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Old 23rd February 2007, 03:02 AM   #291
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Why is that my UCD clone has a "bird" hidden inside a cct, making intermittent chirping sound? It's annoying, I wanted clean reproduction without any bird sound within the music.

Is there anything wrong with these traces?

Residual at idle 1V36 (p-p).

Why is the residual has 2 blips on left and right of sinusoidal?
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Old 23rd February 2007, 03:04 AM   #292
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It is oscilating at 398khz.

Why is the residual is not sharp, but the traces seems to be blurry, have duplication?
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Old 23rd February 2007, 03:05 AM   #293
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Top square.

How to remove the blips at the edge?
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Old 23rd February 2007, 03:06 AM   #294
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Bottom square.

How to remove the blips at the edge, making clean square?
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Old 23rd February 2007, 03:11 AM   #295
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Where the chirping sound comes from? I couldn't see anything in the scope.

My UCD will blow mosfets if played loud. Why is that? With IRF540 it just 1 second to blow. With IRF640 5 seconds to blow. With FDP3672 5seconds. Before the mosfets blowing, the sound is distorted much first, then the mosfets blown away. When the sound is distorted, the current flowing into the cct rises very much.

What is the mosfet failure mechanism when the amp is playing loud? My amp doesn't have any protection at all. Gate resistors are 22ohm. Rail voltage = +/-45V, speaker =4ohm.
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Old 23rd February 2007, 07:02 AM   #296
fumac is offline fumac  China
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which fet that u use on your test.

How to remove the blips at the edge
----------
u can try a large resister on the g of fet.
but i think ur filter is not correct.

RG

FUMAC
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Old 23rd February 2007, 09:54 AM   #297
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The fet is IRF640.

The filter I use is 24uH+680nF (not 30uH+680nF). This is the filter that according to my scope gives -3dB at 35khz at 4ohm.
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Old 23rd February 2007, 01:15 PM   #298
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I would say that you have a combination of high peak currents and poor layout. The blips after the filter come from EMI going through the output filter, the overshoot of your square wave comes from poor layout of the inner current loop of the switchers => inductance.
You can lessen the effects of this by switching softer resulting in lesser current peaks drawn through the FETs, but to what extent depends on your design and layout altogether.

You say your waveforms are fuzzy is this with no signal driving the UcD? The UcD will shift frequency when driven, so you can only observe the cleanness of a signal with no input drive.
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Old 24th February 2007, 12:42 AM   #299
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Hi, Zilog,

All the pictures I attached is condition with no load. I guess this can conclude to 1 thing, if we want to make UCD, SMT component is a must, where we can have short tracks everywhere. Using ordinary components will lead to long tracks everywhere.

Before the mosfets blown, the sound becomes distorted first, and the current draw is rising very much. Why is this? Is there a shootthrough between top and bottom mosfets?
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Old 24th February 2007, 01:04 PM   #300
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Ther could be many things wrong to make the mosfets burn.

SMD will for sure be the better choise, but I don't think this is what's wrong.

The ringing on the mosfets (what you call blips*) can be dampned with snbbers. Try 10 ohm in series with 1 nF over each mosfet, and see on the scope whether this helps.

The bluring on the scope can as Ziglo says be variations in the switching freq, or just som higher harmonics of the the carrier freq. Remember that the residual is not a single sinus but a series of sinus tones making up the square wave.

The bird sond could be some parts of the circuit (think output stage/filter) emmiting EMI that couples into the amp again.

Try to post schematics, the layout and some pictures of the amp .... otherwise it will be dificult to help you further
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