The BA-3 as preamp build guide

[r580808]

If I replace 2sk170/2sj74 with 2sk147/2sj72, do I need to change the bias resistor from 100Ω to 1kΩ? Thanks.

 

[Zen Mod]

no, just shoot

 

[r580808]

I ask this because my other BA-3 FE is installed with the 2sk170/2sj74 GR version instead of the BL version. The bias resistor is changed to 1kΩ to drive the MOSFET. Thanks for your answer.

 

[r580808]

Grok is also a suggestion, as you said, no need to change.

R = Vgs / Id = 0.293V / 0.005A = 58.6 Ω

 

[r580808]

The P1 and P2 bias resistors are 500 ohms. They were written incorrectly and cannot be modified. Sorry.

 

[Giovanni1968]

Hello,
question, thinking of turning my SE BA3 preamp into balanced (a second PSU and transformer already installed in the same case) but I don't remember if the JFETs I got (one or two of which weren't good and changed with some from an EU source) were 8-11 or 6-8mA, what does it change if on the second BA3 board I have different than the other one's JFETs?

Grazie

p.s. Nelson says: "

• These would be my choices for various projects: BA3 Gain Stage: 6-8 mA (2SJ74 operated at 5 mA) / 8-11 mA (2SK170 at 10 mA)"

 

[anystereo]

Hi,

I asm building a BA-3 pre amp, and am looking for currently available mosfets to replace the original specified 2SK2013 & 2SJ313'S, could some please suggest alternatives.

best wishes,

David

 

[6L6]

IRF610PBF IRF9610PBF

 

[ndiyer]

Hi anystereo, you could also ask Tamra for the original ones
https://www.diyaudio.com/community/threads/toshiba-2sk2013-2sj313.416435/latest
I bought from him and can recommend as reliable source.

 

[Giovanni1968]

Are these attached gonna work to populate a second BA3 board to make of mine a balanced one?

The actual board been populated with the Toshiba ones

Grazie

 

[6L6]

Those are the “A” Idss range, you need “B” for the BA-3.

 

[NightFlight]

The boards are out of stock, do they get re-stocked often? I set the notification for when they are back in stock. Several times...

 

[birdbox]

I suspect they will be back in stock eventually. Just gotta be patient.

If anyone wants to try the FQP3P20/FQP3N30 parts instead of the hard to find and spendy Toshiba 2SJ313/2SK2013 in a BA3 front end build, I have some to share. I have both matched NN channel and matched PP channel quads. I also have a fewas NNPP matched quads (the latter not really necessary for BA3 FE). If you feel you must use the Toshiba 2SJ313/2SK2013 in your BA3 FE build, I believe @tamra and @prakit both have provided those to "Greedy Boy" diy'ers in the recent past.

 

[NightFlight]

Do the input transistors benefit from matching as well? If so, it would seem they are a store buy at this point. Looks like the alternates are also Toshiba. @birdbox if you could PM me for pricing on the output alternates your offering you can likely put me down for those.

 

[ItsAllInMyHead]

Do the input transistors benefit from matching as well?

The JFETs should be matched, yes.