The BA-3 as preamp build guide

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#82
Hi all

I will use 2 or 3 F4 in parallel in a multiway system, 97dB efficiency. Upfront I have a Najda digital Xover and preamp (see thread at Diyaudio) which has selectable output level from 1v RMS to 6 v RMS, and an analog level control.

I fear (but would be happy to get your advise) this is not enough to drive unity gain amps to their full scale, although I am not planning PA use, so am considering to use 2 or 3 BA3 FE in between. I have a couple of questions you may help before I order the newly announced boards :

1) If I set the 3xBA3 boards in a single preamp case, is it a good thing to share one 2x24 trafo for the 3 boards ? What would be the VA rating for the Trafo then ?
2) If yes, it it much better to have 3 regulator boards ?
3) If I include one BA3 in each amp case, may I use the 2x18v trafo from the power amp + an additional regulator board or is it definetly better to have a second 2x24 trafo.
4) If I can use the 2x18v trafo, what components should I change ?

Thanks a lot
Jean-Louis
 
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#83
Jean-Louis,

If you construct a separate enclosure for the BA-3 gain stages -

One PSU can power multiple boards.
A transformer with 50VA will be more than enough.
One regulator can power all 3 boards.
Rail voltage of more than +/-24VDC is not necessary.

If you want to build the BA-3 front-end into the same case as the F4, then just use the PSU from the power amplifier. No changes will be necessary - rail voltage will be the same as the power amp.
 
#86
Has anyone listened to this pre with headphones? I would like a preamp for my F5 and a bigger headphone amp than my Mini3 and thought maybe b3 could be both. Im guessing that the output cap would have to be bigger to drive phones. maybe two coupling caps , one for pre out and the other for headphone out?
I love listening to phones straight off the F5 but feel a little guilty running it just for phones.

Thanks
 
#87
You could certainly try, but the output stage isn't a follower, it's not particularly suited to driving headphones.

I would just wait a month or two for the PassDIY headphone amp... 🙂 🙂 🙂 🙂 🙂
 
#92
It's not too hard of a circuit, I'm sure you can figure it out. A physical layout similar to the schematic will work nicely - that's similar to the PCB Nelson made.

The PCB will be back in the store shortly.
 
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