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Old 6th March 2012, 09:17 PM   #11
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Default audio amplifier section

The audio amp is an existing AB class design, that has been modified.

Also here everything is hand made, starting with the pcb
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Old 6th March 2012, 09:26 PM   #12
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There are 6 high ripple 3300/100V capacitors, used as bypass to the output mosfets.

The trafos are shielded with a mu metal sheet, as well as the driveer circuit of

the audio amp.

Two following pics are from the older version pwm (sorry dont have any newer)
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Old 6th March 2012, 09:28 PM   #13
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Since this is a mosfet amp, i used low inductance fukushima 5W resistors to

ensure stability.
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Old 6th March 2012, 09:38 PM   #14
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Two things describe this amp :

Speed and bandwidth.

Both pics are taken with the amp fed with 4Ω/1% resistive load, at 37Vp-p.

The small overshoot at the square, dissapeared with a different setting of the

idle current.
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File Type: jpg 1KHz triangle out at 37p-p.jpg (141.2 KB, 61 views)
File Type: jpg 1KHz square out at 37Vp-p.jpg (107.8 KB, 31 views)
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Old 6th March 2012, 09:49 PM   #15
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and some high frequency tests.

Please note that in all pics the load is 4Ω/1% resistive.
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File Type: jpg 50K square medium idle idle.JPG (128.8 KB, 27 views)
File Type: jpg 200K square medium idle.JPG (97.0 KB, 19 views)
File Type: jpg 300K square medium idle.JPG (101.0 KB, 18 views)
File Type: jpg 400K sine.JPG (96.6 KB, 20 views)
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Old 6th March 2012, 09:59 PM   #16
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Default power

The output power with a 4Ω load (unclipped) was 119Vp-p (442Wrms/4Ω)

and it reached 123Vp-p (475Wrms 4Ω at clipping).

Efficiency was measured at 410Wrms/4Ω, and was about 56%.

I cant be more specific, as my ammeter is not that accurate (for now)

At 2Ω load the output at clipping was 37.5V, resulting in 703 Wrms.

The consumption was around 110A, therefore Efficiency was about 47%.
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File Type: jpg 442Wrms at 4Ω before clipping.jpg (199.9 KB, 26 views)
File Type: jpg 475Wrms at 4Ω at clipping.jpg (169.5 KB, 18 views)

Last edited by ultra; 6th March 2012 at 10:05 PM.
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Old 6th March 2012, 10:11 PM   #17
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In a Greek forum where this amp was presented, i was asked to provide photos

of the amp driving a resistive load with a capacitor in parallel.

First pic is 4Ω with 2,2μF in parallel

second pic is 4Ω with 4,7μF in parallel
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File Type: jpg NEW 1K 4Ω+2.2μF.jpg (190.0 KB, 26 views)
File Type: jpg 1Ksquare at 4Ω+4.7μF.JPG (197.7 KB, 22 views)
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Old 6th March 2012, 10:20 PM   #18
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For me, i think that the best way to test the stability of the amp

-especially when mosfets are used to the output-

is to drive the amp with a high frequency square signal, unloaded.

The two pics below, show the same event.

In the frist one we see the 100K square frequency,

and when i changed the setting of my scope we see that this is 142Vp-p.

In my opinion, not all mosfet amps are capable of this.
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File Type: jpg 100K NO LOAD.jpg (131.5 KB, 23 views)
File Type: jpg FULL OUTPUT AT 100K SQUARE NO LOAD.jpg (107.7 KB, 24 views)
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Old 7th March 2012, 03:40 AM   #19
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Impressive piece of workmanship !!!
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Old 7th March 2012, 05:17 AM   #20
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schematic ?
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