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Jordan Roy 26th October 2006 06:24 AM

Help the noob!
 
Hi there guys!

My crazy plan to make the 8 channel LM3886 amp is now officially started.

I got extreme noob questions for you pros.

My choice for the amp section is Mick Feuerbacher's version:

http://dogbreath.de/Chipamps/ThreeRe...reeResAmp.html

And my PSU choice is Carlos Machado (CarlosFM)'s design:

http://myweb.tiscali.co.uk/nuukspot/...clonesnub.html

Question #1 : Are they compatible? Is there any changes I would have to do on either schematics to have it work?







Here is the inside of the amp:

http://jrd-solutions.net/assets/imag.../ampspace1.JPG

http://jrd-solutions.net/assets/imag.../ampspace2.JPG

http://jrd-solutions.net/assets/imag.../ampspace3.JPG

http://jrd-solutions.net/assets/imag.../ampspace4.JPG

The 2 cds represent the 2 toroidal that are gonna drive the 2 main channels. One toroid for each channel. Here are their specs:

220 VAC primary, 50/60 Hz. operation. Secondary: 2*18V 120VA Si 2*4A Dimensions: diameter 3 1/2" X height 1 1/2"

The three other toroids you see are gonna driver 2 channels both


Question #2 : Is there any problem with the disposition of the transformers?











Here are the heatsinks I wish to use:

http://jrd-solutions.net/assets/imag.../heatsink1.JPG

http://jrd-solutions.net/assets/imag.../heatsink2.JPG

http://jrd-solutions.net/assets/imag.../heatsink3.JPG

Question #3 : Do you think there might be an overheating problem with usign 1 heatsink for 2 ICs?





Thanks in advance for your answers!

To come: More noob questions... ;)

Jordan

Wynand 26th October 2006 07:43 AM

1. There's more than 1 power supply design on decibel dungeon's page. Which one do you wanna build.

2. The Amplifier schematic is nothing more than the datasheet schematic.

3. Have a look at Russ White's version of the Mauro Penasa amplifier. This amp is EXTREMELY Good. Many say so. So do I, why??? I've built it(Mauro's).

The benefit of a design like Russ's is that the power supply is on the pcb. That eliminates PSU PCBs and personally I don't like caps hanging on pins of IC's...It will break, if not now, in 10 years.

4. Have you bought your other transformers yet? If not Why not go for a higher secondary voltage? Look at Russ's design again.

I personnaly would like to build Russ's because I've got a huge heatsink that I think can take 6 amps. Then I want to mount them all vertically, spaced with hex spacers and then corner brackets on the sides. Nice and Sturdy.

5. Mauro's design also has protection on it. Its a bit more effort, but I sleep more tightly knowing my flat won't burn down, or my speakers won't blow.

Wynand 26th October 2006 07:46 AM

Sorry, your question.... The Basic aplifier should work on any powersupply, limits being max dc voltage which you can find in the datasheet.

18 volt secondaries is ok, a bit low though for the Mauro amp.
18*1.414=25VDC. Exactly what my other LM4780 amp runs from.

Wynand 26th October 2006 07:53 AM

Afterthought....
 
Afterthought....

There's nothing wrong with the basic schematic(i've got an amp like that aswell)....
I just like the fact that everything is on the same PCB.
Power Supply, Amp and protection.
Coupled with the fact that Mauro's amp is a single side PCB.
It makes construction a breeze!!!

Nordic 26th October 2006 08:16 AM

Think one CPU heatsink will be enough?

Wynand 26th October 2006 08:48 AM

Howzit Nordic, long time no see!

Weren't you looking at a 6 channel preamp a while ago?

AndrewT 26th October 2006 09:39 AM

Hi,
the quiescent dissipation from some of these chipamps is quite high.
Check your datasheet.

One unblown CPU sink may be enough for one high bias chipamp or two low bias chipamps. But they are going to run hot if you ask them to play party music. (who will hold you back when all those friends come round to listen to your new creation).

But there is a solution.
Add variable speed CPU fans to each and they can run (or not) as the heatsensor demands.

Add plenty of case ventilation.
Are the sinks outside the case or in beside the guts?

Jordan Roy 26th October 2006 02:48 PM

Thanks fo the replies guys!

1 - Your point on the Caps that might break sometime is good. But the reason why I chose that design is because of the really short signal path lenght. Regarding the advantage or short signal path, would you still recommend usign a board?


2 - The reason why I linked to that page in Decibel Dungeon is because I know I want a snuberized PSU but I just don't know wich design is best suited for the amp design. What are your opinions on that?


3 - Here is an illustration of the disposition of the heat sinks in the amp.

http://www.jrd-solutions.net/assets/...pheatsink1.JPG

http://www.jrd-solutions.net/assets/...pheatsink2.JPG

I have read the datasheet but since I have not much knowledge in electronics, I just don't really understand their specs.

The other alternative could be to attach the 2 main IC's ( those channels are probably gonna drive the main speakers) to the case, wich is aluminium, and attach the 6 other IC's (wich are gonna drive satellites and center channels) to the heatsinks inside the amp.

What do you think?

Nordic 26th October 2006 02:55 PM

Hey Wynand... Mooi dag innie Kaap vandag!!!!!!!

I'm always chopping and changeing between projects, but I get a few done every month.

I pretty much know how I want to do my 6 channel pre... using 3 ECC88 valves... got one driving my Rev c at the moment, butI think I may have reached the end of my chipamp route... sure I got a few more chips that need to be used up, but after that I'll focus on discretes and more valve stuff.. as well as PIC based interface etc... for a well rounded unit.

Jordan Roy 26th October 2006 03:48 PM

Wynand,

I just read a bit about the Mauro Penasa's design. I has a lot of very good reviews! How did you do it? I guess it would be a good altenative since everything is straight on one board. What transformers aren't compatible with the design?

Jordan


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