Finished my switch/soft start card, and moved on to SissySIT. Got zeners, resistors, sockets for optos, and jumpers placed. About to move on to pots. Do I remember something about pre-setting the pots? I’ll run through the threads when I get back from walking.
Geez, I’m getting old, this work is getting so hard to see. I imagine I need to get a magnifying station, or loupes.
Geez, I’m getting old, this work is getting so hard to see. I imagine I need to get a magnifying station, or loupes.
Thanks for the pointers guys. I was looking in the middle of the thread. I manage the pot setups by no cutting the tails until after the pots were set.
Did the sacrilegious trimming of the Cinemags, and finished my boards today. (still need their alcohol bath)
It will be weekend after next before I can tear apart my current Aleph J and mount the new switch/soft start board, and mount the SissySIT boards (which will involve unmounting the heat sinks to tap for the SIT)
Thanks again ZM for the kit, and all of you for the help.
Random question - How will the SissySIT R3 compare/contrast with my current M2x amps? I would think that the only (minimal) complaint I have with the M2x is that they are a bit "polite", and paired with my Pre-Amp, might be a bit underpowered.
Did the sacrilegious trimming of the Cinemags, and finished my boards today. (still need their alcohol bath)
It will be weekend after next before I can tear apart my current Aleph J and mount the new switch/soft start board, and mount the SissySIT boards (which will involve unmounting the heat sinks to tap for the SIT)
Thanks again ZM for the kit, and all of you for the help.
Random question - How will the SissySIT R3 compare/contrast with my current M2x amps? I would think that the only (minimal) complaint I have with the M2x is that they are a bit "polite", and paired with my Pre-Amp, might be a bit underpowered.
you'll read in plenty of places that I said that M2 is best amp
period
now, more precise - M2 is most peculiar FW amp, and not just FW
but, DEFiSIT is ......... having just one drawback in race for being most peculiar - it came second in time (M2 being made first)
and - Sissy is special sort of DEFiSIT
I know that I didn't help you, but I also know that you'll be happy when you hear it for first time
period
now, more precise - M2 is most peculiar FW amp, and not just FW
but, DEFiSIT is ......... having just one drawback in race for being most peculiar - it came second in time (M2 being made first)
and - Sissy is special sort of DEFiSIT
I know that I didn't help you, but I also know that you'll be happy when you hear it for first time
Still battling offset instability
Still battling offset instability here.
I changed R125, the gate resistor for the IRFP9140 to 221R. Seems to have helped somewhat, as offset instability comes after amp being on for a longer time (heatsinks opposite to 9140 at 53-54 degrees C). Instability can still be triggered by touching washer of 9140.
Also, I let the amp run for half a day yesterday. Offset instability was observed in the other channel as well, though here the offset instead of rising by approx. 100 mV, it went to -100mV and fluctuates not that much (around 20 mV)
To recall:
- bias rock-solid and stable in both channels, cold or warm
- current through level shifter resistor stable
- I could not see obvious signs of oscillation on scope; frequency range, square waves, distortion measurements stay inaffected
- when measuring distortion, a small short burst of something could be seen every minute or so, resetting averaging of REW because of brief overload
- gate current of SIT well under 1 uA
- when amp gets very warm or when I touch the washer of the 9140 in the left channel, offset jumps by +100mV or +200mV and fluctuates by maybe 50mV or somewhat more.
The observation of the instability in the other channel makes a soldering or single component issue unlikely in my view.
Interesting development today:
In the left channel, I have a THF-51S that I measured with 2.2V Vgs at 25V Vds and 2A Ids. Originally, I chose the level shifter resistor by setting Vgs of IRFP9140 and IRF510 of equal magnitude and had a 100R as level shifter resistor.
This morning, I changed the level shifter rsesistor to 74R, according to the Vgs of THF-51S measured before out of circuit.
-> Offset instability started almost immediately after the amp biased up, while still cold.
Does this hold a clue ?
Any ideas ?
Regards, Claas
Still battling offset instability here.
I changed R125, the gate resistor for the IRFP9140 to 221R. Seems to have helped somewhat, as offset instability comes after amp being on for a longer time (heatsinks opposite to 9140 at 53-54 degrees C). Instability can still be triggered by touching washer of 9140.
Also, I let the amp run for half a day yesterday. Offset instability was observed in the other channel as well, though here the offset instead of rising by approx. 100 mV, it went to -100mV and fluctuates not that much (around 20 mV)
To recall:
- bias rock-solid and stable in both channels, cold or warm
- current through level shifter resistor stable
- I could not see obvious signs of oscillation on scope; frequency range, square waves, distortion measurements stay inaffected
- when measuring distortion, a small short burst of something could be seen every minute or so, resetting averaging of REW because of brief overload
- gate current of SIT well under 1 uA
- when amp gets very warm or when I touch the washer of the 9140 in the left channel, offset jumps by +100mV or +200mV and fluctuates by maybe 50mV or somewhat more.
The observation of the instability in the other channel makes a soldering or single component issue unlikely in my view.
Interesting development today:
In the left channel, I have a THF-51S that I measured with 2.2V Vgs at 25V Vds and 2A Ids. Originally, I chose the level shifter resistor by setting Vgs of IRFP9140 and IRF510 of equal magnitude and had a 100R as level shifter resistor.
This morning, I changed the level shifter rsesistor to 74R, according to the Vgs of THF-51S measured before out of circuit.
-> Offset instability started almost immediately after the amp biased up, while still cold.
Does this hold a clue ?
Any ideas ?
Regards, Claas
see what 1nF , soldered from B to E of BD139 (Q103/203) can do
maybe there is a need to make CCS tougher
in analysis, even I need to remember that - in AC domain , gates of SIT and output mosfet are practically shorted together and - whatever happens with one is automatically transposing to other one, not just as annoying side bother, but directly to head
tricky little devils, these no-NFB amps .......
maybe there is a need to make CCS tougher
in analysis, even I need to remember that - in AC domain , gates of SIT and output mosfet are practically shorted together and - whatever happens with one is automatically transposing to other one, not just as annoying side bother, but directly to head
tricky little devils, these no-NFB amps .......
Update on offset instability
Update after having the amp run for 4 hours:
With the amp cold, touching the washer of the IRFP9140 did not trigger the offset instability. With the amp warm, I could trigger the instability by touching the washer for maybe 5-10s. Switching off , and after 1-2 minutes on again: stable.
I could not get the instability to occur by temperature (heatsink opposite 9140: 55-56 degrees C). Running for 4 hours, everything was nice and stable for this run.
Should I leave it at that ?
Zen Mod, should I up the gate resistors either at the IRF510, or the SIT, or on both to 220R as well ?
Would I lose bandwidth if I raise the gate resistor at the SIT ?
Regards,
Claas
Update after having the amp run for 4 hours:
With the amp cold, touching the washer of the IRFP9140 did not trigger the offset instability. With the amp warm, I could trigger the instability by touching the washer for maybe 5-10s. Switching off , and after 1-2 minutes on again: stable.
I could not get the instability to occur by temperature (heatsink opposite 9140: 55-56 degrees C). Running for 4 hours, everything was nice and stable for this run.
Should I leave it at that ?
Zen Mod, should I up the gate resistors either at the IRF510, or the SIT, or on both to 220R as well ?
Would I lose bandwidth if I raise the gate resistor at the SIT ?
Regards,
Claas