BA-3 As Preamp

@angrypat
my incompetent brain says:

- 2 x (100mA max Mosfet bias + 8 mA Jfet bias) = 216 mA current draw per rail from BA-3 front end...say 250
- R3 filters the AC and you can choose what fits the load: say 10 Ohms - gives 2.5 volts drop and 0.7 watts dissipation
- better use dual secondaries 2x(20-24)V xformer no centre tapped
- test with fuse and current limiter (e.g. low wattage light bulb) in place

Dual/Bipolar LV-Reg
 
Member
Joined 2017
Paid Member
For starters: I'll use a Ultrabib...

Hi!

I'm approaching in on the continuation of my BA-3.
I'll power it with an Ultrabib, recommendation is to "allow 50-150mA extra"...

[Edit: Just reading ozorfis post saying I'd need 250 mA / rail, while Dennis says 45 mA... :scratch: ]

What difference would it make wether I'd go smallish (total of 100 mA / Channel) or biggish (200 mA / Channel)?
I'm [edit: was] pretty sure everything in-between would work, but …

(ok, I know I should go and test it myself, but sometimes I'm :lazy:, sometimes I'm just hesitant :scared:, and maybe this is knowledge so easy as a this/that because so or otherwise?)

But but but, the
 
Last edited:
Official Court Jester
Joined 2003
Paid Member
when shunt reg is in the case, I'm usually allowing 25-50% of headroom, that being difference between programmed reg current and loading circuit current

if reg is made properly, no difference in sound between 25% and 250% headroom, under condition that load is pure A Class thingy (not being able to overstep Iq)
 
Hi!

[Edit: Just reading ozorfis post saying I'd need 250 mA / rail, while Dennis says 45 mA... :scratch: ]

Depends on the bias you like to run and if you refer to one or two channels.
Stock setting according to Papas article:
2 (channels) x (45 (Mosfet bias) mA + 8 (Jfet bias)) = 106 mA

I like to run my Mosfets at 100 mA Bias hence the higher figure.

:cheers:
 

Attachments

  • art_ba_3.pdf
    2.3 MB · Views: 212
Member
Joined 2017
Paid Member
ah, cool, thank you! (I had it right, Woohoo! :D)

:cheerful::cheers:

and then :sleep:

usually allowing 25-50% of headroom

I probably didn't quite understood this, please ignore if completely off: Do you let the resistor decide wether it's closer to 25% or 50% or is there a deeper understanding that leads you to either number? (I'd go for my favorite colour codes, hahaha)
 
Last edited:
Official Court Jester
Joined 2003
Paid Member
easy; example:

stage is having Iq (quiescent current) of 20mA

heat is nothing (hottest part in reg asking for just small heatsink), so programmed current of reg is , say, 70mA (that being headroom of (70/20)= 350%

second example:

stage is having Iq of 100mA

current becoming an issue, so reg's programmed current being , say, 135mA

that's 35% of headroom

pick figure which you want, being aware of dissipation of every part; two most critical parts being CCS main transistor and Shunt transistor (transistor being mosfet or bjt, irrelevant)
 
The original output devices for the BA-3 front end are 2SJ313 and 2SK2013, matched at 20v and 45mA. These devices, though, have been discontinued by Toshiba. A few members here may still have some inventory of these parts, so check the Swap Meet section if you are seeking original parts.

Edit: I believe you can substitute the P-channel 2SJ313 with part number FQP3P20 and substitute the N-channel 2SK2013 with FQP3N30 without any appreciable difference in outcome. It also appears that the replacement parts are now in End-of-Life stage as well. Not sure which parts are appropriate for an alternate to the alternate... I'm sure someone else can make a recommendation for you.
 
Last edited:
Member
Joined 2007
Paid Member
Transformer requirement...

Hi friends
Can the BS-3 run on a PSU consisting of a 2x24V 100VA transformer into a Ultra-bib?
And, how much current-draw should I aim for?
Asking because I got an offer for the trannies, Ultrabibs are already in the plan...

Thank you
david
It's been a while but I believe a BA-3 FE channel draws ~45mA and I set the BIB (not the Ultra) to sink ~100mA. The BIB drops ~7V so in your case the output after ratification and losses at the BIB would be around 26V, which would be good. I know others have used this same setup (BIB->BA-3 FE) with success. It would be appreciated if someone would confirm my numbers.