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Old 18th June 2011, 08:01 PM   #31
hurtz is offline hurtz  Germany
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Quote:
Originally Posted by Juergen Knoop View Post
there is a short between pin 10&11 and pin 7 doesn't need to connected to ground via such a large track width, 0,5-1mm would be enough
Yep, but since pin 11 is not connected, it doesn't matter and I wanted to give the input line more room.
Wait isn't pin 7 the ground pin on the board? where at least the dissipated power flows through?

Quote:
Originally Posted by infinia
Also since this a gain clone copy, ie minimal design
A) there is NO DC block on the inverting network. so it's possible to have significant DC offsets at the speaker.
B) there is NO RF filtering either on the input or output. The user can and should provide some provision for this in the final design. Same is true on the PS PCB.
And again I have no idea what this is about could you explain this a little bit further/point me in the direction where I can read about this?
Since I plan to use single sided PCBs with a dimension of 120x80 it would still be convenient to have a 40x30 board rather than 40x24 now.

mü-amp v3.1
Click the image to open in full size.

Some minor changes, I moved some parts around to use caps with 8mm diameter, and nearly four times the capacity, 2.54mm pads are still present, so updated:
Code:
-Cs1,Cs3: Panasonic   220uF   35V   20%   5mm   Impedance:0.09Ohm   Ripple:730mA *2
cheers!

Last edited by hurtz; 18th June 2011 at 08:04 PM.
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Old 19th June 2011, 12:30 AM   #32
hurtz is offline hurtz  Germany
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Just for the fun of it I made an even tinier version, with smd components(the dark blue stuff). Enjoy

nü-amp:
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Old 19th June 2011, 12:36 AM   #33
infinia is offline infinia  United States
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The NS schematic with some parts marked "optional" are not really, except for advanced users or risk takers. The major item that impacts your amp PCB is the DC blocking cap in series with Rg. almost everything you need is in the NS data sheet.
RF filtering on all inputs / outputs including AC entry, is generally good design practice and depends on the PCB final application circuit/s or parts, layout wiring, and chassis design.
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Last edited by infinia; 19th June 2011 at 12:39 AM.
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Old 19th June 2011, 09:51 AM   #34
AndrewT is offline AndrewT  Scotland
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We could all make the chipamp smaller if we choose to omit essential components.
That choice comes at the expense of reduced reliability.
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Old 19th June 2011, 06:26 PM   #35
hurtz is offline hurtz  Germany
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AMP v4.0

Click the image to open in full size.

New: RF-Filter to Input/Output

New Parts:
Code:
Cc: BCC   220pF   50-100V   5%   2.5mm   *2
Rb:  10k  0.25W     *1

R: 10R   2W
L: 1uH   7.5A   0.6mOhm   5mm
cheers!
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Old 20th June 2011, 09:06 AM   #36
AndrewT is offline AndrewT  Scotland
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Try reducing Rb to 1k0 or 2k0
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Old 20th June 2011, 11:04 AM   #37
hurtz is offline hurtz  Germany
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Ah sorry typo..

Rb: 1k 0.25W *1

Click the image to open in full size.

With updated, slightly more separated return of the speaker.

cheers!

Last edited by hurtz; 20th June 2011 at 11:17 AM.
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Old 20th June 2011, 11:22 AM   #38
AndrewT is offline AndrewT  Scotland
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I cannot agree with your layout philosophy of mixing the Signal Ground with the everything else Ground.
I recommend that Signal Ground and what needs to be connected to it, be kept completely separate from the Power Ground and Zobel Ground and PIN7 Ground and Speaker Ground.
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Old 20th June 2011, 11:31 AM   #39
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Agree 100% with Andrew on this point The data sheet is your friend.

Quote:
LAYOUT, GROUND LOOPS AND STABILITY
The LM3886 is designed to be stable when operated at a
closed-loop gain of 10 or greater, but as with any other
high-current amplifier, the LM3886 can be made to oscillate
under certain conditions. These usually involve printed circuit
board layout or output/input coupling.
When designing a layout, it is important to return the load
ground, the output compensation ground, and the low level
(feedback and input) grounds to the circuit board common
ground point through separate paths.
Otherwise, large currents
flowing along a ground conductor will generate voltages
on the conductor which can effectively act as signals at
the input, resulting in high frequency oscillation or excessive
distortion.
It is advisable to keep the output compensation
components and the 0.1 μF supply decoupling capacitors as
close as possible to the LM3886 to reduce the effects of PCB
trace resistance and inductance. For the same reason, the
ground return paths should be as short as possible.
In general, with fast, high-current circuitry, all sorts of problems
can arise from improper grounding which again can be
avoided by returning all grounds separately to a common
point. Without isolating the ground signals and returning the
grounds to a common point, ground loops may occur.
You might note that this is a larger excerpt to what I posted before

Tony.
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Old 20th June 2011, 12:46 PM   #40
hurtz is offline hurtz  Germany
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Just to make sure we're on the same page here, the marked grounds are those that the datasheet speaks of right? the common ground point can now be either on the AMP itself or on the PSU as I understand it. (I assume with the cGND on the AMP it is better to have seperate grounds on the PSU)
And interpreting the datasheet, Those GNDs should be returned individually, except for (low-level) feedback and input?


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Note to self: Get better in english >.<

Last edited by hurtz; 20th June 2011 at 12:53 PM.
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