I am building a pair of Aleph 2s and upon power up ran into major problems. After about 20-30 minutes, POP, the Source pin on one of the Q6-11 current source MOSFETs fried!
Prior to the POP, I ramped up the voltage using a VARIAC with no smoke. I plug a tape deck into the input and a 30yr old speaker in the output, but I heard no music. At one point during the ramp of voltage the speaker produced a high pitch whine.
At full voltage, my rails were about +/- 46V. It was at full voltage for about 20-30 minutes before the POP, but producing no music. I probed a few spots and voltage drops seemed fine. At the end before POP, the current source heatsinks were noticeably warmer than those of the output MOSFETs (although they were barely warm).
Since the incident I have re-check my outboard power supply (it is working fine). I tried powering up at low VARIAC voltages (with the one blown MOSFET), but with immediate power supply hum and blown fuse.
I have powered at low VARIAC voltages the other amp and have done limited probing. Here's my results, with the VARIAC dial at about 27 VAC:
1) Voltage rails at +/- 10.1 VDC.
2) Voltage drop over 4.75K R17 is 7.4 volts.
3) Voltage drop over Z5 is 8.7 volts.
4) Voltage drop over 221ohm R11 is 4.9 volts.
5) There is NO voltage drop over the 1ohm R40-45.
6) There is NO voltage drop over the 1ohm R46-51.
I have made a few minor variations to the basic Aleph 2:
1) Power supply is outboard.
2) Power supply has a Pi filter (8 - 24,000uF caps, with 2 - 2mH air-core 16ga inductors per channel).
3) Each power supply cap is by-passed with a 220uF .
4) Signal boards are wired point to point on a sheet of teflon.
5) The 220uF capacitor C9 is connected to the emitter of the bipolar, instead of to the OUT+.
6) ZTX-450 bipolars are used instead of MPSA18.
7) All 220uF electrolytic capacitors are by-passed with a 1uF polyester film caps.
Does anyone have any ideas what is wrong?
At what minimum power supply rail level should the amp work and minimize blowing the other amp, while checking?
Thanks!
Prior to the POP, I ramped up the voltage using a VARIAC with no smoke. I plug a tape deck into the input and a 30yr old speaker in the output, but I heard no music. At one point during the ramp of voltage the speaker produced a high pitch whine.
At full voltage, my rails were about +/- 46V. It was at full voltage for about 20-30 minutes before the POP, but producing no music. I probed a few spots and voltage drops seemed fine. At the end before POP, the current source heatsinks were noticeably warmer than those of the output MOSFETs (although they were barely warm).
Since the incident I have re-check my outboard power supply (it is working fine). I tried powering up at low VARIAC voltages (with the one blown MOSFET), but with immediate power supply hum and blown fuse.
I have powered at low VARIAC voltages the other amp and have done limited probing. Here's my results, with the VARIAC dial at about 27 VAC:
1) Voltage rails at +/- 10.1 VDC.
2) Voltage drop over 4.75K R17 is 7.4 volts.
3) Voltage drop over Z5 is 8.7 volts.
4) Voltage drop over 221ohm R11 is 4.9 volts.
5) There is NO voltage drop over the 1ohm R40-45.
6) There is NO voltage drop over the 1ohm R46-51.
I have made a few minor variations to the basic Aleph 2:
1) Power supply is outboard.
2) Power supply has a Pi filter (8 - 24,000uF caps, with 2 - 2mH air-core 16ga inductors per channel).
3) Each power supply cap is by-passed with a 220uF .
4) Signal boards are wired point to point on a sheet of teflon.
5) The 220uF capacitor C9 is connected to the emitter of the bipolar, instead of to the OUT+.
6) ZTX-450 bipolars are used instead of MPSA18.
7) All 220uF electrolytic capacitors are by-passed with a 1uF polyester film caps.
Does anyone have any ideas what is wrong?
At what minimum power supply rail level should the amp work and minimize blowing the other amp, while checking?
Thanks!