BA BA2 BA4 BAD Dual99v Build Thread

[Dais3]

Hi Joe
I built a couple of baby animals last year without an output transformer using the JLM op amp and they do sound fantastic.
I recently acquired a few LUndahl LL1517 out put transformers. I'm considering adding two of these wired 1:2 to give a 6dB boost to the output.
The 1517 is speced to work optimally with a very low source impedance. Do you think these would work well with the baby animal?
Many thanks
Dave

[Joe Malone]

Hi Joe
I built a couple of baby animals last year without an output transformer using the JLM op amp and they do sound fantastic.
I recently acquired a few LUndahl LL1517 out put transformers. I'm considering adding two of these wired 1:2 to give a 6dB boost to the output.
The 1517 is speced to work optimally with a very low source impedance. Do you think these would work well with the baby animal?
Many thanks
Dave

HI Dave yes that will work great as the BA has low output impedance of 51 ohm on green pcb and 33 ohm on black pcb.

You can change the output impedance to more or less by changing one resistor on the BA pcb.

[Dais3]

Great thanks Joe. That R13 and R16 yes? Is there any minimum value you would suggest on those?
Thanks

[Joe Malone]

Great thanks Joe. That R13 and R16 yes? Is there any minimum value you would suggest on those?
Thanks

R13 is the only resistor that needs adjusting sometimes to maximise the low end of the output transformer as the primary return should go to 0v not -out. To small a value can put a bump in the low end and to larger can roll off the low end early. 33R is perfect for our JLM111DC and compact versions.

Use Rightmark RMAA to do a freq sweep to see how the low end looks before changing R13. Lowest value usually would be about 10R.

[Camsown]

I'm currently building a BAD Dual99v module and I've only just noticed that R7 is left blank. I've already added R7 to the board and before I cut it off, I just wanted to understand what would happen if I left it in place?

[Joe Malone]

I'm currently building a BAD Dual99v module and I've only just noticed that R7 is left blank. I've already added R7 to the board and before I cut it off, I just wanted to understand what would happen if I left it in place?

Doesn't matter if R7 is fitted or not. Just make sure you fit the E to C wire link for 48v phantom to work.

[Camsown]

Doesn't matter if R7 is fitted or not. Just make sure you fit the E to C wire link for 48v phantom to work.

Thanks Joe. Picked up on the E to C thanks to the errata notes.

[Camsown]

Hi Joe.

On the Dual99v kits, where do I attach the phantom power led? Do I just attach it to the legs of the 48v toggle?

[Camsown]

Hi Joe.

On the Dual99v kits, where do I attach the phantom power led? Do I just attach it to the legs of the 48v toggle?

Also, the photo of the output pot wiring (on the first page of this thread) looks different than what is in the PDF for the Dual99v build. The pins on that switch look to be wired differently. Can you confirm that I should reference the PDF for these pins?

[Joe Malone]

Hi Joe.

On the Dual99v kits, where do I attach the phantom power led? Do I just attach it to the legs of the 48v toggle?

Yes led solders to the top 2 legs of the 48v switch. Long led leg goes to the switch leg closest to the edge of the pcb.

[Camsown]

Hey Joe,
Should I follow the output pot wiring in the schematic pdf? Looks different from the image of it on page the 1st page of this thread.

Cheers.
Cam

[Joe Malone]

Hey Joe,
Should I follow the output pot wiring in the schematic pdf? Looks different from the image of it on page the 1st page of this thread.

Cheers.
Cam

HI Cam the overlay pdf is the easiest to follow

[Camsown]

Hi Joe,

I've just found the time to finish the dual99v build. One channel sounds great. The other seems to be lacking volume. I can get a distorted signal from the effected channel when I turn the output up high but it tails away very quickly as I slowly back the pot off.

I've isolated it to being something on the preamp module or connected pots by swapping it with the working channel's preamp module. I've also swapped over the JLM99v opamps with no change to the distorted output on the affected module.

I've attached some photos of the module and pots. Any advice on what and how I should test from here?

[Camsown]

More photos

[Joe Malone]

check for shorts as shown in red.jpg

Check the pads in the red circle are not shorted together. Especially the 2 with the extra red circle around them