All Hitachi Lateral Fet amplifier for DIY described by Paul Kemble

[gaborbela]

Hello

Thank you wahab!
I did some mod on the layout, now should be better all do Q5 & Q6 no longer thermally attached to each-other.
Those are cascode only, I think still acceptable these way.
I try to avoid to do anything with Q7 & Q8, a lot of connection around Q8. They are thermally connected.......
I found a bad mistake, I forget to connect Q7 to the base of Q10.
Now that is corrected. One more jumper but what can I do?
I draw all on paint program with out any help. Just think and think...
I'll go over once more to look for errors but I think now these should be OK.
I draw dozens of layout but these was one of the most difficult (took a lot of time and thinking).
Resistors R17 & R18 will goes under the PC board and will be 2W type.
Soon I will post the black layout, if someone else interested on the amp please do not hesitate.
I will help with the layout if you have question!
Thanks one more time
Greetings Gabor

[gaborbela]

Hello

Here is the black layout.
It was (made) designed easily can be used by iron transfer method.
Do not mirror image it. Just print it out with laser printer, iron on the copper clad board, do the eaching and ready for use.
I will do one more check up on the layout but I think is OK how it is.
I moved the input capacitor in to the center of the layout a bit further from the + Voltage.
Any question, advise welcome.
Soon I each the PC board and start test it.. Of course I have to get(purchase) the VAS & other transistors and resistors.
wahab 1W zener diode will be acceptable?
Thanks
Greetings Gabor

[wahab]

The hotter zener is the one of the VAS current source , D2 ,
wich dissipate about 0.035W , so 1W give quite a margin...

A few points about the tests process to prevent any bad surprise.

The laterals gate voltage threshold dispersion is quite large on the datasheet
and it can be quite low , the ones on my amplifier are at about 0.25V Vgd
for 100mA current , so usually there s components whose value is to be set
when doing the tests.

As a result when setting your amp use a 100R trimmer instead of 220R ,
and replace the diode that is in serial with the led by a strap, this will
limit the total biaising voltage to 1.2V max value should the trimmer have
a faulty contact , laterals are expensive and one is never cautious enough...

If thoses conditions dont allow to reach a high enough quiescent current
then put a 220R trimmer and remove the strap to put the diode instead ,
all this will extend the biaising voltage range to about 1.9V.

[wahab]

On the PCB i see no boucherot/zobel cell connected to the output ,
that is 10R in serial with 22nF , R31/C5.

Otherwise it can be valuably deported in a separate PCB along
with the output LR network , this will ensure that no significant
AC current run in the amp PCB ground.

[gaborbela]

Hello wahab
Yes you right!
I know what happened, I left out the source resistors 0R22 and with those I forget the Zobel.
I will put on the speaker terminal if that good enough.
I read some opinion even better than on the PC board.
If you disagree I will try to find some room on the PC board.
To be honest I work on a amplifier Pass F5 turbo V1 enclosure, so I didn't went over on the layout again..
I will do that before I each the PC board! That must be done again.....
Thanks for the warning!
I know you wrote about the bias set up. A bit confusing to me..... To set up the bias it work the same way like at other amplifiers- higher resistance I measure on the trimmer between Collector Q8 & Q10 that cause lower bias?
From your instruction I understood exact the opposite.
I will use a 100W light bulb something like the att. picture until I set up the bias. If there is any problem the light bulb glows (will take away the current, and that help to minimise the damage)
AndrewT always advise the light bulb at start up...

Greetings Gabor

[gaborbela]

Hello
I can ad the Zobel net. here.
The R18 anyway will goes under the PC board.
What do you think?
Greetings Gabor

[wahab]

Originally Posted by gaborbela

I will put on the speaker terminal if that good enough.

That s the best solution from all points of views.

Originally Posted by gaborbela

I know you wrote about the bias set up. A bit confusing to me..... To set up the bias it work the same way like at other amplifiers- higher resistance I measure on the trimmer between Collector Q8 & Q10 that cause lower bias?
From your instruction I understood exact the opposite.

That s it , the lower the resistance of the trimmer the lower the quiescent current , so it should be set at minimum resistance before powering on .

Originally Posted by gaborbela

I will use a 100W light bulb something like the att. picture until I set up the bias. If there is any problem the light bulb glows (will take away the current, and that help to minimise the damage)
AndrewT always advise the light bulb at start up...

Indeed mandatory when doing the first real world steps....
You can also use the output stage supply rails to supply the front end
for the tests , in fact it will make no difference other than about 20%
less max ouput power , still it will remain roughly over 100W/RMS/8R.

[wahab]

Originally Posted by gaborbela

Hello
I can ad the Zobel net. here.
The R18 anyway will goes under the PC board.
What do you think?
Greetings Gabor

In fact , the PCB ground should be separated in two different grounds
that will have their own ground wire that goes to PSU.

The first ground area should enclose all paths that have variable currents,
that is the return ground of the power stage decoupling capacitors
and the one of the zobel network.

The second ground area will enclose all the other grounds return paths ,
that are the ones of the frond end circuitry , including its own decoupling
caps.

Doing this way will reduce vastly eventual ground pollution
induced distorsion and noises.

[Smiley 09]

Originally Posted by gaborbela

Hello

Here is the black layout.

I will do one more check up on the layout but I think is OK how it is.
I moved the input capacitor in to the center of the layout a
Any question, advise welcome.

Hello Gabor,

Instead of a question, Here rather a nice suggestion. If you'll have any need just PM me and I'd gladly explain the details, You'd be very happy with.

Cheers

[gaborbela]

Originally Posted by wahab

In fact , the PCB ground should be separated in two different grounds
that will have their own ground wire that goes to PSU.

The first ground area should enclose all paths that have variable currents,
that is the return ground of the power stage decoupling capacitors
and the one of the zobel network.

The second ground area will enclose all the other grounds return paths ,
that are the ones of the frond end circuitry , including its own decoupling
caps.

Doing this way will reduce vastly eventual ground pollution
induced distorsion and noises.

Hello

I agree with you wahab!
I just try to test the amp now to get some idea of the performance.
Later I'll use separate grounds.
Even on simple amplifier (with one PS) I use two ground. I do separate the signal ground from the PS ground with a 10R resistor.
I test the amp and after I'll start to upgrade. Even like these I can get some idea about the sound quality.
At the test I'll use only one PS how you advised. If I like what I'll hear I will increase the front end with 10V rail voltage.
I'll separate the ground even the signal ground.
I just each one PC board for test! After it will be easy to mode the PC board.
Right now I try to keep my PC board a certain size.
Your advise well appreciated! If I like the amp I want min. DALE or PRP resistors, and I'll upgrade the PC board to.
These only a test board, I don't want to mess with PP connection.

Greetings Gabor