Giovani You may have read this information already but it's worth remembering.
The BA3 pre is very temperature sensitive when you are trying to bias it.
You need to make small adjustments, then put the top on and let it stabilize.
Any air movement will cause the bias readings to drift a bit.
It may be a case of getting "close enough" then leaving it alone.
The BA3 pre is very temperature sensitive when you are trying to bias it.
You need to make small adjustments, then put the top on and let it stabilize.
Any air movement will cause the bias readings to drift a bit.
It may be a case of getting "close enough" then leaving it alone.
@ColinA123 did you think this was my last question???
I actually went through already 110 pages off the whole thing and copying and pasting notes here and there so once done with the shopping list I will start with questions, a lot of questions...
By the way yes, I read about temperature and also about some who biased at 0,9 and then back to adjusting weeks later not to say Class A needs time to get warm
Will I do it or not this think is teaching lot of stuff and life, to me, is all about curiosity and learning process, grazie mille for yours all patience, expertise and to rip off precious space and time
Giovanni
I actually went through already 110 pages off the whole thing and copying and pasting notes here and there so once done with the shopping list I will start with questions, a lot of questions...
By the way yes, I read about temperature and also about some who biased at 0,9 and then back to adjusting weeks later not to say Class A needs time to get warm
Will I do it or not this think is teaching lot of stuff and life, to me, is all about curiosity and learning process, grazie mille for yours all patience, expertise and to rip off precious space and time
Giovanni
I think I got it. The right channel wires coming from the attenuator board crossed at the board.
Easy fix.
Attachments
Just found this out looking up for "dual mono BA-3" and got a doubt, till now all the dual mono ones I read about have two transformers, two PSUs but one BA-3 board, what am I missing???
Each BA3 board is wired to run balanced:
https://www.diyaudio.com/community/threads/burning-amp-ba-3b-balanced.201281/
https://www.diyaudio.com/community/threads/burning-amp-ba-3b-balanced.201281/
I see, for a moment I thought I didn't understand much about Stereo vs Dual Mono but something I still miss is if built in Stereo with one transformer and one PSU the layout is pretty clear, on the BA-3 there are positive and negative markings on both sides of the board on top and bottom if I recall correct, the PSU, in my instance the Sigma 22 (which I am looking forward to order) has 2 couple of positive and negative outputs, what happens when I use two transformers and two PSUs to feed one BA-3 board, how does the wiring works, what happens with the PSUs outputs?
Grazie
Ciao Dirk,Hello Giovanni1968,
for my a BA-3-preamp I used transformers with primary input 1x 230 V AC (or 2x 115 V AC connected in series) and secondary output at
2x 18V AC or 2x24 V AC.
The transformers with 2x 18 V AC sec. will have an outputvoltage after a CRC-filter of around 2x 24 up to 2x 28V DC (without any load).
The transformers with 2x 24 V AC sec. will go up to approximately 2x 32 V DC to 2x 34 V DC (after a CRC-filter). Perhaps a little bit higher
without load.
I don't know what voltages you will get with the classA-parallel-regulated-supply you showed in your pic? But You will have for sure some losses
in the voltage-output.
I most often use series regulated powersupplies. with the 'old' LM317/LM337 or LT1085/LT1033-regulators. There are very good lowdropout-regulators available today.
For a real dual - mono - BA-3-preamp you would need 2 completely seperated PSUs for the left and right channel. This means:
You can run a BA-3-preamp easily up to +-30 V DC on the rails. I also used/tested up to +-32V DC without any problems. But then it starts to become 'dangerous' for the JFets.
- 2 trafos with symmetrical output (BA-3 wants a symmetrical voltage at around +24 up to +32 V/ and a negative voltage at around -24 up to -32V.
- 4 cap banks ( if you use a CRC-filter = 8 caps; if you want to go with a CRCRC-filter = 12 caps)
- you will have 4 voltages (for 2 channels / dual mono) = 4 regulators (if you want to use them)
I have no idea what voltages you will get with that ClassA-PSU in your last post?
I hope this helps?
Cheers
Dirk
fellow and very patient @ItsAllInMyHead my head is helping me in a dedicated thread where I asked for informations on which PSU to pick for my project and how to size the various components and given for granted that 30V is the target voltage to feed the BA-3 as to have a little more gain to better drive the FW F4 which is in the build and to also get that slightly better noise figure PaPass states on his own written BA-3 description I opted, with Patrick's precious help, for the Sigma 22 boards which can deliver the desired voltage to the frontend.
As by transformers he did the calculations for me and since here we run 220V he suggests 32V secondary ones, 30VA of the Toroidy Audio Grade (no supreme, too big and too expensive!), each would feed a Sigma 22 and forgive me but I don't remember all the calculations involved and the board voltage drop but it should deliver the about 30V target, on this point I will have to go back to that thread to understand the involved math which is what matters to me, I want to at least understand how does this thing work rather than to buy parts and put them all together.
This is it for today's morning, I can't stress once more how helpful you all are and how interesting this whole thing is, it gives a much better Experience to know what goes on under the hood than just switch it on and get it to work.
Grazie mille e happy fool's day
Giovanni
Ah, while I appreciate your effort into solving my Nth issue with the BA-3 I really much appreciate the "ragazzo" bitCiao Ragazzo,
the outputs of one Sigma 22 PSU are all on the same rail. Dual mono is wired as shown in the pic attached - doesn´t matter, which DC-out (1-4) or which ground connection you use on one PSU board.
Very clear how it works for the wiring, saving the pics for reference 🙌
That phrase stuck with me a long time ago, when we were drinking too much with some Italian hooligans. I´m glad it didn´t come off as offensiveI really much appreciate the "ragazzo" bit
Not at all, anzi, if you wanna make things right with somebody off the gulf of Naples then add "guagliò" to your dictionary!That phrase stuck with me a long time ago, when we were drinking too much with some Italian hooligans. I´m glad it didn´t come off as offensive
Make sure you use 35 or 50 volt rated capacitors
Those in your basket are rated @ 25v, 5 volts less than your planned rail voltage. Haven’t checked your resistors, but ensure they fit the board if not allready done.regards,
Andy
Buongiorno Andy @andynor and thank you so very much for noticing that, I updated the BOM with these caps rated 35V and it also helped me to notice that there were with different leads spacing so I went for the 5mm ones after measuring the gap on the board itself, great help!Make sure you use 35 or 50 volt rated capacitors
regards,
Andy
Now I have a question, running the PSUs to get 30VDC is 35VDC caps safe?
Same question will arise when choosing C3, besides audiophile preferences like brand vs brand or stuff like that, BOM says 10uF, to say one I found Audyn ones rated 400VDC and 5% tolerance, dimension wise 27x35mm which would fit the board but I can tell some members using much bigger stuff (yeah, it seems dimensions still count and not just for females...), what would dictate the choice of this component?
Last one, I can tell there is another C3 pad on the board but that's left empty, what is it for? Attaching picture from another member's populated board, the pads right below the big C3 caps
Grazie
50v is safer than 35. people here use different margins. I use 25v for a 24v PSU, and guess I am assessed an idiot for doing so. I also used 25v ones in my BA-3 with 32v rails, without blowups. But probably quite unwise.
Voltage for big C3’s is nothing to worry about. They are all immensely overrated.
the small C3 pads are there if you choose to use small caps instead of biguns, for example Silmics. Papa sez you can populate with both big and small ones at the same time, but this may affect low end rollof so I guess that means some calculations are needed.
if using small ones instead of biguns, some bypass these with film caps in the big caps position. 6L6 did this in the BA-3 poweramp build guide.