Bub,
Bub, here is the internal schematic for the BA312 if you want to build your own boards.
BA312 replacement
- Thread starter bubhardy
- Start date
slowpat
Slowly but surely....
That’s a great option at 5 bucks! Didn’t realize Eastpoint carried them…thanks for posting the link
My pleasure!
Here's a pic of a Sansui QRX9001 where the front right channel was out. You'll see the Left Channel BA312 still in-place and the new Right Channel module just to the right.
Attachments
You can buy drop in premade BA312 replacements on eBay from this fellow, magnepanman!
https://www.ebay.com/itm/354573373847
They work perfectly!
https://www.ebay.com/itm/354573373847
They work perfectly!
It's been a long time, Vinyl David! Hope you found that Hayseed Hamfest cap years ago for your MC2300! Great seeing you out here again!
Here's the same guy I posted where he assembles the kit for the buyer. I prefer the $5 kit option.
https://www.ebay.com/itm/1155761229...hxKUyrjQlnJGU0VNNXWmp3pZjYTJVVjEaAudAEALw_wcB
Your module has a MUCH cleaner look! Thanks for sharing this one, David!
Hi there!
I actually don't ever recall owning a MC2300!! MC30s, 40s, 2100, some 2105s…yes! I’ve got one MC40 left, one that’s tagged “Aaron Copland’s Amp”. No way I know to prove it though. I’ll rebuild it later this year and I’ll definitely need a can cap then!
There’s definitely a number of other options for the Ba312, but the one I linked to on eBay is drop in, which is worth the time and energy reduction for me!
TupolevFan
Super Member
Funny, if you look at the beginning of this thread and take the adapter i presented here for non-smd version you surprisingly find out that the adapter i presented and the one selling on e-bay are twin brothers but i am not selling those
). Anyway gerber files for both versions(smd and non-smd) are available at the beginning of this thread. Anybody are welcome to use those and order from JLCPCB )).Dennis.
These are the best available for fit and look.
I think I used your schematic!Funny, if you look at the beginning of this thread and take the adapter i presented here for non-smd version you surprisingly find out that the adapter i presented and the one selling on e-bay are twin brothers but i am not selling those
Dennis.
I got mine from JLBPCB. I did a 4x4 array.
TupolevFan
Super Member
In the beginning @bubhardy was interested in using operational amplifier as a potential replacement for BA312. I also was "carrying" this idea for a while as sparkos modules to replace BA312 are nice but quite expensive. I went through several schematics which could suite this task. And i have first iteration . However i must warn that this is not complete drop in replacement and some adjustments will be necessary. First i decided to create the replacement for phono stage in 9090db . There are several points which can prompt a discussion (hopefully in a constructive way )))
Here is the Phono corrector of 9090db :
)))Here is the Phono corrector of 9090db :
TupolevFan
Super Member
As a base for my adapter i took the following schematic of Phono corrector on OA TL072 by Texas Instrument. 
TupolevFan
Super Member
Here OA is fed by 12V which is reduced to 9. Second zener is biasing non-inverting input at aprox 4.5V (half of 9 volts). Second zener is necessary because as one can see we are feeding this OA via Single polarity power supply. This suits us as we have Single polarity PS feeding BA312. The only difference I decided to feed it via 18Volt (much less voltage drop from 43 Volts. So Second zener should be 9V in this case.
Of cause i will not use all of the components on adapter as some of them already on the board. Now for the first variant I decided to use RIAA circuit on the adapter as it is advisable that those components kept as close to OA as possible. But i am opened for objections. So the components for original RIAA circuit should be removed (R22,R14,R16,R18, C14,C16,C18,R12). Aslo C26, R06,R08,C10, C06 should be removed as well).
Here is what will be on Adapter :
Of cause i will not use all of the components on adapter as some of them already on the board. Now for the first variant I decided to use RIAA circuit on the adapter as it is advisable that those components kept as close to OA as possible. But i am opened for objections. So the components for original RIAA circuit should be removed (R22,R14,R16,R18, C14,C16,C18,R12). Aslo C26, R06,R08,C10, C06 should be removed as well).
Here is what will be on Adapter :
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TupolevFan
Super Member
As you can see from schematics of my adapter i will not use pin 1 and 3 of original BA312. On pin 5 i plan to install 22 uF or one can install even larger cap. Pin 7 will be connected to slightly modified circuitry on F-2653 of 9090db. So on F2653 besides removed components mentioned above resistor R10 will need to be recalculated. Voltage drop on R10 will be 43 -18 = 25 V Current should ve around 10 -12 ma. Which means R10 should be 25V / 0.012A which is about 2k. Will dissipate a bit less than 0.3 Watt. So i would install 1-2 Watt capable resistor to keep it cool and sound. Also in addition to C08. 18V zenner should be installed (in parallel to C8). I would choose BZX85B18 by Vishay.
now the shaky part. for C3 and C4 on my adapter schematics i was going to use SMD film caps BUT (there is always BUT)) I could not find 2nF for smd version of film cap. But i did find 1% G0G/NP0 ceramic and plan to use them. Any objections using this type of ceramic in RIAA ???
This adapter should have no issue to be used in preamp section (just do not instal R8,C3, C4) but values for R7 and R6 will need to be adjusted to get correct gain ( I think usually it is about 14dB or voltage gain of 5-6 ?
Also as OA I decided to use OPA1641 also by TI. But TL072 can be used as well as OPA604 and others
Remember all of the above should be done to the components of the other channel.
now the shaky part. for C3 and C4 on my adapter schematics i was going to use SMD film caps BUT (there is always BUT
)) I could not find 2nF for smd version of film cap. But i did find 1% G0G/NP0 ceramic and plan to use them. Any objections using this type of ceramic in RIAA ???This adapter should have no issue to be used in preamp section (just do not instal R8,C3, C4) but values for R7 and R6 will need to be adjusted to get correct gain ( I think usually it is about 14dB or voltage gain of 5-6 ?
Also as OA I decided to use OPA1641 also by TI. But TL072 can be used as well as OPA604 and others
Remember all of the above should be done to the components of the other channel.
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Should be fine.
It just strikes me that the use of an OP amp might be overkill? - the three transistor equivalent seems sufficient for the purpose?
If anyone tries this, I would be interested to hear if any improvement is noticeable (listening or measuring) when using the OP amp version compared to the 3 transistor version.
Good bit of work though.
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TupolevFan
Super Member
So OPA1641 in SOIC-8 package is $2.20 + probably another 10 USD for other components. + if one orders 20 boards which with shipping going to be about 25 USD and it would mean about 2 USD per adapter Totaling about 15 USD per kit. Comparing to 100 USD sparkos modules it may by worth attempt to try out lowering the noise floor )
)
TupolevFan
Super Member
You might be right about overkill, however point of this exercise is to lower the noise floor. People after installing the Sparkos module reported reduction in noise floor and their module is a monster comparing to this oneShould be fine.
It just strikes me that the use of an OP amp might be overkill? - the three transistor equivalent seems sufficient for the purpose?
If anyone tries this, I would be interested to hear if any improvement is noticeable (listening or measuring) when using the OP amp version compared to the 3 transistor version.
Good bit of work though.
)) as they introduced discrete OA