Burning Amp BA-3

[Backbones]

There is only one supplier of chassis kits which incorporate heatsinks in Europe to my knowledge and that is MODU in Italy. I have ordered a chassis from them in the past and they delivered without problems to UK. This is one way to go if metal work is not your thing. The build on these chassis is not perfect but at least you get metal parts of the right dimensions with drilled holes. However, I still ended up tapping holes in the heatsinks for the screws to hold the mosfets. The biggest issue I had was deciding how big the heatsinks had to be to cope with the heat output from the mosfets. It depends of course on how much bias you give the output devices but the bigger the better is the rule of thumb and to this end companies in the UK such as Birmingham Aluminium could supply some really big heatsinks and were very helpful on the phone. If you can then attach some metal work to this you are half way there. One aspect not mentioned is the importance of a sturdy base plate (which I think can be ordered from MODU). This is important because it needs to be stable and strong enough to support your transformers and large heatsinks. I have to say that the most difficult part of the build was the metal support infrastructure. The placing of the mosfets on the heatsinks is important also to allow them to dissipate heat for maximum efficiency and Andrew laid out some important information if you search the BA-2 thread.
Hope this helps.
Chris

[Tichu]

Thanks a lot BackBones !

I found their website, and the "Pesante Dissipante" high end ones with heatsinks on the sides seem indeed nice.
I will have to wait to get the boards, transformer and capacitor to decide on the depth I need.
Just hoping 400mm will be enough.

[Backbones]

If you look on their site they give the heat dissipation characterisitics of their heatsinks, however, the heatsink I think beyond 300mm (from front to back) consists of two 200mm heatsinks bolted together. I never did find out how this altered the heat dissipation characteristics. Instinctively (not scientifically) I would prefer the heatsink to be a single unit. In fact looking back on my experiences I would now start with some really big heatsinks with very efficient cooling characteristics and then look for some metal plates to bolt on after tapping some holes in the heatsinks. If the latter are fairly substantial they will physically take quite a load.
If this is your first build don't rush--good idea to get the parts and then you'll be better able to judge the chassis dimensions.
Chris

[Tichu]

Another Black hole for me at this point is the power supply parts.

I have a 2x20V 630VA toroid Xformer (for two channels), and I am wondering about wicht value I should put on C3..C6.

I guess between 47.000 and 100.000 uF per channel and per rail ?
I know some like to get big bottles there.

As for the resistor for the RC lowpass, I guess it should drop about 1 Volt at 3 Amps, so three 1 ohm / 3Watt resistors in parallel should be OK.

Am I burning ?

[altium]

What is part number of Q3 and Q4?
IRFxxx, some lateral or..?

[Zen Mod]

it's written in text

[altium]

Originally Posted by Zen Mod

it's written in text

2SJ313 and 2SK2013 output Mosfets

Okay, thanks!

[jormajj]

There is at least one more heatsink-chassis manufacturer in Europe, Fischer Elektronik ( Kühlkörper, Steckverbinder, Optoelektronik, Gehäuse - Fischer Elektronik - Home* - see "19" Plug-in box with integrated fins"). Their most massive chassis are the 400 mm deep SKE5400 and SKE6400 with 5U and 6U heights. Adding the Modushop 10 mm front plate to the 5U model makes a very nice box...

[Backbones]

Originally Posted by Tichu

As for the resistor for the RC lowpass, I guess it should drop about 1 Volt at 3 Amps, so three 1 ohm / 3Watt resistors in parallel should be OK.

Am I burning ?

Try four of the 3watt, 1ohm resistors as in the circuit diagram; then you'll have some headroom when things warm up.

As for the caps, the bigger they are the more difficulty the rectifier diodes have in charging them. I used two 10,000uF 63V Mundorfs per rail for each channel and they sound fine. More importantly in my view is to get the 10uF cap of the power supply right. Definitely go for a good polypropylene--I used an Ampohm (£10) and am currently getting good results with a Clarity Cap ESR rated at 250V (£8) which is smaller. I'm going to use the latter with the BA-3 front end.
Chris

[Solushunz]

i am impressed to this good posting comment...........