo version? I dont' recall seeing that in the schematic? However there is a pot parallel to the source resistors to the mosfets though, which is also in the regular F5.
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Old 15th October 2012, 02:47 AM   #6
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Check out F5t article and potentiometer P3. It allows for harmonic adjustment. For me, the extra fets made a difference. The IRf fets are said to be darker sounding and have a naturally higher 2nd hamonic due to an irregularity in the P channel device, I think. Could be wrong. If you can add P3 from F5t to your boards, then yo should be able to achieve similar sonic signature.
IRFP9240 is also a 12A device.
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Old 15th October 2012, 03:28 AM   #7
dazed2 is offline dazed2  Canada
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Hmm yes thanks the for the tip thats a great idea. So I may be able to add in a little more 2nd harmonic to "sweeten" the amp.
Also a little off topic but, is it possible to lower the feedback and increase the gain as per V1 to the F5 regular without much change and worry that something may overheat?
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Old 15th October 2012, 03:39 AM   #8
dazed2 is offline dazed2  Canada
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Hmm yes thanks the for the tip thats a great idea. So I may be able to add in a little more 2nd harmonic to "sweeten" the amp.
Also a little off topic but, is it possible to lower the feedback and increase the gain as per V1 to the F5 regular without much change and worry that something may overheat?
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Old 15th October 2012, 05:13 AM   #9
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Without having doe it, i cant say for sure what would happen to overall sound and performsnce, but it should be ok.
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Old 16th October 2012, 11:45 PM   #10
dazed2 is offline dazed2  Canada
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Buzz, just thinking aloud here, if the 12p20c are only rated to 12A, would the diodes in the turbo versions really be of much use?
In NP's article, he goes on to say that the reason he uses the diodes in parallel with the source resistor is to lower that source resistance at high currents. But he is using the example of Fairchild MOSFETs which have a max current capability of 22A.
In the schematic however, Q3 and Q4 are FQA12P20 which have a max current of 12A....
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