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Old 24th July 2006, 04:18 PM   #1
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Default Whats this for?

What is R14 for in this picture. It is Doug Selfs Blameless Class B amp.
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Old 24th July 2006, 04:24 PM   #2
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It changes the slope of the thermal compensation mV/degC.
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Old 24th July 2006, 04:41 PM   #3
mikeks is offline mikeks  United Kingdom
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See Hawksford here
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Old 24th July 2006, 04:42 PM   #4
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I went and read the Hawksford paper on the circuit. My understanding from reading it is that this circuit will minimise the changes in the bias voltage based on changes in the current going through it. So it would then keep your bias voltage more stable for any changes temperature wise in your VAS stage.

So, richie00boy, your saying you can change your compensation slope as well? You could then change it from -2 mV/degC to -3 mV/degC or what ever you want to put it at by changing the R14 resistance?
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Old 24th July 2006, 05:13 PM   #5
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by davidallancole
..... this circuit will minimise the changes in the bias voltage based on changes in the current going through it.
Correct.
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Old 24th July 2006, 05:45 PM   #6
sreten is online now sreten  United Kingdom
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Hi,

From what I remember from Selfs book :

it changes the slope of the Ivas vs Vb curve to a gently peaking
characteristic, with the right value you can set Vb to be in the middle
of this peak. Consequently Vq thus Iq becomes less dependent on
ambient temperature, variations in mains voltage and power supply
droop.

It does not change the thermal compensation mV/C in Selfs design.
Its purpose is to stabilise Vq, i.e. in Hawkfords paper R3opt is used.

Self shows elsewhere in his book how to manipulate mV/C of the bias.

/sreten.
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