Beginner to build an Aleph30 needs some help

[Zen Mod]

that looks pretty well and sufficient , now

regarding biasing - give me exact schmtc you are going to use , and I'll tell you what to fiddle

in a meantime - print this one (tnx to Algar_emi , as always ) and stare at it ( as in Goat ) few days

principle is the same

 

[cowneko]

It's this schematic (BrianGT mini Aleph)

 

[BobEllis]

Adjust R13 (TBD) Higher values mean higher current. It can go anywhere from ~10K to infinity.

 

[cowneko]

Thanks BobEllis. R13 is now 47.5K.

I mesure the resulting current across R13 right?

 

[BobEllis]

Nope, resulting current is measured across the Source resistors.

 

[cowneko]

Ok, so I mesure the current across each 0R47 res on the header boards right?
And I shall aim for 2A.

How can I find the right res, shall I use a trim resistor in place of the 47.5K in R13 then mesure it after reaching 2A?
If yes, how can I solder this 3 legs trim res (100k) in place of standard res, Is one of the legs go to ground?

 

[BobEllis]

On the Aleph 30 schematic posted long ago there was a chart showing the current per fet that various values of your R13 would produce. Since NP has pulled the schematic from his website I won't post it here.

But the chart numbers are
R13 I/ Fet (each)
47K5 0.8A
33K2 0.6A
30K2 0.5A
26K7 0.4A

You can use these to extrapolate other values. You don't need to hit exactly 2A, I think I'd drop 39K in and call it a day.

 

[cowneko]

Yes, calculation gave me something like 38.73 for 0.7A/Fets, so yes, 39K shall be good for nearly 2A

Thanks a lot.

However, do you agree with Zen Mod about going fanless (Zen Mod, I don't disregard your advises, don't get me wrong), as it will cost me quite a bit more than the fan design I already planned?

 

[Zen Mod]

point is that you don't need to scorch innards of amp

I'm not arguing with fan solution , just pointing that caps , xformers and even Jfets don't like oven temp - without fan

with fan - and tiny holes area , there is no benefit ............. while increasing uncertainty/eveness of air flow

 

[cowneko]

I try to find small enough resistors to replace r13, I only can find 0.4w 1%, instead of 0.5w, good?

 

[Dennis Hui]

I try to find small enough resistors to replace r13, I only can find 0.4w 1%, instead of 0.5w, good?

That's fine.

 

[cowneko]

res ordered 😀

Well, this is my last Enclosure design, it's a mix between the two older ones; a bottom plate with lots of venting holes and a top plate with an extracting fan (a slow and quiet 140mm fan)



Do you validate this design?

 

[Zen Mod]

 

[cowneko]

God! Zen Mod, you've made my day 😀
I'll go tweak it a little and make my order!

Next week will be interesting 😉

 

[Zen Mod]

you know - you can always put some risers between bottom plate and heatsink , same as between top plate and heatsink ;

say that 5mm around circumference will do the job

that way you can entirely avoid perforation of plates

 

[BobEllis]

Way to throw a wrench in the works ZM!

 

[cowneko]

Way to throw a wrench in the works ZM!

Quite true 😀
However, Zen Mod, this is a brilliant idea, but I doubt the enclosure can keep its stability with gaps between plates and heatsink (think about bending at the spacers), and optionally it will be less sexy, so I think I'll stick on the last design I posted (Well I shall admit that I'm also a little tired tuning this damn thing 😛).

I started the drilling and taping process on one of my heatsink. I still have to drill the fets holes, but I need to do a test fit before.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[cowneko]

Test fit!! It matches, yeah😎

 

[BobEllis]

Looking good.

 

[cowneko]

Fets fitting.......



PS: In the first pictures I've mounted the header boards in the wrong direction