6 x lm3886

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Hi guys...

I have for a long time been building small amplifiers, mostly small transistor amps.
I have been building 1 x 50Watts lm3886 setup, what you might know as gainclones. But only after the applikation in lm3886 datasheet.

However, one of my nad214 effekt amps has recently choosen to let go of its life. So here i am, building a competitor to my second nad214 amp.

I have thought of building 2 x 3 parallel lm3886, and then hook them up balanced an invert the output on one terminal, så i will get 300 watts max output power - teoretically.

But - heres my questions:


  • I need a good trafo, but they are extremely expensive here in denmark, so is there any place with some cheap ones?
  • The same question with the cap-bank, have been lookin at rifa, but they are expensive, which might be a good replacement?
  • What is the smartest way to build this rig to make unbalanced to balanced? The signal is from preout at my denon avr 2802.
  • How do i overcome the problem with a cap in the signal way, the sound quality cannot be better than the cap?
  • Would it be possible to place a relay at the input, and let it be acting as a softstart, without suffering from lack of soundquality. I have some 48V 8A goldplated relays lying around. They might be of any use?

I probably have more questions, but these are the most urgent right now.

The amp (and hopefully its sister) will be powering my Dali Blue 8008 front speakers, and they need juice - loads of juice :).

Hope theres one out there who can help.

Thanks in advance.

Henrik

* Forgot the schematic, i will be uploading it tomorrow morning.
 
AndrewT said:
build a proper 300W into 4ohm amplifier.

The Leach clone using a 3pair output stage managed 311W into 4ohm using a 0-40, 0-40Vac transformer.

Well, i have been building some transistor amplifiers, but i was not satisfied with them.
I might build a leach clone after this one :).

pacificblue said:
...or use the search function. Look for BPA 300.

Okay, i will look for that.
 
CJ900RR said:
There is other more cost-efficient way to achieve 300W into 4ohm, but I like the sound of a good old BPA300 and therefore I recommend that you build it :)

Monster's design, I think he was first...

My attempt, it difference from Monster's design with dc-servos and non-inverted topology...

I searched the forums, and found also that monster design, it is quite nice :), i think i might go for that design, and then afterwards i might be lookin at your design.

But i havent got any answers to my questions yet?




:smash: :smash:
 
FlexQ said:
[*]I need a good trafo, but they are extremely expensive here in denmark, so is there any place with some cheap ones?
That is the same all over the world, and prices are still rising. I cannot give you tips for Denmark, of course. Here is a good place to buy in Germany. They used to have that page in English as well, but that option does not seem to be available any more.

FlexQ said:
[*]The same question with the cap-bank, have been lookin at rifa, but they are expensive, which might be a good replacement?
If you can hear any difference at all from one power supply cap type to another, you will have to find out on your own, which one suits your taste best. If you don't know whether you hear the difference, start with inexpensive no-name caps and use small MKPs or even ceramics to snubber them. You can experiment later.

FlexQ said:
[*]What is the smartest way to build this rig to make unbalanced to balanced? The signal is from preout at my denon avr 2802.
There is no smartest way. Many ways lead to Rome. Anyhow, the balanced option only makes sense for the signals between components. So, if you balance, do it at the source, not at the amp.

FlexQ said:
[*]How do i overcome the problem with a cap in the signal way, the sound quality cannot be better than the cap?
If you don't like the cap, don't use it. Provide other means of protection then, like DC servos (as proposed on page 7 in AN-1490, and as applied in AN-1192) and/or a dedicated DC protection circuit at the output.

FlexQ said:
[*]Would it be possible to place a relay at the input, and let it be acting as a softstart, without suffering from lack of soundquality. I have some 48V 8A goldplated relays lying around. They might be of any use?
The LM3886 has a mute input, which you can use for that purpose (see datasheet). The relays may be of better use for a protection circuit at the output or for input source selection.
 
Re: Re: 6 x lm3886

es44 said:
What voltage and VA do you need for transformers ?

my trafo needs 230V/2x18V maybe around or over 350VA?

AndrewT said:


depends on the load.
Check the datasheet and application note.

My loudspeakers is 4Ohms, think it is over/underrated?

pacificblue said:

That is the same all over the world, and prices are still rising. I cannot give you tips for Denmark, of course. Here is a good place to buy in Germany. They used to have that page in English as well, but that option does not seem to be available any more.

They really do have a great deal of different trafos, the same price as where i look in denmark, but they have many more ... many many many more. :).
It has been bookmarked right away :).


