need to contruct a 2.1

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bollywoodguyy

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Joined 2004
thanks for the pointer

after buying the amplifier how do i make the connection ?

i bought a capacitor. there are two wires coming out of it (one long and one short). i am looking at a design of circuit and capacitor is shown as |( . which wire (long/short) to connect to which end :- | or (

please excuse my novice questions
 
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bollywoodguyy

Member
Joined 2004
i did some reading at

http://www.iguanalabs.com/Begtut.htm

it was very helpfull for some basics of electricity

i found a website with a guide to build a amplifier

http://www.reprise.com/host/circuits/lm386.asp

i then went to national.com and downloaded the specification for LM386 with the pin out description (and even bought one from local store)

and pointers into how to calculate the values of the resistors, capacitors using any chip similar to the LM386 ?



I went out today and bought few leds, few resistors, a pot, few capacitors, a multimeter and a soldering rod (25W).

damm...i even fried the soldering rod after 1 hour of use. guess i will need a new one. LOL :smash:

i am 16 yrs and this is my first project with electronics :D people at diyaudio hv been very helpful
 
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soundNERD

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Joined 2003
electronet.dyndns.org
Hey, a couple of months ago I was asking the same questions, so no problem. What is the value of the capacitor? And what voltage is it rated at?

You are going to need a few capacitors to do this, and a few resistors too. You will also need a transformer (to power it), a rectifier (to turn the AC to DC, some wire and a heatsink.

I would suggest going to www.national.com and ordering some free samples of the chips, rather than buying them.

What are you going to use? the 3886 and 2 1875 or the 3886 and 1 1876? I would also suggest the 3886 and 1 1876. Another idea would be to use an LM3875 for the sub since you wouldn't have to worry about resistors to bring it out of mute mode.

How do you plan to wire it? With a custom made PCB, perfboard, a generic board designed for any circuit, or point to point (no board, just soldering parts directly to the pins)?

The capacitor, as long as it is shaped like a can, should have a row of + or a row of - indicating which is + and which is -. The | in the |( symbol is the positive side, and the ( is the negative side.

As far as a schematic, go with the ones on the datasheet.

Let me know what you decide, and I hope I didn't just confuse you more about the gainclone.

-Mike
 
li_gangyi

li_gangyi

Member
Joined 2003
iexitsolutions.com
a quick question on the 3875 sub...I've tried those in inverted mode...and parelled inverted mode...the subs distorts in mid volumes...izzit because of the slow slew rate of the LM chips or am I missing something?? I jused a low-pass filter at the front end...with a "noirmal" amp...like the p3A...it works ok and gives good bass...but on a GC it distorts like hell...even on low volumes it does it a little...any suggestions to fix it?? oh yes...the sub is 8ohms...
 
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bollywoodguyy

Member
Joined 2004
thanks again.

Hey, a couple of months ago I was asking the same questions, so no problem. What is the value of the capacitor? And what voltage is it rated at?
Click to expand...


220UF @ 25V

actually i bought a few cap and resistor yesterday (but my pervious post was n still is under moderation and this post is also)according to the guide at

http://www.reprise.com/host/circuits/lm386.asp

only thing i cant get is 0.05UF cap over here :(

You are going to need a few capacitors to do this, and a few resistors too. You will also need a transformer (to power it), a rectifier (to turn the AC to DC, some wire and a heatsink.
Click to expand...

i have a old computer speaker adapter - 9V / 1 AMP i will be using that for now

next project most probably will be a power supply (2 - 25V) but i cant find any guide on net ( i live in asia, we dont have 110V VAC which most of the guides assume. we have 240VAC)

I would suggest going to www.national.com and ordering some free samples of the chips, rather than buying them.
Click to expand...

I am not in USA ..

