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-   -   A few general amp building questions? (http://www.diyaudio.com/forums/chip-amps/198848-few-general-amp-building-questions.html)

thunk303 19th October 2011 09:51 AM

A few general amp building questions?
 
Hello all.


I am building a 6 channel LM4780 (Audiosector) amp using 3 kits.
Thought I would open this thread so I could ask any questions that come up.

1. Do the RCA connectors need to be isolated from the alloy back panel they are attached to.

2. Would I need to drill ventilation holes in the top and bottom plates or will the Conrad MF35-151.5 heat sinks keep it cool enough? The internal dimensions are 150x350x360

Cheers
Dean

thunk303 19th October 2011 10:12 AM

Anybody with experience putting the LM4780 in a semi-sealed case??

Dean

wintermute 19th October 2011 10:28 AM

Hi Dean, I would isolate the inputs from the rest of the chassis, you are likely to get ground loops if you don't. However I'd have a read of this post from 5th Element as well http://www.diyaudio.com/forums/power...ml#post2497568 He put all of his input rca's on their own sub panel (not isolated from that panel).

If your heat sinks are going to be internal then I'd say you will need ventilation. The fins on heatsinks are there to increase suface area to allow more heat to be exchanged with the air around, if it is sealed inside a box then the ouside of the box will be the only interface with the air and will become the limiting factor in your heat dissipation ability. Note I'm not talking from experience here (unless you count adding a decent fan to a pc case) :) and noting how big a difference a bit of additional airflow made to the temperature inside).

Tony.

thunk303 19th October 2011 11:43 AM

Hello Tony.

At the moment the only thing separating the connectors from the casework is paint, so I will open the holes up and add some nylon/plastic washers just to be sure.

The heat sinks are external, think big enough for use with an F5 and you have the idea. I guess I could leave the holes out for the moment and simple add them later if I notice any heat issues.

By the way, I have painted the alloy with $2.50 a can 'Fiddly'Bits' from Bunnings (2 coats primer + 3 coats black) and it looks great. To anybody in Aus, I am very happy with this product.

Cheers
Dean

thunk303 19th October 2011 11:51 AM

Just ordered 2 x Eminence Delta15LFA's from Essential Audio.
Should be here on Monday. The last major parts of the build so I am very excited.

Dean

wintermute 19th October 2011 11:54 AM

ah ok if the heatsinks are external then no problem! :) (and I just went to conrad's site and yes F5 size!!!)

I've seen quite a few chip amps with the heatsinks inside the case so thought that must be why you were asking :) I assume you are just worrying about heat from the transformer(s) and power-supply. With heat sinks that size I think they will help with dissipation of internal case heat as well ;) just monitor the temp of the top panel of the chassis for a while and if it seems cool enough you are probably fine :)

Tony.

thunk303 19th October 2011 11:59 AM

The panels will look allot better without holes up and down each side so I will follow your advice and see what happens. The Conrad gear is really well made and a competitive price if you ever need heat sinks Tony, highly recommended.

Cheers again
Dean

! 20th October 2011 03:47 AM

^ Consider at least putting some holes in the bottom towards the front edge (assuming the case has /will have feet on it) and some more holes near the top of the rear panel. That way you have full chassis flow-through and no holes visible as it sits for use.


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