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Old 22nd September 2010, 06:46 PM   #1
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Default 100watt amplifier

is this circuit is working?

how can i convert this sub amplifier to normal amplifier
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File Type: jpg 100-w-subwoofer-amplifier-circuit.jpg (75.8 KB, 592 views)
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Old 22nd September 2010, 06:53 PM   #2
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'Subwoofer' amplifier in that context translates to 'lousy'.
In most contexts actually...
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Old 22nd September 2010, 07:43 PM   #3
lineup is offline lineup  Sweden
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I have to agree with darkfenriz
And say that I have seen 100-reds of better amplifiers.

Some points:

A) Q5 and Q7 is the same(NPN). So called Quasi complementary.
There is no need to make such a solution today.
We have good True complementary NPN+PNP pairs.

B) D1, D2, R9 and R10. They form a bias control for output stage.
There is no reason not to use a proper Transistor for this.

C) C4, R11 and R12. A so called Bootstrap.
Bootstrapping is an old technique.
This was probably because of lack complmentary VAS transistors.
Better to use a proper current source. 2 transistors + 2 resistors.

D) The input pair Q1, Q2 get their current from R3, R4.
Just like in the Bootstrap case, we should use a proper current source to feed Q1.Q2.
This will improve performance with several levels!

It is not that amplifier will not work.
It is that the quality of the work it can perform is bad.
If we compare with even a basic amplifier like the Blameless.

Here is the Blameless.
You can find those details I mention.
You have to mirror it upside down to compare
Click the image to open in full size.
We can find more reading at Douglas Self amplifier Institute
The Amplifier Institute.
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Old 22nd September 2010, 08:29 PM   #4
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If other circuits are too complex for you, this is also a good choice:
Click the image to open in full size.

Its based on the harman kardon citation 12 and modified by nelson pass to use mosfets in the output stage.
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Old 22nd September 2010, 08:31 PM   #5
mjf is offline mjf  Austria
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hello.
to me it looks like a cheap old style schematic.
c1,c3 are too tiny ,they cut off the bass...........c5 is very big........bias control is primitive...........and so on.
there are better schematics ,simple and cheap,like p3(a) or so........
greetings
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Old 23rd September 2010, 01:57 AM   #6
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Quote:
Originally Posted by Tekko View Post
If other circuits are too complex for you, this is also a good choice:

Its based on the harman kardon citation 12 and modified by nelson pass to use mosfets in the output stage.
3904s and 3906s ? Better not be running more than +/- 20 Volts - and that's at the red line. 40 Volts would give 25 Watts into 8 ohms. Seems a wee bit shy of 100 Watts or is it for 2 ohm loads? The current rating of the output devices is high but won't there be problems with adequate gate drive to Q6?

G
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Old 23rd September 2010, 02:22 AM   #7
lineup is offline lineup  Sweden
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Quote:
Originally Posted by stratus46 View Post
3904s and 3906s ? Better not be running more than +/- 20 Volts - and that's at the red line. 40 Volts would give 25 Watts into 8 ohms. Seems a wee bit shy of 100 Watts or is it for 2 ohm loads? The current rating of the output devices is high but won't there be problems with adequate gate drive to Q6?

G
Quote:
Originally Posted by Tekko View Post
If other circuits are too complex for you, this is also a good choice:
Click the image to open in full size.

Its based on the harman kardon citation 12 and modified by nelson pass to use mosfets in the output stage.
About the Nelson Citation 12 MOSFET.
I have great confidence in Nelson Pass. It probably works.
But I would not do that way. Probably not even Nelson today!

The weak spot is the VAS in my opinion.
The current in VAS is: Vsupply/(4.7k+4.7k)
For 30 Volt we get ~3 mA in VAS.
For 20 Volt we get ~2 mA in VAS.

If I was to drive big MOSFET (HEXFET), I certainly would use more current than 2-3 mA.
Not below 10 mA, for me.

Which means I would use other transistor than 2N3904 for Q3.
To hot up the gain we could even consider a 2 transistor darlington for VAS.
But I think this is not necessary.
It all boils downto how much global gain and feedback you want.
And how much total harmonic distortion (THD) you think you can tolerate.
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Old 23rd September 2010, 05:25 AM   #8
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What?? Im running 2x35VDC and getting over 100W continous into 4 ohms.
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Old 23rd September 2010, 06:50 AM   #9
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Quote:
Originally Posted by lineup View Post
About the Nelson Citation 12 MOSFET.
I have great confidence in Nelson Pass. It probably works.
But I would not do that way. Probably not even Nelson today!

The weak spot is the VAS in my opinion.
The current in VAS is: Vsupply/(4.7k+4.7k)
For 30 Volt we get ~3 mA in VAS.
For 20 Volt we get ~2 mA in VAS.

If I was to drive big MOSFET (HEXFET), I certainly would use more current than 2-3 mA.
Not below 10 mA, for me.

Which means I would use other transistor than 2N3904 for Q3.
To hot up the gain we could even consider a 2 transistor darlington for VAS.
But I think this is not necessary.
It all boils downto how much global gain and feedback you want.
And how much total harmonic distortion (THD) you think you can tolerate.
I have lots of faith in Nelson Pass but you missed the point. Gain doesn't mean squat when the transistor fails because you're trying to use a 40 Volt transistor in a 70 Volt system. It lets the smoke out.

G
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Old 23rd September 2010, 12:13 PM   #10
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None of the small signal transistors actually have 70v between C and E.

Im running 2x35V just fine, no prollems at all. I'll leave it up to you to believe that or not.
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