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Old 6th August 2006, 02:04 PM   #1
matt09 is offline matt09  United Kingdom
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Lightbulb Amp design Newbie help anyone?

Hello,

I have recently bought the highest quality speaker drivers I can find for the cheapest price. I have 4 sets of 2 pairs altogether which include Wharfdale Diamond 2 drivers. 2 sets are for a high quality unit around my monitor, while the other 2 sets are for a design in the room. Both use an MTM speaker design. Anyway, I now need to get round to designing 2 identical stereo amps, something I have never done before. I have decided on using the LM3886 amp, as these are cheap and seem to be used quite commonly.

I was looking for a balance between quality and effectivness. Firstly, what would be the most effective circuit for the AMP itself? as there are so many different designs for it I don't know which would be te best to chose.
I was going to run the amps on a 4 ohm load with two 8 ohm speakers in parallel to save needing 2 more amps and more components, or would this result in poor quality?

I have attatched a home diagram, nothing technical, I know it isnt really drawn right, but it shows basically what I want to make and the features. I was hoping some of you would know of circuits needed to make these controls possible?

I have searched around the forum a bit, but none of the circuits have the controls I'd like.

Any help would be very much appreciated.
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Old 6th August 2006, 05:24 PM   #2
matt09 is offline matt09  United Kingdom
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It doesnt look like anyone is going to answer so I will make it more simple...

I have not seen a single project on this site or on the internet where controls are incorporated in to the LM3886.

Does anyone therefore know of nice effective circuits for the following operations with the LM3886?

A bass gain control
A treble gain control
A balance control
A loudness boost ( optional )

The amp will be hooked straight up to the lineout of a computer sound card so what is the best op amp to use for this?

Should the controls stated above be used with the op amp of the power amp chip, the LM3886 ?

I would like to drive four 8 ohm speakers altogether, 2 on each channel, should this be no problem as this amp can deliver 68w into aa 4 ohm load or will the quality be poor?

Please help, I have never built amps before and would like to get this one built while I have the time.

Thanks.
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Old 6th August 2006, 05:50 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Tone controls are built into the pre-amp not power amplifier.

This is because they require unity gain stability for the gain
stages whilst power amplifiers are only stable at high gain.

edit : using a soundcard ? why not EQ in the computer ?

/sreten.
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Old 7th August 2006, 06:09 AM   #4
matt09 is offline matt09  United Kingdom
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Hello,

I have a selection of speakers connected to my soundcards output, so I prefer to have the flexbility of altering the controls of the amp for the different speakers around the room.

Please could anyone reccomend a nice pre amp circuit with bass, treble, balance and loudness control for the LM3886?, or without the loudness control if it is not necessary? What would be a good chip to use? Also, what should the gain be at for the low signal out of a soundcard?

Any help would be much appreciated!
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Old 7th August 2006, 06:53 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
start by looking up the ESP articles and projects.

I would recommend you keep it simple.
Flat gain power amps with a volume control, with input filters giving wideband response of -3db @2Hz & 150kHz.

The treble and bass units will be connected with a crossover. The impedance of the combined drivers and crossover will be the same as the lowest driver.
One 8ohm treble and one 8ohm bass/mid will be an effective 8ohm total.
One 8ohm treble and two parallel connected bass/mid will be 4 to 8ohm, with the 4ohm being at the bass/mid end.
__________________
regards Andrew T.
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Old 7th August 2006, 01:31 PM   #6
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Default What are ESP articles ?

My wish list

I want to build a chip-Amp with 3 channels the 3rd for a sub,

or a powered sub, I also would like a DIY preamp with controls

and a remote control for on-off, volume. Treble, bass, with

selectable inputs for dvd-TV, CD, Aux. I am a student so I do not

have the knowledge to design. I have learned very much reading

this forum, perhaps someone could that designs faster than most

can build, would design something.

Thank You
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Old 7th August 2006, 02:19 PM   #7
sreten is offline sreten  United Kingdom
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http://sound.westhost.com/index.html

Elliot Sound Products

If you search the internet you can find designs with all the
features you are asking for, so no-one will design it for you.

/sreten.
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Old 7th August 2006, 07:22 PM   #8
matt09 is offline matt09  United Kingdom
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Hello,

I too am actually a student.

I am now looking at various designs, etc.

I would just like to know, how good is the power regulator circuit off chip-amps.com for the LM3886 ? Is it suitable for any voltage in the working range of the amp - about 18 - 40 , and is it fine for running the amp on 4 ohm loads or would it need biggers caps or something?

Overall, is it a nice circuit or are there any modifications needed?

Any help would be great!
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Old 7th August 2006, 09:52 PM   #9
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Default If you have AIM add BrianGT2 to list

Brian is on AIM alot of the time. He is very helpful and

encouraging to all, even us noobs. Asking for help or a design in

this forum and recieving an insulting answer like go search is

not the way to promote the DIY world. I wanted to know how to

build a 3 to 5 channel GainClone LM3886 with soft on and off,

using Brian's kits or Maurio's design. You can download the

manual from Brian's web site. http://www.chipamp.com/ The

design is in this forum, How to connect the additional channels

and any extras do not seem to be here. Good luck.
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Old 7th August 2006, 10:17 PM   #10
BrianGT is offline BrianGT  United States
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Hello Matt,

For the controls portion, you could try to use the National LM1036:
http://www.national.com/search/searc...eywords=lm1036

It seems to be able to do what you are looking for.

The chip will be in series with the input going into the LM3886 amp, not in parallel with it.

Input => LM1036 => LM3886 => output

The LM3886 can handle a 4 ohm load without issues. A 500va 2x25vac transformer shoudl be fine for running 4 channels off of. For the preamp (lm1036), you will need to have another power supply to provide lower power supply voltages.

You could start with a single stereo kit, and try running the 4 speakers off of it, with 2 in parallel per channel. This should work, unless the impedence drops too far below 8 ohms. It is worth a try. It might be best still buying a larger transformer, in case you would like to expand to more than 2 channels in the future. As for the transformers, the cost for a 330va is now $60, while the 500va is now $74 (man, metal costs have gone up a lot lately). 625va is the same price as 500va as well.

Best of luck with your project,

--
Brian
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