The BA-3 as preamp build guide

Thanks for the quick response .
As I am not an expert, I know how to weld and make the necessary measurements.
I will ask an innocent question, which components should I check? Replace Trimmers?
The resistances were measured before assembly, the mosfets is 2SJ and 2SK purchased to Prakit.
Thanks.
P. Dias
 
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I'm using the H9KPXG in my BA-3 preamp. Works like a champ.

I'd like to move to the Khozmo 64 steps relay-based ladder type attenuator with remote.

This set-up requires a 5VDC feed. I thought I could just use the 5Vdc from the board. But the Khozmo requires linear power supply, not SMPS. I'm trying to work out how to provide a linear power supply. I'm hoping I can use the Glassware LV-Regulator set to 5VDC which is currently sold out.

If that all holds together, I'm stumped as to how I feed or connect a 2nd transformer for the LV from the H9KPXG?

Appreciate any help.
 
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What's in your current power supply for your BA3 preamp? Have you considered just tapping something from there and regulate it down to 5V?
Dennis, I'm using a Antek AS-0520 @ 50VA 20V. I've been trying to find guidance on how to use the 0520 but haven't found anything yet. If I know that I can plug in the Glassware LV-regulator @ 5V. That linkage would come from the H9KPXG correct?
 
Hello everybody,

how are you all DIYers doing? Just out of curiosity, any from Europe who built the pre?

By reading the whole thing I am getting more and more intrigued, I have a skilled friend to build the F4 for me but I'd really love to pair the BA-3 to it later on but would love to do it myself, will buy a proper soldering station and a second and reliable DMM but will then need to figure:

  • boards from DIY shop, once I place an order what else can I get off the store?
  • does it make sense to make it dual mono or is it a futile exercise? The F4 is gonna be dual mono
  • Size and specs of transformers for 220V as by Italian standards
  • Power boards, reading about different ones and how they can affect the sound as well as caps, which ones would you suggest?
  • potentiometer, how much they affect final quality and which are the parameters to pick the right one to match power amp it being the F4?
  • fets, which ones?
  • P1-P2-P3 pots, reading about them being 25 turns, is that correct?
  • which size would comfortably fit the whole thing so I can check a box to fit the dissipante which is gonna host the F4?
  • can it be done with dual output?

I know you already mentioned a novice can put it together and read about a few who as novices made it work nonetheless some smoke, which parts do you think better to get in abundance as to replace smoked ones?

Oh well, loads of questions...

Grazie
 
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Dual mono is worth it (I think.)
Pesante case, https://modushop.biz/site/index.php?route=product/product&product_id=154
2 X 50va transformers, 2 X shunt regulated power supplies, 10k stepped attenuator.
Big caps are Russian FT3 bypassing the Clarity caps.

DSCN0238.JPG
 
Ciao @ColinA123 and @myleftear and to the whole group, this thing is tickling me, so far my guess is that it takes the boards off the DIY store as per the link in my above post, if I am not wrong this board as PSU should do it (2x in case of dual mono), great to know about which Case you used, 2U and 330 wide so plenty of space to also make it dual mono if that is the choice.

I too would use Toroidy to buy the transformers, would you please tell me which ones to look for as an EU 220v user?
Don't know what a shunt is, is that what in Italian we call a "ponte a diodi" or a rectifier or is it a transformer's characteristic?

I like this stuff to be plain and simple, I am a passionate photographer and even there to me the less the better, I love autofocus of course but stabiliser bla bla bla is all stuff which can lead to failure so I'd like it to be the plainest possible also to make it the easiest to build.

Grazie
 
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Per the PSU parts list, you need a transformer with dual 25VAC secondaries or a 50VAC Center tap for a +- 24VDC supply. There's 'a lot' of voltage drop in that circuit.

Toroidy specs their transformers at 230VAC input, so if you really wanted to get closer, to 25VAC output on 220VAC input, you could get a 2x26. The BA-3 isn't going to care, but since Toroidy offers it...

As for power rating, 20VA is more than enough, (even if you don't do dual mono) and is the smallest standard size from Toroidy.

After that, it's a matter of preference and some cost vs. performance.

