Whats this for?

davidallancole · 24th July 2006, 04:18 PM

What is R14 for in this picture. It is Doug Selfs Blameless Class B amp.

richie00boy · 24th July 2006, 04:24 PM

It changes the slope of the thermal compensation mV/degC.

mikeks · 24th July 2006, 04:41 PM

See Hawksford here

davidallancole · 24th July 2006, 04:42 PM

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?

mikeks · 24th July 2006, 05:13 PM

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.

sreten · 24th July 2006, 05:45 PM

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.

24th July 2006, 04:24 PM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	It changes the slope of the thermal compensation mV/degC. __________________ And yes, there are capacitors in the circuit. One is even employed to form the dreaded bootstrap on the voltage gain stage. Get over it. -Burning Amplifier #2, Nelson Pass www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

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24th July 2006, 04:41 PM	#3
mikeks Account Disabled Join Date: Jun 2004 Location: Animal farm	See Hawksford here

24th July 2006, 04:42 PM	#4
davidallancole diyAudio Member Join Date: Nov 2005	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?

24th July 2006, 05:45 PM	#6
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	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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