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Old 17th July 2011, 01:43 AM   #81
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I know but for me for some reason it just doesent feel right, though it might be a habit from designing switching stuff where any stray inductance was a liability to the operation of the circuit.

Thin long traces makes good inductors at higher frequencies.
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Old 17th July 2011, 02:16 AM   #82
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Quote:
Originally Posted by Tekko View Post
I know but for me for some reason it just doesent feel right, though it might be a habit from designing switching stuff where any stray inductance was a liability to the operation of the circuit.

Thin long traces makes good inductors at higher frequencies.
Most current will return from the speaker right to the faston/centertap. The decoupling returns will just pass the ripple back to the center star. I agree , this ripple - current might get high at ungodly power levels.

I won't defend this PCB style as the "best". If I had 125mm heatsinks , I would
layout in Alex's style. My subamp - luxman/DBT is this style. My altec chassis HAS to use a 32mm aluminum L bracket , so my personal amps have to be long/thin. Therefore ,I would have no use for Alex's board unless someone gave me a $300 chassis/ trafo "gift".

The long thin 75mm X 250mm PCB can go on a L bracket or flat. One could even mount it at a 90 degree angle flat without an aluminum bracket. I was given a set of drawings to adhere to , with a end objective to make it as universal as possible.



If wanted , I'll make the other style , whatever is wanted.

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Old 17th July 2011, 03:41 AM   #83
Bigun is offline Bigun  Canada
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OS,

I think both pcb's will work just fine. Sure, there are engineering reasons to argue for one over another and in the end each engineer picks the compromises that he/she likes best. I prefer asymmetric layout (and can't resist a good arguement!) but I think you should stick with what you are confident will work well and you've made more pcb's than most of this forum

Speaker return currents are an interesting thing. I guess it has to go through the caps rather than the power trafo since the trafo is only 'available' when the rectifier diodes are forward conducting. So the point where the most current flows in the ground will be between the speaker gnd binding posts and the gnd side of the rail caps. Keeping these current paths separate for the two channels is important for channel-channel cross talk control. It's also why I used the speaker gnd binding posts (or close to) as my start earth in the amps I built so far - everything with high current is then all made with big wire except the short pcb traces that take the power rails to the output transistors and the output to the speaker binding posts. After that, the rest is all small beer.
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Last edited by Bigun; 17th July 2011 at 03:45 AM.
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Old 17th July 2011, 04:19 AM   #84
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Default Fatter traces....

I fixed it..... 16.7A returns from the caps. 25A Imax for the rails.

2 workarounds ,

-one could also solder wires from star to cap if 16.7A's are not enough

- one could only use 1,000uf local decoupling caps in addition to a large external power supply. My first "Mongrel" had 1Kuf@100V with 10mm lead spacing - they will fit these universal capacitor pads.

I am "juggling" the 2 worlds of some who would use this board stand-alone (without external capacitance), and the FANATICS that would hook it to 50,000uf of external capacitance. Hopefully the fatter traces will bridge the gap.

Another factor is that Mark wanted me to keep the burning amp form factor so DIY'ers could swap "burning amps" for real power if they desired.... with minimal rework of the existing DIYA chassis. So , a few compromises were there right from the start.

I must thank all the forum , even DX , for the many examples of the best DIYA amps. Cordell's and Self's books are the "old and new testaments" of amp design even they are quite " interpretable" I think this project will hit the performance of the original "blameless" or even exceed it. Faster devices (self uses MPSA's for VAS , tiny MJE's for the drivers), and a much larger output stage with 3 pairs = lower output stage THD. We can't forget TMC ! , Self's present kit has high 5Khz + thd compared to this one.

I think this will have to do (final draft of PCB)

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Old 17th July 2011, 04:26 AM   #85
Bigun is offline Bigun  Canada
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Nice !!
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Old 17th July 2011, 04:56 AM   #86
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looks good OS !


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Old 17th July 2011, 06:58 AM   #87
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Default Revised PCB ...

..... I have rerouted somes parts from PCB, including grounding circuit , I hope now it's better ...
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File Type: jpg DIYLIN OS PHOTO.jpg (385.7 KB, 1406 views)
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Old 17th July 2011, 08:15 AM   #88
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Default I am not picking....really!!

In fact , you might avoid problems like in the apex thread.

Make the board bigger ... 200-225mm
Make it square - not really essential , but any total diy'er might not be into cutting (like that).
Make it to accept to247 , not just to-3p (more OP spacing - like the apex sr200 ) ... some may like to throw anything they have into this.


Now to the "fine print"

Thermal -
Q1-2/ input pair ... essential, "face to face" thermal compound and heatshrink.

Q3-4/ cascode ... no gain here , not essential

Q5-6/ current mirror ... a little gain here, preferred "face to face" , but not absolutely essential.

Q7-8/2Q- CCS... best to be tightly coupled as the coefficients cancel out to keep current vs. temp. constant. A slightly negative coefficient overall.

Q9-12 - same heatsink for all ,(or at least some heatsink). Since I now run at roughly 9ma with the 68R emitter resistor (r27) , I am glad for the 30-40 sq.CM heatsink I have spanned across Q10,11/12. They get pretty hot without one.

Q13 is under (beneath) where a small heatsink should go.

Drivers and outputs are too close together... "hotspot" on main heatsink , not ideal.

I did not finish the BOM yet , some resistors need to be bigger (r27 and 23 -1/2w).

You still did not get the ground right ... look very closely at mine. The schema is the same (no component changes) my last board post is final.

I'm just curious , Alex ... do you do layout from mind like me , or do you have some fancy schema-to PCB / auto routing that you use ???

PS- next, I will post the real final overview and a workable JPG image to be toner transferred , the design can be done on single sided FR-4 ( connect XYZ) ... WE NEED A VOLUNTEER !! ( I am moving and ran out of material)
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Old 17th July 2011, 08:17 AM   #89
Bonsai is offline Bonsai  Taiwan
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Both nice looking boards. Great job guys!
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Old 17th July 2011, 08:48 AM   #90
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Default Prototype...

(attached)

BOM , schematic , the overview , a 300dpi (tested on my printer)PCB image , and a list of input devices.

PCB should be 100%. BOM , schema are still in draft form - (not pretty) ... but correct.

PS- single sided , just join the X's , Y's , and Z's (and the OP NFB)with thin wire under board. All J's geta standard jumper. When this is double sided - NO jumpers at all (the board store units).
OS
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Last edited by ostripper; 17th July 2011 at 08:58 AM.
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