If you can hear any difference at all from one power supply cap type to another, you will have to find out on your own, which one suits your taste best. If you don't know whether you hear the difference, start with inexpensive no-name caps and use small MKPs or even ceramics to snubber them. You can experiment later.

I frankly dont think i can hear the difference, so i found these, they are, at my opinion extremely cheap:

http://dk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5436886

200DKr = 40US$ = 28 Euros.
For 47.000uF 40V.
With screw terminals.

There is no smartest way. Many ways lead to Rome. Anyhow, the balanced option only makes sense for the signals between components. So, if you balance, do it at the source, not at the amp.

I cant make the signal balanced from the amp, it is unbalanced from my preamp, so you think i should just parallel mount all 6 LM3886?

If you don't like the cap, don't use it. Provide other means of protection then, like DC servos (as proposed on page 7 in AN-1490, and as applied in AN-1192) and/or a dedicated DC protection circuit at the output.

Hmm, i will look into that, sounds interresting. :).

The LM3886 has a mute input, which you can use for that purpose (see datasheet). The relays may be of better use for a protection circuit at the output or for input source selection.

Smart thought, it looks quite easy to get that working :).

Thanks for the answers guys :).

If ya have any thoughts, then let me know :).
 
Re: Re: Re: 6 x lm3886

FlexQ said:


my trafo needs 230V/2x18V maybe around or over 350VA?


Okay, the two transformers i have just sitting here are 2x24.5V and only 300VA, so they are not useful, 'twas just a thought ;-)

Last time i went for a couple of 2x18V, i found them cheapest at "El-supply.dk", Don't know about prices today though.

Happy hunting :)
Ebbe
 
Re: Re: Re: Re: 6 x lm3886

es44 said:


Okay, the two transformers i have just sitting here are 2x24.5V and only 300VA, so they are not useful, 'twas just a thought ;-)

Last time i went for a couple of 2x18V, i found them cheapest at "El-supply.dk", Don't know about prices today though.

Happy hunting :)
Ebbe
what is wrong with 300VA?
what is wrong with 24.5Vac?
It seems to me that both characteristics will suit a chipamp, if you choose the speakers to match the transformer.
 
Re: Re: Re: Re: Re: 6 x lm3886

AndrewT said:

what is wrong with 300VA?
what is wrong with 24.5Vac?
It seems to me that both characteristics will suit a chipamp, if you choose the speakers to match the transformer.

I guess nothing's wrong with it, but if FlexQ wants to feed a pair of 4Ohm speakers it may be a little to high voltage. I have used two identical trafo's with single 3886's to drive 6Ohm speakers with great results.

Best regards
Ebbe
 
Re: Re: Re: Re: Re: Re: 6 x lm3886

SpittinLLama said:
AN-1192 from National.

-SL



pacificblue said:
In National's AN-1192 one possible solution is shown. If you go for either of the two designs CJ900RR proposed, follow the respective schematic.

I am lookin at it right now, looking interresting :).

es44 said:


I guess nothing's wrong with it, but if FlexQ wants to feed a pair of 4Ohm speakers it may be a little to high voltage. I have used two identical trafo's with single 3886's to drive 6Ohm speakers with great results.

Best regards
Ebbe


Exactly, i think i will order 2 300Va 2x18V, they cost around 300Dkr, or 60$.
 
AndrewT said:
what a terrible way to post a schematic.
I wonder how many will bother to read it?

Why 1% resistors when the application note quotes 0.1%?

What are the two filters, in the lower half of the posting, doing?

[
An externally hosted image should be here but it was not working when we last tested it.



Because i have a load of them lying around. I am then handmatching them when in need. :).

Well, as you can see there is two different GND's, one for signal, and one for power.
My thought was, if there should be any noise from the power supply, then i will not accept it in my signalway, so i just added a little RC-filter to take that noise :).

If that is a good idea, at all?

And the other one, it was only a thought, could make an LP-filter in the power supply, to filter out 100Hz noise. But it is not connected, it was just for remembering that this was also a thing to consider?

I am merely guessing here, if it is stupid, then say it :). I am open for ideas :).
 
AndrewT asked
Why 1% resistors when the application note quotes 0.1%?


and FlexQ said
Because i have a load of them lying around. I am then handmatching them when in need. :).

Well it's OK to hand match, and cheaper, but what if someone, not so experienced, finds your schematic and decides to use it, not reading this tread? Than he will have a amp that most likely going to oscillate.

It's always good to write the correct values, if not for your own sake then for somebody else's.
 
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