Thank you, Mr Pass for your kindness and participation!
I read this entire thread back and forth a couple times, it doesn't seem like anybody built an F5 with paralleled outputs. I have a working F5 over here and was thinking to double up the outputs and up the bias so it would have full 4 ohm driving capacity. Incidentally, I just ordered a full complement of Toshiba mosfets from the Dunhill loving person here. So I intend to try 2xToshibas instead of original 1xFairchild. Any tips/suggestions?
OK, now you know R11 is broken Q3 and probably Q4 are gone also...
I assume both voltages +/- 24V are still present?
If the cause was shorting R12 I would advise to test Q1 and Q2 (like you have matched them)
And check R1,2 and R5,6,7,8 (especially if you did not overdimension them)
If you have a tone generator and scoop you can remove Q3 and Q4 and measure on the "open" gates dc and ac level. (maybe disconnect the emitter of Q5 and Q6 during measurement)
Good luck, and remember, this way you really learn how this fine amp works
Finally, i have reset the offset of my tweeter's F5.( after monthes working)
I obtain about 15mv when cold (both channels)
Stabilising to o mv / 2mv after a few minutes.
Stable after one hour or so.
Thermistors are in touch with mosfets cases + white goo.
No need to insert a cap in the outputs (but to prevent from an accident).
I obtain about 15mv when cold (both channels)
Stabilising to o mv / 2mv after a few minutes.
Stable after one hour or so.
Thermistors are in touch with mosfets cases + white goo.
No need to insert a cap in the outputs (but to prevent from an accident).
I did this some time ago with 3 pairs of paralleled output devices (irfp240/9240), and it runs absolutely fine.
I am sure several other people have also done it.
I assume you also are using active crossovers, if not then you already have a capacitor in the tweeter's crossover which will block dc.
By itself, using parallel devices is not the issue with distortion.
Depending on the use, you can have too few and too many
devices - too few when the power is high, too many when the
combined capacitances get too high or each device is starved
for more bias current.
Has anyone built F5 mono blocks. I have four 10" X 6" X 2.5" heat sinks, one for each output Mosfet. I was planning to attach leads going from the PC board to the outputs connectors for the Mosfets. Any recommendation would be appreciated. In removing the current limiter thermistors, for more involving sound, is a short use for bypass on the PC board and the ground?
Ray
Ray
By itself, using parallel devices is not the issue with distortion.
Depending on the use, you can have too few and too many
devices - too few when the power is high, too many when the
combined capacitances get too high or each device is starved
for more bias current.
Hi Nelson.I meant about number of harmonics.which is natural?1st 2nd 3rd ?someone say tube amps gives natural harmonics and sounds better.what is natural harmonics for ears?and tonight I saw you in my dream.We were talking about something and then you became a singer Baris Manco(He was very popular pop singer here in my country Turkey and also in Japan.But he died
) here is his picture Attachments
Hi Nelson.I meant about number of harmonics.which is natural?1st 2nd 3rd ?someone say tube amps gives natural harmonics and sounds better.what is natural harmonics for ears?and tonight I saw you in my dream.We were talking about something and then you became a singer Baris Manco(He was very popular pop singer here in my country Turkey and also in Japan.But he died
your quilt is fall down when you were sleeping
Hi Thanh1973,
I checked and the devices were flush and tight with the heat sink. The other channel with the fairchild mosfets biased at 1.3A the temps were 110C & 120C
Apparently they had been running so for weeks. I replaced the mica/artic silver with sil-pad K-10's and the fairchild now lives at 60C & 65C.I think I've figured out what I was doing wrong. As per my days of building computers, I would use only a very thin even layer when mounting the CPU to the heat sink. A thin layer allows too much contact with the mica, which is a poor thermal conductor. The photo of the F5 in the 6moons article shows a lot of grease was used.
Wouldn't it be more effective if the mica had a cutout in the center to filled with grease? Just wondering if such a "mod" makes sense.
Hi Thanh1973,
I checked and the devices were flush and tight with the heat sink. The other channel with the fairchild mosfets biased at 1.3A the temps were 110C & 120C
I think I've figured out what I was doing wrong. As per my days of building computers, I would use only a very thin even layer when mounting the CPU to the heat sink. A thin layer allows too much contact with the mica, which is a poor thermal conductor. The photo of the F5 in the 6moons article shows a lot of grease was used.
Wouldn't it be more effective if the mica had a cutout in the center to filled with grease? Just wondering if such a "mod" makes sense.
Mica is a pretty good thermal conductor. I think you need enough grease but not too much. Maybe you didn't use enough. If you put too much you will raise the the thermal resistance of the joint and the device will overheat. The idea is to use enough grease to fill the tiny gaps between the surfaces. Not spread it like peanut butter.
HelloJudging by the curves on those parts, when paralleling them
you can raise the Source resistor to 1 ohm and get greater
thermal stability yet.
I'm planing to use 3pair 2SK1529 & 2SJ200 Toshiba mosfet .
What would be the best value for Source resistor 1 Ohm or even I can go bit higher 1.2 Ohm .
Thanks
Greets
Merry Christmas