Aleph J illustrated build guide

[Zen Mod]

metal case must be on safety gnd

audio GND - it is clever to have it connected to safety gnd in shown way, especially if using switchers

frankly, I trust much more in regular xfrmers, safety wise

even if all of this is academic, why risking of being unlucky one in milion?

and, amps are much less prone to hum problems when grounding is proper

one more thing - investigate with ohmmeter - is output GND on switcher floating , or is connected with switcher case ?

if connected, no NTC needed, you already have direct connection between amp case and audio gnd

 

[ElliJ]

Ok that makes sense. I will investigate my switchers ground and if it floating I will add a NTC there like my diagram.

I will only need one NTC for the amp and one NTC for the psu depending on the switchers ground. Got it.

Thanks ZM

 

[Zen Mod]

you don't even need mains NTC for amp - I can bet that switcher is soft starting device

so, just one NTC for amp, between Audio GND and safety GND/case, and that only if switcher's output GND is floating, ref. to its case

 

[Mark Johnson]

Lots of switch mode power supplies actually include an inrush current specification on their datasheet. For example, here is the one that Nelson Pass supplied with his VFET amplifier kit, sold by lottery at the diyAudio Store. Apparently this one is NOT a soft starting device. So, check the manufacturer's datasheet for your SMPS and see what it has to say about inrush current.


_

 

[ElliJ]

Almost finished. The case is a work in progress as it needs paint, feet and a decent faceplate. I had both channels at about 410mv and near 0 dc offset after 30minutes of being on. I could not resist having a listen. First off it is dead silent, no noise could be heard when my ear was on the tweeter. The highs and mids were very clear. I only listened to Hotel California at low volume and I could hear more detail than normal. I normally use a quad 405-2 and the AJ is noticeably more musical at low volume. I will try it at a decent volume when my daughter is not sleeping.
At the end of the song the 2amp fuse blew, I changed it and the amp carried on. Should I put a 3amp in there?

 

[Zen Mod]

which fuse?

 

[ElliJ]

Mains 230v 2amp slow blow

 

[Zen Mod]

Fuse=Donut VA/Mains Voltage, then first close standard value, Slow Blow

depending on Soft Start used, go one notch up

no biggie

 

[ElliJ]

500w llc smps +-24v no soft start.

 

[andynor]

4A @ 120vac should do it, at specced Iq, according to: https://www.firstwatt.com/pdf/prod_aj_man.pdf

2A @ 240vac. You sure you set the Iq right? Not familiar with your PSU, only used to linears. Which in a class A SE circuit with CCS either blows the fuse at turn on, or never, or almost never

 

[Zen Mod]

500w llc smps +-24v no soft start.

if SMPS, look in datasheets, maybe you'll find declared value

 

[Vunce]

Doesn’t the SMPS have its own onboard fuse?

 

[ElliJ]

No data sheet, it’s an Aliexpress It already blew a 2amp @ 230vac? I have 3amp slow blows. My psu does not have any any caps, it’s just an external smps.
Aliexpress 500w

 

[Zen Mod]

then 3A

 

[ElliJ]

Thanks. I will try a 3amp.

 

[e_fortier]

If you enlarge the pictures of the AliExpress link you provided, you can see a primary fuse on the power supply itself rated T4A, 250V meaning 4A slow blow. I would use 4A or 3.15A to prevent blowing fuse.

Your cat will love this warm cozy spot..👍

 

[ElliJ]

I’m sorry everyone, I think I wasted your time last night. The fuse hadn’t blown, the smps had tripped out. The tiny thing can’t handle 200w continuous for more than 10 minutes. I even put it in a larger enclosure this morning and that did not help, the Heatsink still gets too hot. However I have managed to test the amp and I am impressed, absolutely totally silent with better bass, mid and treble than my 405-2. I’m sure it would continue to get better after a couple of hours of being on.
I still want to use an external smps so I have found a 1000w ±24v that should cope with an AJ. It’s LLC soft switching.
1000w smps
What is the lowest I can set the bias? Maybe I can run the amp on less power for a bit until I sort out a better smps.

 

[Vunce]

If your set on using an SMPS for power, I would highly recommend looking into one of Sami’s (MicroAudio) units. The quality is far superior than anything your going to find in Ali.
https://micro-audio.com/store/product/smps500-cla/

 

[Extreme_Boky]

Meanwell SMPS sold with ACA will do the job nicely. I checked them on the bench with 6 ohms 100W resistor load and they worked stunningly well. The voltage drop was only a few mV at 4A constant draw. I tried them with my Aleph J and the sound was really great. Just one thing: remove the ground connection at the output, so that the DC floats with reference to the mains ground. Then you can connect two in series for +24V, zero, -24V.

Heck, you could even get 4 of them for a true dual mono construction.

 

[ElliJ]

I will try a fan in the external psu case. I will also try with the psu case open when there are no people or cats about and then a mesh top could be a solution. When I was running it on my workbench/table with only one channel it was fine and stayed cool, it was naked and dangerous just sitting on standoff’s.