As far as possible tweaks to the A75, the only thing I have done already was to use bigger caps in the power supply board for the front end. I noted a little more ripple than I like in the regulated DC waveform, so I stuck in the largest caps that would fit on the board and reduced the ripple by about 1/2.
I think I used used mosfets in place of the regulated power supply transistors also. I don't remember if that reduced the ripple in the regulated power supply. But, it was much cheaper than the replacement parts that show up as recommended replacements when searching for the original parts on Digikey's website. I started out with the replacement transistors recommended by Digikey, some of which were $4 apiece. When they blew out, 70 cent mosfets made a perfect replacement.
JJ
I think I used used mosfets in place of the regulated power supply transistors also. I don't remember if that reduced the ripple in the regulated power supply. But, it was much cheaper than the replacement parts that show up as recommended replacements when searching for the original parts on Digikey's website. I started out with the replacement transistors recommended by Digikey, some of which were $4 apiece. When they blew out, 70 cent mosfets made a perfect replacement.
JJ
Ah, yes. I had considered lowering the front end supply voltage to maybe 30 volts and using some jfets for the input devices that are rated for a minimum Vds breakdown of 40V. Siliconix 2N4392 and 2N5462 are what I am considering.
I know this would reduce the total wattage the amp can put out, but then I don't need that much power.
The question is -- would this give better performance than the mosfet input devices?
Will 30+V across a jfet cause increased distortion, even if it is rated for 40volts min?
JJ
I know this would reduce the total wattage the amp can put out, but then I don't need that much power.
The question is -- would this give better performance than the mosfet input devices?
Will 30+V across a jfet cause increased distortion, even if it is rated for 40volts min?
JJ
I have tested my 2sk170 / 2sj74's and find that they
actually break down around 43 volts or so. The
manufacturer's ratings are conservative, and they also
take into account Gate leakage figures, which typically
aren't an issue in these applications given the relatively
low impedance of the input and feedback networks.
So you have a little margin here, but I don't think I
would exceed 35 V rails under any circumstance.
😎
actually break down around 43 volts or so. The
manufacturer's ratings are conservative, and they also
take into account Gate leakage figures, which typically
aren't an issue in these applications given the relatively
low impedance of the input and feedback networks.
So you have a little margin here, but I don't think I
would exceed 35 V rails under any circumstance.
😎
Hi JJ not seen you around forums for a while.
Hi Papa
I am starting up with the F5 from that I have found
2sj74 and 2sk170 are difficoult to came by so is the 2SJ109
there is an issue with the Irf9240 (shelvin) and you suggest changing to FQA12P20 and FQA19N20C those are no longher in production as well.
We can mix and match and quite few members more capable and experieced than me may came up with good alternatives.
What would be an inprovment would be your input on current updated semis that get to the sweet spot.
Humbly yours
Al
Hi Papa
I am starting up with the F5 from that I have found
2sj74 and 2sk170 are difficoult to came by so is the 2SJ109
there is an issue with the Irf9240 (shelvin) and you suggest changing to FQA12P20 and FQA19N20C those are no longher in production as well.
We can mix and match and quite few members more capable and experieced than me may came up with good alternatives.
What would be an inprovment would be your input on current updated semis that get to the sweet spot.
Humbly yours
Al
One answer is: buy Toshiba 2SJ201 and 2SK1530 while you still can.
Another is to learn to like the sound of the IRF9240 -
many people do.
😎
Another is to learn to like the sound of the IRF9240 -
many people do.
😎
Hi Nelson
Unbelivable the dedication and support you give us .
Just the kind of answer I was expecting, don't get me wrong you are quite right.
Answer 1 will do
Answer 2 shure will like it once I got answer one sorted and shure it be better of many out there.
I was Just asking for more.... I am shure Papa know as litle cildren
Tanks
Al
Unbelivable the dedication and support you give us .
Just the kind of answer I was expecting, don't get me wrong you are quite right.
Answer 1 will do
Answer 2 shure will like it once I got answer one sorted and shure it be better of many out there.
I was Just asking for more.... I am shure Papa know as litle cildren
Tanks
Al
Nelson
The question is are you included in the many of people that do? Or do you just use them cause like many things you use lots of is ( I have large box of that item).
All joking aside Nelson thank you for your support of our hobby. One days I hope make to BAF and meet you in person.
Chad😛
The question is are you included in the many of people that do? Or do you just use them cause like many things you use lots of is ( I have large box of that item).
All joking aside Nelson thank you for your support of our hobby. One days I hope make to BAF and meet you in person.
Chad😛
The sound of the IRFP9240 has an artifact. If you place
emphasis on measurements, then you would not use the
IRFP9240. I personally don't care for it when the device
is used in common-source mode.
Comparisons between it and the Harris and Fairchild
equivalents in common-drain mode, particularly in
balanced circuits reveal a subtle warmth that is preferred
by a percentage of listeners.
😎
Nelson--
Is the SFH9240 from Fairchild one of the above mentioned equivalents? I know the FQA...... parts have been talked about, but I don't think I have ever seen any comments from you regarding the SFH9240.
Thanks,
JJ
Soon....
I am finishing up a project, then I hope to get back to the A75 build. This thread has inspired me!
JJ
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