Troubleshooting Aleph P 1.7

[swede]

Hi,

I just finished a board for Aleph P 1.7, thoug it (obviously) doesn't work.

The PS is fine though, and on a different board. It gives a rock steady 62-something volts.

Are there any points on the diagram having "well known" voltages to look for when troubleshooting? Vec for Q11, Q12, Q13, Q14? Stuff like that.

I also did an ugly thing. I used BC546 and BC556 instead of the ZTX550 and ZTX450. And irf9620 instead of irf9610. AND irf540 instead of irf610. Could that be really bad? ;=) (e.g should I mount the REAL components instead of my ugly ones?)

Well, I would need some pointers!

Thanks,
//magnus

[panos29]

Dear friend,

Just check the polarity of those BC transistors as might be different (ceb instead of ebc) than the ZTX450 because i am sure that MPSA18 are indeed the other way around BC546.
And no there is no reason for the circuit to not operate without the specified mosfets.
Maybe there may be some degradation of sound quality due to the large gate capacitances, but should function perfectly otherwise.

Regards,

Panos

[swede]

Hi,

Thanks for the suggestion. I'll check it up right away. The reason for not using the correct FET's was actually to give bad luck a try. I've got plenty of the "wrong" FET's and very few of the "right" ones. I'll build it using the right components when I'm happy with the board.

My Aleph30 built on your PCB layout has been running for almost 1000 hours now! Costs a lot, but hey, it's worth it. ;=)

//magnus

[swede]

;=)

My bad, ofcourse...

The BC546/BC556 is CBE while the ZTX450/ZTX550 is EBC in the package...

Will solve that when I get home tonight! Hopefully it works.

//magnus

[panos29]

Good to know I helped you!

Keep up the good work.

P,S last minute correction on your aleph boards, due to my silly mistake there should be a very minor mistake there, you should add a 0.1uf cap between the C and B (and not between B and E)of the transistor in the active current source of your amps , it works without it too but its better to add it, should not be that hard.

[swede]

Hi,

Panos was pointing in the right direction, though I had already put the transistors in the right "angle". That doesn't help when the human "stupidity" factor plays a big role in the game...

In my neatly marked box for BC556B transistors (which I use instead of ZTX550 in my prototype) I found a handfull of BC546A transistors. The game of chance showed that I had taken BC546A from the box, thinking they were the proper PNP transistors I intended... Bummer.

As soon as I replaced them, the Aleph P board worked!

My contribution from this is that the Vce for Q11 and Q13 should be just above 4V. If not, you have a problem. ;=)

Best,
//magnus

[swede]

Hi,

Panos, I've finally gotten to move the cap from BE to BC in my Aleph 30. I've not really cared too much, since the amp was kind of working.

But today I started measuring my system from CD to preamp to Aleph30 and found the A30 to occilate heavily. I then recalled this thread somehow and went through the schematic and your board. Since you had already been nice enough to have both pad and drill hole marked on the board I just had to desolder C7 and move it 5mm.

Now my amp is no longer occilating and it seems to work fine. I just hooked it up to a Denon 3802 (used as a pre amp) and at least it is sounding. I'll wait a few hours to see how it sounds after warming up.

I did some minor tricks before, pumping up the bias to some 2.2 Amp. After moving the cap the bias bumped up to 3 Amp immediately. Well, I've got big heatsinks, so I might just leave it at that.

Best,
//magnus