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Old 14th August 2005, 07:34 PM   #1
cowanrg is offline cowanrg  United States
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Default fed up with bosoz

after many many problems:

bosoz buzzing problem

more bosoz problem. when will it end!

bosoz PSU help!?

im finally at the point to where its almost done. it plays music seemingly fine, but its NOISY and there is still turn-on thump. i built and installed a velleman K4700 circuit, but it still thumps on turn on. after the 6 second delay, the light on the kit goes off (as it should), the relays click, and THUMP. i thought that was the whole point, it was supposed to get rid of that. maybe i need a longer delay, but i doubt it.

also, one channel is getting a nice loud hum now (didnt happen before) and the other channel has a quieter hum. both are unacceptable, you can hear it from a few feet away. and when no input is connected, it is very loud.

it sounds like a grounding issue, but i cant seem to track it down. does the velleman kit need special grounding (i just connected it as it said, with the ground connected to the RCA output grounds). thanks guys.
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Old 14th August 2005, 07:36 PM   #2
Magura is offline Magura  Denmark
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Don't you have a star ground you could try to connect it to?

A star ground have solved many a grounding problem for me.

Magura
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Old 14th August 2005, 07:44 PM   #3
cowanrg is offline cowanrg  United States
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i dont really have a star ground.

here is how ground is connected...

it comes in from the IEC connector, then it goes straight to a euro-style connecting block, where it connects to chassis ground and out to both of the power supply boards (maybe that is a star ground point). a ground wire goes from here to each power supply board, goes out each board to the main preamp board (along with + and - power).

on the inputs, ground goes from the input jacks to the volume control, then to the main board. on the outputs of the main board, it goes out to the output RCA's.

thats pretty much it... should the input and output RCA's be connected to that star ground as well? i would think that would create a ground loop.
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Old 14th August 2005, 07:47 PM   #4
Magura is offline Magura  Denmark
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Nope, the whole thing to the star ground. There are other solutions that I have little experience with, but all to star ground is 99% proof.

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Old 14th August 2005, 07:48 PM   #5
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Sounds like you have some dc on the output. That's usually the cause of thumps, especially as it happens when the relay kicks in.
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Old 14th August 2005, 07:51 PM   #6
Magura is offline Magura  Denmark
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a quick solution to tell if DC is the issue is to put a 50 uF cap in series with the output.

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Old 14th August 2005, 08:02 PM   #7
cowanrg is offline cowanrg  United States
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magura,

thanks. so, all RCA input jacks and output jacks straight to a common star ground? so on my board, instead of connecting + and GND, i would just connect the +, and connect the RCA jack's ground to the star ground instead?

i want to make REALLY sure of that because thats like 6 hours of re-wiring...

pinkmouse,

i tried measuring DC on the output and just got like 3-7mv. i watched the meter when it turned on, and it went from 0.1mv or so to about 3mv when the relay clicked on. it wasnt like it shot up really quickly and backed down, it just slowly went up. my meter has a little bar graph thing at the bottom that shows spikes and stuff, and it didnt move.

so, now i just realized that the turn-on thump is random . i went in the shop really quick to see again if i could measure it, and i didnt get it this time. which is REALLY strange. i tried it 3 times. nothing. i made sure the amp was on first and everything. but im still getting a nice buzz which changed volume with the volume knob.
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Old 14th August 2005, 08:10 PM   #8
Magura is offline Magura  Denmark
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Quote:
Originally posted by cowanrg
magura,

thanks. so, all RCA input jacks and output jacks straight to a common star ground? so on my board, instead of connecting + and GND, i would just connect the +, and connect the RCA jack's ground to the star ground instead?
That's how I usually do it, works fine.

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Old 14th August 2005, 08:13 PM   #9
cowanrg is offline cowanrg  United States
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ok, ill give that a try. im just wondering why one channel is much louder (buzzing) than the other.

and also why i cant seem too measure any of these problems. it measures like its dead quiet. i think it might be my amp that could be causing some of it. im going to bring down on of my rotel amps and test it with that...
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Old 14th August 2005, 08:46 PM   #10
cowanrg is offline cowanrg  United States
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i brought one of my rotel 2-ch amps down to test it out with. its much quieter, but still has the same problems really. still no turn on thump, maybe thats fixed?

the humming/buzzing in one channel is now more of a hissing (like when you turn your volume knob all the way up and it just has that hissing background noise). its still much louder on one channel than the other.
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