One Aleph-X working, One to go

[yoke]

Hi...
Eric I think this version have 22V and 6A

http://web.vip.hr/pcb-design.vip/alephx.html

regards
Josip

[yoke]

or is it 5A

I think it's 5A at the end...
But I think you cen use this shematic and just change source resistors on mosfets ?

Bit I'am not shure !!! I have enough problems with my AX !!!

[Eric]

Yoke - yeah I understand! After all of this time, there still seems to be some "mystery" around how to design an Aleph-X to suit particular needs...

Thanks for the link, I had forgotten about Kristijan's work.

Eric

[yoke]

We are the unstoppable diy-ers...little failer can't frighten us...

[wuffwaff]

HI,

I also planned for a 20V supply but somehow the losses were not as high as calculated (18V transformers, schottkys and 2,2mH Torobars)

The values should work well with a 20V supply. AC-current-gain can be measured with a multimeter and a cd player with test-disc or a funktion generator (as described many times on the forum)

William

[Eric]

Thanks for the help William and Yoke!

So then, it looks like I can follow William's parts list, use 20-22v rails, adjust V1/3 for bias, and then adjust ac current gain accordingly...

This is making me feel better, thanks! Also, it looks like I might be able to source some Seifert KL271 extrusions locally...

Thanks!

[wuffwaff]

Hi all,

after discussing the zener in the curent source that feeds the input diff pair I had a look at some data sheets and did some calculating:

a Zener 9.1V with a TK of 0,07% / K will change the current through the diff pair when heating up from 20 to 65 or 70°C by a bit over 4% (going from 9.1 to 9.4V).

Seeing the changes you can make with relativ small changes of VR2 this seems a bit too much.

I did some measurements this afternoon measuring the zener from cold (9,08V to warm9,19V) without the lid on the amp. Cooling the zener (earbud with ice spray) changed the absolute offset nicely, heating it a bit with a solder iron too.

I also tried cooling the IRF9610 with not much effect. Also cooling the diff pair wasn´t that effective.

So now I´ve ordered a pair of 1N825A (6,2V, TK 0,002% / K) and will try these this week. I´ll only have to change R17 (for 7mA through D1) and R24 (220R) and R26 (120R).

The other thing I noticed is that a 10000uF/16V cap is not enough for a dc-filter (230V / 340Watts).
I measured 0,66V AC over it wich means that the diodes will be working a bit too. Changed it to 20000uF and got 0,23V AC so that seems to be fixed too

I´ll let you know if the 1N825A changes the absolute offset behaviour.

William

[Netlist]

Interesting findings William, I should try similar test on the TL431.
I didn't follow the thread enough to understand what you mean with the DC-filter. Is it the one to get rid of the trafo hum?

/Hugo

[wuffwaff]

Hi Hugo,

yes that´s the one. I used 10000uF per channel and never checked if this was enough
I still have some mechanical hum though I´m not shure if it´s the transformer or the torobars.
It was allright until I placed a sheet of mu-metal between transformer/chokes and caps and maybe this is vibrating....

William

[wuffwaff]

Hi,

just an update. After replacing the cheap 9,1V Zeners with an 1N825A absolute offset behaviour has changed although not really that much. One channel stayed almost the same, now starting at +5V and going to near zero in an hour. The other channel went from -8V to +5V also going to ca. 0V in an hour.

maybe finding a zener with the right temp. coefficient would be the better sollution but for now I will leave it as it is.

The amps have run in quite nicely now and are really sounding very nice. What´s not so nice is that the transformers are also running in and have developed a nasty buzz
You can hear it from 3meters away when everything else is quiet and it is driving me slightly mad

Until now I tried the following thing to get them quiet again:

1. put some DC filters directly in the amps (20.000uF/16V and two diodes). This reduced it a bit but not enough.

2. put a 0,22Ohm resistor in the mains (230V). A small reduction was noticable (but not enough)

3. put 3 0,22Ohm/5watt resistors in parallel between bridge and caps to reduce the current peak from a theoretical 38A to 30A. I´m not shure this worked cause the resistors started smoking after less than half a minute. I will try again with some 25W / 0,12Ohm resistors I ordered yesterday. This will also reduce the voltage at the fets from 22 to around 20V so I will have to listen if it has an influence on the sound through the speakers.

4. decoupled the transformer from the frame with rubber. No influence

Both amps are connected to a balanced ac supply (115V-0V-115V). When I connect them directly to the mains the buzz gets really loud...
I already tried putting them on different mains phases (I´m not shure this is english) but without effect.

After reading a nice article by Menno van der Veen on the Plitron website about measuring transformer noise and the causes thereof I hope I won´t have to throw away my transformers.

So what I will do next is to try the bigger resistors for a R-C-L-C supply and I will remove the mu-metall sheet (the buzz started after putting it in and although I´m almost shure the noise comes from the transformers I will just try)

Any suggestions are more than welcome!!!!

William