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Old 6th July 2013, 03:15 PM   #1
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Default Need Help with 3 way LM3886 Gainclone active amplifier

There are many LM3886 threads but still I created this thread as I need help with many things to complete this project right from building the PSU to the making of the cabinet.

As I am a noob, I need guidance/ suggestion/ handholding from the kind audio gurus here as usual with this project.

Thank you for your patience with me.

Here is my current progress of work.
I made 6 set of LM3886 amps following the design of Mr Mile/ Apex.
I tested all of them in stereo mode and they are working fine.

The PSU consists of 6 X 4700 uFd per channel.
I made the PSU following this Spanish site
http://construyasuvideorockola.com/proyect_fuentes_simetricas.php
Also I am using two transformers, one for each channel.

Now time for some more complex task.
I placed the amps on a wooden board for testing.
I want to make a compact cabinet.
Is this placement okay?

Please feel free to suggest.

Thank you.
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File Type: jpg LM3886-triamping-under-cons.jpg (190.2 KB, 674 views)
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Last edited by csom; 6th July 2013 at 03:28 PM.
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Old 6th July 2013, 05:16 PM   #2
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Could anyone kindly tell me if this ground connection is okay or not?
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File Type: jpg LM3886-Ground-connection.jpg (65.2 KB, 641 views)
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Old 7th July 2013, 02:21 AM   #3
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how does it sound?
did you try it?
i think there´s a thread where multiamp
grounding schemes are commented.
are the three upper amps in a common
ground? or is the conection the same asthe other 3?
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Old 7th July 2013, 06:03 AM   #4
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Caps across diodes is not a good idea. They just lower the frequency of any resonance, instead of damping it like a snubber should.

The post at the following link might be useful:

paralleling film caps with electrolytic caps
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Old 7th July 2013, 07:31 AM   #5
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Quote:
Originally Posted by martin martinez View Post
how does it sound?
did you try it?
I am testing each amp with a passive X-over with crappy speakers in series with a 60 watt lamp in stereo mode. Even then the sound is pretty awesome I must say.


Quote:
Originally Posted by martin martinez View Post
i think there´s a thread where multiamp
grounding schemes are commented.
are the three upper amps in a common
ground? or is the conection the same asthe other 3?
Some months ago, our respected moderator and audio Guru Mooly ( who helped me a lot by helping me fix the preamp section of this project yesterday ) advised me to open a thread for my personal project with LM3886 so that I can get more specific help with my problems ( as this project is a moderately complex one for my brain and without thread-jacking, LOL ) . Here I can bug all of you more with my problems.

I did a search before creating a new thread but I couldn't find the ground scheme of multi amp, I'm sorry.

All the amps have the common ground.
I want to put all of them together in a single unit/ cabinet due to space constraint in my man cave.
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Old 7th July 2013, 07:38 AM   #6
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Quote:
Originally Posted by gootee View Post
Caps across diodes is not a good idea. They just lower the frequency of any resonance, instead of damping it like a snubber should.

The post at the following link might be useful:

paralleling film caps with electrolytic caps
Thank you so much Gootee.

Your reply with a nice explanation is just what I needed!
"Why you shouldn't do this" is always thousand times better than "Don't do this" !
I am checking out your link and will ask you more questions if I get stuck there.

Kindly keep an eye on this thread.

Thanks a ton.
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Old 7th July 2013, 09:14 AM   #7
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Hi Som,
From your posts, I believe you are tri-amping active speakers, but doing it with separate cabinets for the speakers and all of the electronics in a case. Please confirm this is correct?

I have built active three way speakers but have housed all of the electronics in the respective speaker boxes. Since you have the basic necessities (two traffos, one for each speaker), you could do this but would need another traffo for the pre-amp.

I use a similar earthing, but allowing for separate boxes, of course. It works well because I followed the advice of Rod Elliott. I also used his earth loop break circuit suggestion so I get minimal hum.

I didn't worry about snubbers; I may do so some time but it is secondary to getting this working properly. Unless it is fairly guaranteed to make an audible difference, I probably won't bother.

Also similarly, I have used LM3886TF amps, with complete success with tri-amping.

If you would like any details of my system, I am happy to help. (After all, I would like everyone to have what I enjoy so much.)

Last edited by Absconditus; 7th July 2013 at 09:15 AM. Reason: Add smiley, of course.
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Old 7th July 2013, 09:20 AM   #8
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Quote:
Originally Posted by Absconditus View Post
Hi Som,
From your posts, I believe you are tri-amping active speakers, but doing it with separate cabinets for the speakers and all of the electronics in a case. Please confirm this is correct?
Exactly sir! You are very much correct!!!

Quote:
Originally Posted by Absconditus View Post
I have built active three way speakers but have housed all of the electronics in the respective speaker boxes. Since you have the basic necessities (two traffos, one for each speaker), you could do this but would need another traffo for the pre-amp.

I use a similar earthing, but allowing for separate boxes, of course. It works well because I followed the advice of Rod Elliott. I also used his earth loop break circuit suggestion so I get minimal hum.

I didn't worry about snubbers; I may do so some time but it is secondary to getting this working properly. Unless it is fairly guaranteed to make an audible difference, I probably won't bother.

Also similarly, I have used LM3886TF amps, with complete success with tri-amping.

If you would like any details of my system, I am happy to help. (After all, I would like everyone to have what I enjoy so much.)
Kindly feel free to provide as much information as possible. I need them all.
A step by step guidance with explanation would be really a great help for me.

Thanks a million.
Eagerly awaiting your valuable inputs.
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Old 7th July 2013, 09:35 AM   #9
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Quote:
Originally Posted by Absconditus View Post
..............................................

I have built active three way speakers but have housed all of the electronics in the respective speaker boxes. Since you have the basic necessities (two traffos, one for each speaker), you could do this but would need another traffo for the pre-amp.
......................................
Sir, I could have made the system like you did i.e. housing the electronics in the separate respective speaker boxes. This is very convenient. And I have another transformer for the preamp system too.

But the problem is I have already made the 3 way Linkwitz-Riley active X-over board which is a left-right channel combined one. It is working very satisfactorily.

But I can build two mono 3 way X-Over boards per channel again, if I get a good, well-tested 3 way X-over design with PCB layout in PDF.
I still have some TLO72 and TLO74 chips with me.
But I don't have the ability to design the board using mathematical calculation etc.
So any help in this regard will make me highly obliged.

I was interested in active amplifiers after reading Rod's site and advice. I now find how right he is. Sound wise an Active amplifier is a whole new level of excellent experience even with crappy speakers.

Thank you sir.
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Last edited by csom; 7th July 2013 at 10:00 AM.
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Old 7th July 2013, 10:54 AM   #10
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Before I can give advice of a primary constructive nature, you have to decide on the configuration of your design.

First off, the configuration described means that with all of the electronics in one box, there will be three lots of speaker cables going to each box, as well as three inputs for each. As I said, I did not choose this route, instead opting for a low level balanced signal to each speaker box, which is also supplied with a mains input.

I'm not trying to influence one over the other but you do need to make a choice. All part of the wonderful decision tree in a massive process, but it WILL be worth it.
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