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Old 2nd April 2011, 06:12 PM   #11
wahab is offline wahab  Algeria
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If THD is not the main concern, (about 0.02%), a symetrical differential + vas
using a pair of low power bjts to drive a few lateral fets pairs is the way to go.
Since the psu has relatively low voltage, you can increase the
quiescent current to something like 120mA/device and get
class A at higher level than with bipolar outputs using the same
current, thanks to the lfets caracteristics..
Indeed, it will blow out any F4 or other Fsomething like amps...
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Old 2nd April 2011, 06:42 PM   #12
lineup is offline lineup  Sweden
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The problem is 2SK213-216/2SJ76-79 are hard to find.
Dgikey has 2SK214 and 2SJ77
FETs - Single | Digi-Key
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Last edited by lineup; 2nd April 2011 at 06:49 PM.
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Old 2nd April 2011, 06:50 PM   #13
wahab is offline wahab  Algeria
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3 pairs of 2SJ162/2SK1058 per channel will do it just fine.
I use the older siblings 2SJ48/2SK133 in such an arrangement,
since i downgraded the PSU from 2X55V to 2X22V DC...
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Old 2nd April 2011, 07:04 PM   #14
knutn is offline knutn  Norway
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Quote:
Originally Posted by lineup View Post
The problem is 2SK213-216/2SJ76-79 are hard to find.
Dgikey has 2SK214 and 2SJ77
FETs - Single | Digi-Key
So maybe 2sk214/2SJ77 as vas transistors...

Quote:
Originally Posted by wahab View Post
3 pairs of 2SJ162/2SK1058 per channel will do it just fine.
I use the older siblings 2SJ48/2SK133 in such an arrangement,
since i downgraded the PSU from 2X55V to 2X22V DC...
and 3 pairs of 2SJ162/2SK1058 as power outputs will do it....
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Old 2nd April 2011, 07:25 PM   #15
lineup is offline lineup  Sweden
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One thing with 2SK214/2SJ77 is they are LATMOS.
So, have much lower VGS for given current.
Maybe like 1 Volt instead of 4 Volt to give 60mA bias.
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Old 2nd April 2011, 08:25 PM   #16
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by wahab View Post
Indeed, it will blow out any F4 or other Fsomething like amps...
I like your spirit!!!

20W is not too useful for me. There are so many good amps within this power rating that I cannot decide which one is better than the other.

But if it is subjectively better than F4 and is using laterals, I'm looking forward to building it
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Old 3rd April 2011, 05:22 PM   #17
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Here is my


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Old 3rd April 2011, 07:44 PM   #18
wahab is offline wahab  Algeria
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Federmann, the noise density vs frequency of your amp show
an overshoot at half a megahertz, which tells that your amp
has a gain overshoot at the said frequency.
The low pass input filter cancel this resonnance seen from
the input of the amp, but this will not change tha fact that
internaly, there s a large phase dip at this frequency, leading
to mediocre stability..
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Old 3rd April 2011, 08:38 PM   #19
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This is the noise Operating amplifier
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