BA-3 As Preamp

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#1,381
@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
 
#1,382
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
 
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#1,383
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)
 
#1,384
ZM lightsabremasterfastansweringmachine justalittlebittoofast buttheanswerseemstofit - somehow...

250 mA + 25% = 312
100 mA + 250% = 350

Now I have to find out which is righter. Trusting Dennis but need to find a good 3rd opinion.
 
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#1,385
myleftear said:
Hi!

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

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:
 

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#1,386
ah, cool, thank you! (I had it right, Woohoo! 😀)

:cheerful::cheers:

and then 😴

Zen Mod said:
usually allowing 25-50% of headroom
Click to expand...

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)
 
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#1,387
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)
 
#1,388
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
 
#1,392
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.
 
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#1,393
myleftear said:
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
Click to expand...
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.
 
#1,395
As mentioned, that information doesn't really exist in one simple place, this is about as good as it gets - https://www.diyaudio.com/community/threads/the-ba-3-as-preamp-build-guide.258022/

BOM can be discerned from schematic and having the PCB in hand.

PSU is yours to choose. Also true with attenuation and selection.

This is a very straightforward project, but in the old style of "Here is schematic and PCB, it's up to you."
 
#1,397
Hello, couple questions, provided some Toshiba FETs are still available I'd like to turn my BA3 preamp into a balanced version so:

  • I suppose the volume pot has to be swapped for a balanced version, correct?
  • Which is the size of the box you used? I think I used a pesante 3U which is huge, there's plenty of space to fit a second PSU/Transformer/BA3 board but too tall and deep, just wondering which size you used
  • Is there a dedicated thread for the balanced version of the BA3 as a preamp?

Thank you
 
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