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?
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?
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).
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.
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.
IRFP9240 is also a 12A device.
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?
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?
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?
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?
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....
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....
at 12A pr device. and 4 pairs. that is hell of alot of power
nelson use FQA12P20 and FQA19N20 in the schematics for F5 turbo.
regarding feedback resistors. you can increase gain to 22db without loosing any sleep it will change 2. ond 3.harmonics a bit(i think) but with P3 instaled, thats not a problem
nelson use FQA12P20 and FQA19N20 in the schematics for F5 turbo.
regarding feedback resistors. you can increase gain to 22db without loosing any sleep
it will change 2. ond 3.harmonics a bit(i think) but with P3 instaled, thats not a problem
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It depends. In reality, if you have reasonably efficient speakers, you may never leave Class A levels abd the diodes are inconsequential. If your amp is being pushing a tough load, the diodes serve to slowly reduce the amount of degeneration, yielding more gain and ouput current. It is like bypassing source resistor in tube amp with cap. On the surface, 12 amps doesnt look like much, but in reality, it is a level you will rarely see out of a multi pair amp, much less a single fet.
When you parallel devices, the effective transconductance goes up -- with the Toshiba's you're starting around 5 S, while the Renesas (nee Hitachi) devices are around 1 S. The MOSFETs from IRF/Vishay are around 7. More Siemens are better than fewer Siemens! But you've got to worry about the kinked THD curve with the latter devices.
The interesting thing about the Toshiba units is that you might be able to use other JFET's than the K170/J74, i.e. 2N5460/2N5457 in their smt versions. Same goes with the Renesas MOSFETs. It's the old "dog food" problem that you learned in linear programming.
It's time for an F5 bake-off with the various output devices.
The interesting thing about the Toshiba units is that you might be able to use other JFET's than the K170/J74, i.e. 2N5460/2N5457 in their smt versions. Same goes with the Renesas MOSFETs. It's the old "dog food" problem that you learned in linear programming.
It's time for an F5 bake-off with the various output devices.
I would like to try you version with the 2SK175/2SJ55.
Do you have a schematic or a link to it ?
Ric
see my signature . . although I have no triode in the F5: it is not triodes_all over the place anymore
Just one thing...
Could you please tell witch resistors and values you used for this version?
Repairing amps is something I can do but changes in components values is really not my thing.
I was looking for some components today and realized my transistors are the 2SK135/2SJ50 and not the 175/55
Ric
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