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Old 23rd September 2007, 11:25 PM   #1
JakeDN is offline JakeDN  United Kingdom
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Default Hello, can i have some help please?

Hey, this is my first post as i have been trying to resist temptation to rely on others to solve my newbie problems for me!

I have been building speakers for a while, and decided i wanted to start building amps and possibly doing something silly like having a fully active system. I am a student, so for now im just doing and learning and making some mistakes!

Anyway, to the problem at hand.

I bought the LM3875 kit from audiosector and finished building it a couple of days ago. It works! But something is wrong. It does hum, but not too bad and i totally accepted it due to the proximity of all the parts. The problem im having is the popping. When i turn the amp off the cones pop really badly (LF cones) even with the pre amp off. I checked the circuit as i went along, and all checked out fine. However, on the speaker out terminals, im getting -2v reading off my avo. Of course, that shouldn't be there!

I have no experience with chip amps so i am totally lost. Please help!

Cheers.
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Old 25th September 2007, 03:54 AM   #2
jerishi is offline jerishi  United States
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Default chip amp

Hi, there are a few different reasons for 'pops'... in firing up (any) amp. I'm no expert, but if you've got sound... you're more than half way done with your project. Many resources here- I find self constantly looking for more information....
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Old 25th September 2007, 07:13 AM   #3
gootee is offline gootee  United States
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With the speakers disconnected, and both inputs shorted to ground (and source disconnected), what are the DC voltages across each set of speaker terminals? If you have a volume pot, try the measurements at min, max, and mid settings. And what are the DC voltages from the + and - power pins of each LM3875 chip to ground?
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Old 25th September 2007, 04:49 PM   #4
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"It does hum, but not too bad and i totally accepted it due to the proximity of all the parts."

JakeDN,
Just as a side note while you're trouble-shooting the start-up pops;
you should be able to kill the hum as well. Dealing with GC hum is well documented on this site. My first couple of IGCs had some degree of hum(and FM reception), but my latest pair are DEAD quiet... Good luck sorting it all out and happy listening.


7/10
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Old 26th September 2007, 06:55 PM   #5
JakeDN is offline JakeDN  United Kingdom
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Hey, thanks for your replies. Me being so impatient and this being my first amp (it was always meant to be a practice) i ripped it apart and pretty much started again. Used the other rectifier board and got on with it.

I did realise i wasn't using a star ground, and so put one in, and then looked over everything etc.

IT WORKS!!! It hums a little but i will rectify (ha.ha.ha) that with the next one i build in a few weeks. And the popping is all gone, and no voltage of any kind out of the terminals.
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Old 26th September 2007, 06:55 PM   #6
JakeDN is offline JakeDN  United Kingdom
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Quick question, how long does it usually take for a gain clone to burn in?
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Old 29th September 2007, 02:19 AM   #7
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I don't really think there's a 'burning in' period for all solid state devices, especially if You do not use electrolytic capacitors in the signal path... The only thing that changes within the few hours or days of listening is You, ears are getting used to the sound... not the sound itself gets warmer, tigter, deeper, brighter etc...

(in electromechanical equipments, such as speakers, 'burning in' really happens)
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Old 29th September 2007, 07:08 PM   #8
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I have noticed a difference in back-ground noise level over the course of the first few hours of listening to my last couple of IGCs. On both occasions, I was using an existing PSU. Maybe the 1000 - 470UF with paralleled .1UF supply caps on the amp board? Perspective? On power-up, with the volume wide open and an ear to the speaker cone a slight hiss/hum was evident from about 6-8" away. After 6-8 hours of play, the only person in the household who could reliably detect noise under the same conditions was my 14 Y/O daughter. I would not have believed it had I not been a participant... That said, I did not notice any audible difference while listening to music.


peace,
7/10
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Old 29th September 2007, 08:40 PM   #9
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I don't know if it is the electronics or just your ear/mind being trained but, I noticed a sweeter sound after about 80 hours on all four GCs I have built.

Subtle details.
__________________
Poor stereo mix? Switch to mono! Perfect.
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Old 9th November 2007, 05:37 PM   #10
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Quote:
Originally posted by JakeDN

I did realise i wasn't using a star ground, and so put one in, and then looked over everything etc.
I have the same popping at power down on an Audisector board, How did you hook up the star ground?

cheers
Norman
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