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Old 15th April 2014, 01:54 PM   #1
miftah is offline miftah  Indonesia
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Default (ask) ZCA 2sk1058 mosfet amplifier

Hi all .. I has build class a amplifier.
ZCA 2sk1058 mosfet amplifier. From Mark Houston
schematic. Using irfz44n and replace big resistor with 12v/20watt bulb.
I build 2 channel for stereo. I can't find 2sk1058 in
my town. This amplifier is very great sound, i love it. But I get the problem. The
transformer is very hot. I use 18vac / 5A
with capacitance multiplier from rod elliot site.
with diode bridge 25A . Her question why I
was so hot transformer? sorry my bad english.
Thanks for help...
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Old 15th April 2014, 02:21 PM   #2
Bigun is offline Bigun  Canada
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Some transformers are perfectly happy running hot and many of them you would expect to get hot if you operate them close to their power ratings. For example, my tube amplifier uses a Hammond power transformer that is being operated close to it's ratings and it gets quite hot indeed, over 50 degC in operation. But it's not a problem.

The usual solution is to get a bigger transformer.

Another design that you might like: SEWA - Seven Watt Amplifier
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Old 15th April 2014, 11:11 PM   #3
miftah is offline miftah  Indonesia
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hi bigun .. but this is very very hot .. even
though I just turned on briefly just 10
minutes .. does this effect my use irfz44n?
from datasaheet 49A/55V . while 2sk1058
7A/160V. I have not tried the other mosfet.

what irf530 sounds good ..?
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Old 16th April 2014, 12:38 AM   #4
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Most cheap transformers are wound with smaller wire than is optimum causing the windings to have higher resistance and creating more heat. Even though they may meet advertised specs, they generally aren't made to be run at full spec for very long. The type of mosfet used won't change this, however, the irf530 should sound better than the irfz44n if for no other reason than the 530 having ~half the capacitance of the 44. There will be lower gain though since the 530 has about 1/4 the transconductance.
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Old 26th April 2014, 07:09 AM   #5
miftah is offline miftah  Indonesia
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this schematic Click the image to open in full size.
how many volts should I fix the drain ??
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Old 26th April 2014, 07:43 AM   #6
miftah is offline miftah  Indonesia
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this is schematic




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Old 26th April 2014, 07:49 AM   #7
mikvous is online now mikvous  Greece
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Is it a toroid transformer?
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Old 26th April 2014, 08:01 AM   #8
miftah is offline miftah  Indonesia
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no.. i used 2 5A EI transformers in parallel. (but not really 5A)




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Old 26th April 2014, 12:25 PM   #9
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Quote:
Originally Posted by miftah View Post
hi bigun .. but this is very very hot .. even
though I just turned on briefly just 10
minutes .. does this effect my use irfz44n?
from datasaheet 49A/55V . while 2sk1058
7A/160V. I have not tried the other mosfet.

what irf530 sounds good ..?
Are you using for a 2SK1058 design IRFZ44n fets?The 2SK1058 are lateral fets not vertical
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Old 26th April 2014, 12:42 PM   #10
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by miftah View Post
no.. i used 2 5A EI transformers in parallel. (but not really 5A)
Then you have even smaller transformers. Such small transformers usually are designed for low power circuits and may not perform very well with such a high constant power loading as Jerluwoo has said already. I'm also not so sure how well they will do wired in parallel, they may not be that well matched. Changing to a better transformer seems like the best option at this point.

One thing to note about vertical mosfets, is that they tend to draw more current as their temperature increases, which makes them warmer still - and so this can lead to overheating. The lateral mosfet that was specified for this circuit tends to draw less current as the temperature increases (once the current is above 100mA or so) which means it has better thermal stability.

The attached plot is from the data sheet for the vertical mosfet. If you pick a Vgs of, say, 4.5V then look at the curve for a junction temperature (Tj) of 25degC it indicates a current (Id) of around 9A. If this heats the device up to 175degC the other curve shows the current will increase to nearly 20A. Where the two curves cross is roughly where the device will be thermally stable which is at very very high currents and you can't operate the device at that point. So you would be advised to seek out some lateral mosfets for this amplifier.
Attached Images
File Type: jpg irfz44n.jpg (96.1 KB, 12 views)
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 26th April 2014 at 12:57 PM.
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