Greetings All,
I'm trying to get an Aleph J build running and while in the homestretch I've hit a snag that I'm not technically savvy enough to resolve myself. I'm good at following directions, but a lousy EE.
My trouble: One channel is functioning as expected, and I've been able to zero the output and set the bias, but the second channel is sending V+ (25.7V) to the output. Messing with R7 has no effect.
What I know:
Swapping power supplies has no effect.
I measured each resistor before populating the boards.
Q2, Q3, and Q4 are oriented correctly, though untested.
I'm using 2SJ74's instead of the 2SJ109. Also oriented correctly but untested.
Gate voltages on Q5 and Q6 read +25.7V and on Q7 and Q8 read -25.7V.
On Q5 and Q6: Source and Drain voltages are approximately equal at ~25.6V.
On Q7 and Q8: Source reads -25.8V but Drain reads +25.7.
I haven't seen any smoke from any of it (yet)😀.
I'm not sure where to go from here and hope someone with more familiarity with the amp/board/electronics-in-general would be willing to share their wisdom. No suggestion is too rudimentary as analog electronics is entirely new territory for me. I have extras of most components for swapping as appropriate.
Thanks very much in advance, all.
I'm trying to get an Aleph J build running and while in the homestretch I've hit a snag that I'm not technically savvy enough to resolve myself. I'm good at following directions, but a lousy EE.
My trouble: One channel is functioning as expected, and I've been able to zero the output and set the bias, but the second channel is sending V+ (25.7V) to the output. Messing with R7 has no effect.
What I know:
Swapping power supplies has no effect.
I measured each resistor before populating the boards.
Q2, Q3, and Q4 are oriented correctly, though untested.
I'm using 2SJ74's instead of the 2SJ109. Also oriented correctly but untested.
Gate voltages on Q5 and Q6 read +25.7V and on Q7 and Q8 read -25.7V.
On Q5 and Q6: Source and Drain voltages are approximately equal at ~25.6V.
On Q7 and Q8: Source reads -25.8V but Drain reads +25.7.
I haven't seen any smoke from any of it (yet)😀.
I'm not sure where to go from here and hope someone with more familiarity with the amp/board/electronics-in-general would be willing to share their wisdom. No suggestion is too rudimentary as analog electronics is entirely new territory for me. I have extras of most components for swapping as appropriate.
Thanks very much in advance, all.
Please post well-lit, in focus photos of your channel.
Also, a few basic measurements if possible: What voltages do you measure across D1, R8 and R7?
Also, a few basic measurements if possible: What voltages do you measure across D1, R8 and R7?
Hi Dennis,
The drops you asked about measure as follows.
D1: 9.07V
R7: 0.0V 😕
R8: 8.27V
Also attached are photos. I think the clarity is decent but I can retake as warranted.
Thanks!
The drops you asked about measure as follows.
D1: 9.07V
R7: 0.0V 😕
R8: 8.27V
Also attached are photos. I think the clarity is decent but I can retake as warranted.
Thanks!
Attachments
With the channel powered, adjusting R7 doesn't change the voltage drop across it from 0. Measuring the resistance across it (with the power off) I can read between 0.1 - 1.8k ohms.
Also of note: The LED's on the misbehaving channel take MUCH longer to dim than on the working channel. ~1min vs 10sec or so.
Also of note: The LED's on the misbehaving channel take MUCH longer to dim than on the working channel. ~1min vs 10sec or so.
THIS WAS IT!!!
I swapped in another pair of LSJ74's and I've been able to dial in 0V at the output.
I hadn't thought I'd get to the bottom of this tonight. Thank you both so very much! Now to put it all back together.
Kindest Regards,
Graham
I swapped in another pair of LSJ74's and I've been able to dial in 0V at the output.
I hadn't thought I'd get to the bottom of this tonight. Thank you both so very much! Now to put it all back together.
Kindest Regards,
Graham
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