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can you see a problem with this set up ?

glenn jarrett

glenn jarrett

pfm Member
i have been offered 2x transformers with 240v pri (BONUS) and 35-0-35 sec 220va rating
will be fed in to 6x 10000uf with 8a 200v diodes to power a single ncc200
whats your thought go for it or buy 2x 300va 230v ones which will probably buzz on my mains :rolleyes:
20210307_155917 by glenn jarrett, on Flickr
 
I’m biased because my mains supply is usually around 248 Vac so I’d take the 240v transformers. 220 VA will be more than enough with a single NCC200.

Don’t forget the coupling inductors for the PSU boards.
 
220VA per board means you would have a stereo amplifier with a transformer of 440VA so this is good enough IMO.
I always prefer by far two smaller transfos than one larger one to avoid any hum anyway.
On top of that, if your capacitor banks are using low ESR caps, you will never miss a beat.
 
When using a steel case as a heat dissipation device, I prefer to install a thermal switch to avoid overheating.
When I have the option, I always use a larger than needed aluminum heat sink for peace of mind.
 
glenn jarrett said:
will a 2mm pressed steel case be ok for the modules ?
Click to expand...

You will have to try it and see.
Steel is 3X less thermaly conductive than alu. This means that the heat from the U-sections will not spread by conduction all that effectively.
Convection cooling is helped by airflow (minimal in this situation) and cooling area (see above comment).
At hifi case temperatures there is almost no cooling by radiation.
It also depends on the thermal coupling between the output devices and the Vbe muliplier. If the output devices can get a lot hotter than the Vbe you could get thermal runaway.

Of course it depends how much power you are trying to dissipate.
2 channels with Iq = 50mA and 50V rails will result in 10W during no-signal conditions.
When driving speakers it depends of speaker efficiency, impedance and loudness.

I would recommend adding a 3mm alu plate under the modules to provide more heatspreading.
 
I have owned two and still own one Avondale monoblock power amps, both built by Les. The enclosures are sealed, no ventilation, and the boards are bolted to steel via the heat sink mounts.

You can affect emmisvity ENORMOUSLY by surface finish too - far more so than steel v. aluminium.
 
Rubbish! I would never use steel at all ever under any circumstances and I'd take mirrored aly over matt black steel all day long. Apart from heat dissipation steel is just really horrible to work with.
 
Vinny said:
I have owned two and still own one Avondale monoblock power amps, both built by Les. The enclosures are sealed, no ventilation, and the boards are bolted to steel via the heat sink mounts.

You can affect emmisvity ENORMOUSLY by surface finish too - far more so than steel v. aluminium.
Click to expand...


The effect of radiative cooling is low for hifi cases - see table 2 here:
https://www.heatsinkcalculator.com/blog/the-importance-of-radiation-in-heat-sink-design/

With a case temp of 50C, it is <<5% of the total cooling.
Inside the case, it is mostly conduction (sealed case). Outside the case it's mostly convection.
 
glenn jarrett said:
will a 2mm pressed steel case be ok for the modules ?
Click to expand...
As I've learned (painful memories), steel is not a good heatsink material. Therefore, I would strongly suggest you use something different. For a stereo NCC200, an aluminum base is adequate.
 
I have a Modushop Pesante 2U case bought from here its pretty basic pressed steel case but I was going to put 3mm slab of aluminium across the base so 400x300 roughly I assumed that would be enough to dissipate heat if not what about bolting with heat compound some finned heatsinks to areas needed?
 
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