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Old 26th January 2013, 09:29 AM   #1
scafas is offline scafas  Italy
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Default new discrete opamp for line preamplifier

Hello everyone, I built this operational transistor and let me know which circuit and 'suitable to build a line-stage preamplifier.
must be supplied with dual voltage and the more 'simple as possible.
I tried to replace it with a NE5532 and I can say that it works very well but I would like a circuit that uses all its potential
Click the image to open in full size.
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Click the image to open in full size.

it's use bc550c /bc560c and bd135-bd136
tks
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Old 26th January 2013, 11:36 AM   #2
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This topology gives excellent results (it's similar to the Jensen JE990, but complimetary) - a few improvements are possible:

1) A current mirror on the LTP helps increase loop gain as well as equalize input offsets at the LTP.

2) Instead of a Darlington VAS, and emitter-follower driving a common-emitter VAS gives better results with the same number of transistors.

3) The Miller compensation may be referenced to the output (Cherry compensation), rather than the collector of the VAS, and helps reduce distortion of the output stage also.
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Old 26th January 2013, 08:39 PM   #3
scafas is offline scafas  Italy
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Default opamp jensen

Quote:
Originally Posted by linuxguru View Post
This topology gives excellent results (it's similar to the Jensen JE990, but complimetary) - a few improvements are possible:

1) A current mirror on the LTP helps increase loop gain as well as equalize input offsets at the LTP.

2) Instead of a Darlington VAS, and emitter-follower driving a common-emitter VAS gives better results with the same number of transistors.

3) The Miller compensation may be referenced to the output (Cherry compensation), rather than the collector of the VAS, and helps reduce distortion of the output stage also.
Can you explain with a diagram maybe intervening on my drawing?
the schematic it's a clone of jensen 918
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Old 21st January 2015, 10:13 AM   #4
scafas is offline scafas  Italy
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Default new clone

Quote:
Originally Posted by scafas View Post
Hello everyone, I built this operational transistor and let me know which circuit and 'suitable to build a line-stage preamplifier.
must be supplied with dual voltage and the more 'simple as possible.
I tried to replace it with a NE5532 and I can say that it works very well but I would like a circuit that uses all its potential
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

it's use bc550c /bc560c and bd135-bd136
tks
this is my new clone with lower dimension pcb
Click the image to open in full size.
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Old 21st January 2015, 04:02 PM   #5
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Very nice - I use a similar kind of construction in my LF03c discrete dual opamp. You can save some space by using 1/8W resistors like Dale ERL/RLR05 at some locations where the dissipation permits it.
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Old 21st January 2015, 04:21 PM   #6
scafas is offline scafas  Italy
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Quote:
Originally Posted by linuxguru View Post
Very nice - I use a similar kind of construction in my LF03c discrete dual opamp. You can save some space by using 1/8W resistors like Dale ERL/RLR05 at some locations where the dissipation permits it.
now i can same more space with a new pcb design.
so i have a 27x30mm max. ,, very good for replace some ic-standard operational amplifier.
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Old 21st January 2015, 04:33 PM   #7
scafas is offline scafas  Italy
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Default pcb for sale

i've some pcb of this clone , if interest contact me.
the kit is composed of 3 pcb.
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Old 13th February 2015, 06:40 PM   #8
Blondie is offline Blondie  Poland
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I'm curious how this opamp play. I hope that one day will be available for purchase this prototype. Regards!

Last edited by Blondie; 13th February 2015 at 07:01 PM.
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Old 16th February 2015, 06:01 AM   #9
scafas is offline scafas  Italy
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Quote:
Originally Posted by Blondie View Post
I'm curious how this opamp play. I hope that one day will be available for purchase this prototype. Regards!
you can :
operazionale. a discreti jensen 918 clone | eBay
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Old 23rd February 2015, 07:10 AM   #10
Joffe is offline Joffe  Norway
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I would guess this will work fine on +24/-24 V rails as well.
Have you tried? Does it get warm (unloaded)?

Last edited by Joffe; 23rd February 2015 at 07:22 AM.
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