Hi chaps, just powering up my Aleph J for the first time! PSU ok on bulb tester and producing the expected voltage but when I attach an Aleph board, the bulb lights then dims and then brightens a bit again finally settling on what I would call quite bright but not as bright as a 100w bulb would normally be.. Both boards have the same result. Bias reads about 340mv and offset 140mv. Am I being too cautious in thinking there's a problem or should I just try without the bulb tester next??
If you tested the psu with the bulb tester and everything checked out fine, then you’ll want to disconnect the bulb tester when testing the main boards
Looks like the power supply draws a bit of current, which makes the bulb light up. This is how it's supposed to be! Someone else may know more about the right bias values, but I say if there is no bangs or smoke you're ready to go without the bulb tester. Then adjust the bias and offset, hook up a (cheap) loudspeaker and see if you get music!
Correct. The brightness you see ramping up after the initial charging of the capacitor back is the amplifier boards biasing up.
I now have beautiful glowing blue lights and DC offset of 0v, bias of 350mv
Leaving her to warm up 😀
Leaving her to warm up 😀
Absolutely fantastic! Put the lid on (resting) let it warm up for 30min or so, set bias to 400mV and re-check offset. Let sit another 30 with the lid on, measure again, if stable, listen and enjoy!
The Aleph is a beautiful and beguiling amplifier, you will love it! Enjoy
The Aleph is a beautiful and beguiling amplifier, you will love it! Enjoy
OK, so Aleph No 2 hasn't gone so well! One channel seems to work as expected but when I power up the other one the bulb tester goes out and I measure 0v bias. Any suggestions on where to start looking?
These are to be used with my latest diy creations that are based on the D&D 8c except using a PHL 3020 10" 95dB midrange driver and a Faital Pro compression driver
at DMM , and its probes , where to put them ?
Indeed! Where to put them is the question.
Both LED's on the board light and I've just checked R27 pot and I measure 68K which is what I set it at when I assembled the boards..
Your output stage is floating, there's no current running through the output MOSFETs.
So, check the input JFETs and make sure the voltage drops are correct. This will generate a required voltage drop across R7, to "open" the "amplifying" MOSFETs into a conductive state.
The other, current-setting MOSFETs, are set into a conductive state by Q4 Vce. This also needs to generate 4.3V to let the current flow (through the output MOSFETs) from the positive rail.
See the 3 voltages in the attachment, measure yours, provide few photos...
So, check the input JFETs and make sure the voltage drops are correct. This will generate a required voltage drop across R7, to "open" the "amplifying" MOSFETs into a conductive state.
The other, current-setting MOSFETs, are set into a conductive state by Q4 Vce. This also needs to generate 4.3V to let the current flow (through the output MOSFETs) from the positive rail.
See the 3 voltages in the attachment, measure yours, provide few photos...
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