My new SymAsym PCB design Rev_1.3 - diyAudio
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Old 10th November 2009, 03:27 AM   #1
AAK is offline AAK  United States
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Default My new SymAsym PCB design Rev_1.3

Hi All,

I'm happy to say that after two-years away from this great hobby that my creative side has never felt better and I'm back and really happy to be able share my work once again with the members of this great forum.

My new PCB design is based on MikeB's conceptual circuit design found in post #2 of the following link,

Symasym - the sequel

and Roender's great work in completing, building, and testing the design.
Roender's work is found here.

Symasym - Roender Style

The new board measures 5Ēx3Ē like my original. This was no easy task considering the number of additional components I had to add in an already tight space.

In addition to adding components, the output transistors (OT) can now mount under the board so that a 3Ē heatsink can be used. The OT can also be extended 0.5Ē beyond each edge of the board like my original board design. Iíve added leds to each PS rail that also serves as a blown fuse indicator, and moved the AC inputs so that a terminal block can be used as well as fastons. I moved the Gnd terminal further from the PS caps to make it easier to access. I also added two full wave rectifier circuits before the PS caps on each edge of the board for those that would like to add a speaker protection or soft start circuit using the main transformer.

Enough said for the moment since it's getting late. Iíve attached the schematic that's currently implemented on my Rev 1.3 prototype board, and two THD plots at 100 watts into 8ohms, and 150watts into 4ohms at 1Khz. For the THD plots I've included the input signal's THD as a reference. Itís interesting that some of the harmonics improve over the original, something that also happens in MikeBís original 5.3 design. The new design improves THD by a factor of about 2.5 to 3 over Mike's 5.3 design.

Regards,

Al
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Old 10th November 2009, 03:32 AM   #2
AAK is offline AAK  United States
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I think I forgot to upload. Here they are.
Attached Images
File Type: gif NewSymSch.gif (26.3 KB, 4736 views)
File Type: gif Sym_100watts_8ohms_1khz_Right.gif (33.7 KB, 4511 views)
File Type: gif Sym_150watts_4ohms_5khz_Right.gif (33.3 KB, 4294 views)
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Old 10th November 2009, 03:42 AM   #3
AAK is offline AAK  United States
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Here's a pic of the PCB layout, THD plot at 150watt/4ohms, and the prototype boards.
Attached Images
File Type: gif NewSymPCB_Rev1.3.gif (72.0 KB, 4384 views)
File Type: gif Sym_150watts_4ohms_1khz_Right.gif (33.1 KB, 4137 views)
File Type: jpg CIMG1122.jpg (374.1 KB, 2164 views)
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Old 10th November 2009, 06:47 PM   #4
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Hi Al

my hifi has a pair of your old boards doing sterling service. I have made several other power amps since making them, but the old Symasym boards still rule the roost. And some commercial power amps have also been found wanting. The thing I love the most is the bass - the amp seems so fast and dynamic. Consequently, if the new boards have improvements then bring 'em on. I can't wait to get my hands on a pair of boards. Thanks for all your hard work.

Aidan
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Old 10th November 2009, 08:15 PM   #5
AAK is offline AAK  United States
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Hi Aidan,

I've built many amp kits and listened to some of the best high end amps and I agree MikeB's design using my original boards has held it's ground firmly. That said I must be crazy to do all this work to try improve on an already great design but that's just me. I love this hobby. And Mikeís and Roenderís work is was just to good to not try it.

Hopefully this week Iíll get around to doing a thorough A/B comparison to see how the sound of the new design stacks up with my old design. On paper the new design flat out measures better, but as you know it does not always translate to better sound. The nice thing though is that on the new board you can easily bypass components like the cascodes so that the circuit is more like Mikeís original design. Or you can try different combinations. You can even use Lateral Mosfet output transistors by simply using the jumpers provided on the board.

I also designed an external power supply board for those that would like to use a single transformer for two amps. And I just completed a dual output transistor version.

Best regards,

Al
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Old 10th November 2009, 08:38 PM   #6
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Hi AAK

Are you using single pair of output transistors with +/- 50V supply voltage? If so, then you are pushing to the limit those poor trannies.
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Old 10th November 2009, 09:25 PM   #7
Piersma is offline Piersma  Netherlands
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Default Resistive loading VAS

hi Al,

Congrats on your design, a beautiful compact designed lay-out.
You did omit de resistive loading of the VAS, is there special reason?
To gain more open loop maybe?

Did you do the boards yourself?

regards,
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Old 10th November 2009, 09:27 PM   #8
AAK is offline AAK  United States
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Hi blueskynis,

I know I'm exceeding the SOA or close to it. I should of used a MJL3281/1302 pair but I didn't have any handy. Earlier iterations where tested with the MJL3281/1302, 2SK1530/2SJ201, and a pair of BUZ900/905.

Regards,

Al
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Old 10th November 2009, 09:36 PM   #9
AAK is offline AAK  United States
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Hi Piersma,

I omitted the VAS resistors because Roender determined that removing it improved THD in his testing. It also didnít seem to make a whole lot of difference in my original board design, and it was confirmed by MikeB.

Yep, I did the board lay out.

Al
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Old 10th November 2009, 09:46 PM   #10
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Nice one.
No problem not to mount the driver transistors in the heatsink?
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