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

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#301
Hi Adason,
Thanks for pointing that out. Yes, does look similar but the coupled transformer load provides several key benefits: increased efficiency (50% thermal) since it’s a reactive load, inductive coupling feedback between the two legs makes it technically a SuSy topology so that the distortion is reduced, and the peak power is now 4x what is normally possible with the same rail voltage. 100w from 28vdc rail that makes 80Vpp is quite a feat if you think about it.
 
#305
X, your SUSY design certainly looks interesting. I'm curious what the difference might be contrasted to a simple bridged LuFo pair with a single similar center tapped choke.

Regarding the choke, I suppose buying two identical MOTs, cutting the welds to remove the coils and assembling the two primaries on one core should do the trick. Winding two new primaries (with a few more turns?) would be the alternative.
 
#306
The SuSyLu is a bridged LuFo with a center tapped transformer. Except the windings need to be such that it follows the phase shown in the schematic. The cross coupling between the two sides provides inductive feedback between +ve and -ve. The balanced or bridged load makes symmetric. You can skip the output cap - some people like the DC coupled output.
 
#308
xrk971 said:
Hi Adason,
Thanks for pointing that out. Yes, does look similar but the coupled transformer load provides several key benefits: increased efficiency (50% thermal) since it’s a reactive load, inductive coupling feedback between the two legs makes it technically a SuSy topology so that the distortion is reduced, and the peak power is now 4x what is normally possible with the same rail voltage. 100w from 28vdc rail that makes 80Vpp is quite a feat if you think about it.
Click to expand...

did I hear you say 'all you need is one watt?' 🙂
 
#309
@Ryssen,

I am considering building mine with enough space such that I try an MOT, then Hammond, then Lundahl. The MOT and Hammond are not that expensive, imho, and I could easily resell them to another enthusiast.

I should also work on purchasing and/or building up a simple analyzer with REW to see if there are measurement differences as well. This choke has a big role in this circuit, although I would assume that the role is really for LF extension and not much of anything else, but I could be wrong. The input and output caps are also important as wide bandwidth filters.

Best,
Anand.
 
#315
Well, one thing is for sure, there are a several attempts at sourcing a suitable inductor for LuFo other than the ones currently available. Hopefully another option will come out of this. Excellent work Fellas!! 😉
 
#316
Apart from efficiency, inductively loaded transistor power amps have something special.
Be it Susan Parker's Zeus, Grandinote Shinai, and hopefully (BTL)LuFo, they sound effortless and very natural.
Nice thing is that there are so many options for "tuning" in the voltage gain part (tubes; step-up transformers...).
 
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