LM3875 kit puzzling problem: thoughts appreciated - Page 2 - diyAudio
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Old 23rd January 2011, 12:57 PM   #11
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Thanks all for your thoughts on this matter, it is highly appreciated.

Based on some remarks I decided to redo my grounding, following the kit guide more closely by using a solid copper wire attached to OG instead of CHG. On top of that I noticed that I got LM3875TF's, which should be insulated from a grounded heatsink. Since both the chips are attached to the chassis, which is grounded, I should have insulated them but I didn't. Wrong assumption on my part, I somehow figured the kit would come with the easier type

After changing that, I believe the ear pressuring is gone and it sounds more like an amplifier should, meaning it is no longer tiresome to listen to.

Final verdicts will have to wait though, I currently have a cold which is affecting my ears, besides giving me a stuffed head
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Old 23rd January 2011, 01:46 PM   #12
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Default Insulation

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Originally Posted by simplicity View Post
Thanks all for your thoughts on this matter, it is highly appreciated.

Based on some remarks I decided to redo my grounding, following the kit guide more closely by using a solid copper wire attached to OG instead of CHG. On top of that I noticed that I got LM3875TF's, which should be insulated from a grounded heatsink. Since both the chips are attached to the chassis, which is grounded, I should have insulated them but I didn't. Wrong assumption on my part, I somehow figured the kit would come with the easier type

After changing that, I believe the ear pressuring is gone and it sounds more like an amplifier should, meaning it is no longer tiresome to listen to.

Final verdicts will have to wait though, I currently have a cold which is affecting my ears, besides giving me a stuffed head
Hi
The lm3875tf are an insulated package. if you had fixed then to the chassis and they where the non insulated version at least you would of blown a fuse in the -v rail and if no fuse a flash and a bang maybe.
Mad mark
Ps let your amplifier burn in for a while and will/ should sound much smoother.

Last edited by madtecchy; 23rd January 2011 at 01:48 PM. Reason: added ps
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Old 23rd January 2011, 01:58 PM   #13
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Default hello waki has you neck retracted yet

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Originally Posted by wakibaki View Post
Mad Mark

Please do not quote entire posts in this fashion where it performs no useful purpose and eats up bandwidth.

w
My question had a very valid reason . i guess you have been snooping around my posts and got a lttle sore with a comment i made to someone not being at all helpfull and in fact being totaly unhelpfull.

Then again it could be that i quoted his post, i have tried to delete the unwanted imformation when quoting but it never seems to work.
Im sorry i offended you and i will make a note " i must improve my quoting"
Friendly with Regards Mad mark. please let me know wich it is . pm me if you must
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Old 23rd January 2011, 01:59 PM   #14
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I would rather attribute a feeling of pressure with low frequencies. That would correspond to the rise below 50 Hz.

Did you try the AC-coupling already?
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Old 23rd January 2011, 02:24 PM   #15
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Quote:
Originally Posted by simplicity View Post
However, what is really bugging me now, is that there seems to be some sound pressure/problem beyond the range of human hearing which results in a feeling of pressure on the ears, it even starts to get a little painful after a while.

Does anyone care to share their ideas as to what might be causing the ear pressure problem? I don't really know how better to describe it, besides there seeming to be a unheard sound that irritates the ears.

The extra puzzling thing is that it almost sounds ok, and it is hard to pinpoint what is wrong with the sound. I'm not an expert at this. It just sounds hard edged somehow.
Often such impression is related to phase reversal on one of the speakers.
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Old 23rd January 2011, 08:56 PM   #16
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Hmmm, indeed I misread. My chipamps are the insulated type after all. So that shouldn't have mattered. Plodding on... will try AC-coupling this week.
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Old 26th February 2011, 09:58 AM   #17
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Finally an update about my problem...

Yesterday 'That Guy Eric' was here, and we did listening tests using his fresly built LM3886 kit, and mine. His sounded much better, as expected. Upon inspection of mine, he exclaimed in triumph: "Duh, you didn't connect the ground pads, small wonder ". I thought: "How st*pid , can it really be...".

I believe I wired everything as described in the kit manual though, which only seems to connect a solid copper wire from OG's to a star ground, and it does not do so for PG- and PG+. So I didn't connect PG- and PG+ to the star ground. This left the impression on casual inspection I didn't connect the ground .

Because I thought I had tried everything else anyway, we invoked Murphy's law, and went ahead and did it, connected PG+ and PG- to the star ground.

And what a difference! The difference is so remarkably big and huge and gargantuan, I would almost say it works as it should now. Great stuff

(Eric said it still sounded horrible, but that is due to a different taste in music )
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