Thermistor questions for Nelson.

gl · 20th July 2007, 04:47 PM

Nelson,

You have used thermistors in the bias circuits of the 400/4000 and stasis amplifiers and even more recently than that. My questions are these:

1) It is my understanding that the heating of the thermistor varies the bias current in the output transistors to offset heating effects. Is this so?

2) Does the thermistor self-heat or is it heated by it's environment or both. If both then which effect dominates.

Thank you.

Graeme

Nelson Pass · 20th July 2007, 07:56 PM

The thermistor is used to provide temperature compensation
on the output stage, the goal being to reduce the bias drift with
temperature and provide a faster warmup for the amplifier.

The self heating of the thermistor is negligible.

puginfo · 22nd July 2007, 07:48 AM

some where in the aleph' s user manuals as well there is a mention of thermistors being used to isolate the signal ground and the power ground.

what is the relationship between the grounding parameter and temp? thks

GRollins · 23rd July 2007, 01:40 AM

Unless the circuit malfunctions, there's no temperature to worry about. Only if there is a circuit fault of major proportions does the part carry any significant current. Otherwise the part functions as a low-value resistor.

Grey

Nelson Pass · 23rd July 2007, 03:52 AM

The nice thing about using a thermistor as a ground conductor
is that usually it's around 5-10 ohms, but if a lot of current
starts to flow, the resistance is reduces. Of course in a production
situation you need to test the fuse versus the thermistor in a
fault condition to ensure that the fuse croaks first.

20th July 2007, 04:47 PM	#1
gl diyAudio Member Join Date: Dec 2003 Location: Sierra Foothills - California	Thermistor questions for Nelson. Nelson, You have used thermistors in the bias circuits of the 400/4000 and stasis amplifiers and even more recently than that. My questions are these: 1) It is my understanding that the heating of the thermistor varies the bias current in the output transistors to offset heating effects. Is this so? 2) Does the thermistor self-heat or is it heated by it's environment or both. If both then which effect dominates. Thank you. Graeme

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20th July 2007, 07:56 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	The thermistor is used to provide temperature compensation on the output stage, the goal being to reduce the bias drift with temperature and provide a faster warmup for the amplifier. The self heating of the thermistor is negligible.

22nd July 2007, 07:48 AM	#3
puginfo diyAudio Member Join Date: Apr 2007	some where in the aleph' s user manuals as well there is a mention of thermistors being used to isolate the signal ground and the power ground. what is the relationship between the grounding parameter and temp? thks

23rd July 2007, 01:40 AM	#4
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Unless the circuit malfunctions, there's no temperature to worry about. Only if there is a circuit fault of major proportions does the part carry any significant current. Otherwise the part functions as a low-value resistor. Grey

23rd July 2007, 03:52 AM	#5
Nelson Pass The one and only Join Date: Mar 2001	The nice thing about using a thermistor as a ground conductor is that usually it's around 5-10 ohms, but if a lot of current starts to flow, the resistance is reduces. Of course in a production situation you need to test the fuse versus the thermistor in a fault condition to ensure that the fuse croaks first.

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