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Old 15th October 2012, 06:55 PM   #241
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Quote:
Originally Posted by Joachim Gerhard View Post
When i think more about it maybe there is simply too little current in the input stage.
I have 40mA running on the input stage with 6 BFs each side.
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Old 15th October 2012, 07:10 PM   #242
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Acting on the input current acts on the gain.
With 6 BFs 3.3ohm degeneration and 60mA LTP I get 63dB.
63mA per side is a huge amount of current. hmmm!!!

anyhow increase of input current and sqeezing everything to the max, it looks like there is not so much gain avaialbe anyway.
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Old 15th October 2012, 07:17 PM   #243
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For high Gm you need a lot of current that flows in the Fets. A bipolar has 10x higher Gm for the same current so with bipolars you have a much better relationship of idle to Gm.
That is unavoidable.
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Old 15th October 2012, 07:27 PM   #244
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Quote:
Originally Posted by Joachim Gerhard View Post
For high Gm you need a lot of current that flows in the Fets. A bipolar has 10x higher Gm for the same current so with bipolars you have a much better relationship of idle to Gm.
That is unavoidable.
true consideration.

Then can this be re-arranged for BJT?
It is a thought I am considering now since the many disadvantages I am encountering with FET, i.e. : of low gm, problem driving a lo Z source, avaialability.

What is your thought on this?
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Old 15th October 2012, 07:28 PM   #245
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Sure, you can use a bipolar long tail pair but then you have the issue of input DC.
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Old 15th October 2012, 07:31 PM   #246
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Quote:
Originally Posted by Joachim Gerhard View Post
Sure, you can use a bipolar long tail pair but then you have the issue of input DC.
DC offset seems to be a minor ptoblem compared to the others. I don't know what you think.
I am trying to re-arrange it but I can't make it properly operate.
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Old 15th October 2012, 07:32 PM   #247
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This has to be rearranged to balanced but it shows the principle.
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Old 15th October 2012, 07:34 PM   #248
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Old 15th October 2012, 07:36 PM   #249
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Quote:
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This has to be rearranged to balanced but it shows the principle.
Is it a scan of the linear audio issue you have recommend? I didn't have time to order it I will do it today and get over with.

I would like to know your opinion if for this balance desing you think we should persue the scheme in rev 7 and try the InterFet device or re-arrange for a differential BJT kind of technology.
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Old 15th October 2012, 07:41 PM   #250
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I am eager to see the Interfet at work, bipolar works anyway. That is always an option and i did it in the Paradise.
See an even better bipolar low noise circuit. Forget the post before.
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