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Old 31st October 2012, 01:24 AM   #171
wahab is offline wahab  Algeria
diyAudio Member
Join Date: Nov 2009
Location: algeria/france
Hi Gabor ,

For some reason my previous post was badly edited.....

I ll put the text again since the page where i did edit it was still
opened and the text available by the same way....

Originally Posted by gaborbela View Post
About the transformer what is troubling me.
My question the 800VA still will be enough to power both channel??? I use only 8R speakers!
If the answer YES that would resolve a great transformer issue for me!
To power both channel front from one transformer what would be the right VA rating?
This will make 600mA for the whole amplifier , that is (2 x 55V) x 0.6A = 66W ,
we are far from the available 800W...
Overall, such a transformer is largely within specs , it will never be used at its full
power even if the amp is 4R loaded.

Originally Posted by gaborbela View Post
The 1R resister will give enough filtering between the HC and LC ground?
I usually use 10R to separate the signal ground from the main ground.
At second thoughts not sure about this one....
In principle this resistor is not needed at all as both HC and LC have their
own returns to the star point so it is only here to provide a path to the zobel
network if ever one forget to connect the HC ground to the star point, hence
the low value of 1R, but if all is connected correctly this resistor becomes useless.

Originally Posted by gaborbela View Post

I will have to purchase something. To feed the front must be 65V or I can go up 2-3V higher.
Easier to get a transformer when we have some tolerance. Otherwise I may have to order specially
manufactured= which cost $$$..
Just use what you have at hands , eventually you could add two windings of a few
dozen turns of 0.5mm2 to your toroids that will be connected in serial with the 40V windings ,
allowing to squeeze at zero cost the few volts that are needed for the front end higher voltage.

Originally Posted by gaborbela View Post
About PS capacitors I have 10PC Nippon CC 100 000uF, I don't know nothing
about the quality since I never use those.
I can use 2PC Philips (those are great caps) and 2PC Nippon.
I know it will overkill but if does not degrade the sound I don't care.
I have 10PC Nippon 10 000uF 63V with solder lug type.
I will test which gave better result.
I do like large can capacitors if they are good quality, Philips, Mallory, Mepco, Cornel Dub. etc.
I did used these type successful in many Class A/B amp. 4PC set up as CRC .
[B]Any opinion about PS caps?
Such big caps are often more of a problem than a real advantage
as transient currents are huge when powering on but also when
charging the caps at each alternance , hence the PSU might
be noisier than with smaller caps...

Capacitors life expectancy and lifetime ability to work within their ratings
is mainly decided by the voltage and temperature at wich they are used.

In this respect , 63V caps do not suit the purpose , better less capacitance
and higher sustainable voltages and temperature than the opposite.

For total capacitance 2 x 20 000uF is a minimum.
Anything above 2 x 50 000uF wont bring anything substancial for this kind
of amp but it must differ with low feedback designs ,such as the Grandmos,
that have low power supply noise rejection.
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Old 31st October 2012, 02:15 AM   #172
wahab is offline wahab  Algeria
diyAudio Member
Join Date: Nov 2009
Location: algeria/france
Originally Posted by gaborbela View Post
I just found out I have a 6PC 30 000uF 75V capacitor bank Cornell Bubblier.
That should be good for the high power PS.
I have no need for those so I can use it here.
Great, the voltage rating is high enough and it s always a relief
to usefuly recycle valuable parts...

Originally Posted by gaborbela View Post
wahab I assume you didn't forget the bias when you calculated the transformer rating, so the 800VA will be OK.
Be assured that this transformer will enjoy a quiet and lazy life....

Originally Posted by gaborbela View Post
The next step to purchase the transistors and resistors, each the board and test it.
Now all look promising of course after the test I will know more!
According to simulations it s quite better than all other popular amps
using this topology without going into complexe additions such as error correction
or non switching circuitries , so i hope it will live up to your expectations.

Last edited by wahab; 31st October 2012 at 02:19 AM.
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Old 1st November 2012, 02:52 AM   #173
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Join Date: Sep 2005
Today I went over again on the layout, no mistake or error was find.
wahab I have a question to you
I see the R12 & R10 resisters in series, can I replace that two resister with one. I could use (fix up) that place on the layout....
Please let me know.
Thank you
Greetings Gabor
Attached Images
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Old 1st November 2012, 11:46 AM   #174
wahab is offline wahab  Algeria
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Join Date: Nov 2009
Location: algeria/france
Hi Gabor,

You can use a single 68K 1 to 2W resistor instead but be aware that
the current through theses resistors is about 2mA when using a separate
higher voltage PSU for the front end , while the total voltage across them
is almost the full rail to rail voltage , about 125V , so the dissipation
will be about 0.25W , wich would be too high for 0.5W resistors , hence
i did put two in serial to reduce the burden to 0.125W per resistor
and the stress inflicted to the PCB as a single resistor , even if you take
a higher power one , will inevitably damage not only its own soldering
but also the PCB itself on the long term.

