All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble - Page 8 - diyAudio
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Old 12th October 2012, 06:42 PM   #71
wahab is offline wahab  Algeria
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The diode D3 in the DP400 schematic can provide a few nA
reverse current wich is enough for fets bias but this
allow the zener to sink an eventual drain/gate excess current
leading to hasardous current source current value that would become
device and Vgd dependant.

All in all , i dont think that it s a good design practice.

A best solution is to put two diodes in parralel , reverse connected,
or better , no diode at all....

Last edited by wahab; 12th October 2012 at 06:45 PM.
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Old 12th October 2012, 07:02 PM   #72
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[QUOTE=wahab;
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.[/QUOTE]
Hello wahab

Thank you very much. Now is much more understandable to me your advise!
When you gave me some details like how you did in the previous post much better than just write these or that is bad.
Now I can see why do you think is bad!
Thank you very much.
I read many of your post on the forum and I have all my respect to you and everyone who come here with a positive advise!
I didn't purchased the parts (resistors, diodes) yet and I only each one PC board for test purpose.
I would like to keep the circuit as all mosfet (accept cascose)amplifier but in case if we can improve the sound later we can think about to use BJT some place!
At first let s see what we can achieved how is it.
If I would revers the diode how you suggest sill I would need the 100K resistor?
If is not a big request please draw the circuit how you like it with red or any other color so I can print it out! In these case we can avoid confusion to those people who follow the thread.
Otherwise always I have to go back and reread and reread all the posts.

Greetings Gabor
Here is the corrected circuit how donpedru advised a couple days a go!
Attached Images
File Type: jpg Hitachi.JPG (63.8 KB, 310 views)

Last edited by gaborbela; 12th October 2012 at 07:05 PM.
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Old 12th October 2012, 07:30 PM   #73
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Hello Wahab

Is these correct after your advise?
Please let me know!
Thank you
Greetings Gabor

I want to keep it organised in that way so when refer to the circuit we can have it right away.
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Old 12th October 2012, 07:57 PM   #74
wahab is offline wahab  Algeria
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Well , either no diode at all or two parralelled reverse connected diodes....
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Old 12th October 2012, 09:44 PM   #75
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Hello

So D1 is OK how you advised.
D2 I can leave it out you say.
Now these is important because there is a major mod I have to adjust the layout after that.
In these case I can keep how it is.
Thank you very much.
So these circuit is after wahab advise!
Greetings Gabor
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Old 12th October 2012, 10:19 PM   #76
wahab is offline wahab  Algeria
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Suppressing the zener would have nefarious consequences ,
so a few pictures will tell more than a thousand words...

Either one of these two variations below will be adequate...
Attached Images
File Type: gif CSS1.gif (6.0 KB, 259 views)
File Type: gif CSS2.gif (6.5 KB, 253 views)

Last edited by wahab; 12th October 2012 at 10:22 PM.
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Old 12th October 2012, 10:31 PM   #77
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Quote:
Originally Posted by wahab View Post
Suppressing the zener would have nefarious consequences ,
so a few pictures will tell more than a thousand words...

Either one of these two variations below will be adequate...
What is the purpose of the external zener D1, the 2SK214 has built in gate protection.
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Last edited by Nico Ras; 12th October 2012 at 10:38 PM.
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Old 12th October 2012, 10:42 PM   #78
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Nico Ras View Post
What is the purpose of the external D1, the 2SK214 has built in gate protection.
That s a voltage reference for the differential and VAS current sources,
not for protection purpose.

In this schematic it will withstand the full half VAS current ,
so it should be a 1 to 2W component , it would be better
to use a lower voltage and set the fet sources resistors
accordingly.

Edit : i thought you were talking of the zener.

As for the diode in serial with the gate , well , i m
still in the expectation about the reason why it was
connected in such a way in the first iteration.

Last edited by wahab; 12th October 2012 at 10:46 PM.
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Old 13th October 2012, 01:39 AM   #79
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Hello
wahab thank you very much!
From picture easier to understand what is in your mind. I'll make room on the layout for the extra 4148 diode
I corrected.
Nico welcome on the board

Greetings Gabor

Circuit according to wahab!!!
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Old 13th October 2012, 12:21 PM   #80
AndrewT is offline AndrewT  Scotland
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I would throw away T7 & T8 & T9 and go back to a BJT CCS and a BJT mirror.
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