diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Class D (http://www.diyaudio.com/forums/class-d/)
-   -   What does this do? (http://www.diyaudio.com/forums/class-d/145811-what-does-do.html)

agithegreat 13th June 2009 01:34 PM

What does this do?
 
Ok i've been fiddling with amplifiers for about 3 years now, just replacing various components which are clearly blown (normally black or the like.) I know the names of the components, it's just sometimes i feel unsure of what they do.

I mean you see capacitors everywhere and zener diodes. But why them?

My main question is:
Can you tell me what these few things do?
All ref. this pic:

http://ampguts.realmofexcursion.com/...0D/inside2.jpg

1. The first (from the left) set of 12 fets (6 either side of the board), bound with 6 clamps to the sink.
Also the further right on either side of these is the same and have 3 legs but 2 of the legs are soldered together? Why is this?

2. What is purpose of the 8 caps around the fan. They are stabilising the voltage i assume? Part of a smoothing/rectification ciruit?

3. The board that sticks up by the 3 toroids?
I think it has a name? smcc board? Something like that.

I know it's a lot of questions. But if someone could please give me a run down of the various parts of the board and what they do i would greatly appreciate it!
I'll ask about the output side in a minute.

If anyone has any links or anything of the basics of class D design, please would you send me them.

Thank you.

luka 13th June 2009 07:26 PM

Hi

This is car amp so:

1.Those are output mosfets.
Those that have 2 pins together are diods, rectifiers... makes DC from AC...

2. To make DC you need rectified AC, and capacitor(s) make it solid DC.

3. I'm not really sure what you mean, but those toroids are output inductors of this amp. board is called PCB, if you wanted to know that, not sure..


And BTW, this is output side...

agithegreat 13th June 2009 08:14 PM

Hmmmmmm.
So what are these 20 fets???

http://ampguts.realmofexcursion.com/...0D/inside3.jpg
either side of the board. I thought they were output fets?

Also on the near side of the amp here, there are 4 random fets what are they?
http://ampguts.realmofexcursion.com/...0D/inside1.jpg

Yes it is a car amplifier.

I'm confused now, cheers for the help :)

luka 13th June 2009 09:21 PM

How many would you like to have?

Some amps draw 300A easy, some even put out more then 100A ac, on coz of this you need lots of fets to share current

Quote:

Also on the near side of the amp here, there are 4 random fets what are they?
Where? can you show on picture?

what are you confused about?

agithegreat 13th June 2009 11:17 PM

Yeh it's 3kw rms at 1 ohm.
So easily into 300a probably.

Half way up on the right hand side (not identical there....)

So what are the 20 fets doing then, if the 8 fets are output mosfets?
Thansk for your help.

luka 14th June 2009 06:42 AM

Well you know, 3000w amp, if this is true output, and can hold overall eff. of say 85% and pretty low voltage, say 12v for this amp, it would have to be 300A..


Those are probably rectifiers, I guess this amp has them on only one side, it could have them on both

yea 20 for input, probably 5 for every primary and it has 8? output fets [you dont need so many of them, coz current is lower, but voltage is much higher then on input]

agithegreat 14th June 2009 09:44 AM

I see, so the probable reason for the input fets blowing is too low a voltage.
Thus to still produce the same power they draw a lot more current.
Makes sense, thanks.

Also i found this, as i get about 110v across the 8 fets (output) and 14v ish across the inputs.
What do the 2 toriods do then between the set of 20 fets (input side)
http://ampguts.realmofexcursion.com/...0D/inside1.jpg
The caps by them, on this amplifier i a struggling to repair, are buzzing quite agressively. Wheras others of this model which work fine i have pulled apart do not make any noise other than the fan spinning and a tiny high pitched noise.

luka 14th June 2009 10:06 AM

Low input voltage is bad yes, they can fail too if output goes..


Those are two main transformers, making 14v to 110v. This is core of supply/amp

Sounds like caps could be dead, did you check if they are getting how? also did you check if there is pure DC on them?
Also what is amp current draw it on state?

luka 14th June 2009 10:06 AM

Low input voltage is bad yes, they can fail too if output goes..


Those are two main transformers, making 14v to 110v. This is core of supply/amp

Sounds like caps could be dead, did you check if they are getting how? also did you check if there is pure DC on them?
Also what is amp current draw it on state?

agithegreat 14th June 2009 10:44 AM

Amp current draw is minimal, i have blown my dmm so i cannot test the draw bit i can tell you it's tiny as it's running off a 4a battery charger which is paralleled to a pair of 3ah batteries.
I have tried it connected to a load and got no change in the condition of the amplifier. No power lights just fan spinning and caps buzzing.

I'll test the caps later. I just have to remove the entire board again.
So those caps will be part of a rectifier? Why would i need another low voltage other than the 12/14v side?

On my output side (specifically by the rca input connections and the gain crossover knobs) i also noticed that a resistor was getting very hot, i have no idea what it does, but it's not directly connected to the battery (+ve or -ve). I checked this using the conductivity setting on my multimeter.


All times are GMT. The time now is 11:53 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2