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Old 7th August 2011, 09:16 AM   #61
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Thanks Nico. I agree completely that the amp as simple as it is performs quite well, especially in speed and stability domain. For the DIY-ers the most important thing is to get a stable amp in any conditions and if there is a nice sound too, even better.

Also we could easily radically improve the schematic to more complex one but the question is where to stop. If there is possibility to make some little improvements to sch, it is reasonable to do so, otherwise it is better to leave it like it is.

Maybe the use of IRF610/9610 as drivers to power BJT outputs would give much better results (higher transconductance), since this would not complicate the sch to much?
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Old 7th August 2011, 09:16 AM   #62
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Lazy Cat,

I have changed the shunt resistors from 100R to 330R and the Feed-back resistors from 1K to 3K3 resulting in THD at 10kHz reducing to 0.32%, maybe do a little playing/listening here.

Nico
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Old 7th August 2011, 09:21 AM   #63
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Finally, I noticed in the photo that Lazy Cat has bypassed the electrolytics with 100nF, Alex maybe your layout should include them.

Again a very nice non-complex design one of the best ones of late.

Nico
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Old 7th August 2011, 09:25 AM   #64
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Yes, it is all about fine tuning the sch. I'll check the values you proposed but can not do before the end of the week, when I'll be back at cockpit.

Can you make sim as proposed, turning the output mosfets to IGBT's?
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Old 7th August 2011, 09:44 AM   #65
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Quote:
Originally Posted by Nico Ras View Post
Lazy Cat,

I have changed the shunt resistors from 100R to 330R and the Feed-back resistors from 1K to 3K3 resulting in THD at 10kHz reducing to 0.32%, maybe do a little playing/listening here.

Nico
Good, will check the sound with new feedback loop resistors values.

Quote:
Originally Posted by Nico Ras View Post
Finally, I noticed in the photo that Lazy Cat has bypassed the electrolytics with 100nF, Alex maybe your layout should include them.

Again a very nice non-complex design one of the best ones of late.

Nico
Yes good observation Nico, actually they are 1uF ML bypass caps, as I do it automatically every time. PCB should have them cause they take little space (5mm pins distance).

Thanks again Nico, I said to myself why not to share it, so lets just fine tune the circuit-values for DIY-ers.
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Old 7th August 2011, 10:12 AM   #66
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Quote:
Originally Posted by Lazy Cat View Post
Can you make sim as proposed, turning the output mosfets to IGBT's?
Yes I can. Which ones did you have in mind?
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Old 7th August 2011, 11:01 AM   #67
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Default I found it a little bit strange.... my simulation show it becomes very unstable

if you try to overdrive...needs huge current in stand by mode to operate fine...... distortion was big in my simulations 0.026% THD....maybe i have made something wrong.

Interesting circuit....maybe some tweaks...i will wait you tweak it for tuning.

regards,

Carlos
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Old 7th August 2011, 11:02 AM   #68
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Something like that for the outputs, as these were inside my test configuration

Would it give any better THD results?

Before that change, please check the results if adding one BC550c to 1k bias trimmer forming thermally adjusted zener to give proper stabilisation to the quiescent current of the input pair. Should do some improvement with only one BJT added, so not a big change.
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Old 7th August 2011, 11:04 AM   #69
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Default Oh!...not simple anymore.

The beauty on that amplifier...that excited me..was it was simple.

Seems you publish a "very basic frame" to be improved.

thanks.

Carlos
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Last edited by destroyer X; 7th August 2011 at 11:07 AM.
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Old 7th August 2011, 11:13 AM   #70
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Quote:
Originally Posted by destroyer X View Post
The beauty on that amplifier...that excited me..was it was simple.

Seems you publish a "very basic frame" to be improved.

thanks.

Carlos
No, no, don't worry it will stay simple as possible. We just have to investigate the idea which will give better results, than we will return to a basic sch and give just a little push in that direction. It must stay simple as it was intended to be. BTW thanks for your interest Carlos.
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