Little GEM

[dadod]

I use Output triple in my TT amp ThermalTrak+TMC amp but that is another animal.
This one is simple, very stable and unbelievable musical.
dado

[dadod]

Loop Gain

[dadod]

Output transistors power dissipation at 50% of the max power(+-40 V power supply, 4 ohm load) where the dissipation is at its max (efficiency 50% for B class).

[AndrewT]

post4 closed loop gain & phase, post12 open loop gain & phase.
They are quite different.
Could you show the .op for each and explain the plots we see?

[AndrewT]

NJL3281 are 180W or 200W devices depending on which misprint you read in ONsemi's datasheet.
Total Pdmax is either 360W or 400W.
Divide the lower by 6 (for running pretty hot) and the predicted maximum output power is 60W. Using the more optimistic of 400W divided by 5 (very large heatsink or domestic listening when the sink never gets hot) predicts 80W.

Those maximum power predictions are just about ideal for use with a 30Vac transformer giving ~+-45Vdc supplies, assuming a severe 8ohms speaker reactance.

[dadod]

Originally Posted by AndrewT

post4 closed loop gain & phase, post12 open loop gain & phase.
They are quite different.
Could you show the .op for each and explain the plots we see?

Post12 is Loop Gain not Open Loop Gain and in the rectangle you can see Phase Margin, point when the Gain plot cross 0 dB, and Gain Margin the poit where the Phase reach -180 degree. Higher values are better and here, I think, they are quite good.
Post4 Close Loop Gain shows -3 dB bandwidth.
Tell me what you want with .op? First post shows(third plot) how the bias current depends of temperature( separate drivers temperature and output transistor temperature). This plot was generated with .op
dado

[dadod]

Originally Posted by AndrewT

NJL3281 are 180W or 200W devices depending on which misprint you read in ONsemi's datasheet.
Total Pdmax is either 360W or 400W.
Divide the lower by 6 (for running pretty hot) and the predicted maximum output power is 60W. Using the more optimistic of 400W divided by 5 (very large heatsink or domestic listening when the sink never gets hot) predicts 80W.

Those maximum power predictions are just about ideal for use with a 30Vac transformer giving ~+-45Vdc supplies, assuming a severe 8ohms speaker reactance.

This is exactly how I think.

[AndrewT]

Originally Posted by dadod

This is exactly how I think.

since we are agreed on this, can I suggest you test into a 4r0 load for a few seconds to see how well the output voltage holds up. (-0.6dBV is good, -1dB probably indicates that lower resistance is not worth testing).
If this looks particularly good, are you willing to try a few seconds into 3r0, and/or 2r66?
This is a good test of how well the amplifier delivers current.
Any longer than a few seconds becomes a test of the heatsink and I don't need that. I can model it well with the data the sink manufacturers give out.

Are you aware of the -20dB switch technique I use for testing at, or near maximum powers/dissipations?

[AndrewT]

what is the difference between loop gain and open loop gain?
What do the .op statements look like for the three conditions you are examining, closed loop gain, loop gain and open loop gain?
Is loop gain the 1/NFB ratio = beta?

[dadod]

Originally Posted by AndrewT

since we are agreed on this, can I suggest you test into a 4r0 load for a few seconds to see how well the output voltage holds up. (-0.6dBV is good, -1dB probably indicates that lower resistance is not worth testing).
If this looks particularly good, are you willing to try a few seconds into 3r0, and/or 2r66?
This is a good test of how well the amplifier delivers current.
Any longer than a few seconds becomes a test of the heatsink and I don't need that. I can model it well with the data the sink manufacturers give out.

Are you aware of the -20dB switch technique I use for testing at, or near maximum powers/dissipations?

Working prototype has quite small heat sink, and I don't have lower load then 4 ohm.
I have to look back when I tested previous version(with standard TMC) to see if I did the 4 ohm measuremen. You can look into this thread too. bootstrapsCCS+T-TMC
I know nothing of the -20dB