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Old 14th October 2008, 05:06 PM   #1
FlexQ is offline FlexQ  Denmark
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Default 6 x lm3886

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.
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Old 14th October 2008, 05:23 PM   #2
AndrewT is offline AndrewT  Scotland
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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.
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Old 14th October 2008, 05:37 PM   #3
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...or use the search function. Look for BPA 300.
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Old 14th October 2008, 10:38 PM   #4
FlexQ is offline FlexQ  Denmark
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Quote:
Originally posted by AndrewT
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 .

Quote:
Originally posted by pacificblue
...or use the search function. Look for BPA 300.
Okay, i will look for that.
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Old 15th October 2008, 07:21 AM   #5
CJ900RR is offline CJ900RR  Sweden
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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...
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Old 15th October 2008, 09:08 PM   #6
FlexQ is offline FlexQ  Denmark
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Quote:
Originally posted by CJ900RR
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?




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Old 15th October 2008, 09:38 PM   #7
es44 is offline es44  Denmark
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What voltage and VA do you need for transformers ?
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Old 16th October 2008, 08:20 AM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by es44
What voltage and VA do you need for transformers ?
depends on the load.
Check the datasheet and application note.
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Old 16th October 2008, 08:27 AM   #9
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Default Re: 6 x lm3886

Quote:
Originally posted by FlexQ
[*]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.

Quote:
Originally posted by FlexQ
[*]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.

Quote:
Originally posted by FlexQ
[*]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.

Quote:
Originally posted by FlexQ
[*]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.

Quote:
Originally posted by FlexQ
[*]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.
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Old 16th October 2008, 04:37 PM   #10
FlexQ is offline FlexQ  Denmark
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Default Re: Re: 6 x lm3886

Quote:
Originally posted by es44
What voltage and VA do you need for transformers ?
my trafo needs 230V/2x18V maybe around or over 350VA?

Quote:
Originally posted by AndrewT


depends on the load.
Check the datasheet and application note.
My loudspeakers is 4Ohms, think it is over/underrated?

Quote:
Originally posted by pacificblue

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 .


Quote:
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/s...duct&R=5436886

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

Quote:
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?

Quote:
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. .

Quote:
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 .
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