Aleph 2 IRF9610 matched pair

[Thago]

Hello

I'm currently building a pair of Aleph 2 monoblocs, base on Kristijan Kljucaric's PCB's. Which of the IRF9610's in this design (called T1, T2 and T3 on the PCB) is the matched pair?
Thx for helping me out!

[Zen Mod]

Originally posted by Thago
Hello

I'm currently building a pair of Aleph 2 monoblocs, base on Kristijan Kljucaric's PCB's. Which of the IRF9610's in this design (called T1, T2 and T3 on the PCB) is the matched pair?
Thx for helping me out!

link to schmtc,as first ; then we can help .

btw- why don't you ask him?

[Thago]

Hi

Here is the link to the schematic: http://www.kk-pcb.com/aleph-2.html

BTW: I did ask, without result untill now (I'm convinced I will get an answer from Kristijan, the question is when).

Thanks!

[Zen Mod]

Originally posted by Zen Mod



link to schmtc,as first ; then we can help .

btw- why don't you ask him?

I just can presume that on pcb mosfets are located according to little pic I attached
anyway- you are on your own here ,regarding physical placement .

T1 and T2 on my little pic needs to be matched,as tight you can

[Lau700]

Hi,

I asked some questions to Kristijan Kljucaric by mail. An extract of his reply:

“Also, for best performance, the IRF 9610 transistors (on the PCB
marked as T2 and T3) should be matched to obtain low DC offset voltage
at the amplifier output (anything up to 100 mV would be ok, but if you match
the transistors well, you could probably get 20-50 mV).”

But Kristijan doesn’t give me the correspondence ref on PCB / ref on original Pass schematic.

I tried to follow the connection on PCB and my conclusion is here:



So I matched T2 and T3. I hope I don’t make mistakes. (It's better to Check it)

I replace 221R (R6 on PCB or R11 on Pass schematic) with a adjustable resistor to adjust Offset to 0mV +/-3mV

Laurent

[Thago]

Thank you very much for helping me out! I tried to follow te schematic and the PCB, and I think you're right: T2 and T3 are the matched pair IRF9610!

[Lau700]

On this PCB, it’s easy to thermally connect the three IRF9610, good for offset stability too:

Laurent

[Thago]

What material did you use for the thermal connection? Do the IRF9610 need to be electrically isolated from each other?

[Lau700]

I used a simple piece of aluminum (3mm thickness) with isolated pads.
It’s not necessary to use a heatsink (except if you have one), these IRF9610 don’t get hot at all. It’s just to keep the matched pair at the same temperature.
Laurent

[Thago]

Thx for replying, I have some left-overs of copper foil (1.5mm), they will do the job (WITH isolated pads of course)
I am planning on using silver cable (0.8mm) for the signal wiring. Easy enough from the XLR-input to the main board, but now I'm wondering which path the signals follows from the main board to the gain/constant current devices, and back. Which of the D-G-S-R connections carry the signal? All of them? And will 0.8mm silver cable do the job, or do I need a larger section?

(it's amazing how many questions arise once I started building this amps, I thougt everything was rather clear