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Old 23rd November 2008, 07:39 PM   #11
PMA is offline PMA  Europe
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Nico, frankly speaking, I did not get it now. I answered to AndrewT that my example of 2 x 30W/8 class A is a real amplifier, that I designed in 2002.

BTW, I think that you and me have many similar views of audio.
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Old 23rd November 2008, 08:30 PM   #12
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Quote:
Originally posted by PMA
Nico, frankly speaking, I did not get it now. I answered to AndrewT that my example of 2 x 30W/8 class A is a real amplifier, that I designed in 2002.

BTW, I think that you and me have many similar views of audio.
Hi Pavel,

yes I think we do share some common views. My comment is that there is no audio circuit that does not find its way into the public domain somehow.

Nico
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Old 23rd November 2008, 08:32 PM   #13
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Quote:
Originally posted by PMA

BTW, I think that you and me have many similar views of audio.
Our age is starting to show
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Old 24th November 2008, 05:30 AM   #14
lineup is offline lineup  Sweden
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Quote:
Originally posted by Nico Ras
Our age is starting to show
yes, nico


Here are my first results from The 100 watt 'light' version.
Facts & Figures:
- 22k input Impedance
- 33 Volt supply
- 3 A idle current
- Single End (SE)
- 6 power bjt, MJL3281A
- Nominal load 8 Ohm
- Gain voltage ~6.8; +16.6dB

Comments:
How fast is ths amplifier?
Is no problem to get several MHz out.
As it works in open loop with very low gain; Gv ~6.8 (+16.6 dB).
But I have rolled it off at ~400 kHz.
The -45 degree phase response is at same frequency.

The THD figures (actually tells not much of expected sound quality).
1 watt: 0.007 %
4 watt: 0.015 %
8 watt: 0.027 %

----------------------------------------------------------------------------------

One General criteria for a good Class A amplifier is >=8-10 Watt output.
The fourier test below for 1, 4, 8 watt looks good to me.
Excellent 1 and 4 watt. Nothing above 100dB for higher harmonics than 2 and 3.
At 8 watt we are beginning to see some 4th and 5th. But no higher than those.

Enjoy
Lineup
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Old 25th November 2008, 11:14 AM   #15
lineup is offline lineup  Sweden
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Default Class A Pre Amplifier part

.
The premplifier part work in Class A.
Only 2 stages.
PSU 1, +-25 Volt
PSU 2, +-30 Volt, output stage
Total Supply current 55 mA.
Gain x10, +20 dB
Power Bandwidth -3 dB at 10 MHz

Fourier Analys shows the perfect quality
Regards
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Old 25th November 2008, 12:34 PM   #16
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With a small change in my Class A super preamp
I managed to get the higher harmonics down further 20 dB !!!
The level of all above 4th is now -190 dB
And 3rd is at -155 and 4th is at -187 dB.


This amplifier uses only 12 Transistors in the 2 stages.

My circuit is unique and I have not seen the topology used before.
Only one time I saw some amplifier schematic that had a similar idea.
But it was not the way I do it.

Lineup
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Old 25th November 2008, 01:05 PM   #17
lineup is offline lineup  Sweden
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Quote:
Originally posted by MJL21193
Hi Lineup,
When I use Multisim analysis, having any other instruments connected to the circuit ruins the reading. I see a lot of stuff in yours above, but I'm not sure if these were there when you ran the Fourier.

You are looking for the "tube" sound maybe?
MJL21193
Yes, you are right. especially we should avoid to insert Current Measurements instruments. These are series elements.
Those can even cause instability in a MultiSim circuit.

In my circuit I have a couple of Volt meters in the output.
I do not think they effect anything. As they have very high impedance, in parallell.
And so takes only very tiny currents.
I could remove the voltage meter from the input, though.

Yes, tube sound.
My dream is to once build one nice Tube line preamp.
Maybe I will some time.
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Old 25th November 2008, 01:06 PM   #18
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Quote:
Originally posted by PMA
I am not only predicting, it is my main amplifier and my design
PMA
I thought this was about my amplifier.
But maybe i am wrong

Lineup
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Old 25th November 2008, 01:14 PM   #19
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Quote:
Originally posted by Nico Ras

I used a CCS instead of the 8 ohm source resistance. It is possible to wind a non-inductive resistor from wire but it may be quite large. I have in the past achieved this from using about 400 mm length of element wire from a broken toaster.
--------
Regards
Nico
Nico.
My 100 Watt 'light' version (see test results above) uses one CCS of 3 x MJL3281A.
And the active part is another 3 x MJL3281A.
Still this version has only one supply (33V at 3 A) with 2 x 4700uF output.

I will have another look at your website http://www.digisec.co.za/ras/
I know you have done a lot of work with Class A.
Regards
Lineup
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Old 25th November 2008, 02:41 PM   #20
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Push-Pull was suggested.

Above my light SE version (100watt running) shows 8 Watt 0.027% THD.
It uses one CCS for the output.

This below is one Push-Pull, running at 50 Watt.
Shows 8 Watt 0.228 % THD.
This is not even close !

What is wrong with the Push-Pull here?
What can I improve?

Because if Push-Pull is so great,
then I would be able to come close to those 0.027% THD.
At least !!!
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