increase the bias current of an opamp final stage

herve · 12th September 2003, 08:58 AM

please can you help me?

I want to increase the bias current of my final stage.
But it is not necessary to have a powerful output.

What can i do?

-Do nothing,it's a stupid idea and let the opamp like it is.

-Do a discrete opamp with class-a output like here:

http://sound.westhost.com/project07.htm

-Driving a buffer with an opamp bias in class A

like ppl do with opa637,el-2002,and mpf-103
(http://www4.head-fi.org/forums/showt...current+source)

or like linear technology do in the data sheet of the LT-1115

Thank you,herve.

carlmart · 12th September 2003, 01:30 PM

Quote:

Originally posted by herve

-Do a discrete opamp with class-a output like here:

http://sound.westhost.com/project07.htm

That discrete amp certainly looks interesting.

But perhaps I'd leave an option on the pcb to add a 68 ohm resistor between Q3's emitter and the V- supply. You can use the resistor or a wire later.

Carlos

peranders · 12th September 2003, 01:38 PM

herve, what is the whole purpose of this? Signal, load etc?

If you use any good opamp (AD8610, OPA134, OPA627 etc.) plus a buffer like BUF634 you'll get very good results.

Jan Dupont · 12th September 2003, 01:55 PM

If you want to make a discrete opamp, then take a look here:

http://www.passdiy.com/pdf/diyopamp.pdf

PMA · 12th September 2003, 01:56 PM

I would follow Per's advice and his (for example

) circuit solution.

PMA · 12th September 2003, 01:59 PM

ACD,

that's just a basic, nothing more (DIYopamp). 34 years ago there was a better example of Sinclair Z-30 or Z-50.

Jan Dupont · 12th September 2003, 02:08 PM

I know

It was only meant as a source of information

PMA · 12th September 2003, 02:15 PM

ACD, I have guessed that

.

Jan Dupont · 12th September 2003, 02:22 PM

Why are you always

on all???

herve · 12th September 2003, 02:28 PM

Well,an option on the pcb to add a 68 ohm resistor it's maybe a good idea.
But for Q1,Q2 do i need a pair of transistors in the same package like with an LM394?

The purpose of this is not for making an headphone amplifier.
The amplification factor is around 1000.
Maximum output around 1 volt.
Load: 10 to 100 kilo resistor.

The "idea" is to make a final stage with transistors which work "far away" from the cutoff current..
Forgive me for my English.

Regards,herve.

12th September 2003, 08:58 AM	#1
herve diyAudio Member Join Date: Jan 2003 Location: france	increase the bias current of an opamp final stage please can you help me? I want to increase the bias current of my final stage. But it is not necessary to have a powerful output. What can i do? -Do nothing,it's a stupid idea and let the opamp like it is. -Do a discrete opamp with class-a output like here: http://sound.westhost.com/project07.htm -Driving a buffer with an opamp bias in class A like ppl do with opa637,el-2002,and mpf-103 (http://www4.head-fi.org/forums/showt...current+source) or like linear technology do in the data sheet of the LT-1115 Thank you,herve.

12th September 2003, 01:38 PM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	herve, what is the whole purpose of this? Signal, load etc? If you use any good opamp (AD8610, OPA134, OPA627 etc.) plus a buffer like BUF634 you'll get very good results. __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

12th September 2003, 01:55 PM	#4
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	If you want to make a discrete opamp, then take a look here: http://www.passdiy.com/pdf/diyopamp.pdf __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

12th September 2003, 02:08 PM	#7
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	PMA I know It was only meant as a source of information __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

12th September 2003, 02:22 PM	#9
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	PMA Why are you always on all??? __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com


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12th September 2003, 01:56 PM	#5
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	I would follow Per's advice and his (for example ) circuit solution.

12th September 2003, 01:59 PM	#6
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	ACD, that's just a basic, nothing more (DIYopamp). 34 years ago there was a better example of Sinclair Z-30 or Z-50.

12th September 2003, 02:15 PM	#8
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	ACD, I have guessed that .

12th September 2003, 02:28 PM	#10
herve diyAudio Member Join Date: Jan 2003 Location: france	Well,an option on the pcb to add a 68 ohm resistor it's maybe a good idea. But for Q1,Q2 do i need a pair of transistors in the same package like with an LM394? The purpose of this is not for making an headphone amplifier. The amplification factor is around 1000. Maximum output around 1 volt. Load: 10 to 100 kilo resistor. The "idea" is to make a final stage with transistors which work "far away" from the cutoff current.. Forgive me for my English. Regards,herve.

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