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Old 18th February 2013, 05:41 PM   #1
mika111 is offline mika111  Finland
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Default Class D amp problem

Hi!

Im a new user on this forum and my english quite bad also, so forgive me already

I have a problem with D -class amplifier, there is noise from speaker even when no signal (only power) is on.

I have already changed TL494, every electrolyte from it, cleaned it up and varnished those transformers.

Id be very thankful if someone could help me with this.

The noise is quite high Hz and raises and falls at a steady pace.

If I measure DCV from speaker output it shows 25-35mV.

Thank You!!
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Old 18th February 2013, 08:24 PM   #2
DUG is offline DUG  Canada
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Greetings milla111,

Did you build it or buy it?

Do you have a model number or schematic?

What sort of frequency or waveform is the noise...do you have access to an oscilloscope?
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Old 18th February 2013, 10:29 PM   #3
mika111 is offline mika111  Finland
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Oh...I bought it, brand is Autostudio and model E-1200

I don't have a schematic for this and neither oscilloscope..so my measure -tool at this point is only universalmeter (don't know what it is in English)

I was wondering that could the problem be in HIP4080 or some op -amps controlling that HIP?

The frequency from speaker is quite high Hz and it sails up and down between about 1kHz-15kHz

E: hah..think it's 'digital multimeter'

Last edited by mika111; 18th February 2013 at 10:57 PM.
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Old 19th February 2013, 04:35 AM   #4
manojtm is offline manojtm  India
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Hi mika111,

something wrong with your GND line/missing/shield not proper.

Quote:
measure DCV from speaker output it shows 25-35mV
DC SPK out is ok, no problem found on your amp.

Regards
MANOJ
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Old 19th February 2013, 07:40 AM   #5
mika111 is offline mika111  Finland
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Thanks Manoj..the supply ground is 0,00 ohm at one point and signal ground is 'floating' 1kOhm at that point. From that point it goes to amp chassis via 100nF polko..I changed that polko -> did not solve the problem :/
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Old 19th February 2013, 11:38 AM   #6
mika111 is offline mika111  Finland
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Here is some pictures from the board..

http://kuvaton.com/k/YrWK.jpg
http://kuvaton.com/k/YrW7.jpg
http://kuvaton.com/k/YrWN.jpg
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Old 19th February 2013, 05:18 PM   #7
mika111 is offline mika111  Finland
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Changed those LM393, LM833 and MC14013 from the HIP control -> no effect

Anyone?
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Old 19th February 2013, 06:11 PM   #8
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Without an oscilloscope, a repair is impossible as theres no way to see if you have the proper signals.
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Old 23rd February 2013, 10:49 AM   #9
mika111 is offline mika111  Finland
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Okay, I have now measured some things from the amp. All measurements are from power ground. Oscilloscope is set at AC.

Speaker output http://kuvaton.com/k/Yr3F.jpg
Power FET1 http://kuvaton.com/k/Yr3P.jpg
Power FET2 http://kuvaton.com/k/Yr3q.jpg
Chassis ground http://kuvaton.com/k/Yr3b.jpg
TL494 Vcc http://kuvaton.com/k/Yr3E.jpg
HIP4080 Vcc http://kuvaton.com/k/Yr36.jpg
4013BP Vdd http://kuvaton.com/k/Yr3e.jpg
LM393 Vcc http://kuvaton.com/k/Yr3c.jpg
LM833 Vcc http://kuvaton.com/k/Yr3K.jpg
Amp FET http://kuvaton.com/k/Yr37.jpg

FETs are measured from Drain to Power Ground
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Old 23rd February 2013, 01:44 PM   #10
DUG is offline DUG  Canada
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The big electrolytics...the ones on the right both have + to the right and the ones on the left the + are towards each other.

Verify that they are in correctly.
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