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Old 24th August 2007, 03:20 PM   #1
yellow5 is offline yellow5  Germany
diyAudio Member
Join Date: Aug 2007
Question Problems with µDimension 420.4


i'am new here and my english ist not very good

i have a problem with my 4 Channel Amp µDimension 420.4.

I hear some distortion when i hear for example pianomusik and guitar (no e-guitar)
it's terrible

If i have radiorushes (no receipt) on the amp and set the Lowpass 200Hz, i hear
some scratches as with a dirty vinyl.

I tested already much.
- another HU
- another Car
- another Speaker

with a laboratory power pack is it the same.

Its definitely the amp.

which problems could be the cause?

I'am a electrician, but here i don't know more.

Please give me some Tip, thanks!

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Old 24th August 2007, 10:20 PM   #2
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
I'm not familiar with that amp but if this is an amplifier that has the RCA shield tied directly to the center tap of the power transformer's secondary windings, an open trace between the shield and the center tap could cause the problem.

If the problem is not the same in all channels, the problem could be a dirty switch or potentiometer but it's likely you would have noticed this when moving the various controls.
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Old 27th August 2007, 12:31 PM   #3
yellow5 is offline yellow5  Germany
diyAudio Member
Join Date: Aug 2007

the shield go not to the center of the transformer.

The signal come from the RCA and goes directly with a shielded
cable to the operation amplifier.

Heres a picture:

Click the image to open in full size.

The Potis are good.

Someone still another tip?

Greetings, Franz
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Old 27th August 2007, 01:15 PM   #4
yellow5 is offline yellow5  Germany
diyAudio Member
Join Date: Aug 2007
I have found a discrepancy.

The rail for 2x -15V and 2x +15V have 4 condensers pro rail.
3 rails have 100µF an 1 rail have 220µF

Click the image to open in full size.

perhaps come the problem because of different sieving?

i have after the operation ampflifiers with a amplifier and a
loudspeaker attached and i have hear no distortions.
distortions are only at the exit (loudspeaker connection) of the amplifier

PS: the amp is new, but no warranty -> exhibition piece
before nobodoy use ist
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