Build This MoFo!

[Dennis Hui]

I think it's the equation for the inductive reactance:

X = 2 * pi * f * L

So if X = 8 ohms, L = 0.06 H, we get f ~21.2 Hz.

 

[Eric]

Thanks, Dennis! I've seen that formula before, I just haven't used it in this context... Now I get it.

 

[kp93300]

thank you.

I want to thank all the people who have helped me in my build.
It is a very nice and simple amp to build.
bass is surprisingly good driving Markaudio 12 P full ranger.
The sound is much more engaging and toe tapping . It sounds much better than many of my more complex build.
My major problem is heat management . I have to use fan to achieve a bias of 1.8 amp. Power supply is 24 V dc.
Is there an audible sound difference with a bias of 2.5 amp ?

 

[autox]

Put the fans on top of the fins. Experiment with flow direction.

 

[kp93300]

I did consider the fan blowing towards the fin or the top of the heatsink.
The problem is the difficulty to mount the fans .
Any suggestions ??
i am considering whether to do another build with a 2X size heatsink

 

[Vunce]

I did consider the fan blowing towards the fin or the top of the heatsink.
The problem is the difficulty to mount the fans .
Any suggestions ??
i am considering whether to do another build with a 2X size heatsink

Hi kp93300,

Dell CPU coolers work great, I’m running 2.5A bias without a problem 😀

Regards,
Vunce

 

[autox]

I'd start with tape just to figure out what works. Then consider there's no need to point the fins outward. You could point the fans directly at them.

 

[kp93300]

Vunce, what are the dimensions of the heat sink ?

 

[zman01]

kp93300,

Congratulations on your build, and Happy New Year! 🙂

What inductors are you using in your MoFo amp?

 

[kp93300]

Hi zman01,
the inductors are made in china. 50mH and specified for 4 amp . the resistance across the terminals is 0.9 ohm.

 

[Vunce]

Vunce, what are the dimensions of the heat sink ?

Hi Kp93300,

Dell FD841 dimensions

Aluminum fins: 88x75x85(w,d,h)
Mounting base: 88x65
Overall height : 160mm (base to pipe tip)

You can find these used units on marketplace’s similar to eBay and such, they do not include a fan, you have to add that yourself. The other solution is to buy new aftermarket units where the fan is already connected to the CPU cooler. Power is from a 12vdc source feeding a PWM fan control module w/temperature sensor.
The Noctua Nf-a8, 80mm fans always stay on the slowest speed and are near silent.
It’s not a classic Class A ‘look’ and you have to get creative to mount the MoFo board but, even with the additional circuitry it’s more economical than big heatsinks, saves a ton of weight and cooling performance is amazing!

Regards,
Vunce

 

[xrk971]

Yes, with good fan cooled CPU heatpipe cooler, one can run a Class A at 150w dissipation (assuming one is using a MOSFET rated for 450w, 150w is only 1/3rd so no problem) and fins stay relatively cool. It's quite amazing what modern thermal engineering aimed at server racks can do vs natural convection based on massive slabs of aluminum fins and slow rising air buoyancy (the Grashof number). Imagine a MoFo at 37v and 4.25amps. 😀

The CPU cooler that Vunce is using is an excellent one with a very large copper surface that can handle two MOSFETs side by side if needed.

That is one badass looking MoFo, right out of a Mad Max movie!

 

[prazza1]

Very nice looking 😀

 

[e_fortier]

Hi kp93300,

Dell CPU coolers work great, I’m running 2.5A bias without a problem 😀

Regards,
Vunce

Hi Vunce

I love the look !!

Eric

 

[e_fortier]

Hi guys

Found these FD841 on eBay but wonder why one of them doesn’t seem to have copper pipes...looks like aluminum pipe which doesn’t make sense for optimum heat transfer.

Thanks for the hint Vunce.

Please provide a link for your PWM temp sensing control.

Thanks

 

[Vunce]

Hi Eric,

The FD841’s come with two different copper base designs.
The ones with the rounded indents for the screwdriver to fit down past the aluminum fins has a large copper base that can fit two mosfets next to each other.
The coolers with square fin indents have a smaller diamond copper base perfect for a single mosfet.
I haven’t seen the FD841 with silver pipes?

12V PWM PC CPU Fan Temperature Control Speed Controller Module High-Temp Alarm | eBay

Cheers!

See pics:

 

[e_fortier]

Thanks a lot Vunce, this is great infos.

The one I’m wondering is the unit on the right side from my previous pic. It’s probably just silver paint.

Thanks also for the link.

Eric

 

[prazza1]

I read the 170 pages, but in the end I did not find the answer about the power supply: is there a definite gain to switch from the SMPS power supply to the linear power supply (transformer + diode bridge + C).

 

[vdi_nenna]

IRFP250 Mosfet

Why was the IRFP250 mosfet chosen?

 

[tubesguy]

Hi Vunce

I love the look !!

Eric

Pretty cool, in a technology-in-your-face way. I'm thinking of the "Pass" chassis you've used, but instead of the big heatsinks, one of these per chassis, sitting on top, with the mosfet sandwiched between the chassis and the cooler.