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BA312 replacement

If you are looking for a 3 transistor phono board, here is one I made
similar to the TC750 phono preamp. It is a small board, about 3.75"x2".
I can post gerbers if any interest.

It is designed for ECB pinout devices like the KCS1815/1845, but I added
extra pads to allow using EBC transistors too.

Caveat - I got the boards made at Jlcpbc, but never got round to assembling them,
but it should work - fairly simple circuit.
 

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quadtech said:
If you are looking for a 3 transistor phono board, here is one I made
similar to the TC750 phono preamp. It is a small board, about 3.75"x2".
I can post gerbers if any interest.

It is designed for ECB pinout devices like the KCS1815/1845, but I added
extra pads to allow using EBC transistors too.

Caveat - I got the boards made at Jlcpbc, but never got round to assembling them,
but it should work - fairly simple circuit.
Click to expand...
Sure, nice work. However the goal here is to replicate BA312 (may be replicate is not a correct word) and to make a board which would be almost a drop-in replacement. If you read the whole thread then you know that people replicated the circuitry of BA312 (which is nothing but 3 transistors) and @bubhardy and me as well independently created adapters where we replicated BA312 and made it drop-in replacement instead of existing chip. There are also Sparkos modules as they call them discrete OA which can be used to replace BA312 and people reported significant reduction in a noise floor in their 9090db units while using Sparkos. But those Sparcos are expensive. And i was "carrying" this idea to use OA instead of BA312. With OA i can only come so much close to an easy replacement with some minimal changes on existing boards. But they should work well.
 
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Referring to the schematic (of the phono amp), I'd like to know where I can get some '0nF' capacitors - I'm sure they'll come in handy sometime :D
 
After thinking a bit more decided to change a layout of the adapter schematics. Added capacitor (C5)in a feedback circuit which initially i planned to use outside on pin 5. instead of NOT using pin 1 and 3 desided NOT to use pin 7 and USE pin 1 and 3. In original BA312 pin 1 is actually collector of the first transistor and usually connected to positive rail via resistor. So the idea here to connect together pin 1, 3 and 5. Then via resistor(will need to be calculated and calculation is simple) connected to Rail feed the zener ( 18V) connected to pin 3 and on pin 5 attach zener shunting capacitor. So the circuitry providing needed supply to new module will be outside of the module (so all potentially heated components (resistor and zener) will be kept out of the adapter.

Here is the new schematics :
BA312_OA_Version.png
 
So Comparing to previous schematic C5 was renamed to C2 (as on Phono corrector which is my prototype) Decoupling capacitor (Pin 7 of OA - positive supply) now C5. added R10 as on prototype phono corrector - if one does not need R10 jumper can be installed.

Will explain what needs to be done on original board in order to use this module later. But it is relatively easy.
 
So basically to install this module into the phono of 9090db one will need to first remove following components:
C06,C10,C26, C12, R12, R06,R08, R22,C14,C16,C18,R14,R16,R18.
In place of C12 install 470uF x25V low esr cap(connected to pin 5 of former BA312), in place of R12 install 18v Zener -> i choose BZX85B18 1.3W zener by Vishay.
In place of R08 install 1.4k capable of dissipating 1/2 Watt or more (Remember some of those resistors rated for 1/2 actually look like0.25W) I would use here Vishay RN60 or RN65 series (CMF60 or CMF65 in commercial variant). C04 can be replaced by any film cap from 0.47uF to original 3.3uF. Some question remains about output part of circuit. Prototype phono corrector (see schematics on previous pages) uses 10uF as interstage coupling cap (Capacitor C5 on phono corrector prototype and C20 on 9090db phono board) and 9090db phono board used 1uF. this all depends on input impedance of the next stages and output impedance of our Phono board, value of R10 of 1k has to do with it as well possibly. Well It is possible to calculate but for now i think we leave it 10uFx 25V UKL type? or if Wima suitable in terms of size? So after the above manipulations are completed, then module can be installed.

EDIT: By the way i took a look what it takes to install Sparcos modules and it surely looks like they modify the board and removing a lot of components as well. Those are no doubt nice modules but they look really bulky with multi layer adapters....
 
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I received a notification that adapter boards arrived. Will try to assemble first 2 when i get back home. By the way anybody willing to experiment with those ? You are welcome to get boards to try. Unfortunately currently i do not have unit to try this BA312 version out. Really curious.
Dennis.
 
Hipocrates said:
this is not my work... that's information from a guy on diyaudio. I don't know where I put the link.
Click to expand...


Modern pre-amp IC 7 pin in line?

I'm rebuilding a Sansui AU-5500, I came across an IC, BA312 manufactured by Rohm. It's a Dual preamplifier from the 1970s, it has 7 pins inline so I'm wondering if anyone knows of a modern drop-in replacement with better specs or just sounds better? Its the pre-amp for the phono section by the...
www.diyaudio.com www.diyaudio.com

This maybe?
 
I have a couple of these BA312 to replace in a Marantz 2325. When I do things like these replacement boards, I generally do them in larger quantities, I will probably order a minimum of 100 boards and all of the associated parts. I definitely think for me the SMT boards are going to be the way to go as the form factor is smaller overall. I’m wondering what should I go? I see there is the replacement using three transistors and some resistors and that will get me going down the road. Thank you to TupolevFan and Hipocrates it looks like there are attempts at making lower noise packages.

IMG_1509.png
IMG_1510.jpeg
IMG_1511.jpeg

Is this the closest to the Sparkos package so far?

IMG_1512.png
Is this?

I’m curious, yet doubtful that someone has tested multiple versions of this replacement to see which performs the best. Even if I went with just the three transistor board would want to get the absolute lowest noise devices possible. I’ve heard what the sparkles package can do to the noise floor and it is a pretty significant drop. I’m not paying those prices though. So if something could be had close I’d love it.

Dan
 
saabracer23 said:
I have a couple of these BA312 to replace in a Marantz 2325. When I do things like these replacement boards, I generally do them in larger quantities, I will probably order a minimum of 100 boards and all of the associated parts. I definitely think for me the SMT boards are going to be the way to go as the form factor is smaller overall. I’m wondering what should I go? I see there is the replacement using three transistors and some resistors and that will get me going down the road. Thank you to TupolevFan and Hipocrates it looks like there are attempts at making lower noise packages.

View attachment 3225470
View attachment 3225471
View attachment 3225472

Is this the closest to the Sparkos package so far?

View attachment 3225473
Is this?

I’m curious, yet doubtful that someone has tested multiple versions of this replacement to see which performs the best. Even if I went with just the three transistor board would want to get the absolute lowest noise devices possible. I’ve heard what the sparkles package can do to the noise floor and it is a pretty significant drop. I’m not paying those prices though. So if something could be had close I’d love it.

Dan
Click to expand...
Dan, if you rewind this thread couple of pages back you will see that one of the AK member @aldena007 did test my versions of the boards (transistor version). And conclusion is that they perform as originals not worse not better. Schematics was given by @Hipocrates I think. By the way smd version is only 10mm tall. My current idea is to use OA in attempt to improve it. It might or might not work. Will see
 
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