BA312 replacement

[saabracer23]

I did test these and the noise went down but, from memory, no more than 10dB. As @Hyperion says, only to be sucked up by the noise floor of the rest of the unit. All that voltage gain to get the big watts out causes a lot of that.

I kind of want to do this testing, just to see, but I have a very strong feeling that I’m just going to be wasting my time. I want to test the Marantz 2325 with the factory BA312 in it. It has been fully restored otherwise, all new capacitors, many films. So it’s not completely factoring. I had some parts delivered today, so after testing with the BA312 I will put in the boards with the original schematic.

Obviously those are the TO92 part numbers, these are what I used.


And then after those use the boards with the low noise 2SC2713. I don’t suspect a huge difference, if at all. Maybe a difference from the original BA312.


But we will see. I’m still very new to the analyzer, I do have to figure out how to do a frequency response and a distortion graph. Basically all I’ve used for is measuring distortion at a given output.

Hopefully I with some results

Dan

 

[Warren-Oates]

I did test these and the noise went down but, from memory, no more than 10dB. As @Hyperion says, only to be sucked up by the noise floor of the rest of the unit. All that voltage gain to get the big watts out causes a lot of that.

I just replaced four BA312 chips on a 9090, the two on the tone board and the two on the phono board. After replacement I tested with cheap headphones and volume at zero, listening to the hiss. I did notice a bit of improvement after replacing the tone board BA312s. A few days ago somewhere I stumbled on the fact that the Mic board also had one BA312, and the Mic board is always in circuit even with the mic volume down. I thought about that and looked at mine, you can replace the Mic board BA312 without removing any boards, a little awkward getting the new one in blind but not too bad. When I went to test at first I thought perhaps the headphones were not plugged in, but they were, the hiss was just gone. So in my case the big culprit was the Mic board BA312. Listening to a record on a 9090 involves five BA312s, if you have one noisy one that's all it takes. To me as easy and inexpensive as they are to replace my opinion is do them all on an 8080 or 9090.

 

[rBuckner]

I just replaced four BA312 chips on a 9090, the two on the tone board and the two on the phono board. After replacement I tested with cheap headphones and volume at zero, listening to the hiss. I did notice a bit of improvement after replacing the tone board BA312s. A few days ago somewhere I stumbled on the fact that the Mic board also had one BA312, and the Mic board is always in circuit even with the mic volume down. I thought about that and looked at mine, you can replace the Mic board BA312 without removing any boards, a little awkward getting the new one in blind but not too bad. When I went to test at first I thought perhaps the headphones were not plugged in, but they were, the hiss was just gone. So in my case the big culprit was the Mic board BA312. Listening to a record on a 9090 involves five BA312s, if you have one noisy one that's all it takes. To me as easy and inexpensive as they are to replace my opinion is do them all on an 8080 or 9090.

Great info, thanks!

 

[Namlook]

Anybody have a part number for the appropriate right angle (7) pin headers for the BA-312 boards for sale online?

 

[Hyperion]

Anybody have a part number for the appropriate right angle (7) pin headers for the BA-312 boards for sale online?

Up until now, I've been using those provided to me by helpful members.

However after some searching I found this, which is the same specification part.

Mouser p/n 538-22-28-8360
Which is a 36 way 'breakaway' strip of 2.54mm (0.1") spaced pcb pins, with right angle mounting (i.e. upright board).

 

[Hyperion]

Mouser p/n 538-22-28-8360

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www.mouser.co.uk

Something weird happened to my post, so edited it so it didn't look like a double post.

 

[TupolevFan]

For the last two years i was passive on this forum as I was going throug not very pleasant times for myself. But BA312 with OPA1641 for 9090/8080db was on my mind. In last couple of weeks i was reconsidering the design and i came up with the solution. I already orderd adapter boards. For phono board i plan to use OPA1641 plus TI REF7050 for absolutley quiet OA biasing and additional adapter board to drop voltage from 43 V to aprox down 13 V using Capacitance multiplier using darlington transistor instead of existing RC filter. what saves me is the fact that quincent current for OPA1641 is only 1.8 mA and REF7050 is another 5ma totaling around 7 to 8 MA. For any TO-126 should be easy to handle it. I even will install some dropof resistor to share the power dissipation with transistor a bit. For line preamp schematic is going to be similar but istead of expensive REF7050 will use 8.2 version of TI LM4040 voltage reference for biasing of OPA1641. LM4040 is higher noise than RF7050 but still much quiter that regular zener (even 5.6 or 6.2V zener) so for line amp should be good enough. For line amp there may be no need to drop voltage too much, just make it more stable 28 to 29 volts also via Capacitance multiplier as well. I needed to drop to 13V for phono as max recommended supply voltage for REF7050 is 18V and absolute max is 20V. I decided that 13V would be a sweet spot

 

[The Fuxtor]

I just replaced four BA312 chips on a 9090, the two on the tone board and the two on the phono board. After replacement I tested with cheap headphones and volume at zero, listening to the hiss. I did notice a bit of improvement after replacing the tone board BA312s. A few days ago somewhere I stumbled on the fact that the Mic board also had one BA312, and the Mic board is always in circuit even with the mic volume down. I thought about that and looked at mine, you can replace the Mic board BA312 without removing any boards, a little awkward getting the new one in blind but not too bad. When I went to test at first I thought perhaps the headphones were not plugged in, but they were, the hiss was just gone. So in my case the big culprit was the Mic board BA312. Listening to a record on a 9090 involves five BA312s, if you have one noisy one that's all it takes. To me as easy and inexpensive as they are to replace my opinion is do them all on an 8080 or 9090.

Is this the same with the db models??

 

[TupolevFan]

here is the version of BA312 for Sasui 8080/9090db phono back and front of the adapters. REF7050 is really tiny chip

 

[TupolevFan]

by the way i looked and it seems to me that for Marantz it might be even easier to replace. For OA I used OPA1641. However it cooud be interesting to try OPA1655 (looks like even lower noise then OPA1641 but OPA1655 is a faster amp and I am not sure if my board's layout is optimal. So worry is oscillation(hopefuly no but who knows) Another nice option might be LT1007 by analog Devices and i like it because of the max rail

 

[absolve2525]

here is the version of BA312 for Sasui 8080/9090db phono back and front of the adapters. REF7050 is really tiny chip

Are these available for sale?

 

[TupolevFan]

Are these available for sale?

Me and the other member will evaluate those first as this should be considered prototypes for now. But now I do not see any reasons why the would not work. In addition to this there would be capacitance multiplier board which would be installed in place of the rail caps installed on Phono board (C07, C08). This capacitance multiplied board purpouse is to drop 43 V to 13V and additional filtering of the rails. The size of the board will be comparable to the size of C07, C08.. Once given green light they will be avail.