For testing the amp a single resistor can be used but for a definitive build
it would be better to use two resistors to ensure long term reliability.
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Old 1st November 2012, 12:51 PM   #175
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Thank you wahab!
That is the reason I ask You before just I change it. I live it how it is than start using bulky resistors.
Greetings Gabor
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Old 1st November 2012, 01:48 PM   #176
AndrewT is online now AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
I will suggest a very small, but what I consider to be a very important detail, in the grounding schematic.

The sch shows the star ground (Main Audio Ground - MAG) coincident with the junction of the smoothing caps.

I suggest that the MAG be moved just a couple of mm along the wire from the PSU Zero Volts plate.

An alternative is to bolt through the plate and tighten up a nut to secure the brass bolt to the plate. Attach the MAG terminal tags to the bolt and use a second nut to fix the MAG to the plate. This way the charging pulses across the plate do not influence the multiple and different physical connections that are on the "other side" of the first fixing nut.

Recently this has been discussed and the general conclusion is that this separation of PSU Zero Volts from the MAG is the better solution.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 1st November 2012, 06:37 PM   #177
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Join Date: Sep 2005

Thank you for the advise Andrew!
The ground will be somehow different since I separated the HC and LC ground on the board.
Now I got these transformer from Ebay to these project,(it was very cheap so I didn't wanted to pas by all do the shipping close to $20).
47.5V the right voltage I need to drive the front.
Big Toroidal Transformer 120V in 166VA 47 5V 19V 0 19V 47 5V 1 75A | eBay
Soon I will etch the PC boards (I need some P3A to) and I can start test it.
For the front what would be the min. capacitance requirement? like 4X 4700uF or I can use less (I have 2200uF 80V Nippon CC probably I'll need higher uF caps)
Thank you
Greetings Gabor
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Old 1st November 2012, 07:12 PM   #178
wahab is offline wahab  Algeria
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Join Date: Nov 2009
Location: algeria/france
If your 4700uF are 100V just slap a single pair , it s more than enough ,
otherwise you can use your 2200uF , a pair of wich would also be adequate...

As for the front end transformer 160VA is overkill as the two front ends
will consume together 60 mA at most , that is 8 W , so a 22VA
transformer would already be at ease dealing with such little power.
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Old 2nd November 2012, 09:20 PM   #179
diyAudio Member
Join Date: Sep 2005
Default I need help with my transformer

I'm in trouble because the Ebay seller does not fund the transformer I purchased!
Dear gabor222_---___,

Correct - I had it at one point. Again, the item has been misplaced in my inventory. I keep everything pretty meticulous so not sure how this happened, but I spent about 2 hours going through multiple times trying to find it. I'm sure you have lost something in your lifetime - and can understand. It's like when you go to the store, and the inventory system says they have something, but when they look on their shelves it's not there.

Again, sorry for the confusion. I refunded your money completely and immediately once I discovered the item was nowhere to be found.

Best, Ken
- usedstereoguy

So I do started to ad some wire to my existing 2X40V transformer. To be 100% correct I added 10M wire.
I connected one side to the V continuously. Now when I measure it to the ground I get 15V only!
When I leave out the ground measure the the 2 white wire I get the 80V.
When i measure the opposite Voltage wire I get 56V see the pict.
In other word when I include the added wire I get only 56V instead 96V.
What is going on?
I include picture maybe someone can explain what is going on.
2 black 120V
White 40V, red center tap, other white 40V
I know 10M wire to much but now that second question.

Greetings Gabor
Attached Images
File Type: jpg Picture 013.jpg (119.1 KB, 211 views)
File Type: jpg Picture 014.jpg (145.1 KB, 203 views)

Last edited by gaborbela; 2nd November 2012 at 09:29 PM.
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Old 3rd November 2012, 12:01 AM   #180
wahab is offline wahab  Algeria
diyAudio Member
Join Date: Nov 2009
Location: algeria/france
You did a 24V winding and it is connected in antiphase with one 40V winding ,
hence when you measure the total voltage you will see a difference not a sum.

Just invert the ends of this cable and you ll see 64V when measuring from ground...

What is needed in fact is two 8V windings , about 26 turns each , depending
of your transformer , then connect one 8V in serial with a 40V one and you ll
have two 48V outputs wich will be connected to a separate bridge rectifier
and its dedicated caps.

The schematic below give an indication of how to procede with the added
Attached Images
File Type: gif XFORMER MOD.gif (4.6 KB, 200 views)
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