What are you going to use? the 3886 and 2 1875 or the 3886 and 1 1876? I would also suggest the 3886 and 1 1876. Another idea would be to use an LM3875 for the sub since you wouldn't have to worry about resistors to bring it out of mute mode.
right now i am using a LM386

this is m first project so its ok. maybe next time i will get the good ones

How do you plan to wire it? With a custom made PCB, perfboard, a generic board designed for any circuit, or point to point (no board, just soldering parts directly to the pins)?
Click to expand...

i have no experience in soldering. so i am trying to get a breadboard. i searched every local shop but couldnt find one. so i bought a perfboard (the one with lots of holes in it)

i fried my solder tool. here is how i did it. i heated it up , then i touched the tip with the solder wire till there was a lump of molten metal hanging...then drop it over the joint n pray it works. LOL :cannotbe: anywayz the solder rod died after 2-3 drops i made.:bawling:

then i hit the net and searched for solder guide. after reading how it actaully done i laughed my *** off on how i was trying to do it :D

anyway i am stuck unless i get a breadboard or soldering rod n the 0.05UF cap :(

The capacitor, as long as it is shaped like a can, should have a row of + or a row of - indicating which is + and which is -. The | in the |( symbol is the positive side, and the ( is the negative side.
Click to expand...

Thx m8 :D

As far as a schematic, go with the ones on the datasheet.
Click to expand...

i will let you know when i complete the first project. u have been of gr8 help
Click to expand...
Click to expand...
 
G

guitargully

Member
Joined 2003
The capacitor, as long as it is shaped like a can, should have a row of + or a row of - indicating which is + and which is -. The | in the |( symbol is the positive side, and the ( is the negative side.
Click to expand...

That would be a polaized capacitor then? if it's a regular one it can go in either way right? the "l" and "(" dont matter as long as there's no "+" by one of them?
 
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soundNERD

Member
Joined 2003
electronet.dyndns.org
Let me inform you that the LM386 is a 250mW (1/4 W) chip no where near powerful enough for a sub. You need the LM3886 which is a 68W chip. I would almost reccommend, though, to use the LM3875 so you don't have to worry about mute pins and resistors.

Get the datasheets from www.national.com for the chips and use the schematics for that.

DO NOT use that 250uf capacitor on the output. The LM386 can run from a battery, meaning a single supply (no negative, just + and gnd). When operating, there is DC on the output. The capacitor blocks the DC. The LM3886/3875 and 1875/1876 are split supply operated (+, gnd and -). They do not have DC on the output and do not need a capacitor on the output. Besides, a 250uf cap would defeat the purpose of a sub amp since it would act as a high pass filter. Somebody else could explain it better

Just so you know, you will need a different power supply. a single supply power supply will not power the 3886/3875 and the 1875/1876. Correct me if I am wrong, but you will need a minimum of I think somewhere around +12 , 0(gnd) , and -12V. 1A will most likely not power it, or power it too little. I have had a pair of LM1875s running off of a +-20V 1A supply, and when I tried to run both channels, they would, with little volume, begin to oscillate or something, then die. If I ran only 1 channel, it didn't do that.

lil_ganyi, about your sub, is the lowpass filter you are using formed with a opamp? If so, the gain could be too high and you could be overdriving the input. Also try increasing the gain of your 3875 amp. What size resistor are you using now? Also, 10mF is WAY too low for PS filtering caps. You need more like 5000uf or higher.

-Mike
 
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soundNERD

Member
Joined 2003
electronet.dyndns.org
Well, I couldn't think of anything else, and besides, its only 1 resistor 2 swap so what r u going 2 lose.

I have never used the 3875 before. My sub uses a 3886. I only suggested the 3875 since it produces almost as much power, and it doesn't require mute resistors. I guess though that if bollywooguyy tells us what his power supply is rated at, we could calculate it for him.

So, bollywoodguyy, what did you decide on for your system? Of all that has been said, I would reccommend the LM1876 for the satellites (although I have never used it before, but it is 2 1875s in one package right????) and an LM3886 for the sub.

A little warning about chips:
REMEMBER, UNLESS YOU GET THE INSULATED VERSION OF THE CHIPS, AND NATIONAL DOESN'T HAVE IT FOR THE LM1875 (NOT SURE ON THE 1876), THE TAB IS CONNECTED TO THE NEGATIVE SUPPLY. And I found that my dvd player's case was grounded too late, with a huge spark. I just thought you should no that before something blows up...:D.

sorry 4 the bad grammer, im sorta in a hurry :bawling:

-Mike
 
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