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anatech 3rd October 2006 03:08 PM

Troubleshooting your Symasym
This is where to find help for your Symasym if it doesn't work when you build it.

Mike and Pavel have created a fine amplifier, other members can help you get them working, or fix them after an oops. :D

The original thread is here.


MikeB 5th October 2006 07:11 PM

No one having problems ? :scratch: :clown:


anatech 5th October 2006 07:18 PM

I'm having a problem with my Symasym. It works fine on my bench supply, but I haven't had time to build it's own supply. :clown:


MikeB 5th October 2006 07:28 PM

Oh... But time is an issue i can't help with... Oh, maybe i can, desolder c7, the resulting oscillation will create a time warp sphere, giving you all time you'll ever need. :clown:
But, this will only work it the outputcoil is made out of neutronium. :D


anatech 5th October 2006 08:14 PM

Hi Mike,
Darn, only the power transformer is made of neutronium.

Actively direct people from the original thread over to this one as they request help.

Not many people have had problems anyway.


keantoken 7th October 2006 03:00 AM

2 Attachment(s)
Since you're a mod, please delete this post if you think that it is in the wrong thread or if there is a better thread for it. I didn't want to disturb the original thread, they seem to be on to something and I didn't want to disrupt their progress.

I have been messing around with symasym5.3, just testing stuff, and I found that the bias on Q13 and Q14 wasn't balanced and wondered that if I messed with the resistor values that the distortion might decrease slightly. I know that I'm not qualified to mess with this stuff but I wondered if anyone really bothers with the small stuff like that.

I have my schem in the attachment.
I increased R17 (in my schem) to decrease the bias voltage on Q14 to better match it with Q13 which made the biases around 710mV.

This is the FFT before the optimization:

This is it after the optimization:

NOTE: My site manager delays the time it takes for things to actually show up on the website, so if you don't see pictures, come back later

Here is my schem:

keantoken 7th October 2006 03:38 AM

OOP! Just saw the symasm - the sequel thread. Is there any way to move threads? If I could edit my post I would copy and paste, but my 30 minutes is up... Think you could allow me to edit my post? I frown upon such evil deeds as putting a post in the wrong thread. :mad:

BTW: mikeB, I like your sense of humor, I think you should use it more often.

MikeB 7th October 2006 02:32 PM

keantoken, i personally don't like the idea of adding an extra unbalance to compensate another. I can't see the fft-plots...
A Wilson current mirror (the 3 bjt thing) does remove the unbalance, but does not cancel the distortion.


Edit: I checked that in my sims, i would need 153ohms for your r16 to balance that out, in any case i had increased distortions. You might not fully trust in sims.
Where did you get the models for the output devices ?
How big was your unbalance ? I have unbalance of 2% (currents)

anatech 7th October 2006 03:41 PM

Hi keantoken,
No need to change anything. I'm just happy you didn't post in the old one. Your question does address a troubleshooting issue as you are working with the existing design.

If you get a chance to build one, do so. It works great and it will be a very good experience for you to compare sim to real life.


keantoken 7th October 2006 08:08 PM

2 Attachment(s)
I got all my models from onsemi.
sorry, my host server is still delaying the stuff...
I will attach my images. Maybe there is something wrong with my software? (LTSpice)
Here is my FFT without the mod:

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