The BA-3 as preamp build guide

[Zen Mod]

show us SMPS

are they connected to mains with 2 wire or 3 wire cables ?

 

[codyt]

show us SMPS

are they connected to mains with 2 wire or 3 wire cables ?

Will take pic when I get home. They’re connected with three powers/safety ground, BUT many of the receptacles in my home do not have safety ground wired. In fact, I’ve yet to find one that does.

 

[codyt]

I’m using two of these: GST40A24-P1J MEAN WELL USA Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey

 

[Zen Mod]

check with ohmmeter - is center pin of IEC (safety GND ) connected with negative leg , on output side ?

 

[codyt]

check with ohmmeter - is center pin of IEC (safety GND ) connected with negative leg , on output side ?

No, doesn’t appear to be continuity there. I’ve attached a pic of the ‘PSU’ in one frame. I originally had planned to connect each SMPS via separate barrel connectors, but my jacks are in contact with chassis. For right now I’ve just wired SMPS’s directly to the cap bank. The barrel jack in the photo is not connected.

 

[Zen Mod]

just connect audio GND to chassis , in one point

 

[codyt]

just connect audio GND to chassis , in one point

Perfect, thanks ZM!

 

[codyt]

Waiting on a couple parts, but hope to report back with a finished pre in a couple days!

 

[McQuaide]

Question on input impedance of the BA-3 - Nelson's article states that the 47K resistor to ground on the input sets the nominal input impedance. Is this the actual impedance? I want to calculate the value of the output coupling cap on a source.

 

[Zen Mod]

it is actual impedance

 

[McQuaide]

it is actual impedance

Thanks ZM.

 

[Russellc]

BA3 is warming up at bias ≈890mV. It sounds very controlled and relaxed with fine details. At 90% bias 1V gives 2.5V out. In a few day I will turn up the bias. The FFTs are done with almost no warming up without tinkering with P3s. 1K/1V sine wave from RCA input, so through a 10K pot at minimum resistance. More testing with full bias. Feets and an indicator led is scheduled.

Thank you 6L6 for bildguide, NP for a nice design and everyone else for tributing.

I need to check the bias on my BA3 units, 1 Power amp and 2 preamps. What are you aiming for as 100%? My power amp in Deluxe 5U isn't really all that hot yet. It's quite warm but not "burning" yet.

Russellc

 

[donhughes111]

WOW, Russellc, how many boxes do you have?
Don

 

[Russellc]

WOW, Russellc, how many boxes do you have?
Don

Well you see them in signature except I did build Aleph J
In my F6 box. Will revisit it later with Semisouth outputs.
It just didn't get me like the others and I felt F5 did it similarly.

Russellc

 

[evershumi]

hello does anyone in europe have a BA-3 pre-amp card that they can sell me? or some components? i have a pair of original j74 / k170 and wanted to put it to good use. thanks

 

[Russellc]

hello does anyone in europe have a BA-3 pre-amp card that they can sell me? or some components? i have a pair of original j74 / k170 and wanted to put it to good use. thanks

You will need 2 pair.

Russellc

 

[evershumi]

You will need 2 pair.

Russellc

Sorry i have 2 pairs. 👍

 

[codyt]

Waiting on a couple parts, but hope to report back with a finished pre in a couple days!

Thanks again to ZM and 6L6 for your help on this. Still need to finalize wiring and reroute, but it’s up and running. Sounds great!

Hope to build a proper PSU soon, but the two SMPS bricks are working great for now.

 

[Russellc]

Sorry i have 2 pairs. 👍

Good! No disappointment 😁

Russellc

 

[ggetzoff]

BA3 is warming up at bias ≈890mV. It sounds very controlled and relaxed with fine details. At 90% bias 1V gives 2.5V out. In a few day I will turn up the bias. The FFTs are done with almost no warming up without tinkering with P3s. 1K/1V sine wave from RCA input, so through a 10K pot at minimum resistance. More testing with full bias. Feets and an indicator led is scheduled.

Thank you 6L6 for bildguide, NP for a nice design and everyone else for tributing.

Nice build. You have quite the ac filtering going on there.