F5X -- the EUVL Approach - The Build Thread

> Are the 24pcs of 1k ohm Fukushima resistors for the CRC boards?

24 pcs 1R MPC74, not 1k I hope.
They are for the CRC board.

> We'll be using CRC until the regulator boards are confirmed to be working, correct?

Yes, because the mechanical parts will cost a bit.
Nic will get a set in a couple of weeks, so he will test and then report.
You can then all make up your mind whether to zse CRegC at extra cost, or stay with CRC.

> I have done up my control board and waiting for ashaw to provide instruction on testing.

It appears that there is still a minor bug in the PCB.
We are sorting this out on Nic's 3x protection boards.
Once that is done and proven the solution will be published.
To make life simpler for all of you, please put your protection boards on hold, including soldering.
Bug fixing is easier with an unsoldered board, but Alexis'll also provide a solution for soldered ones.

In the meantime, thank you for your patience.


Patrick
 
Fukushima resistors

This is the one.
 

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Question regarding thermal compound. I read through the Linear Audio article on the F5X case/Class A chassis design, and there was a discussion about isolation pads. It sounds like the Keratherm pads do not require thermal compound if the clamping force is high enough (and it may provide better performance this way as well). I'm guessing in our situation, we are not going to be able to achieve a high enough clamping force to justify omitting the compound.

What have you guys done on your builds, and what would you recommend?
 
No thermal compound required for Keratherm.
It is the whole idea behind such a elastic pad.

If you want to experiment, use a 9V battery and a 10k trimpot to provide a Vgs at any MOSFET.
You may use e.g. a IRFP240. Mount it as if in your normal F5X.
Apply Vgs of say 16V and set the trimpot such that bias is 2A.
Measure both MOSFET case temperature and heatsink temperature immediately next to the FET.
You should find that the difference is between 2~4°C.
Then you are doing just fine.

One or two degrees difference is not going to kill your FET.
The thermal resistance between substrate and case varies a lot more.


Patrick
 
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I'm ready to stop testing and start listening, so before I close it up for a few weeks here are a few pictures of my build.
Everything is perfectly functional with the exception of the output protection circuit where there still are a few bugs to fix (at least in my builds). Power and relay control works so it is functional enough to be used.
 

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I am about to "dock" the transformer cradle, but there is one thing that does not convince me.......

The cradle is fixed to the chassis by screws from the top side. However there is no way of tightening (or even insert) these screws when the back-panel has been wired up - and absolutely no way when the cradle is in.
A tiny construction flaw;)

Unless Patrick stops me with a better idea, I will glue in bolts on the chassis (in)side, drill out the cradle, and fix with washer and nuts from the button.....
 
> A tiny construction flaw

No.

You should mount the cradle onto the chassis first without the top plate and the bottom covers.
Once it is tightened and fixed onto the chassis, you then mount the bottom covers, making sure there is a gap between covers and cradle.
Then you put the amp in its final position.
And only then would you loosen the screws and lower the cradle onto the floor to separate it from the chassis.

Of course you can always choose to just leaving the cradle bolted tightly to the chassis.

Mark, correct me if I am wrong.


Patrick
 
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>You should mount the cradle onto the chassis first without the top plate and the bottom covers.

This is the difficult part. I will get myself a magnetized long-necked screwdriver and hope for the best. In daylight I can actually see the hole where the screw goes so it is possibly doable:)
 
[There are also clips to be put at the end of the screw driver with which you can "connect" the screw to the end of the screw driver. ]
You may use a little bit of "blue tag" to glue the screw to the screw driver.

BTW, I suggest to do it like this.
Put a paper, say a newspaper, on the table. Put the F5x case on it.
Mark the outline of the case and mark the location of the 4 cradle screw holes on the paper.
Raise the F5X case approx. 5mm on the foots by any means, books/ plywoods.
Put hte 4 Cradle mounting screws inside their holes respectively.
Take away the F5X case.
Put the cradle assembly on the paper with the mounting holes "target" to the markings previousely marked.
Put back the F5x case to "cover" the cradle assy to sit on the "books". This way the back mounting screws will not drop out. Align the Case with the outline markings.
Use a "long" screw driver to tighten the mounting screws. You may need to "search" for the tapped holes a little bit. I sugest to do the back mounting screws first because there is more space.
Take away the books after you managed to tighten all acrews.
Turn the whole case upside down. Turn the 4 "M4 self-lock nut" to the 4 mounting screws to prevent accendential loosen the mounting screws later on.
Do your wirings and listenings etc.
When you are ready, loosen the 4 mounting screws until the cradle assembly just touched the table and unscrew 4-5 turns more (2-2.5mm floating).
Enjoy DIY!
Mark