Modular mic - tube/solidstate, custom wooden case, interesting PSU case, pics...

Rossi · May 2, 2011

I'm not easy to impress, but this is pretty insane. In a good way!

Grooveteer · May 2, 2011

That's just beautiful! Congratulations!!

snipsnip · May 2, 2011

amazing! really really amazing!

okgb · May 2, 2011

Fine craftsmenship !
it could be a comercial product , No wait
most comercial stuff doesn't look that nice

Gus · May 2, 2011

To add to the connector issue.

How hot do the power semiconductor devices without heat-sinks get in the power supply? I did not see any heat-sinks in the pictures.

renx · May 2, 2011

Thank you guys one more time for all of your nice replies.

Gus:

Excellent question!

The voltage regulators are the LM317T in a TO-220 case which have thermal resistance junction-to-case = 4 K/W and junction-to-ambient = 50 K/W and a max junction temp = 125C.
I presumed that the maximum ambient temperature would be 40C.
Now, the high voltage rail (160V) regulators dissipate around 50mW (pre-regulator) and 30 mW (main regulator) which means that they would need a total thermal resistance from junction to ambient to be smaller than 1700 K/W or 2833.3 K/W and these conditions are over satisfied by the TO-220 case itself (50 K/W). In other words, these devices dissipate very little heat because only 10mA flows through them.
If we look at the most stressed regulators, the ones on the 6.3V rail, which are used to power the tubes heater, we have to consider a possible usage of the heat sinks.
The current flowing through both the pre-regulator and the main regulator is around 250mA so the power dissipation is 1.54W and 0.708W.
In this case the needed thermal resistance would have to be smaller than 55.2 K/W for the pre-regulator, and smaller than 120 K/W for the main regulator which is also satisfied by the TO-220 case.
From the above mentioned, one can conclude that no heat sinks are required in this design, unfortunately things could go wrong so a reserve was made.
It is not on the PSU pic I posted, because it was taken before, but I did place some heat sinks on these regulators.
What is visible on the posted pic is the white line on the PCB around the regulators which is actually an outline of the heat sink "footprint".
I used heat sinks with a thermal resistance of 21 K/W and when you add junction-to-case and thermal pastes thermal resistance you roughly get a 26 K/W which allows 3.27W to be dissipated by each regulator - more than twice I needed.
I would post some pics of the PSU with the heat sinks on, but the mic is not in my possession at the moment.

gemini86:

The price for one PSU case made out of 2.4mm thick FR4 and with two panels (front and back) was 27 euros + 7 euros for spray painting = 34 euros.
The price for one raw aluminium case (no sanding and no anodization) of the same size (2mm thick) for an order of 10 pieces (MOQ) without the front and back panels was 41 euro each.
These prices vary from country to county, I live in Croatia, maybe you could get better prices in your country?

Regards, Renx.