Aleph board voltage measurements

SteveA · 20th January 2006, 05:54 PM

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

Blues · 20th January 2006, 06:17 PM

Steve,

Check status/orientation of Q4. Compare measurements with the other boards' Q4.

Blues · 20th January 2006, 06:22 PM

Do you mean R14=392R and not R18?

SteveA · 20th January 2006, 08:32 PM

Quote:

Originally posted by Blues
Do you mean R14=392R and not R18?

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

SteveA · 20th January 2006, 11:25 PM

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

BDP · 20th January 2006, 11:44 PM

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

Blues · 20th January 2006, 11:48 PM

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.

SteveA · 21st January 2006, 01:25 AM

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

Blues · 21st January 2006, 05:30 AM

Yeah! Go 'Hawks!...beat Grey's Panthers

20th January 2006, 05:54 PM	#1
SteveA diyAudio Member Join Date: Dec 2001 Location: St Paul, MN	Aleph board voltage measurements 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

20th January 2006, 06:17 PM	#2
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: The Milky Way	Steve, Check status/orientation of Q4. Compare measurements with the other boards' Q4. __________________ Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html

20th January 2006, 06:22 PM	#3
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: The Milky Way	Do you mean R14=392R and not R18? __________________ Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html

20th January 2006, 11:25 PM	#5
SteveA diyAudio Member Join Date: Dec 2001 Location: St Paul, MN	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

20th January 2006, 11:48 PM	#7
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: The Milky Way	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. __________________ Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html


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20th January 2006, 11:44 PM	#6
BDP diyAudio Member Join Date: Apr 2002 Location: Washington State	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

21st January 2006, 01:25 AM	#8
SteveA diyAudio Member Join Date: Dec 2001 Location: St Paul, MN	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

21st January 2006, 05:30 AM	#9
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: The Milky Way	Yeah! Go 'Hawks!...beat Grey's Panthers __________________ Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html

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