optimizing the VBE multiplier - Page 2

jaycee · 14th January 2005, 01:24 PM

If you want something different, I have also seen a TL431 used as a vbe device, with a string of diode-connected transistors for thermal tracking. Look at the Stochino amplifier for an example

BTW you can get at least one TL431 for free from a dead PC PSU. I have a stack of them.

hienrich · 14th January 2005, 01:31 PM

jaycee:

hi do you have schemes for this.

hienrich

jaycee · 14th January 2005, 01:43 PM

Here it is:

http://www.soton.ac.uk/~apm3/diyaudi...no_circuit.jpg

I just tried this TL431 in my triple darlington amp SPICE sim (similar to the Leach Amp) and found it to be a bit tricky to control. Maybe a simple Darlington VBE would be best.

hienrich · 14th January 2005, 01:59 PM

thanks Jaycee,

I got it I on to it now.

hienrich

offline........

Jennice · 14th January 2005, 02:14 PM

Heinrich,

When I sent my first reply, I didn't have time up open your schematic.
Therefore I didn't know that you were already using a capacitor. I am using a 100uF in mine, and it works well for me.
I don't see a need for the film too, as the frequencies are low. They're more relevant for HF problems, I think.

Who says your transistor needs to be on the PCB, and you need to redesign your PCB???
I have mine connected to the PCB with wires. Who cares - it's just a DC source with floating potential, so you won't have to worry about inductances in the wires and HF problems with the Vbe multiplier / thermal monitor.

Jennice

richie00boy · 14th January 2005, 02:17 PM

Jennice, your assumptions are not correct according to Leach. See his website.

Jennice · 14th January 2005, 02:31 PM

Which part of my assumptions?

richie00boy · 14th January 2005, 02:52 PM

Quote:

Originally posted by Jennice
Who says your transistor needs to be on the PCB, and you need to redesign your PCB???
I have mine connected to the PCB with wires. Who cares - it's just a DC source with floating potential, so you won't have to worry about inductances in the wires and HF problems with the Vbe multiplier / thermal monitor.

That bit. It's not just a DC source with floating potential because it's in the path of the VAS which is subject to AC and is sensitive to capacitance.

Jennice · 14th January 2005, 03:04 PM

And who tells you thet one cannot have a DC source in an AC path? It just gives an offset.

I know the Vbe isn't an idea DC source with zero output impedance, but that's why the capacitor is placed on the PCB.

Jennice

Cortez · 14th January 2005, 03:16 PM

14th January 2005, 01:31 PM	#12
hienrich diyAudio Member Join Date: Dec 2004 Location: City of Gentle People	do you have schemes for this jaycee: hi do you have schemes for this. hienrich

14th January 2005, 01:59 PM	#14
hienrich diyAudio Member Join Date: Dec 2004 Location: City of Gentle People	thanks I got it.... thanks Jaycee, I got it I on to it now. hienrich offline........

14th January 2005, 02:14 PM	#15
Jennice diyAudio Member Join Date: Jun 2003 Location: Planet Earth	Heinrich, When I sent my first reply, I didn't have time up open your schematic. Therefore I didn't know that you were already using a capacitor. I am using a 100uF in mine, and it works well for me. I don't see a need for the film too, as the frequencies are low. They're more relevant for HF problems, I think. Who says your transistor needs to be on the PCB, and you need to redesign your PCB??? I have mine connected to the PCB with wires. Who cares - it's just a DC source with floating potential, so you won't have to worry about inductances in the wires and HF problems with the Vbe multiplier / thermal monitor. Jennice __________________ I get paid to break stuff. My g/f gets paid to play with children. Life is good.

14th January 2005, 02:31 PM	#17
Jennice diyAudio Member Join Date: Jun 2003 Location: Planet Earth	Which part of my assumptions? __________________ I get paid to break stuff. My g/f gets paid to play with children. Life is good.

14th January 2005, 03:04 PM	#19
Jennice diyAudio Member Join Date: Jun 2003 Location: Planet Earth	And who tells you thet one cannot have a DC source in an AC path? It just gives an offset. I know the Vbe isn't an idea DC source with zero output impedance, but that's why the capacitor is placed on the PCB. Jennice __________________ I get paid to break stuff. My g/f gets paid to play with children. Life is good.


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14th January 2005, 01:24 PM	#11
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	If you want something different, I have also seen a TL431 used as a vbe device, with a string of diode-connected transistors for thermal tracking. Look at the Stochino amplifier for an example BTW you can get at least one TL431 for free from a dead PC PSU. I have a stack of them.

14th January 2005, 01:43 PM	#13
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Here it is: http://www.soton.ac.uk/~apm3/diyaudi...no_circuit.jpg I just tried this TL431 in my triple darlington amp SPICE sim (similar to the Leach Amp) and found it to be a bit tricky to control. Maybe a simple Darlington VBE would be best.

14th January 2005, 02:17 PM	#16
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Jennice, your assumptions are not correct according to Leach. See his website.

14th January 2005, 03:16 PM	#20
Cortez diyAudio Member Join Date: Dec 2002 Location: Hungary

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