Yet another LM3886 PCB post! - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 15th October 2011, 08:04 PM   #11
diyAudio Member
 
Join Date: Feb 2010
Location: Bucharest
Send a message via Yahoo to Th3 uN1Qu3
Single sided will sound just as good if the jumper links are kept to a minimum, and if the ones that you absolutely must use are routed properly. Double sided is just easier to work with when you are getting your boards professionally manufactured.
__________________
"Audio grade" components simply means that they failed at a more critical job.
  Reply With Quote
Old 17th October 2011, 06:27 PM   #12
diyAudio Member
 
Join Date: Dec 2009
Location: UK
Ok, I have finished my ss layout.

Critiques welcome!
Attached Files
File Type: pdf Layout_1.pdf (58.8 KB, 223 views)
  Reply With Quote
Old 18th October 2011, 09:31 AM   #13
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Decoupling is located too far from the power pins. The HF section of Cs1&2 can be 0.1" or 0.2" pin pitch. The smaller can be located right on top of the power and ground pins. Or even underneath if that suits you and aesthetics.

Although very commonly used as a solution, I do not like distance between the Vdd & Vcc lines. I recommend that the Power Lines and the Power Return be fed in, very close to each other.
The speaker output trace could be doubled or even tripled in width.
Add a bigger pad around Pin1 (Vcc). Is Pin5 also Vcc?

You have not implemented the unmute function. This will never allow the amp to turn on!!!

You have no specific connection for Signal Return/Ground. It is shared with Power Ground and Speaker Return. Isolate the Signal Returns on the PCB and give them a dedicated Signal Ground. Signal Hot and Signal Return connect directly to the input signal hot and cold at the chassis input socket

Rm seems redundant. It is normally there before the DC blocking cap to ensure the PCB input pin is always close to Zero Volts. But you have chosen to omit the DC blocking cap, so Rm should be omitted as well.

Spkr Return on the PCB works for a single channel monoblock amplifier.

When you have more than one channel inside the same chassis, all the Returns should meet at the Main Audio Ground (MAG). This cannot be on one of the amplifier PCBs.

That's all I can see, I hope the list does not get any longer,
__________________
regards Andrew T.

Last edited by AndrewT; 18th October 2011 at 09:39 AM.
  Reply With Quote
Old 18th October 2011, 09:33 PM   #14
diyAudio Member
 
Join Date: Dec 2009
Location: UK
Ok,

So I've made some changes, however I have couple of more questions.

Regarding the grounding issue, CHG is the “star” ground that I then take to a central point on the chassis which I was going to use as my MAG.

Quote:
You have no specific connection for Signal Return/Ground. It is shared with Power Ground and Speaker Return. Isolate the Signal Returns on the PCB and give them a dedicated Signal Ground. Signal Hot and Signal Return connect directly to the input signal hot and cold at the chassis input socket
Do you mean that Vcc and Vdd stay as they are, with Speaker, IP and OP ground becoming an Isolated signal ground. Does this then earth via the chassis input?


Many thanks.
Attached Files
File Type: pdf Layout_2.pdf (56.9 KB, 94 views)
  Reply With Quote
Old 18th October 2011, 09:46 PM   #15
diyAudio Member
 
Join Date: Feb 2010
Location: Bucharest
Send a message via Yahoo to Th3 uN1Qu3
That looks decent. You could add a corner in the output trace so it doesn't sit so close to the one connecting R3 and Ci.

All grounds must always be connected together, it's the routing that matters. Power ground should have a separate trace from input ground, that's what everyone says, but let me elaborate on it. Chassis ground should always be connected to input ground, right where the input wire connects to the board. If you connect the chassis ground to the ground of the filter caps (common mistake) you will get hum.

On the other hand, you have created a board with planes. You don't need to separate anything because you basically have solid planes of ground and power. I've yet to have a board made like that exhibit any kind of hum. So don't waste anymore time and build it. One thing i would do would be to route that output trace to the left where it meets Rz, to allow more of the ground plane to connect both sides. It's looking good otherwise.
__________________
"Audio grade" components simply means that they failed at a more critical job.

Last edited by Th3 uN1Qu3; 18th October 2011 at 09:49 PM.
  Reply With Quote
Old 19th October 2011, 04:34 PM   #16
diyAudio Member
 
Join Date: Dec 2009
Location: UK
Excellent, I think that I misunderstood the previous post about grounding!

Is the DC blocking cap correct, in series with the input pin. However the signal goes through C3 then R1 to the input pin.

Also 22uF a fair value (According to personal prefence)

Many thanks.
  Reply With Quote
Old 19th October 2011, 07:56 PM   #17
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I can't follow this layout as easily as your first.

That looks like an electrolytic as the input DC blocking cap.
Use a plastic film type if you can afford the cost. Somewhere from 330nF to 4u7F depending on what Low Bass frequency response you want.

Something seems wrong or omitted in the RF attenuator. But I'm not sure.

The HF decoupling caps (nF between + & G and nF between - & G are too far away from the chipamp power pins.
__________________
regards Andrew T.
  Reply With Quote
Old 20th October 2011, 07:33 AM   #18
diyAudio Member
 
Join Date: Dec 2009
Location: UK
AndrewT, thanks again for your input.

I am going to put the nf caps on the underside of the pcb, directly on the pins as per your previous post.

Relating to the DC blocking cap, I used the electrolytic as I was drawing from effects pedals, as you advise I will replace with no polarised.

Relating to the RF attenuator, which part is that?

Also would you agree, that as power planes are used, the requiremnt for isolated signal ground is delt with?

Once again, many thanks for all advice!
  Reply With Quote
Old 20th October 2011, 09:42 AM   #19
diyAudio Member
 
Join Date: Feb 2010
Location: Bucharest
Send a message via Yahoo to Th3 uN1Qu3
RF attenuator is a lowpass filter with a high cutoff frequency (some 100s of khz), placed at the input. Basically a small capacitor (some 10s of picofarads) across the input resistor. It isn't needed if you're driving the amp from a low impedance source such as an opamp.

In other words, if you also have an input stage for your amplifier you don't need it. If the amp input is accessible directly to the outside world it is recommended to fit it.
__________________
"Audio grade" components simply means that they failed at a more critical job.
  Reply With Quote
Old 20th October 2011, 10:24 AM   #20
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I believe that every input must have a filter to attenuate what is not supposed to be there.
My home has only one transmitter, my mobile phone.
Many homes have literally a dozen transmitters polluting the airspace.
Keep it out !!!
__________________
regards Andrew T.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lm3886 Pcb Azbests Chip Amps 3 4th October 2007 05:53 AM
Yet another LM3886 PCB Tim__x Chip Amps 10 15th November 2004 08:44 PM
Lm3886 Pcb gpsmithii Chip Amps 1 20th November 2003 03:45 PM


New To Site? Need Help?

All times are GMT. The time now is 04:12 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2