Aleph J illustrated build guide

[folkdeath95]

I have a question concerning the schematic. While reading the Aleph J page on the Firstwatt site, I found this:
"[FONT=Arial, sans-serif]8)No electrolytic capacitor in the signal path"

But, on the schematic on page 1, C3 is on the signal path, no? Why this change?
[/FONT]

 

[Zen Mod]

Papa's habit - pulling our legs all the time

that's just audio , and just proper decent engineering

no more , no less

 

[dungdochi1978]

better have capacitor in the signal path for safety (DC voltage ). can be..?

 

[Zen Mod]

C3 is necessary , and in signal loop

C1 too , as foolproof part , so it can be shorted , if there is no short circ between operator's headphones

 

[stlblue]

I thought someone was going to help me put mine together, but too many things got in the way and then I moved about 5 hours away. By chance, are there any plans to post some youtube videos on the build?

 

[folkdeath95]

C3 is necessary , and in signal loop

C1 too , as foolproof part , so it can be shorted , if there is no short circ between operator's headphones

Thanks for your answers.

 

[jdg123]

bias good, DC offset bad!

Hello friends,

I recently had to open up my Aleph J and in revisiting it after a couple years I found the DC offset had risen...a lot! I tried to re-bias and realign the DC offset but cannot get it back down to what I consider reasonable. Right now the left channel is at 47mVDC and the right is at 95mVDC.

Any suggestions?

 

[6L6]

Have you run the R7 pot out of turns?

 

[jdg123]

Yes, out of turns.

 

[jdg123]

adjusting R7 seemed to have no effect no matter how many turns...until the Bias started to drop badly...

Perhaps I should consider a cap at the output instead of the input?

 

[Zen Mod]

inputs grounded , no load on output - while testing ?

 

[jdg123]

Inputs were not grounded. No load on output terminals

 

[jdg123]

Ive biased all my amps without shorting plugs or load across speaker terminals. I usually get DC offset around 9mA, never 90!

 

[6L6]

Is the pot turned all the way up or down?

 

[jdg123]

I've taken it both directions

 

[jdg123]

Would this DC offset be an indication that the 2SJ74s are now no longer matched?

Is there an adjustment I can make to the R7 as in making it a 5K instead of 2K?

 

[6L6]

The Jfet are not going to change.

Assuming that you are at the max. resistance portion of the pot, yes, changing it to a 5K would be fine.

Or just place a 470R-1K resistor in series with the pot. (whatever you happen to have on hand)

 

[jdg123]

Thanks! That I can do!

 

[HeadSh0T]

Hi everyone

I'm a long time member and haven't been on diyaudio for years. I decided to replace my Aleph 30 that I built 7 years ago with an Aleph J.

I built a power supply, populated the boards, and tested one channel. After some adjustment, it seems to work fine.

Now, I power on the other channel. I measure R18 and I get 0.35V. I measure R19 and I get 0.9V. After a few seconds Q8 was smoking.

Why do you think this happened?

I made sure Q7 and Q8 were matched, Q5 and Q6 were matched too.

R27 was set to 68K, R8 was set to 1K.

 

[HeadSh0T]

Anyone? I swapped in another IRFP240 and it still gets really hot within a few seconds.