Building an ultimate low power class A amplifier – my way

[tombo56]

You can use 10Ω for R23 with 100 nF for C12, as is found in most amplifiers.

 

[Vunce]

Perfecto!
Will start the journey towards audio Bliss this evening.😁

 

[TNT]

Vunce - how many amps do you own?

//

 

[Vunce]

A few…

 

[gary s]

He must have a very large listening room.

 

[poseidonsvoice]

Vunce is officially one of my diy heroes!

He understands that the journey and learning is most important, not how many amplifiers one has built or owns.

Best,
Anand.

 

[gary s]

My Latfets arrived this morning from Profusion, and have all other parts (I think) - how is your build progressing Vunce?

 

[Vunce]

I should have both boards completed tonight with the exception of the LatFets. I need to prep my heatsinks before they get mounted.
Question, I don't remember if Tombo addressed the initial setting of the trimpot before soldering?

 

[gary s]

Bias info in post #56 - but I see no mention of what the trimpot should be set at for initial start up.

Did you encounter any problems soldering on the 4 layer pcb?

 

[Vunce]

Not really, smooth sailing so far. I use a Hakko FX951 station, chisel tip for the components/faston tabs installed in the larger copper traces.

 

[gary s]

Good to know, hope all tests OK.

 

[limono]

I only read first post which sounded encouraging. My question is what other world class amps OP heard (had at his own place) to establish a reference point of what's achievable in real world ?

 

[Vunce]

LPCLA boards are stuffed and ready for the next step😁.
These boards are a pleasure to work with! No need to fear smd here, Tombo oversized the pads for very easy soldering. The BJT triplets were assembled separately and gently dropped into the pads, spacing is perfect. For C2 and C3 I used smaller 0805 size 4u7 caps from my stash with the same specs as the BOM.
The next step won’t be as much fun with winter setting in. The garage is cold and thats where the drilling and tapping magic happens.

 

[gary s]

Nice work Vunce, take a heater out into the garage with you, or a couple of Class A amps - just turn them on.

Keep us updated - are you mounting the Latfets under the pcb, or moving them out a bit?

 

[tombo56]

Question, I don't remember if Tombo addressed the initial setting of the trimpot before soldering?

It doesn’t matter much as bias is limited to about 1.4 A. But, for trimmer orientation as on the picture (adjustment screw head toward PCB top) turn trimmer max. clockwise for minimal bias.
If trimmer potentiometer is mounted with adjustment screw toward PCB bottom, then it should be set counter clockwise for lower bias current.

 

[tombo56]

LPCLA boards are stuffed and ready for the next step😁.

Looks great. Just a note for other builders. Thermal paste or pads are not required for KSA/KSC BJTs. They don’t dissipate much heat but paste or pads don’t hurt either.

 

[tombo56]

are you mounting the Latfets under the pcb, or moving them out a bit?

I don’t think that pins are long enough to mount laterals in a different way.
As for drilling the heatsink, just two screws are enough for very firm PCB mounting. You can skip top mounting holes.

 

[tombo56]

I only read first post which sounded encouraging. My question is what other world class amps OP heard (had at his own place) to establish a reference point of what's achievable in real world ?

Hmm. Did you understand first post as my claim that this is THE ultimate amplifier (best in the world)? If so, read again please.

I wouldn’t like that any subjective vs. objective discussion enter this thread. What I listened to in my home (or not) wouldn’t change what I’m able to design even if knowing that something could be better. There are limits and compromises.

Technically (by numbers) this amplifier is mighty fine. My subjective description is actually toned down as my opinion and impressions doesn’t count much (possible bias).
After other members build this amplifier, we will know more for sure.

 

[gary s]

So, if I understand properly tombo, you say the 2 screws for the 2 latfets are enough to mount the whole pcb?

 

[tombo56]

Yes. I have my evaluation build PCB that way and it is very firmly in position. You can press hard and PCB doesn't bend.