ALL TRANSISTOR OpAmp

Samuel Jayaraj · 5th August 2004, 08:33 AM

There is a lot of buzz in the MOX and related threads. All the suggested discrete opamps use JFETs like SK389 and J113 for the input stage.

I tried J111 in moamps circuit but it fails to work on the bench although the sim results are excellent. Other JFETs are very hard to come by except BFW10 and BFW11 and I wonder whether these would be suitable.

Hence, I have been trying various versions of bipolar discrete circuits. They sound very good with the only disadvantage of requiring input and output capacitors. Trimming offset has proved to be nearly impossible.

Does anyone here have any variant of bipolar discrete opamps (either 2 stage or 3 stage) which do not require input and output caps and have inverting and non-inverting inputs. I am asking since I have seen Class A buffers, but they have x1 gain and single inputs. I require some gain in the scheme that I would like to follow.

Any help would be appreciated and I think this would also help many of the forum members who are not able to obtain JFETs in their countries. Thanks!

aparatusonitus · 5th August 2004, 09:22 AM

This one looks promising http://johnhardyco.com/pdf/990.pdf

Regards, Ivo

Upupa Epops · 5th August 2004, 09:23 AM

Simplest discrete opamp you can see on pages of firm Bryston, where is used as input amp of power amps

.

p robertson · 5th August 2004, 10:41 AM

hi samuel. In the wireless world jan 1985 john linsley-hood describes a stunning symmetrical discrete op-amp,which should sound better than most i.c. op-amps.I hope that helps. Pierre
diy audio veteran.

Elso Kwak · 5th August 2004, 10:47 AM

Quote:

Originally posted by Samuel Jayaraj
There is a lot of buzz in the MOX and related threads. All the suggested discrete opamps use JFETs like SK389 and J113 for the input stage.

I tried J111 in moamps circuit but it fails to work on the bench although the sim results are excellent. Other JFETs are very hard to come by except BFW10 and BFW11 and I wonder whether these would be suitable.

Hence, I have been trying various versions of bipolar discrete circuits. They sound very good with the only disadvantage of requiring input and output capacitors. Trimming offset has proved to be nearly impossible.

Does anyone here have any variant of bipolar discrete opamps (either 2 stage or 3 stage) which do not require input and output caps and have inverting and non-inverting inputs. I am asking since I have seen Class A buffers, but they have x1 gain and single inputs. I require some gain in the scheme that I would like to follow.

Any help would be appreciated and I think this would also help many of the forum members who are not able to obtain JFETs in their countries. Thanks!

Hi Samuael,
The complementary part of the 2SK389 is the 2SJ109.
But you can also build a discrete folded cascode opamp with a non complementary frontend as Sonnya and I did:
Jfet/bipolar PCB and Schematic (finaly)
I do not use any input and output coupling caps for my line stage.

lumanauw · 6th August 2004, 03:32 AM

Quote:

hi samuel. In the wireless world jan 1985 john linsley-hood describes a stunning symmetrical discrete op-amp,which should sound better than most i.c. op-amps.I hope that helps. Pierre diy audio veteran.

I dont think there is such as DIY audio veteran. Audio is hobby for life.
I'm diy audio beginner, so I dont have that copy. Where can I see the design?

p robertson · 6th August 2004, 07:50 AM

I dont know if the jan 1985 discrete op-amp is published on the web. When i say veteran,i mean i have built most amp circuits that have been published over the last 20yrs or so,seeking the"perfect" amplifier!

lumanauw · 6th August 2004, 09:41 AM

Quote:

i mean i have built most amp circuits that have been published over the last 20yrs or so,seeking the"perfect" amplifier!

WAW. Which is the perfect SS amplifier from your opinion (the nicest sounding one, not the best measurement one)
Or are you still seeking?

moamps · 6th August 2004, 09:55 AM

Quote:

Originally posted by Samuel Jayaraj
I tried J111 in moamps circuit but it fails to work on the bench although the sim results are excellent.

Hi,
I just tried this opamp with J111 and it will work good with few changes: R7 to 100ohm, R5 to 750ohm, R6 to trimmer 10k (setting DC offset).

Regards
Milan

Jonathan Bright · 6th August 2004, 10:32 AM

The only problem with the WW 1985 Linsley Hood design is that it also has an FET input and that is what Samuel is trying to avoid.

5th August 2004, 08:33 AM	#1
Samuel Jayaraj diyAudio Member Join Date: May 2001 Location: Bangalore, India	ALL TRANSISTOR OpAmp There is a lot of buzz in the MOX and related threads. All the suggested discrete opamps use JFETs like SK389 and J113 for the input stage. I tried J111 in moamps circuit but it fails to work on the bench although the sim results are excellent. Other JFETs are very hard to come by except BFW10 and BFW11 and I wonder whether these would be suitable. Hence, I have been trying various versions of bipolar discrete circuits. They sound very good with the only disadvantage of requiring input and output capacitors. Trimming offset has proved to be nearly impossible. Does anyone here have any variant of bipolar discrete opamps (either 2 stage or 3 stage) which do not require input and output caps and have inverting and non-inverting inputs. I am asking since I have seen Class A buffers, but they have x1 gain and single inputs. I require some gain in the scheme that I would like to follow. Any help would be appreciated and I think this would also help many of the forum members who are not able to obtain JFETs in their countries. Thanks! __________________ Sam

5th August 2004, 10:41 AM	#4
p robertson diyAudio Member Join Date: Jul 2002 Location: london uk	discrete op amp hi samuel. In the wireless world jan 1985 john linsley-hood describes a stunning symmetrical discrete op-amp,which should sound better than most i.c. op-amps.I hope that helps. Pierre diy audio veteran.

6th August 2004, 07:50 AM	#7
p robertson diyAudio Member Join Date: Jul 2002 Location: london uk	discrete op-amp I dont know if the jan 1985 discrete op-amp is published on the web. When i say veteran,i mean i have built most amp circuits that have been published over the last 20yrs or so,seeking the"perfect" amplifier!

6th August 2004, 10:32 AM	#10
Jonathan Bright diyAudio Member Join Date: Feb 2004 Location: Queensland	The only problem with the WW 1985 Linsley Hood design is that it also has an FET input and that is what Samuel is trying to avoid. __________________ "It was the Spring time of the year when aunt calls to aunt like mastodons across the frozen waste." P.G. Wodehouse.

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5th August 2004, 09:22 AM	#2
aparatusonitus diyAudio Member Join Date: Jan 2004 Location: Split, Croatia	This one looks promising http://johnhardyco.com/pdf/990.pdf Regards, Ivo

5th August 2004, 09:23 AM	#3
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	Simplest discrete opamp you can see on pages of firm Bryston, where is used as input amp of power amps .

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