oneplustwo F5 build thread

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#21
I am cought-up in same situation, got the original boards and the updated techdiy parts.

Here's the "un-official" missing parts list: 2-100K resistors
4- .47 3w resistors
4-47 resistors
4- 2.2K resistors
4-1K resistors
4-150 resistors
4-10K resistors
If you have boards with a status LED, you can use "un-used" 4.7K resistors
from the kit.

I ordered the missing ones staying with Dale's CMF series.

Please, correct me if i did a mistake somwhere guys!...
 
#22
One+2,
if you are using a CRC filter for your power supply then the umbilical comes to your aid to assist with attenuating the unwanted frequencies that get past the rectifiers.

Keep the transformer and rectifier and first stage smoothing capacitance in a very tight low loop area configuration. That is the first part of your rCRC giving you r = lead and secondary resistance. C = first bank of capacitors.

The next stage is effectively located in the power amplifier box.
As you may already know, an LC filter performs better than an RC filter, when looking at attenuation of the unwanted versus the voltage stability at the output.

Think of your umbilical as a combined L+R where L = very low value and R = very low value.

Without adding any discrete inductor, nor adding any discrete resistor, the the umbilical impedance provides the L+R in the second stage filter.

This results in a rC(L+R)C cascaded filter. This performs very well if the impedances at either end of the umbilical are kept low.
The attenuation of the unwanteds improves as the L & R of the umbilical increases.
And just to help you along, the inherent core to core capacitance of the umbilical also aids attenuation of VHF trying to impinge on an exposed umbilical.
Use that to your advantage.
 
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#23
Interesting. Thanks for the detailed response. If I may ask a follow up question, is there any special grounding scheme I need to follow as a result? (for context, I plan on having a 3 foot long 4 conductor umbilical with 14ga wires terminated with speak on connectors.)
 
#25
Read the links Andrew speaks about. Good stuff.

If you are going to have an outboard PSU you are going to need at least 2 more capacitors...

Put the transformer, bridges, and a pair of caps (Say 10,000uf or thereabouts and 35v or more, remember, they are going to get the brunt of the ripple) in the outboard case. Your red PSU board will be in the case with the amp circuit boards.
 
#26
Wow... this is complicated. I read through the links but only understood a small fraction. I'm a mechanical engineer... not smart enough to be an EE! 🙂

Would it be any simpler if I kept the rectifiers in the amp case and had AC go through the umbilical?

Maybe I'll just stick with the one box solution...
 
#27
It's not that big a problem, and that article does make it seem much more complicated than it really is.

If you do choose to do the 2-chassis approach, you should make the umbilical DC, so the Transformer, bridges and 1st set of caps are in the same box.
 
#28
Do you have any estimate of the thermal rating C/W/3" of those heatsinks. I am using Heatsink USA E007 heatsinks which are somewhat larger: 10"x7"x2.5" 24 fins, which has a rating of .7 C/W/3".


oneplustwo said:
No pictures yet... but here's where I'm sourcing parts from so far:
...
Heat Sinks:
Got the ones that Antek uses for this enclosure. $25 each shipped with the trafo to help minimize costs (also ordered a B1 trafo and small heatsink.)
...
Click to expand...
 
#33
Hmm... Uh oh. Did not catch that critical detail. But if I do my math...

0.6 C/W/" with 5" long heat sink = 3.0 C/W.

At idle, 62 watts divided by 3.0 is just over 20 C which is what I was aiming for.

Is there a mistake in my reasoning or am I good to go?

-J
 
#34
oneplustwo said:
Hmm... Uh oh. Did not catch that critical detail. But if I do my math...

0.6 C/W/" with 5" long heat sink = 3.0 C/W.

At idle, 62 watts divided by 3.0 is just over 20 C which is what I was aiming for.

Is there a mistake in my reasoning or am I good to go?

-J
Click to expand...
My guess is that the Antek rating of .6 C/W is for that particular dimension heatsink, and the calculation should be dT(C) = .6 C/W * 62 = 37.2 C temperature rise above ambient.

Here is a useful resource about heatsinks: ESP - Heatsink design and transistor mounting.
 
#37
Wow, my math sucks after being out of school for so long. Couldn't even properly keep track of the units.

I will say, Antek claims it can dissipate up to 150W/channel so I have that going for me. 🙂

Thanks for the resources, I'll do some reading.

Ultimately, I'll probably just try it as is and see how much rise I get with an actual measurement.
 
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#38
I believe (although I am still learning about heatsink's myself) if the material is rated at .6 C/W per inch then your 5 inches of heatsink material should be rated at .6/5= .12 C/W.

At 180 watts of dissipation the heatsink will be 180*.12= 21.6 degrees celsius above the ambient Temperature.

This seems to be just about right.

If I am wrong about this please somebody jump in here and correct me on this !!!

I have been scoping out heatsink's for my build and I have been thinking of using some Ximatec CPU coolers.


http://www.newegg.com/Product/Product.aspx?Item=N82E16835233082

For $30 this one is rated at .15 C/W at least and is fairly quiet with a fan at 16-24 dba.

XIGMATEK

One of these will allow 333 watts of dissipation at temperature rise of 50 degrees celsius.
It maybe a bit on the warm side with a total heatsink temp. of 75 degrees celsius.
But, It is still below the safe limit for the devices as long as the heat pipe don't explode.
It is not uncommon for these to be run at levels of 200 watts or so.

I am considering about 2 to 4 of these would be good per channel for a Turbo F5 build.
I will mount these to a thick aluminium or copper bar heat spreader to mount the output devices to.

I am anxious to see how your build turns out.

The only thing holding me back right now is were to source the JFET's so I don't end up paying so much for the shipping for just a few pieces.

Keep on DIYin'

jer 🙂
 
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