LuFo Amp - 39w SE Class A from 28v Rail

[xrk971]

Less iron for sure but mH is about the same. Maybe one has higher current capability. The bigger one handles 10A I think - 1200W. Perhaps smaller one is 5A or 600W.

 

[xrk971]

But 600VA is plenty for a 40W amp.

 

[namghiwook]

I soldered LU1014D to adapter PCB like @lhquam's method. (link)
Indeed. it's working method.
@lhquam Thank you!

 

[xrk971]

I made a 5 part video on how to install the LU1014D’s onto these metal substrate boards here:

https://www.diyaudio.com/community/threads/assembling-the-lu1014d-ims-to-247-adapter.373273/

Not sure what Ihquam’s method is, but it looks like you did not get full melt and could be issue with thermal bonding between back of the JFET and the IMS board. 15W of power needs to flow through that solder pad.

Use a small hot plate/skillet and solder paste - that’s the easiest way to do it. I don’t think any soldering iron can provide enough heat to fully melt and wet the parts to fully flow the solder under the JFET.

 

[namghiwook]

@xrk971
Is this OK?

 

[xrk971]

Might be fine. What I look for is the concave interface of the solder against the substrate and part to show it fully wetted and is a thin layer. Your part forms a convex interface which might indicate the wetting was not complete and you may have a cold solder joint. Although it might just be that there is excessive solder so it forms a convex bulge. It may have higher thermal resistance. Did you use solder paste and a hot plate or wire solder and an iron?

 

[namghiwook]

I did it with solder paste and hot air gun below the pcb.
It's so hard to solder properly.

 

[xrk971]

Ok that’s just too much solder paste but the joint is probably good.

 

[marconi118]

any chance to build a lufo with a 230v Mot?
maybe fir 16 ohm speaker?

 

[xrk971]

The 230vac MOT will have 2x higher DCR so bias current will be 1/2. Thus, could be used for higher impedance speaker like 16ohms. But you may need more voltage swing.

 

[Plott]

Hi X,
would it be possible to mount the LU without soldering? I'm thinking of a kind of aluminum "crossbar" with which the LU is "pressed" against the mounting plate using thermal paste or against the heat sink using Keratherm?

 

[xrk971]

Yes, it depends on how much heat you expect to transfer. I have done this for a headphone amp with a few watts of dissipation. On the LuFo it’s about 12W I think so kind of on the edge there. The metal substrate TO-247 adapters are really the best and easiest to use solution.

 

[Plott]

Okay, thanks, so I have to try the soldering.

 

[Ryssen]

I am listening to my hybrid Lufo and it sounds fine. The front end is 6e5p.Now to the problem ,there is a beeping sound through the speakers about 1khz I can hear it if I am close to the speakers.
I am blaiming the switch mode supply...
How many VA should a toroid be that driver both channels?

 

[MEPER]

Do you have a lab-supply you could connect to verify if the SMPS is the problem?
It could also be from a PSU from another of your amps? ......just "hook it up" with some wires (if the voltage etc. match)?

 

[Ryssen]

Yes I do have a variable bench supply.How much power does Lufo draw per channel?

 

[pinholer]

The design shows 1.5V across the 0.5 ohm choke so that is about 3 amps per channel.

 

[Ryssen]

Ok thanks.

 

[xrk971]

The LuFo is very quiet with a good linear power supply like SLB.

 

[Ryssen]

Yes I am going to use SLB,is a 300VA 2x21v enough?