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Old 16th June 2011, 01:52 AM   #21
infinia is offline infinia  United States
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Consider swapping places with the 0.1uF decoupling caps and small electros to bring the critical parts closer to chip amp power pins.
The 0.1 uF parts look big. Shop for smaller pin spacing (5mm) narrow leads means better HF performance.
Consider wiring the amp output speaker return going off PCB to the stiffer PS PCB instead. This is key to keeping a quiet gnd on the amp board esp since you choose very small value electos.

look at other chip amp power PCB layouts for ideas on central grounding. Think about all yer in /out connectors, their location, connection numbers, and chassis wire dressing with either a mono block, stereo, or even a HT amp for a future growth configuration. IMO Bunching all the ins and outs together in the middle with a circular ground is kinda like painting yerself into a corner.
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Old 16th June 2011, 09:11 AM   #22
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by discrete View Post
In the simulation below, do you want to feed your amplifier with V1, V2 or V3?

Using V1 is a good way to have mains hum on your speakers.
Yes, take account of the wiring/trace resistance.

An ordinary Capacitor Input Filter is actually an rC filter. Don't throw away that useful small r by connecting to the wrong terminal.
Similarly the bank of caps have connections all with a small r. Power comes out cleaner at the opposite end from the rectifiers. Looks like a 15dB reduction in hum/buzz. Note also the frequencies in the hum of V1 ref V3. V3 is substantially 100Hz and a few odd harmonics.
V1 is very spiky and consists of substantial HF harmonics.
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Last edited by AndrewT; 16th June 2011 at 09:16 AM.
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Old 16th June 2011, 12:32 PM   #23
hurtz is offline hurtz  Germany
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Quote:
Originally Posted by discrete View Post
In the simulation below, do you want to feed your amplifier with V1, V2 or V3?
Wow a huge thankyou to you Finally I can visualize what is going on!
PSU design has been altered accordingly (I hear 4 caps are the new wave )

Amp design was also changed quite a bit. 0.1uF caps were moved closer to the power pins, also were exchanged for 2.54mm spacing instead of 5mm.
Also Cin was moved closer to the chip, reduing the path from input to chip significantly. The AMP PCB is at the moment just below 10mm^2.

Quote:
Originally Posted by infinia
Consider wiring the amp output speaker return going off PCB to the stiffer PS PCB instead.
I'll keep that in mind and will try it if I have problems with noise on the speakers, but for now I keep the return on the AMP PCB itself (one less connector ).

Hopefully the nearly last revision:

AMP v3.0:
Click the image to open in full size.

PSU v3.0:
Click the image to open in full size.
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Old 16th June 2011, 01:05 PM   #24
infinia is offline infinia  United States
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like it

last check, can you publish your new parts list for ordering?
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Last edited by infinia; 16th June 2011 at 01:15 PM.
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Old 16th June 2011, 11:55 PM   #25
hurtz is offline hurtz  Germany
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The Parts list:

Code:
-LM3886TF   x1

-Cin: Wima MKS-2   4.7uF   50V=   5%   5mm   *1
-Cz,Cs2,Cs4: Wima MKS-02   0.1uF   63V=   20%   2.5mm   *3
-Cs1,Cs3: Panasonic   68uF   35V   20%   2.5mm   Inpedance:0.35Ohm   Ripple:290mA *2

-Rm: 10k  1W     *1
-Rf: 22k  0.25W  *1
-Ri: 680R 0.25W  *1
-Rg: 22k  1W     *1
-Rz: 2R7  2W     *1
Some changes were made to the layout, the size of some of the components were updated. The speaker out was moved out of the 2.54mm grid, to allow for bigger drill-holes/connectors. For Cs1/Cs3 caps with either 5mm or 2.5mm grid can be used with a diameter up to 8mm. The input was moved into a 3.5mm grid that allows for PCB-connecters with screws (or whatever they are called) The purple box outlines the plastic casing.
also I've decided to call it the "mü-amp" . Size of the board is 40mm * 24mm = 9.6cm².

After printing it today for the first time, I have some doubts whether it is possibly to toner-transfer the PCB... but well, we'll see.

AMP: v3.1
Click the image to open in full size.

PSU: unchanged
Parts List:

Code:
-Cn: Jamicon   4700uF   35V   20%   7.5mm   *8
-Dn: MUR820   *4

As always, further suggestions/critics welcome, around next week I think I will order the parts and build it, when everything fits, I will publish the layout of the mü-amp.

thank you everyone again, I really appreciate the effort you take helping some "random stranger"

Cheers!
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Old 17th June 2011, 03:45 AM   #26
Piggy is offline Piggy  Hong Kong
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Nice work. How about not to connect the zobel and the speaker return on the signal ground bus?
An-1849, fig 11 may be useful for your design.
You may also consider fit the Rm under the Lm3886 and move the Rf closer to the chip.
Leave some space for the feedback cap and RF filter as well.
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Old 17th June 2011, 09:08 AM   #27
AndrewT is offline AndrewT  Scotland
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3.5mm pin/pad pitch does not sound right.
Almost all connectors use increments of 0.1inch (2.54mm) for pitch, The screw down terminals are usually 0.2inch (5.08mm) pitch. The single in-line pin and socket are usually in 0.1inch (2,54mm).
Mica (silvered mica caps) are usually not available in 0.1inch pitch increments.
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Old 17th June 2011, 04:49 PM   #28
hurtz is offline hurtz  Germany
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Quote:
Nice work. How about not to connect the zobel and the speaker return on the signal ground bus?
What do you mean? Technically there is a connector on the AMP for the speaker return, but should anyone want to build this, he/she can still return the speaker directly to the PSU.

Quote:
3.5mm pin/pad pitch does not sound right.
They are from: RIA CONNECT Article: 31059102

Quote:
Mica (silvered mica caps) are usually not available in 0.1inch pitch increments.
I'm not using any

cheers!
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Old 17th June 2011, 07:14 PM   #29
infinia is offline infinia  United States
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The output zobel actually belongs on the amp board or the signal ground. Contrary to some folks belief this RC network is NOT for the speaker. It is used for feedback stability ie phase margin around the unity gain frequency > 2MHz. Due to high frequencies, when wired remotely, it's almost useless. It's very important not to mix power and signal grounds, so it's good to wire the speaker return to the PS common (power ground).

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.
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Last edited by infinia; 17th June 2011 at 07:27 PM.
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Old 17th June 2011, 08:58 PM   #30
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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
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