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Chip Amps Amplifiers based on integrated circuits

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Old 12th November 2004, 01:12 PM   #1
ToG is offline ToG  France
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Default What to choose ?

Well, hello all. First, please ignore my poor english, and just imagine i'm writing in a very good way ...


I'm trying to find how i can make my speaker (4 ohms) fall in love with the new lmxxxx based power amp i want to build.

I've searched a lot on this forum but still can't decide wich one is the one : lm3875 (buffered unbuffered .....) lm3886, lm3886 in parallel .... and the psu that goes with it.


The main problem is the curve below, i'm not sure it will fit with the tons of different lm3875 i've seen ... don't want to burn anything

and on the other way, i'm not sure to need something else.


So please take a look at the impedance curve of my speakers and let me know, what can i do ??

all your suggestions will be very appreciated.

ToG
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Old 12th November 2004, 01:43 PM   #2
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Default Re: What to choose ?

Quote:
Originally posted by ToG
Well, hello all. First, please ignore my poor english, and just imagine i'm writing in a very good way ...


I'm trying to find how i can make my speaker (4 ohms) fall in love with the new lmxxxx based power amp i want to build.

I've searched a lot on this forum but still can't decide wich one is the one : lm3875 (buffered unbuffered .....) lm3886, lm3886 in parallel .... and the psu that goes with it.


The main problem is the curve below, i'm not sure it will fit with the tons of different lm3875 i've seen ... don't want to burn anything

and on the other way, i'm not sure to need something else.


So please take a look at the impedance curve of my speakers and let me know, what can i do ??
To start with I would not think of the 3875 to drive a 4 ohm speaker to rather high levels: think 3886.

Start with one 3886 per channel, with a +30/-30 supply and then see what happens. If you don't get any clippings or strange noises for the levels you listen to then question is solved.

If you do then you can do two things:

1) Parallel two 3886 for each channel.

2) Go for active amping, using the two sides of the LM4780 to drive each channel bass speaker, keeping the 3886s you had for the tweeters or mid/tweeters (if your box is 3-way).

That should take care of it.


Carlos
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Old 12th November 2004, 11:32 PM   #3
ToG is offline ToG  France
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Your explanation is ok for me, very clear and direct.

Thank you, i have now to study the forum to find the shematics i will use.

Do you have one in mind ? maybe the datasheet one ?
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Old 13th November 2004, 01:50 AM   #4
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Quote:
Originally posted by ToG
Your explanation is ok for me, very clear and direct.

Thank you, i have now to study the forum to find the shematics i will use.

Do you have one in mind ? maybe the datasheet one ?

Now you got me. There should be a few schematic options to consider.

Nuuk's site is a very good place to start, particularly because he has been following many alternatives that came up on this forum and applied them. Have a look:

http://www.decdun.fsnet.co.uk/gaincloneindex.html#top1

Even if he uses the LM3875, practically the same things apply on the 3886. The latter only has an extra resistor and capacitor for the mute.

He is also very old fashioned and uses point to point wiring... but that is not catching.

Study your choices and implement them carefully.



Carlos
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Old 13th November 2004, 01:55 AM   #5
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I would use a parallel 3875.

Although in parallel, much simpler due to lack of mute circuitry.

Also, better sound.

Parallel would drive a 4ohm load no problem at full power
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Old 13th November 2004, 08:48 AM   #6
Nuuk is offline Nuuk  United Kingdom
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Quote:
He is also very old fashioned and uses point to point wiring... but that is not catching.
Listen to Carlos' advice. He is also very old fashioned and recommends pots instead of stepped attenuators - but that is not catching.
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Old 15th November 2004, 01:31 AM   #7
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what kind of speakers are they(diy or store bought, 2-way or 3-way).

If a 2-way/3-way look below...

looking at the curve you may want to make a "Impedance Equalization Circuit " for the tweeter from what i can tell.

linky for the circuit:
http://www.mhsoft.nl/spk_calc.asp
then click on "Impedance Equalization Circuit".

hope that might help you out some!
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Old 15th November 2004, 07:27 AM   #8
ToG is offline ToG  France
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Quote:
Originally posted by Nuuk


Listen to Carlos' advice. He is also very old fashioned and recommends pots instead of stepped attenuators - but that is not catching.




ok


Quote:
what kind of speakers are they(diy or store bought, 2-way or 3-way).
it's a 2-way store bought 94db Sensitivity with a 21cm woofer and dome tweeter.

Quote:
looking at the curve you may want to make a "Impedance Equalization Circuit " for the tweeter from what i can tell.
that's an idea.
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Old 15th November 2004, 07:56 AM   #9
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Default Re: What to choose ?

Quote:
Originally posted by ToG
Well, hello all. First, please ignore my poor english, and just imagine i'm writing in a very good way ...
ToG
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Old 15th November 2004, 09:05 AM   #10
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Quote:
Originally posted by soundNERD
I would use a parallel 3875.
[snip]
Also, better sound.
Are you sure?
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