The BA-3 as preamp build guide

Jump to Latest
#2,821
Short answer, the F4 with the SP9 doesn't hum, only the BA-3 does.

I opened it to try and disconnect the BT power supply but can't manage, it takes my friend to come and check himself but before he does I have another doubt, I asked him to hook both PSUs to the BA-3 board but he only wired one for both channels of the preamp, how does this affect output?

How difficult is it to wire the second powered but unwired PSU to the board? A few posts earlier somebody showed me which wires need to be unsoldered and which to wire but I better check twice to avoid mistakes, photo attached (if I don't forget to...)

I seem to recall that what I did to check the voltage output of my SP9 was to play a 1Khz tone on my MacBook, wire the output jack to the input RCA of the preamp, turn volume all the way up and then measure the output voltage in CC, is that correct? This way I can compare the two and find out how much is the gain gap between, I thought I would get 8-9 more db out of the BA-3 but so far it doesn't seem to be the case and I hope it being the unwired second PSU.

Grazie

BA-3.jpg



p.s. the BT module is underneath the switch board (the iSelect)
 
Last edited:
#2,823
The expert builder friend should be able to troubleshoot and fix the hum issue. "Bad out of box" sounds like a warranty claim..

Dual mono is great, I do that all the time. But not required for excellent sound quality. It's maybe 2% better, just throwing a number out. Shame not to go ahead and use the 2nd supply, it's sitting there ready to go. BUT, fix the noise problem first before you worry about the dual mono supply thing.
 
#2,824
I‘d suggest you try to make a schematic drawing of ths set. (Make several attempts, try to make it as clear/nice as you can).
I mean it’s just me (I am a greenhorn), I admit I’m having troubles to identify the wires, and where they go…

The build btw. is very nice, although I ‚d have put the i-select near the inputs for the sake of shorter wires. But as far as I know that’s more an OCD-thing than anything technical. 😁
 
#2,826
Good morning, I made the test with the DMM on the preamp output and measured about 4.7Vdc out, what should I expect to see considering, if I recall correct, my DAC outputs about 1.4V?

Is this what the BA-3 with 30V PSU is supposed to output?

Grazie

edit: my friend asked me to remove a wire to make a test, the wire is actually connected to the iSelect switch board and I guess it also powers the BT module, the hum disappeared.

It bothers me to ask him to wire the other PSU to the BA-3 board but like that it's useless, if he has to take it back to the workshop I'd ask him to to that
 
Last edited:
#2,828
You should give the preamp back to your friend for him to fix the hum. He should make sure it does not hum before he returns it to you.

You should also ask your friend to connect the other power supply. There is no technical issue for him to not connect it. It is your preamp and if you want it to be dual mono, it should be dual mono. 🙂
 
  • Like
Reactions: A Jedi
#2,831
Connected DVM's, started the bias procedure and nothing !. I had 500ohm trim pots fitted (started this project a long time ago, so earlier BOM). will purchase some 1k on Monday and try again.
 

Attachments

  • IMG20230422103919.jpg
    IMG20230422103919.jpg
    443.3 KB · Views: 204
  • IMG20230422103727_BURST001_COVER.jpg
    IMG20230422103727_BURST001_COVER.jpg
    563.6 KB · Views: 196
#2,833
While still waiting for the BA3 being fixed I was wondering what's the purpose of such a big (and empty) case, what if in the future I get a smaller footprint one and remove the extra PSU-transformer and make it a "simple" stereo preamp and not a fancy, and as far as I understand, useless dual mono which only rips more space, I might save the transformer and PSU for another project or yet another BA3 for a second setup?
 
#2,834
Last month I decided to read thru all the postings since I built my BA3 pre a year ago. Really glad I did because I got interested in moving from a 24DCV Dual/Bipolar LV Regulator to a 30DCV Sigma22 PSU. I have been using a 1Amp fast blow fuse and I'm wondering if I should move to a 2.5A given the increase current? I've searched thru the entire forum without gleaning much regarding fuse values. Appreciate any thoughts.
 
#2,836
This is a upgrade for my BA3 preamp. I currently have a Dual Voltage LV regulator that is set at 24DCV and I'm using a 1A fast blow fuse.

I'm moving to a Sigma22 PSU that will provide 30DCV to the Pre amp board. I'm using a AVEL Lindberg model # Y236356 (30+30V @ 80VA) transformer.

Thanks
 
#2,837
I'm making the assumption this is the fuse between the IEC jack and the step-down transformer.

If so, different PS but same preamp circuit so current draw shouldn't be changing much. Might as well try the 1A and see if it trips. the 2.5A fuse would be for something drawing large amounts of current like the 1st Watt clones, ~300W. A preamp consuming 300W would mean something has gone seriously wrong and should have been fused lower.
 
#2,838
#2831
1k pots installed,
Started bias procedure "something started to happen" at around 15 turns. after a week or so,
L/H =.924v-.925v, O/S=.031-.033.
R/H =.919v-.920v, O/S= .014-.016.

Now listening, first impression is very favourable, much detail and enjoying the music.

Q1; can the bias be raised to 1v.
Q2; What effect do the output capacitors have on the sound quality.

Have said this before, need to say again.
Thank you to Mr Pass for being generous with your designs.
And a big thank you for the help received form members.
 
You must log in or register to reply here.
Top Bottom