Personally, I've always wanted to try their "supreme audio grade". They're beautiful, and people in the forum have noted exceptional performance in terms of low radiated EMI. I've also never seen a report of a noisy or humming unit. However, they are comparatively quite expensive.

https://sklep.toroidy.pl/en_US/p/TT...grade-transformer-TSAS20VA-voltage-to-50V/373
Select 2x25V or 2x26 as the output.

For a less expensive, and probably still fantastic option...

https://sklep.toroidy.pl/en_US/p/TTSA0020-Transformer-AUDIO-TSA20VA-voltage-to-50V/303
2x25 or 2x26.

Here is a basic description of a shunt voltage regulator.

https://www.electronics-notes.com/a...gulator or shunt,the voltage across the load.
Those are just some thoughts. Others that have built that specific PSU will surely have better information. If I've made any errors or false assumptions, apologies, but that should get things moving.

Cheers.
 
Another suggestion is to consider running your BA3 preamp at rail voltages higher than +/-24V. There is slightly lower distortion with the higher rails and you can also be sure the BA3 is not clipping before your F3. Personally I would try maybe +/-28 to 30V rails.
Ok, let's say dual mono, if that makes any sense (the F4 is gonna be dual mono), mind you, this is gonna be my first ever DIY (!!!), options for stereo-one board-one transformer dual mono-two boards-two transformers.

Are those boards linked above, the Sigma 22, a good option? I don't have knowledge to understand if there can be a better or worse option within a reasonable monetary cost.

Transformers wise I did look at Toroidy, so, would higher than +/-24V add any benefit? So far you mention less distortion (...), is it worth the extra cost to go for the 28-30V ones? Again, I look forward for it not to get up costing like a Mark Levinson :) audio grade ones would do the pretty well I guess, I will try and evaluate costs once you tell me what should I look for either for a stereo or dual mono:

  • desired VA output
  • mounting pad
  • output voltage

Reading again the thread it seems the MOSFETs are not easy to find, what should I look for when looking for them or eventual alternatives? Are they, again, gonna have an impact on sound quality?

Sorry for tons of questions... :rolleyes:
 
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2U and 330 wide so plenty of space to also make it dual mono
which ones to look for as an EU 220v user?
Don't know what a shunt is
Buona sera!

If you go the 2U 330 route, which is more than I have (I’ll actally run it in a 230mm chassis!), you should be fine. Still, make sure everything you need finds a place and is accessible/wireable…
I can’t explain a shunt good enough, please research! Its a regulation method, after toroid/rectifier.
 

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concerning toroidy:
The supremes are indeed fantastic. But—they really big too.
The prices for a 24V or 30V are the same. It's the Wattage that makes the difference...
(so, a 2 x 24V 20VA or a 2 x 24V 50VA haven't the same price...)

Ah, and, I have to admit: My build as it is looking right now isn't a dual mono! (There's one positive and one negative rail for both...
Shame on me!
 
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Giovanni,

Going with higher rails isn't going to cost much, except perhaps higher voltage rated caps. The price of the Toroidy transformers seems to be the same up to 50V secondaries. 50VA is adequate even for two channels.

As for the voltage you need to decide your target rail voltage and the regulator you intend to use, since the latter determines how much 'extra' voltage above your the target you need.

The 2sk2013/2sj313 are pretty hard to find. You might try Prakit on this thread: https://www.diyaudio.com/community/threads/fs-tos-2sk2013-2sj313.232093/page-7 Papa mentioned in the BA3 article FQP3N30 and FQP3P20 as substitutes.
 
Dual mono is worth it (I think.)
Pesante case, https://modushop.biz/site/index.php?route=product/product&product_id=154
2 X 50va transformers, 2 X shunt regulated power supplies, 10k stepped attenuator.
Big caps are Russian FT3 bypassing the Clarity caps.

View attachment 1020741
Hello,

this photo helps a lot to understand the layout, a lot to a total novice... I can tell the AC reaches the two transformers, ground to the chassis, from transformers to the two boards, from there to the BA-3 board, what I can't tell from the wiring is volume potentiometer, signal input and signal output, how are they wired/where from/to.

Would it be possible to have dual output to drive two power amps?

How much influence the power boards have to the quality of the whole build, any suggestion about which ones to use?

I am waiting to hear about the MosFets, it seems some Thosiba should still be going around, I think this is the most important variable to then build and set the whole thing up.

Grazie for your help, I now understand why the popularity of this forum 🙏🙏🙏