My first LM3875: check my parts please?

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M

meaghers

Member
Joined 2006
Hi all,

building my first project, an lm3875 power amp. I want to use two power supplies for a dual mono setup. I am not looking for all the best here, just want to get this project off the ground finally. Would you mind looking over my parts list as I am planning on ordering from parts connexion? Thanks!

Transformers:
2 x HAMMOND-63179 182P22 225VA 44V ct @ 5.11A

Chassis:
3 x Hammond-56034 1441-16 Steel chassis 10"L x 6" W x 2"H

?? Is Steel or Aluminum better? They are the same price.

Potentiometer:
2 x ALPS 68581 Blue velvet mono 100k continuous rotation

Switches:
2 x SWITCH - 70154

AC Socket:
2 x Connex - 62491 male with fuse holder

Binding posts:
2 x Connex - 53466 5-way posts

RCA Jacks
1 x Connex - 53452 RCA femle outside chassis mount

Power umbilical from psu to amp:
2 x Neutrik - 53048 3 pin male XLR ends
2 x Neutrik - 53045 3 pin female chassis mount

Knobs:
2 x knobs - 64390

Isolation feet;
12 x EAR - 56858 small isolation feet

I am looking to see if I am missing anything or if i'm getting anything silly. I want to build the ultimate sonic device someday, but right now am just looking for a nice experience. I am not interested in scrounging for parts too much, i'd rather get them new and know i have the right stuff for now. I have only a soldering iron and flux right now.

I know i will also need:

Wire:
What guage what colours and how much?

heatshink tubing

standoffs

fuses:
what amperage, and fast or slo blow?

heatsinks:
recommendations?

I know this has probably been discussed a trillion times but it is so nice to have personal contact with the nice people on this board.

Thanks everyone!
 
Nordic

Nordic

Member
Joined 2005
users.tpg.com.au/users/gerskine/dxamp/
THe transformer is too high voltage

44 x 1.414 = 62VDC
The voltage you need depends on if you will run 4 or 8 ohm speakers

You sure have a lot of nice stuff on there, but what are you doing in line of capacitors? first make sure you get good polypropylene and low ESR electrolytics, and then see what you have left before you start spending on aestetics.

It will be slow blow fuses, but we will need to know your mains voltage to advise...
 
M

meaghers

Member
Joined 2006
I thought i needed 44V center tapped transformer to do +22v 0 -22v to give 22 * 1.414 = 31VDC. I'm running 8 ohm only speakers.

Is this incorrect?

I guess it would have been usefull to state that I've already build the LM3875 kit from Peter at audiosector.com with the non-luxury components. So I'm set for caps and diodes and the like.

oh and mains voltage is north american 110 or 115.
 
Kooka

Kooka

Member
Joined 2006
LM3875 dual mono kit (Carlosfm/BrianGT boards)

Hi, stupid question here.
I assembled some months ago these boards and lost my assembling instructions.

Now I want to install the led (place is on the PS board), but I guess I have to put in place R5 since it seems to be in series with the led.
Anybody could tell me what value is the R5 resistor? Is that all I need to install the led on that board?

Thanks in advance, guys. And soffy for going off topics: I tried to post a new thread but the system simply tells me to "search the forum" and does not allow me to post a new thread...
 
M

meaghers

Member
Joined 2006
to avoid the "search the forum" message, be sure to check the box at the VERY TOP of the form when you post a new thread, which says "Have you Searched?". Then you can start your own thread.

i dont mind a little hijacking, but you'd probably be better off starting your own thread.

good luck!
 
Kooka

Kooka

Member
Joined 2006
meaghers said:
to avoid the "search the forum" message, be sure to check the box at the VERY TOP of the form when you post a new thread, which says "Have you Searched?". Then you can start your own thread.

i dont mind a little hijacking, but you'd probably be better off starting your own thread.

good luck!
Click to expand...

Got it, thanks.
 
M

meaghers

Member
Joined 2006
elementx said:

Where are you getting this info from?
http://www.national.com/ds/LM/LM3875.pdf says the chip can handle upto 84VDC,

50W into 8ohm @ +/-35vdc (70vdc)
68W into 4ohm @ +/-28vdc (56vdc)
Click to expand...


I was going by the graph in the datasheet shown below. Where are you looking?
 

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G

gootee

Member
Joined 2006
fullnet.com/~tomg/index.html
Re: Re: Re: My first LM3875: check my parts please?

meaghers said:
What about a fuse before my speaker to protect it from accidents until I'm sure i've got it right?
Click to expand...

You could. But I wouldn't leave it in there permanently. It's possible that at low frequencies (or maybe also with low and high frequencies intermodulating), the fuse's resistance could change with the signal, causing distortion.

For anyone who's interested in checking it out: I haven't seen it, but there's an old JAES paper by Greiner of the University of Wisconson that charted nonlinear distortion due to fuse thermal effects.

- Tom Gootee

http://www.fullnet.com/u/tomg
 
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