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Old 13th August 2007, 11:46 AM   #1
PMA is offline PMA  Europe
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Default Old fashioned simple preamp

I am thinking about a little bit different approach. What would you think about circuit like this?
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Old 13th August 2007, 12:35 PM   #2
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I think it's quite clever.

Since you are using gnfb, have you considered replacing R6 with a CCS to improve PSRR and increase fb factor?

I quite like the cap coupling, because my experience is that if you DC bias these caps, the caps sound much better.

The EF output load R7 would tend to add H2; you might consider a CCS here too.

Hugh
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Old 13th August 2007, 12:45 PM   #3
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As far a I can see, this circuit would not be able work properly . DC conditions would be OK only if R4 is very large and that would in turn create potential problems with the feedback arrangement and amp bandwith, rendering R10 useless. It won't be very stable with temperature as well.

Did you try to simulate it?

Cheers

Alex

P.S. - Dont get me wrong - I like this kind of topology a lot and used this extencively in the past. For instance all MM/MC preamps I've done for Creek did use very similar arrangement of transistors - but with no NFB except local, thought.
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Old 13th August 2007, 12:58 PM   #4
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Sure, I have all the necessary simulation results

P.S.: the R10 has nothing to do with gain. Gain is set by R6/R3. And R4 is just biasing resistor.
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Old 13th August 2007, 01:04 PM   #5
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Quote:
Originally posted by PMA
Sure, I have all the necessary simulation results
In this case you should be using R4 value of few megs and your circuit DC conditions would vary with temperature and transistor parameters. I am usually trying to avoid this kind of complications. However it is a matter of taste after all .

Cheers

Alex
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Old 13th August 2007, 01:08 PM   #6
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Quote:
Originally posted by PMA
P.S.: the R10 has nothing to do with gain. Gain is set by R6/R3. And R4 is just biasing resistor.
Please accept my apologies. I would probably do it somewhat different (as I did in the past), as I would try to avoid any kind of feedback except local in a circuit like that and in your case R4 would affect things at the bottom end.

Cheers

Alex
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Old 13th August 2007, 01:09 PM   #7
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The DC stability was not that bad as it might have looked.
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Old 13th August 2007, 01:12 PM   #8
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Quote:
Originally posted by x-pro


Please accept my apologies.
This is absolutely no problem, Alex. We are having fun here, aren't we?
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Old 13th August 2007, 01:20 PM   #9
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Quote:
Originally posted by PMA
We are having fun here, aren't we?
Absolutely. Here is a (rather poor quality, sorry) phono stage circuit I've done for Creek in about 1994 . It was released as OBH-8 stand alone MM preamp and also was used in Cambridge Audio A3i amplifier as well as in many Creek integrated amps as a plug-in.

Cheers

Alex
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Old 13th August 2007, 04:41 PM   #10
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Distortion at 1V, 10kHz (simulated).
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