The BA-3 as preamp build guide

[Russellc]

Yes, one for each channel.

Russellc

 

[escucalin]

I have a question ; but it needs some framing:


I am also approaching the balanced BA3 FE + OS but coupled with a Phono as well .


I am not willing to put the BA3 balanced FE in the same box with the BA3 output stage (or naked F4 as some refer to) so i took the separate box approach.
Also inside the BA3B Front end box I wish to cram 2 +- of Salas's shunts and a Folded simplistic Phono as well of Sala's creation along with its basic shunt. (reaching the question now)


I went and read all the related threads; but did not found a solid and intuitive solution on how to go about and obtain a BA3B that can function as a Balanced and unbalanced solution from the flip of a switch.


As far I understand is that in order to feed unbalanced signal to the BA3B is as easy as to short the in 1(negative signal) and 3(ground) of a XLR input . That means effectively turn to ground half of pre and giving no signal to the negative side of the output stage.


I assert than, that my understanding is wrong and there is another way!

So how do i feed the unbalanced signal from the phono to the BA3B (consider an added complexity feature of having both BA3 B and Phono powered by the same transformer but from different windings)


Edit: Realizing that i might be off topic; this belonging to BA3 B thread; am I right?

 

[Zen Mod]

BA3 BAL is acting as unbal to bal converter , when neg. input leg is grounded

easy as that

 

[escucalin]

Then coming back to my assertion:
Wouldn't then the negative part of the BA3B FE (being grounded) act only as a white noise generator for the corresponding negative part of the output stage?

 

[6L6]

You could describe it as that, sorta... but;

It's a moot point if you want to drive the output stage balanced.

 

[Zen Mod]

wrong question ;

you need to ask, after reading my reply - how's that achieved ?



BA3 BAL will give you proper drive from both outputs , irrelevant is it modulated at both or just one inputs

that's called unbal/bal converter

 

[escucalin]

Indeed Zen wrong question just because was being afraid all the time that to achieve a one box , one switch bal/unbal version of a pre, high quality unbal->bal transformers are needed which is another barrier .

As reinforced here: by Ken

 

[6L6]

Or you could add a balanced line driver to the output of the Salas Phono - that's a standard way of addressing the issue.

The down side of going balanced before the preamp (which may or may not be any issue) is you'll need a 4-gang pot for volume if everything is balanced.

 

[escucalin]

Balanced line driver ?
I assume i can implement it before the buffer stage and double the buffer stage that means an absurd number of rare jfets Maybe trafo is not such a bad idea after all (found it bare) jensen 1:1 transformer eBay

Thanks for all the guidance!

 

[6L6]

Or add a simple and quiet circuit on the Salas output...

This uses the excellent THAT1646 -

SparkFun THAT 1646 OutSmarts Breakout - BOB-14003 - SparkFun Electronics

And Rod Elliot's site has lots of great information -

Balanced Line Driver & Receiver

 

[Zen Mod]

if BA3 Bal is working as bloody unbal/bal converter , why adding another one ?

 

[escucalin]

As far as i understand, grounding the negative side of the balanced input is no conversion(simply a way to quicky use a balanced pre with an unbalanced source.
I am most certain that what you are speaking of is not really conversion but a pseudo-balanced.

6l6 helped pointing that the unbal signal can be fed to an opamp to buffer the signal, and and invert it hence obtaining a differential signal.
That's again something different than what the point is and not at all useful in audio.
Even if it would be the case I really would not want to use opamps and negative feedback on the chain that is based on almost zero feedback and jfet engineering beauty.

So with all the help you guys gave me i reached the conclusion that what i was avoiding (unbal->bal via a transformer) is the only real solution to integrate an unbalanced source in a balanced chain.

Thank you so much!Hard to come by audience to bounce ideas and find the right way using arguments

 

[indra1]

... Wouldn't then the negative part of the BA3B FE (being grounded) act only as a white noise generator for the corresponding negative part of the output stage?

No, Pass magic (in the form of R5 connecting both sides of jfets summing points) ensure equal magnitude but opposite phase signal on both outputs of the BBA3FE when one of the inputs is grounded. A True Balanced, No pseudo-balanced, No white noise generator, No need for any addition Nor modification.

 

[escucalin]

I forgot about the "summing" resistor ; I always considered the + and - sides as separate.

Sorry Zen,

Thank you Indra!

 

[mbedwani]

Confirm Super Reg wiring

Hi Guys,

Need a bit of clarification regarding the DiyAudioStore SuperReg Wiring for the BA-3 Pre-amp. Some of the info links for the SuperReg no longer work. Seems a bit confusing. I'm used to just AC in then +24v-0-24v out for example.

Have I got it correct in the diagram below ?



Mark.

 

[WalterW]

Hi Guys,

Need a bit of clarification regarding the DiyAudioStore SuperReg Wiring for the BA-3 Pre-amp. Some of the info links for the SuperReg no longer work. Seems a bit confusing. I'm used to just AC in then +24v-0-24v out for example.

Have I got it correct in the diagram below ?

View attachment 703849

Mark.

Hoi Mark,

I built the exact same configuration. You can tie the Vsense to each corresponding Vout, and wire from there. See my edits in black on your picture. That is easiest.

You can also extend the Vsense like I did with a smaller wire to the point where you connect them both on the BA3 PCB.
That's the best way, but difficult.

I have attached a high res picture so you can see how I did it, but wiring is difficult that way. Especially at the GND connection of the BA3 PCB where 4 wires terminate.

 

[mbedwani]

Hi Walter,

Thanks for clarifying

A few questions regarding your build, (Very nice by the way). Why did you use two SuperRegs, I assume you could have just used one?

Also what is that Bridge Board you used, I can't make out the name and are they still available?

Mark.

 

[mbedwani]

Hi Guys, one more, Looks like it’s hard to find good 10µF MKP caps for “C3”, can someone please point me to a link for some not too ridiculously expensive caps, Mouser and Digi-key etc. don’t seem to stock any axial ones. Also what is their use case in this circuit, to me is seems they are being used as a HighPass filer i.e. filtering say above 20khz, am I right?

Mark.

 

[6L6]

Mouser -

Axial Polypropylene (PP) 10 uF Film Capacitors | Mouser

They are output coupling caps to keep any residual DC from your amplifier.

Here's a single suggestion in case the above list doesn't link properly -

C4GADUC5100AA1J KEMET | Mouser

 

[albertNL]

Humble cap test found these OK so I could not resist at this price and bought 10 of these. I have not used them yet.


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