help from pro's wanted.

kmj · 25th October 2004, 03:28 PM

Hi, I have a little problem which is non-diy related but since you guys know these things this seemed lika a good place to ask.

The thing is that i bought an Amplifier from China and had it delivered to me in sweden. When i got everything wired up i noticed a kind of thumping in the loudspeakers....Totally random and it sounds like somone taps a finger on an Acoustic guitar. It doesn't need to be a source (cd etc.) connected. The only manipulations made are the switching of the powercords plug. Theres the same eletricspecs in sweden and China.

Does anyone have an idéa of what it can be and what can be done about it?

Ouroboros · 25th October 2004, 03:44 PM

Is this one of the Chinese valve amplifiers that are being sold on ebay, (among other places)?

If so then I suspect LF instability. Is the noise a variant of the old 'motorboating' sound?

kmj · 25th October 2004, 04:07 PM

No tubeamp, rather this one:
Xindak A100

it's not like motorboating just lika a random thumping...somtimes its not present just to appera minutes later. Tryed to chande powercord by the way...didn't help.

Jan Dupont · 25th October 2004, 04:16 PM

If the "taps" comes randomly, I wouldn't suspect the power supply....

Random taps and noises are most common with bad solderings or connections.....

If you do not want to send it all the way back to China, you may consider to "lifting the hat" of your new amp, and apply some cooling/freezing spay to try to find the bad spot......

kmj · 25th October 2004, 04:25 PM

that could be something to do....but why the coolingspray?

kmj · 25th October 2004, 05:14 PM

update....
it seems like the thumping is present at a greater degree at startup. In the first few minutes and later it lessens, not dissapearing thou.

Jan Dupont · 25th October 2004, 06:12 PM

You are closing in

When the "taps" are more presant when amp is cold, it's seems even more likely that the problem are caused by bad soldering...

When using cooling spray on a wormed up amp, you cool down a specific small part of the PCB (or other connection) at a time... If the "taps" then starts again, you have hit the right spot....

kmj · 25th October 2004, 06:59 PM

"and there was light"
I will investigate this after a visit to the local hardwarestore and come back with the result...or lack of

thanks!

Jan Dupont · 25th October 2004, 08:19 PM

Otherwise I live in Copenhagen

Not fare away

kmj · 26th October 2004, 06:51 AM

thanks, i will save this thread so i dont loose it

25th October 2004, 03:28 PM	#1
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	help from pro's wanted. Hi, I have a little problem which is non-diy related but since you guys know these things this seemed lika a good place to ask. The thing is that i bought an Amplifier from China and had it delivered to me in sweden. When i got everything wired up i noticed a kind of thumping in the loudspeakers....Totally random and it sounds like somone taps a finger on an Acoustic guitar. It doesn't need to be a source (cd etc.) connected. The only manipulations made are the switching of the powercords plug. Theres the same eletricspecs in sweden and China. Does anyone have an idéa of what it can be and what can be done about it?

25th October 2004, 04:16 PM	#4
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	If the "taps" comes randomly, I wouldn't suspect the power supply.... Random taps and noises are most common with bad solderings or connections..... If you do not want to send it all the way back to China, you may consider to "lifting the hat" of your new amp, and apply some cooling/freezing spay to try to find the bad spot...... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

25th October 2004, 06:12 PM	#7
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	You are closing in When the "taps" are more presant when amp is cold, it's seems even more likely that the problem are caused by bad soldering... When using cooling spray on a wormed up amp, you cool down a specific small part of the PCB (or other connection) at a time... If the "taps" then starts again, you have hit the right spot.... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

25th October 2004, 08:19 PM	#9
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Otherwise I live in Copenhagen Not fare away __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

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25th October 2004, 03:44 PM	#2
Ouroboros diyAudio Member Join Date: Dec 2003 Location: Nottingham UK	Is this one of the Chinese valve amplifiers that are being sold on ebay, (among other places)? If so then I suspect LF instability. Is the noise a variant of the old 'motorboating' sound?

25th October 2004, 04:07 PM	#3
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	No tubeamp, rather this one: Xindak A100 it's not like motorboating just lika a random thumping...somtimes its not present just to appera minutes later. Tryed to chande powercord by the way...didn't help.

25th October 2004, 04:25 PM	#5
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	that could be something to do....but why the coolingspray?

25th October 2004, 05:14 PM	#6
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	update.... it seems like the thumping is present at a greater degree at startup. In the first few minutes and later it lessens, not dissapearing thou.

25th October 2004, 06:59 PM	#8
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	"and there was light" I will investigate this after a visit to the local hardwarestore and come back with the result...or lack of thanks!

26th October 2004, 06:51 AM	#10
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	thanks, i will save this thread so i dont loose it

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