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Old 8th September 2011, 01:23 AM   #701
Bigun is online now Bigun  Canada
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I hope Hugh is going to cook something up with this, I'm still looking to build an all-BJT version of this amplifier !

Otherwise, it's going to be Post 183 for me ?
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Last edited by Bigun; 8th September 2011 at 01:40 AM.
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Old 8th September 2011, 01:49 PM   #702
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Ok I am probably limited not to say stupid but wont to try out building this amp SSA BIGBT, just few questions before start
1. Bias is set by 1 K Trimmer, and at first powering on it must be on max resistance?
2. 2K trimmer is for dc offset?
3. the gain is how many , and can it be changed changing what resistors?
4. Thanks all for providing help to me I appreciate it!
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Old 8th September 2011, 03:07 PM   #703
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Quote:
Originally Posted by Idefixes View Post

Click the image to open in full size.
Marc
Strange to see a C comp in a current feedback loop.
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Old 8th September 2011, 04:52 PM   #704
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are you talking C12-C13... they are there to reduce amplification at app 10MHz....and thus prevent oscillation..

there should should be some resistors in the R-C snubbers over the diodes..
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Old 8th September 2011, 05:41 PM   #705
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Originally Posted by MiiB View Post
are you talking C12-C13... they are there to reduce amplification at app 10MHz....and thus prevent oscillation..
there should should be some resistors in the R-C snubbers over the diodes..
Yes, one of the advantages, with current feedback amps and well designed stages is you don't need any Miller compensation on the feedback loop witch reduce bandwitch and slew rates, and turn the phase from their best.
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Old 8th September 2011, 05:58 PM   #706
MiiB is offline MiiB  Denmark
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in simulation.. there is a resonace peak off 8-10 db at app 10 MHz....I think it's this Nico.. is removing with the capacitors...mind you He has build and measured that exact circuit..
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Old 8th September 2011, 06:02 PM   #707
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10 MHz is such a high frequency
It wont disturb or slow much with a feedback RC-filter
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Old 8th September 2011, 06:19 PM   #708
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in simulation.. there is a resonace peak off 8-10 db at app 10 MHz....
Some serial R in the gates of Q7/Q8 ?
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Old 8th September 2011, 06:23 PM   #709
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The amplifier feed-back loop is low impedance and pretty immune to RF and completely stable but the cap was purely in anticipation for RF pick-up from very long speaker leads and difficult load, it is not Miller compensation it is purely a filter.

This amplifier is capable to operate in VHF band depending on the transistors you choose.

Nico
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Old 8th September 2011, 06:30 PM   #710
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If you read some post back, i asked Lasy Cat if these caps must be mouted. I answer same as Nico, so i decided to let the space on board as option.

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