AlephJ Mimi! (Mini)

[MagicBus]

Bravo Jesper! You've been very productive building a whole new system this winter I'm syriously considering building alephJ mimi! It will be some time later but it's good to organize it. So, this is the final schematic I suppose. And I see you used Juma's psu. What is the transformers VA? Also why did you chose +/- 16V from initial +/- 24V?

[lykkedk]

Originally Posted by MagicBus

Bravo Jesper! You've been very productive building a whole new system this winter I'm syriously considering building alephJ mimi! It will be some time later but it's good to organize it. So, this is the final schematic I suppose. And I see you used Juma's psu. What is the transformers VA? Also why did you chose +/- 16V from initial +/- 24V?

Hi.

The schematic is final... I have shorted (omitted) the C1 capacitor, which is only used for balanced operations. -Some other values is changed a bit, mostly to use what i allready got in drawer.
I asked didiet78 to make the changes on his schematic and pcblayout; but due he is busy at work he didn't find the time to it yet... This is hobby right

The PSU i have designed with Duncans psu designer. The PSU is dual mono (2 x torids, 4 x rectivers, 4 x 33000uF, etc...) Unfortunately my schematic and pcblayout have gone due to some computer crash ; but it's just dual aka' Pass psu, nothing special.

I use two 120VA 15-0 15-0 torids, giving ~+19vdc 0 -19vdc rails, feeding the AlephJ_Mimi's.

If it was not because i allready got one of the torids, i would have chosen two 200VA types, but the ones i use, do the job fine... no problems.

The original minialeph, which has been around for many years, use also 15v torids, so we (ZM and others) did the calculations for that voltage. I think lower voltage is needed also for bringing the dissipation down, giving space for higher bias!

The chassis i use, goes around 50C or so, after many hours yesterday... so that is good i suppose.

Good luck.

Schematic changes :
R27' (Potentiometer) = 100K ohm (Was 50K)
R27 = 10K ohm (Was 47K)
R6 = 825 ohm (Was 800 ohm)
R12 = 221 ohm (Was 220 ohm)
R26 = 3,32K (Was 3,3K)

As i wrote earlier... sound is amazing, and setup is deadquiet...

Jesper.

[MagicBus]

Nice! Also, because this is my first dive in Pass Labs I can't find info about Q5 and Q8. Perhaps they are mentioned somewhere in this thread and I missed it...

[lykkedk]

Originally Posted by MagicBus

Nice! Also, because this is my first dive in Pass Labs I can't find info about Q5 and Q8. Perhaps they are mentioned somewhere in this thread and I missed it...

Oh great ... Thoose are IRFP240 mosfet's... preferable matched pairs i think (mine are btw)

Jesper.

[MagicBus]

Thanks Jesper! Coming soon... or later, but it will be for sure!

[lykkedk]

Originally Posted by MagicBus

Thanks Jesper! Coming soon... or later, but it will be for sure!

Those pcb's are for 2sj109, which you cannot get nowhere... I think Didiet78 have pcb layouts for 2sj74 too... Lets hope he is showing up again here soon?

It is what i used... I was in luck, having some 2sj109 in drawer, which was old but working.

Jesper.

[MagicBus]

Good to know! It seems we have to wait for Didiet78 - no rush at all - and then gather updated schems and PCB in one post.

[lykkedk]

As soon as i got the material, i will update post #1, to contain all information needed...

Jesper.

[MagicBus]

Hi again!
I hope Jesper enjoys his amp! I really would like to give it a try too. But I need to ask about some possible modifications.
My speakers require a couple of watts in average but they can benefit from large headroom. From the little I know and read about transistors, the max output power is related to the psu voltage rails. So I'm thinking to move from +/- 16V back to +/-24V. But this means increaced power dissipation. I could bias for lower idle current or could I? Would this affect performance/sound quality? Is there a safe minimum? OTOH, if the hotter the bias, the better the sound then is good to know and take my decisions about heatsinks...And a last question; How does bias affect the gain of this amp?

Thanks and please excuse me for this short hijacking.

[lykkedk]

Originally Posted by MagicBus

Hi again!
I hope Jesper enjoys his amp! I really would like to give it a try too. But I need to ask about some possible modifications.
My speakers require a couple of watts in average but they can benefit from large headroom. From the little I know and read about transistors, the max output power is related to the psu voltage rails. So I'm thinking to move from +/- 16V back to +/-24V. But this means increaced power dissipation. I could bias for lower idle current or could I? Would this affect performance/sound quality? Is there a safe minimum? OTOH, if the hotter the bias, the better the sound then is good to know and take my decisions about heatsinks...And a last question; How does bias affect the gain of this amp?

Thanks and please excuse me for this short hijacking.

Hi Magic... you don't steal anything i guess ...

A few post before this, i wrote the changes i did to the values! .. I think Didiet78 is a busy man at present; i asked him, if he could send me a new schematic and maybee a layout for 2SJ74's (The actual layout is for 2SJ109)
But hey this is DIY, and Didiet78 allready did an excellent job here

Regarding the technical specs. I think it is no problem regarding sound quality, but about raising the rails to 24v could be some parts have to change?

We hope an X fingers that ZM would look at this!

I am for sure satisfied with my amp. as is now!

Jesper.