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Old 21st January 2004, 09:30 AM   #1
Electrons are yellow and more is better!
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Default LM3886, Jax how about offset

Jax, how much offset did you get with your LM3886 design?

http://jax.myphotos.cc/gallery/album02

Jax is http://www.diyaudio.com/forums/membe...fo&userid=9528
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Old 21st January 2004, 12:50 PM   #2
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With 1k from NI to gound it's a question of luck.
In my experience these chips have a huge production drift.
1k may be good for one chip, and in another one you may need 20k.
Some chips don't even need the resistor.

BTW, 1500uf per rail * 5 chips gives 7500uf, and that's too much capacitance.
Bass will suffer.
That's my experience with the National Overture series power op-amps, be it LM 1875, LM3875, LM3886, LM4780 (I've tested all these).
I would use 2x1000uf on a central position and 2x220uf on each chip.


Very nice amp.
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Old 21st January 2004, 01:09 PM   #3
NealG is offline NealG  United Kingdom
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BTW, 1500uf per rail * 5 chips gives 7500uf, and that's too much capacitance.
Carlos, why do you think this is?

I have read many posts preferring just 1000uF per rail.

I started out with 1000uF / rail at the chip but then added 10,00uF per rail near the rectifiers for better smoothing and liked the sound. It seemed to carry more weight and authority.........
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Old 21st January 2004, 01:29 PM   #4
Electrons are yellow and more is better!
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I have made room for 20000 uF per rail at my pcb so any from 20000 uF and less can be used.
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Old 21st January 2004, 01:57 PM   #5
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....4 x lm3886 in parallel, each with its own set of regs - 10.000 uF cerafine and 0,1uF fkp3 film at the reg-input...and 470uF at the reg-output + 0,1uF fkp3 at the power in on the lm3886 chip.....the hole thing is bridged with a similar arrangement....2 x 500va incapsulated talemas....and its noninverted with servos........and, no i don't have a digital camera
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Old 21st January 2004, 02:03 PM   #6
Electrons are yellow and more is better!
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Quote:
Originally posted by tbla
......and, no i don't have a digital camera
... you don't have a friend which has...?
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Old 21st January 2004, 02:30 PM   #7
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don't think so.....but i've heard there is one at work - never used a digital camera before, kind of embarresing
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Old 21st January 2004, 02:30 PM   #8
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Smile The complete guide to the GC PSU capacitance

Quote:
Originally posted by NealG


Carlos, why do you think this is?

I have read many posts preferring just 1000uF per rail.

I started out with 1000uF / rail at the chip but then added 10,00uF per rail near the rectifiers for better smoothing and liked the sound. It seemed to carry more weight and authority.........

Pay attention to the whole thing: bass, mids, treble.
With my tests, more than around 3000uf per rail TOTAL (one PSU for two channels) the bass becomes more prominent but slower, midband gets "thicker" and with less datail, and the treble suffers a little too.
The bass has more "body", no doubt, but it doesn't have detail.
I have recordings with great bass, but even then I have to distinguish between an earthquake and real bass, that is, I have to listen to every string that the guy on the bass is playing.
It's the difference between quality and quantity.
I like a fast and detailed sound.


The ideal capacitance, for me, is around 2,000uf TOTAL.
You have that if you have a GC with 1,000uf per rail, two chips and one PSU.
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Old 21st January 2004, 03:21 PM   #9
Electrons are yellow and more is better!
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Quote:
Originally posted by tbla
don't think so.....but i've heard there is one at work - never used a digital camera before, kind of embarresing
My 4 year old daughter can take perfect pictures... not so hard if you put the dial at "Auto"!
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Old 21st January 2004, 03:41 PM   #10
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Originally posted by peranders

My 4 year old daughter can take perfect pictures... not so hard if you put the dial at "Auto"!
And then?
Does she take the picture out of the camera?

I still think that the easyest thing to operate is a Polaroid.
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