All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble - Page 7 - diyAudio
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Old 12th October 2012, 01:35 PM   #61
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What is the point of an all-fet amplifier with only a few FETs? It may become optimised from an engineering perspective but the thread becomes meaningless - just another standard design with MOSFETS or HEXFETS for the output stage.
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Old 12th October 2012, 01:45 PM   #62
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Right. It's an all FET thread !
It would be interesting to see what the comparison between an all FET amp and a mixed device amp will be like.
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Old 12th October 2012, 02:03 PM   #63
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Quote:
Originally Posted by wahab View Post
Before building this amp , a few points that matters if black smoke
is not the goal...

1)The biaising trimmer should be about 500R , as already pointed ,
if you use Renesas/Hitachi laterals wich have low Vth.

It seems that there is two critical flaws in the schematic.

2) The first is that the VAS current source as well as the differential current
source voltage reference , D2 , is fed by one leg of the differential VAS ,
which is surely a mistake in the schematic.

Second , the differential fet current source has a diode , D1 , in serial with its
gate that is placed the wrong side.

Hello wahab

1) OK I will choose that!
2) Can you help me to correct these mistakes on the circuit (schematic), please..
Thank you very much. I do not want to see any black smoke1 Those aren't cheap devices to see a firework..

Greetings gabor

Last edited by gaborbela; 12th October 2012 at 02:09 PM.
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Old 12th October 2012, 02:08 PM   #64
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Quote:
Originally Posted by ashok View Post
Right. It's an all FET thread !
It would be interesting to see what the comparison between an all FET amp and a mixed device amp will be like.
Hello Ashok
Yes I can replace those after I test the amp!
First and most important to make it work, after we can improve the sound
Thanks for pointing it out.
I already has those mosfets for start!

Greetings Gabor
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Old 12th October 2012, 02:24 PM   #65
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Ian Finch View Post
What is the point of an all-fet amplifier with only a few FETs? It may become optimised from an engineering perspective but the thread becomes meaningless - just another standard design with MOSFETS or HEXFETS for the output stage.
Overall , a BJT VAS works better.

Also , there s no need to use fets for the current sources ,
yet another place where BJTs can be used with much better
predictable behaviour.

Anyway , let s see what can be extracted from an all fet design,
if ever it doesnt suit the expectations changing a few parts
could be done without even changing the layout.
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Old 12th October 2012, 03:30 PM   #66
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Quote:
Originally Posted by wahab View Post
Before building this amp , a few points that matters if black smoke
is not the goal...

The biaising trimmer should be about 500R , as already pointed ,
if you use Renesas/Hitachi laterals wich have low Vth.
I see now that the last electronic diagram was kept trimmer's of 2K, although I made ​​it clear here:
http://www.diyaudio.com/forums/solid...le-naim-5.html
So, if you choose a pair of end 2SK134 / 1057, when Vgs voltage is not the same as with IRFP240 / 9240 and will be changed Rt trimmer value. In fact, if is 2SK transistors, trimmer's value will be less than 2K, in order to avoid accidental adjustment of a high-idle current. The calculation of the value of the trimmer, I expounded on this topic

Quote:
Originally Posted by wahab View Post
It seems that there is two critical flaws in the schematic.

1. The first is that the VAS current source as well as the differential current
source voltage reference , D2 , is fed by one leg of the differential VAS ,
wich is surely a mistake in the schematic.

2. ... the differential fet current source has a diode , D1 , in serial with its
gate that is placed the wrong side.
1. It is not a mistake. If you do not understand functioning electronic diagram, then, please...,"stay away".
2. It is not a mistake.
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Old 12th October 2012, 05:22 PM   #67
wahab is offline wahab  Algeria
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Quote:
Originally Posted by donpetru View Post



1. It is not a mistake. If you do not understand functioning electronic diagram, then, please...,"stay away".
Providing voltage bias calculations for IRFs while the guy use laterals
without taking a look on datasheets is not exactly a professional path
for whom speaks of "staying away..

I guess that you should use this kind of language with people
in the same range of education as you..

Quote:
Originally Posted by donpetru View Post

2. It is not a mistake.
It is, for whom has a decent understanding of how this circuit work...
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Old 12th October 2012, 05:39 PM   #68
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post
Hello wahab


2) Can you help me to correct these mistakes on the circuit (schematic), please..
Thank you very much. I do not want to see any black smoke1 Those aren't cheap devices to see a firework..

Greetings gabor
I put again the schematic for the purpose.

Click the image to open in full size.

The diode D1 provide the gate biaising of T8 wich is connected
as source follower.
The gate must be biaised positively in respect of the source ,
and as connected it will provide no voltage since the voltage
at the zener is positive in respect of the transistor source.

Hence connection of this diode must be reversed.


Second point , the current through the voltage reference zener D2
is provided by T5 but this transistor current is variable and in case
of saturation it can be switched off to some point , hence there will be
no more a voltage accross the zener leading do disfunctionnent.

Moreover , at power on , T5 will conduct only if T8 conduct but this latter
cant enter conduction if......T5 doesnt conduct!!..

A rapid solution to overcome this second point is to connect a 100K
resistor from zener D2 to ground.
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Old 12th October 2012, 06:10 PM   #69
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To get over the expression on the language I used above message, I mean the words "stay away". I apologize if you were upset. Look at these two image extracted from a version of the DP400 amplifier. DP400 version posted here is an intermediate version.

In pictures attached below, you will see the idle currents input stage and VAS and performance in dynamic regime of the amplifier.

Of course, how to make CCS is not the best choice but it can provide a performance drop. Indeed, the MOSFET solution in CCS not really thrills me, and when I say this, consider that tell after I built practically and theoretically simulated a lot of audio amplifiers topologies.
Attached Images
File Type: jpg allFET_DP400_sim.jpg (160.2 KB, 336 views)
File Type: jpg allFET_DP400_sim_2.jpg (303.1 KB, 321 views)
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Old 12th October 2012, 06:35 PM   #70
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[QUOTE=donpetru;3198917]I see now that the last electronic diagram was kept trimmer's of 2K, although I made ​​it clear here:
http://www.diyaudio.com/forums/solid...le-naim-5.html

QUOTE]

Hello donpetru

I apologise about that mistake!
I correct it right away.
Thank you for the warning!

Greetings Gabor
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