Reasonable DIY Project Layout?

[bhjazz]

I'm finally going to get back to some DIY projects. One that's been boxed away is the Bijou. Part of the reason is I want to get a case design going in my head before I get too far on the soldering. And the problem with this is I really am not seeing the kind of case I was hoping for. Oh well. Onward.

My last ditch effort will be to use a fairly boxy-shaped HiFi2000 case. It is 12.20 x 11.02 x 3.14. My main concern, and the question for y'all: with this layout, am I going to pick up any RF with the transformer so close to the two amp boards at the front of the case? They will be about 6" away from a Hammond 370DAX . Here's a pic of the case size.

Thanks!

Brian

[ironbut]

I don't think you'll have any problem with the power transformer mounted on top of the case and the amp boards inside and that far away.

You can always breadboard it before you drill the chassis to find the optimum orientation for the transformer and boards.

You should consider the depth of the case. With stand-offs for the circuit boards and looking at the size of the footprint for the capacitors/heat sinks on the power supply board, make sure you have enough depth in your chassis.

[bhjazz]

Interesting. Although I was thinking of having these all in the same plane, so the transformer would be inside the case with the rest of the components. Should I consider a larger case (or two-chassis design)?

[Craig Sawyers]

The disadvantage of having the transformer inside the case is thermal. A transformer running at its rated VA will heat up to typically 50C+. Inside a case with little ventilation, it will get hotter, all of which will compromise the life of the smoothing caps and other components.

I'd stick it outside (it looks like a Hammond) and run the lead outs through grommets in the top of the case.

Craig

[dsavitsk]

You can easily get regulated 250VDC out of the Triad vpt230 series of toroids from Mouser. These will fit inside the chassis, not get to hot, and not have an issue with stray fields.

[swt61]

... and not have an issue with stray fields.

Strawberry's lesser known Brother.

[Craig Sawyers]

Well, the Triad toroids spec sheets say that the temperature rise at full rated power is 50C - which means 70C if the ambient temperature is 20C.

The only way to escape the inevitible temperature issue is to use a transformer with much higher VA rating than is needed. So if the nominal spec is 150VA, and you use a 300VA transformer, the temperature rise will be closer to 35C (resulting in a transformer temperature of 55C).

Note that is all with the transformer sitting in air at 20C - as soon as you put it in a case, the air temperature is a lot higher, and the transformer will run hotter still.

In this forum we obey the laws of thermodynamics (to misquote The Simpsons)

[bhjazz]

Since I already have the transformer, I'll probably just keep it and use it. I have no idea what else I could do with a 260-0-260 transformer. But it looks like my suspect of stray fields and the unrealized heat render that particular case not quite right. I'll poke around for something that is either more roomy or maybe even a dual-chassis design. Oy.

Thanks!

Edited February 1, 2012 by bhjazz

[Pars]

You could always breadboard the amp on a suitable piece of mdf or plywood and see (hear) what it acts like with the layout as you would need it in the case. Won't tell you about heat, but should tell you if the xfrmr is going to be a problem with noise, and would allow you to play with orientation.

[bhjazz]

I might do that, Pars, and Ironbut mentioned that earlier as well. I am currently digging through the Bijou thread on the Fi to see if anyone has had any issues with noise.

[livewire]

If you dont want to look at a big black lump sitting on top of your case, put it inside

and swiss cheese drill the back end of the casing in the area around the transformer to help with the heat.

To help with shielding, put in a steel "wall" between the trafo and the pcb section.

[bhjazz]

Interesting. Found this.

"...Here in Oz we have no choice, it has to be the 370 DAX (240V mains) & this seems to be a different beast altogether. I'm running an EZ81, choke PS, 6H30 & ECC99's with regal's & amphead's mods & it never gets much above lukewarm. You can certainly leave your hand on it, even after several hours. I tend to listen at a more or less constant volume (fairly low) & haven't noticed any variation in transformer temp."

So maybe the 370 would do fine with some reasonable venting if it really has to be in the case. I'll keep digging.

(but that ignores the heat from the EZ81...crap)

Edited February 1, 2012 by bhjazz

[n_maher]

The 300 series of trafos tend to be very conservatively rated. I ran one in my modified Wheatfield and it while spec wise it was nearly identical to the 200 series that it replaced it was probalby 50% larger and ran much, much cooler. I ran one inside the Exstata that I built and didn't have noise or heat issues.

[swt61]

I can see that there was some nice circle hole cutting involved there. Excellent work Nate!

[bhjazz]

The 300 series of trafos tend to be very conservatively rated. I ran one in my modified Wheatfield and it while spec wise it was nearly identical to the 200 series that it replaced it was probalby 50% larger and ran much, much cooler. I ran one inside the Exstata that I built and didn't have noise or heat issues.

The specs did confuse me a bit - they really are close. I'm happy to hear you used one with no heat or noise issues. If I can find the right case it might get me away from a top-side-only build a'la Cary Audio style. I do like the style, but already had a faceplate idea in my head that I wanted to work towards.

Thanks for posting the picture, Nate. It clarifies your layout and just how close I can venture using this transformer. If I can create good ventilation, I might be in good shape. Breadboarding still might be a good idea before I drop everything in and find out, ah crap....

Cool, thanks!