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Old 26th November 2012, 11:55 AM   #231
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To me it looks like the base of Q20 and the junction of the two resistors connected to it should all go to ground .

Did Wahab also want to do that and forgot to show the ground ?
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Old 26th November 2012, 12:09 PM   #232
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Quote:
Originally Posted by ashok View Post
Did Wahab also want to do that and forgot to show the ground ?
@wahab, I think he forgot ... suppose.
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Old 26th November 2012, 12:25 PM   #233
tinitus is offline tinitus  Europe
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Originally Posted by tinitus View Post
might help to try figure power lines and ground like forming a big T, or like a tree with branches

may need jumpers, but would be perfectly ok
just a very simple drawing, and my humble suggestion
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Old 26th November 2012, 01:08 PM   #234
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ashok View Post
To me it looks like the base of Q20 and the junction of the two resistors connected to it should all go to ground .

Did Wahab also want to do that and forgot to show the ground ?
Quote:
Originally Posted by donpetru View Post
@wahab, in the last diagram you posted would be better to be connected to GND the base pin Q20 transistor. It's better that way.

I attach in the next few days own version of this amplifier with PCB. It will be a surprise.
Hi Donpetru and Ashok

You are right that connecting the said node to ground seems
at first look logical but i willfully connected it this way since
it allow to get rid of current bias running through the ground
as well as limiting the effect of parasistic capacitance.

If this point is connected to ground then there will be an AC
coupling from emitter and collector to ground through
the device parasistic capacitances.

Indeed , the resistors having same value , the potential is
close to 0V at this node.

Last edited by wahab; 26th November 2012 at 01:34 PM.
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Old 26th November 2012, 05:20 PM   #235
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I did some tests with and without the transistor Q20 and arrived at the following conclusions:

- If used Q20, then THD value decreases from 0.008% to 0.007% - keeping C12 = 10nF (the capacitor is not critical but after testing it's better 10nF instead of 1nF);

- If we use three pairs of MOS transistors when power dissipation of each transistor (when the amplifier operates in 4 ohms) is only 25W. Seeing this, I simulated the operation amplifier into 2 ohms and in this case each MOS transistor power dissipation is 46W. So, the amplifier can handle quite stable 2 ohm loads. One advantage that you rarely see in other amplifier diagrams.;

- In the last amplifier diagram posted by @wahab we recalculated the value of C13:
C13 = (0.04 * I) / Uz = (0.04 * 0.0025) / 3.6 = 0.27uF
I will choose a standardized value of 0.47uF (once again, value is not critical, but it's better that way);

- C9 and C10 can be 100uF. I noticed enough that;

- In the input circuit will keep my components (I refer to the R1, R2, C2 ...). It's better that way.

- This week I will make my own version of the amplifier PCB with IRFP240/9240, which again, works flawless and is much cheaper than the proposed version of @wahab;

- VAS and input circuits I chose do not supplied with 65VDC because dynamic performance remain the same, so it is pointless. I chose to work all the + /-55VDC that is exactly what amplifier needs.

In the next few days are going to post schematic and PCB amplifier. It will be something special, do not miss the next message for you do not know what losing. It will be a surprise.
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Old 26th November 2012, 09:36 PM   #236
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Donpetru hardly wait to see your circuit you come up.
wahab
Today I made the laser photocopy for the layout after my design.
I didn't used Q20 because you just came up a few days a go with that idea.
It is worth to implement the Q20 into my layout and go to Staples for laser printing again?
I waited a few weeks and I had that idea it will be no further improvement or other mode on the circuit.
I would like to ahead with these project also.
Guys do you mind if donpetru post his creation here or keep these thread for the Hitachi laterals?
I ask these because once I already ask the moderator (Tinitus) to clean up the mess in these tread... I respect those people interest (opinion) who follow these thread!!! So please vote or just let us know what do you think!
To me is OK but these thread not just about me!

Greetings Gabor

Last edited by gaborbela; 26th November 2012 at 09:41 PM.
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Old 26th November 2012, 09:44 PM   #237
alex mm is offline alex mm  Romania
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Default PCB REV 4.2

New PCB rev4.2 layout acording to last posted schematic
Regards Alex.
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Old 26th November 2012, 10:09 PM   #238
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Very nice Alex!! Congrat...
In did these is so nice it would be great to start a GB if it will be enough interest..
I didn't went over to look for any error. I'm just tired to do that because I made several layout with out any software.
Only one question I have
Do we need all those 100uF caps for each mosfet?

Greetings Gabor
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Old 26th November 2012, 10:13 PM   #239
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela View Post
Today I made the laser photocopy for the layout after my design.
I didn't used Q20 because you just came up a few days a go with that idea.
It is worth to implement the Q20 into my layout and go to Staples for laser printing again?
I waited a few weeks and I had that idea it will be no further improvement or other mode on the circuit.
I would like to ahead with these project also.
I m sorry to come late with this modification as it was consequent
to the choice of 2SA1360 instead of the expensive 2SA1407 and
after i compulsed the datasheets more closely.

2SA1360/2SC3423 have only 5W max TDP while using 65V rails will
lead to about 1.2W dissipation for Q7 , quite a lot for a single device so
i elected to use two devices with each one dissipating 0.6W.

As pointed by Donpetru this reduce THD slightly but this is not
the reason that pushed me implementing this mod , it is a question
of long term reliability as my experience is that local hot spots
on a PCB will forcibly induce failures sooner or later.
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Old 26th November 2012, 10:30 PM   #240
wahab is offline wahab  Algeria
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Quote:
Originally Posted by donpetru View Post
I did some tests with and without the transistor Q20 and arrived at the following conclusions:

- If used Q20, then THD value decreases from 0.008% to 0.007% - keeping C12 = 10nF (the capacitor is not critical but after testing it's better 10nF instead of 1nF);
In fact anything higher than 100pf is enough , i took 1nF since
this allow using cheap MKP/MKT caps.

Quote:
Originally Posted by donpetru View Post

- In the last amplifier diagram posted by @wahab we recalculated the value of C13:
C13 = (0.04 * I) / Uz = (0.04 * 0.0025) / 3.6 = 0.27uF
I will choose a standardized value of 0.47uF (once again, value is not critical, but it's better that way);
Not very critical perfs wise but 100nF for both zeners is optimal
for low power on thump , 220nf works as well but higher values
will increase the amp settling time at power on.

Quote:
Originally Posted by donpetru View Post
- C9 and C10 can be 100uF.
It also works well enough since the amp has basicaly good PSRR.

Quote:
Originally Posted by donpetru View Post
- VAS and input circuits I chose do not supplied with 65VDC because dynamic performance remain the same, so it is pointless. I chose to work all the + /-55VDC that is exactly what amplifier needs.
Indeed , this increase the long term reliability while perfs are not
affected set apart a slightly lower power but who do listen music
at more than 2 x 100W RMS at home ?.....
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