Turns out one of the 2SJ74s was bad. Fortunately I had a matched quad and replacement fixed the problem
Having a low power issue on left channel after removing C1. (if you read my earlier post, the wacky offset problem was due to a bad 2SJ74. Problem has been correct and right channel is working fine) The left channel works fine for a few minutes and then basically disappears. If I let the amp sit for 60 minutes or so, it works again for a few minutes. The left channel is out of phase, but it has always been like that. All transistors measure the same on both channels, as do all the MOSFETs.
0130 hrs in the morning first power up of my first of 6 Aleph J boards, used dim bulb and variac to bring in power slowly, I must say I am over the moon, everything appears to be running as it should, will continue to burn in for another hr then getg some well-earned sleep, I must say a big thankyou to all the people on this forum without their knowledge I don't think this would have come to fruition. I must admit the biggest tip is to check everything several times, I had put transistors in wrong slots and had the Zener reversed but I picked it up before powering up. I have two 600 VA Toroidy transformers that will power two 3 channel amps to drive Zaph 12.3 speakers using active crossovers. will keep posted on progress.
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Does the pic of voltages help? All measurements are at idle.
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I finished building. I have a board with lsj74D and a board with lsj74B the sound is no different from each other, power supplies is 69000 uF , 23 volts rail. My loudspeaker is difficult because dynaudio car and D28 tweeter (3/4 ohm) and I say that ACA first version, Aleph 3, and F5 drive my speakers better. I used B1 and BA3 as preamp. Aleph j is super silent with tight basses and a very correct timbre and the right decay of the notes and details. I will try with Mission and Monitor Audio speaker of my friends. It's June and it's very hot...
Here are the voltages you asked for. let me know what you think. Faulty channel is in red, functioning channel is in green.
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It all looks okay.... for the measurements taken when the amp is cold. Maybe the V drop across R7 is a smidge too high... but it could all be okay because the amp was cold.
Just a couple of equations:
With C1 removed and the wire link sodered in its place, the initial offset (cold) is around 200mV. This then settles quickly to around 10mV. I have Linear Systems JFETs, well matched.
NOTE: based on the R7 trimpot value, the JFET current could be a few mA but also around 10mA or even more... What grade of JFETs are you using?
A test you could do: let the faulty AMP PCB start showing the issue and then hit the semiconductors with a short burst of freeze spray. Start with JFETs.
So, I'd check my soldering
I'd confirm there's a wire link in place of (removed) C1s
Confirm the JFETs are good
I'd use the can of freeze spray
I'd re-do the measurements when the faulty AMP PCB starts to show its "disappearing act"
Good luck
Just a couple of equations:
Bypassing the C1, right?? I.e. you remove the C1 and then soldered a wire link in its place. I want to confirm the mod was done correctly.
This is the behaviour of my Aleph J:
With C1 removed and the wire link sodered in its place, the initial offset (cold) is around 200mV. This then settles quickly to around 10mV. I have Linear Systems JFETs, well matched.
NOTE: based on the R7 trimpot value, the JFET current could be a few mA but also around 10mA or even more... What grade of JFETs are you using?
All I can tell here is that one of your components might be getting really hot with time, or the solder joints are not soldered properly. I know that you replaced the JFETs already. Just a reminder and a check: they need to be of a correct grade, matched, and handled with care - always use an antistatic wristband when handling them.
A test you could do: let the faulty AMP PCB start showing the issue and then hit the semiconductors with a short burst of freeze spray. Start with JFETs.
I need to know more about this "out of phase" thing. Can you explain this better??
Once again, do not handle JFETs (and MOSFETs) without the properly grounded antistatic wristband.
So, I'd check my soldering
I'd confirm there's a wire link in place of (removed) C1s
Confirm the JFETs are good
I'd use the can of freeze spray
I'd re-do the measurements when the faulty AMP PCB starts to show its "disappearing act"
Good luck
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So, I got my Alpha J partially assembled. However, I'm getting very low voltage readings in my power supply. The LED's are also not turning on (made sure the leads were oriented correctly). Any thoughts on what I've got wrong here that would result in this issue? Thanks in advance for the advice.
Dual mono configuration with two Antek AS-3220. Used the standard parts from BOM.
Dual mono configuration with two Antek AS-3220. Used the standard parts from BOM.
Pick which voltage rail (+ or -) you want, but I think you need to re-orient one secondary. I think you have one secondary flipped, causing a phase issue. tl;dr - flip the blue and green wires on one of the bridges each per channel.
I do not know this is correct. Do not do ANYTHING until you're confident.
My post is mainly to prompt another eagle-eyed (but much more knowledgeable) person to chime in... and maybe I got it right.
I do not know this is correct. Do not do ANYTHING until you're confident.
My post is mainly to prompt another eagle-eyed (but much more knowledgeable) person to chime in... and maybe I got it right.
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