Measurement question:
I bought 4 sets of the Mini/A30 boards from BrianGT. I stuffed one set as Mini's and three sets as Aleph 30's. I finished an A5 about a year ago where I learned (courtesy BDP) how to make the voltage measurements prior to installing the output boards/devices.
On all eight boards I see the ~9V drop across Z5, ~4.1Vgs on Q3, ~3.9Vgs on Q1,Q2. On seven boards I see ~4V drop across the 392R resistor (R18), the last board (an A30) I measure a drop of ~2.7V. Seven of the boards would seem to be good to go. Is this 2.7 V too low (ie, do I need to chase down the offending part(s))?
This resistor "sits" between the -V supply and the drain of Q2 and would seem to define the voltage drop across that resistor (I measured 2.7 volts between these points as well). What would cause the drain to be 1.3-2.3V too negative (Is Q2 the problem?)?
Thanks,
SteveA
I bought 4 sets of the Mini/A30 boards from BrianGT. I stuffed one set as Mini's and three sets as Aleph 30's. I finished an A5 about a year ago where I learned (courtesy BDP) how to make the voltage measurements prior to installing the output boards/devices.
On all eight boards I see the ~9V drop across Z5, ~4.1Vgs on Q3, ~3.9Vgs on Q1,Q2. On seven boards I see ~4V drop across the 392R resistor (R18), the last board (an A30) I measure a drop of ~2.7V. Seven of the boards would seem to be good to go. Is this 2.7 V too low (ie, do I need to chase down the offending part(s))?
This resistor "sits" between the -V supply and the drain of Q2 and would seem to define the voltage drop across that resistor (I measured 2.7 volts between these points as well). What would cause the drain to be 1.3-2.3V too negative (Is Q2 the problem?)?
Thanks,
SteveA
Blues said:
I was using the component designations from Brian's boards not the Pass schematics. I believe R18 on Brian's board corresponds to R14 in the Pass schematics.
As to Q4 the orientation is fine but perhaps its condition isn't. I'll replace and see what happens.
Thanks Blues, I appreciate the help.
SteveA
Bad 9610
Blues-
I reheated the joints on Q4 with no effect. I replaced Q4 with no effect. I replaced Q2 (middle one on the Mini board, think it's Q2) and found 3.76V drop. Lower than the other boards by 0.1-0.2 V but it should be okay, right?
Thanks,
SteveA
Blues-
I reheated the joints on Q4 with no effect. I replaced Q4 with no effect. I replaced Q2 (middle one on the Mini board, think it's Q2) and found 3.76V drop. Lower than the other boards by 0.1-0.2 V but it should be okay, right?
Thanks,
SteveA
You should be good to go.
The differential, when connected to the feedback network and the output devices, should cause the currents/voltage thru each leg of the differential to adjust to the output devices. (If that makes sense)
BDP
The differential, when connected to the feedback network and the output devices, should cause the currents/voltage thru each leg of the differential to adjust to the output devices. (If that makes sense)
BDP
Steve, Q2 is fine. Without power on the amp board compare Resistance readings on the Q4 pins (+probe on Base) with your working boards. Or with your meter set to diode function you should get about 0.6V between B-E.
Blues-
Q4 measures (resistance or diode function) the same as the "good" boards. Thanks
BDP-
Go Seattle!!! I'm still enjoying the A5, now with an Aleph P1.7 preamp. I have an Aleph 4 pair approaching the finish line. It'll be interesting to compare the two (and the A30 and the Mini).
Take care,
Steve
Q4 measures (resistance or diode function) the same as the "good" boards. Thanks
BDP-
Go Seattle!!! I'm still enjoying the A5, now with an Aleph P1.7 preamp. I have an Aleph 4 pair approaching the finish line. It'll be interesting to compare the two (and the A30 and the Mini).
Take care,
Steve
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