Symasym - the sequel

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#82
AAK said:
Hi Mike,

Thanks for the info on the soundcard setup.

I'm actually playing symasym right now. First impressions, incredible! They sound beautiful. I'll break them in over the weekend, and get back to you after I do some serious listening. Of course I think It's safe to say that the amp I used to do all those measurements probably needs a well deserved break. :xeye: Thanks for all your help!

Al
Click to expand...

Hi Al, any news ?

BTW, could you show FFT-plots as image ?

Mike
 
#83
Hi Mike,

Nothing new on the symasym front to report on. Just been way to busy with work since Monday. Huge demo Thursday. Should have some news by the weekend.

For the FFT plot, with Spectraplus how do I create an image?

Al
 
#85
Hi Mike,

I spent some time last night trying find a way to take a THD screenshot with Spectraplus with no luck. I tried Alt+print and nothing happend, couldn't find any bitmaps. Any ideas? I'm using the free 30 day demo version with only two days left. Maybe the demo version doesn't allow screenhots. But, I was able to get the signal generator to work simultaneously with THD measuring about 0.002% at 1khz/-10db.

Al
 
#87
Thanks, Mike. That did the trick. Here's the THD image of the signal source input that I'll be using to drive the amps. I think it's good enough, definite improvement over what I was using before. What do you think?
 

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#88
Here symasym with 13.2 Vrms across an 8 ohm load. That's about 22 watts. Some of the fine noise you see between each harmonic is caused by the PC causing the plot to jump around from time to time.
 

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#93
This is my modified symasym, with:

- 2sk170 (BL version) in LTP, matched at 6mA Ids
- wilson current mirror in VAS
- much linear drivers, 2sc4793/2sa1837
- good factory matched finals (mjw0302/0281)
Other modification consist in bigger tail current in LTP (Ids=3.3mA), little more VAS current than original (3.1mA), double class A drivers current (70mA) and bigger suck out capacitor (330nF)

The results are:
1kHz, 1W, 8ohm, THD 0.0009%
1kHz, 10W, 8ohm, THD 0.0031%
1kHz, 50w, 8ohm, THD 0.0074%

20kHz,1W, 8ohm, THD 0.0022%
20kHz, 10W, 8ohm, THD 0.0078%
20kHz, 50w, 8ohm, THD 0.0189%

AC phaseshift at 20Khz < 1grd

All this results are simulated with LTSpice. I want to build it but first I need your expert opinion.

Thank you,
Mihai


1kHz, 1W, 8ohm
 

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#98
MikeB said:
...
Another suggestion: As you doubled the LTP-current, you might half R21/22 and reduce R18. (for symetrical clipping)

I guess, you should build it.

Mike [/B]
Click to expand...

Thank you Mike

I already done that.
r21/22 = 340ohm, r18 = 72ohm and guess what 😀:

1kHz, 1W, 8ohm, THD 0.00088%
20Khz, 50W, 8 ohm, THD 0.01821%
 
#99
AAK said:
Hi Chris,

I'm working on it. I'll provide a schematic with the actual part numbers, and BOM. Also gerbers for top, bottom, and silk for those interested in building there own. The PCB program that I used is called Ivex, they went out business about three years ago. The program is very easy use, much easier than eagle, but not as powerful. I'd be glad to email the .exe plus provide any help necessary for those who would like to modify the board.

But, before I provide all this info on this forum I'd feel better emailing it to Mike so he can go over it to make sure everything is Ok for others to build.

As you can see from the pic, the board is very compact (5"x3") requiring the output and vas transistor to be mounted to the heat sink under the board. It can be a little tricky. I'll also provide some simple assembly instructions.

Best regards,

Al
Click to expand...

Ready to go public with the layout? Getting the ps close to the amp seems like the right direction.

Sheldon
 
#100
Hi Sheldon,
I don't think having the PS directly on the board is too helpful. Mike effectively does that with the local filter/bypass caps.

roender,
That looks very good. You are going in the direction I was thinking of.

-Chris
 
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