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Old 28th August 2008, 01:39 AM   #1
lineup is offline lineup  Sweden
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Thumbs up 120 Volt psu PreAmp - lowest possible G-FeedBack

will soon be posting schematic and my simulation results

promising
and should sure be very good sounding
as lots of neegative global feedback
is very well known to ruin good musical sound

Transistors used
120 Volt 2SC2240 & 2SA970, from Toshiba
http://www.toshiba.com/taec/componen...c//50/6461.pdf
http://www.toshiba.com/taec/componen...c//50/6451.pdf
and 2N5551 + 2N5401, from OnSemi
http://www.onsemi.com/pub_link/Collateral/2N5550-D.PDF
http://www.onsemi.com/pub_link/Collateral/2N5401-D.PDF
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Old 28th August 2008, 02:50 AM   #2
lineup is offline lineup  Sweden
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Here is first image.
2SC2240 & 2SA970 superb low noise transistors
from Toshiba in JAPAN

Recommended!
Attached Images
File Type: png 2s2240_2sa970.png (23.0 KB, 488 views)
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Old 28th August 2008, 03:00 AM   #3
lineup is offline lineup  Sweden
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The 2N5551
from OnSemi in JAPAN
is a very useful NPN transistor

You can see the pin configuration here.
Attached Images
File Type: png 2n5551_pins.png (3.6 KB, 461 views)
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Old 28th August 2008, 06:00 AM   #4
lineup is offline lineup  Sweden
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120 Volt preamp

below you can see the input stage
is one pair of 2SC2240
they each work at 1.0 mA

details:
- 220 Ohm base stopper resistors
these 'protect' the input from acting as antennas
should be placed very close to transistor BASE

- 10 pF capacitor at the input transistor
will increase stabilty of the amplifer
by let input 2SC2240 get negative feedback from its own collector
at higher frequencies

- each emitter resistor is at 3000 Ohm
together this makes one 1500 Ohm resistor to feed the pair
the voltage at the transistor emitters is
(1 mA + 1 mA) x 1500 Ohm = 3 Volt
Attached Images
File Type: png 120vpre_input_pair.png (1.0 KB, 594 views)
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Old 28th August 2008, 11:19 AM   #5
lineup is offline lineup  Sweden
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Any questions, so far?

From normal www.diyaudio.com Members or or Guests.

-------------------------------------------------------------------------------
I would like very much to all besserwissers (E.E. or Amateur)
to stay away from here.
Thanks. Very kind of you.

I could make one list which ones these are at our forum.
it is a pretty long list, I'm afraid, people.

As well as I could easily make a list with those
that see themselves as Audio Gurus. True or not.
This list is a bit shorter with all well known names.

But it wouldn't be very polite and nice of me to publish such lists.
I leave it up to you & your self mind
to decide if you are welcome in this topic.
Hope you respect to stay away, if you should.

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Old 28th August 2008, 11:26 AM   #6
AndrewT is offline AndrewT  Scotland
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6mW of dissipation in the paralleled emitter resistors (tail).
Why do you need a parallel pair 3k0 when most would use a single 1k5?

Is my enquiry welcome or am I on either of your lists?
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Old 28th August 2008, 12:14 PM   #7
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Just for information, Perreaux (from New Zealand) used a similar approach in some of their pre-amp designs in the 1980s - these had a fairly high voltage rail which gave them enormous overload margins, and hence fairly low distortion at normal levels.
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Old 28th August 2008, 01:18 PM   #8
Eva is offline Eva  Spain
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C2 is a nice way to ruin PSRR.

BTW: Are you sure that you didn't get fakes?
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Old 28th August 2008, 09:05 PM   #9
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Quote:
[i]
the voltage at the transistor emitters is
(1 mA + 1 mA) x 1500 Ohm = 3 Volt [/B]
.....Wow...!


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Old 28th August 2008, 11:32 PM   #10
lineup is offline lineup  Sweden
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120 Volt Pre Amplifier
with
- no global feeedback or
- very low global feedback

Output:
one NPN transistor follower 2SC2240 .. for first version

Now, I maybe will use 2N5551 here (for more power output)
or even, several 2N5551 in parallel Class A
for high output power (read: lower load impedances)

Notice:

1. This output follower is OUTSIDE the voltage feedback loop
to the input pair of 2SC2240 differential stage

2. There is the possibility to break Global Negative FB loop completely.
In this case, the THD distortion actually gets lower.
right now my prtotype shows these figures:
Quote:
With low FB: 0.010 % THD
Without GNFB: 0.005% THD
So,what is the use of having any global feedback in this amplifier?

Okay, even if the THD goes up ( especially 2nd ) with feedback
the rest of the harmonics are considerably lower,
than Without Feedback.
The mixture of distortion changes when using feedbac vs. not using feedback.

3. Also for the output follower I use BASE STOPPER resistor, with value 220 Ohm
Attached Images
File Type: png 120vpre_output_follower.png (632 Bytes, 422 views)
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