BA BA2 BA4 BAD Dual99v Build Thread

[cheu78]

Hello Everybody!
The attached pics shows our take of the BA...circuit modified for a DIYed "Melville" 2520, Cinemag input and output xformers..and I wanted to have 8 channels in 1RU.. there's no such thing on the market..! At least with these sonic performances..
This thing is insane! Sounds really amazing..Very fat, tight and punch!! Also the highs are superb..kinda smooth!! simply lovely! THANK YOU Neeno!! And thanks to Cinemag for the awesome xformers!!(Of course thanks to Joe for the BA kits..)..
we were a bit concerned about having the output xformers so close to each other.. but no problems! more than 92db separation between the channels.
The front pics shows that the 812a was not finished yet.. but it is now..!

Have fun building your preamps!

Ciao

Cheu

[sonicwarrior]

I've finally soldered the JLM-14 into my BA but I'm not sure where to solder the black cable.
The text on the JLM-14 says it is the center tap on the primary side but where is the center tap on the PCB?
The two middle pins of the ratio lead to two independent solder pads where I assume the center tap is but
I'm confused that there are two pads.

[Joe Malone]

I've finally soldered the JLM-14 into my BA but I'm not sure where to solder the black cable.
The text on the JLM-14 says it is the center tap on the primary side but where is the center tap on the PCB?
The two middle pins of the ratio lead to two independent solder pads where I assume the center tap is but
I'm confused that there are two pads.

The black centre tap wire on the JLM14 is not used or connected to anything. We usually just cut it short and fold it back into the heatshrink tube the wires come out at the bottom of the transformer or put some heatshrink tube on it so it will not short to anything. The ratio jumpers are not fitted or used with the JLM14 as it has only one ratio.

[sonicwarrior]

Fast answer, thanks a lot!

[BeatStudio]

My BA JLM99V with JLM14 is causing the power supply to go into protection mode. I'm using the 48v 25w 520mA SMPS and have applied the soft start mod. One thing I was not sure about was the BD681, the front (of the bd681 the side with the markings) should be facing out from the pcb? Hope the pics explain better than me....





Scott

[Joe Malone]

My BA JLM99V with JLM14 is causing the power supply to go into protection mode. I'm using the 48v 25w 520mA SMPS and have applied the soft start mod. One thing I was not sure about was the BD681, the front (of the bd681 the side with the markings) should be facing out from the pcb? Hope the pics explain better than me....

Scott

BD681 plastic face outwards is correct.

Is the 48v and 0v wired the correct way around to the BA PCB?

Does the hiccup over current mode happen without the JLM99v fitted?

Do you only have one BA connected to the power supply?

Email me the photo's you have in full size so I can check them over?

[BeatStudio]

Is the 48v and 0v wired the correct way around to the BA PCB?

Does the hiccup over current mode happen without the JLM99v fitted?

Do you only have one BA connected to the power supply?

Email me the photo's you have in full size so I can check them over?

Hi Joe,
Thanks for the quick reply. I double checked the +v and o volt connections they are correct.

The power suply does work, I checked with a meter.

The JLM was never fitted and was the only ba on the supply. I am testing this on the bench, would not having the RL and the gain pot fitted be a problem?
The only other thing was at the end of the night I was tired and forgot I turned the temp down on the soldering station and wondered why the solder was not melting This was on the BD681, could I have overheated and damaged it?

Those are the original size of the pic's. Not sure why they came out so small but I will try to take some more pic's tonight and email them to you.

Thanks,
Scott

[Joe Malone]

HI Scott
From the big photos you sent there seems to be a solder short between the 2 pads in the red circle below. The plated via hole that has solder in it shouldn't but must have happened when soldering the opamp socket next to it. The via is +48v and the bottom pad of the zener is 0v. This would put a dead short between 48v and 0v. So if you measure between 48v and 0v with a ohmmeter while the power is disconnected you should get 10R meter reading. Remove the solder short and you should be good to go. You do need a Rload before fitting the opamp. And to do the voltage tests shown on the BA overlay. Gain pot doesn't need to be connected for first testing.

[BeatStudio]

Brilliant!

Ok, so now I am measuring 48 volts on the center pin of the BD681 but 46 on the Emitter pin (pin1). All pins that should read 48 read 46. Except the Phantom power, that reads 48. All the locations that should read 24 read 23 volts. The other BA without the soft mod, readings are fine. Are the low readings a problem? This is without the JLM99 or the RLoad fitted.

Thanks,
Scott

[Joe Malone]

Brilliant!

Ok, so now I am measuring 48 volts on the center pin of the BD681 but 46 on the Emitter pin (pin1). All pins that should read 48 read 46. Except the Phantom power, that reads 48. All the locations that should read 24 read 23 volts. The other BA without the soft mod, readings are fine. Are the low readings a problem? This is without the JLM99 or the RLoad fitted.

Thanks,
Scott

With the soft mod or BD681 fitted with no zener diode you will get 46v which is fine and half volts will be 23v. All correct.

[BeatStudio]

Thanks!

[benranco]

Hi Joe, I'm helping a friend build a couple BADs that he ordered from you a while ago. They're pretty much finished except for the CLoad. The BA chart on your build page says it should be 220pF for the JLM14 transformer and fixed impedance. Is this the same for the BAD? The kits that he received have two extra 100pF caps, but no 220pF cap. Can I wire the 100pF caps in parallel instead? Thanks!

Ben

[Joe Malone]

Hi Joe, I'm helping a friend build a couple BADs that he ordered from you a while ago. They're pretty much finished except for the CLoad. The BA chart on your build page says it should be 220pF for the JLM14 transformer and fixed impedance. Is this the same for the BAD? The kits that he received have two extra 100pF caps, but no 220pF cap. Can I wire the 100pF caps in parallel instead? Thanks!

Ben

HI Ben
BAD with JLM14 or OEP/VTX with JLM99v. Cload = 100pF and C7 = 100pF. This because the gain out of each 99v is not as extreme since it is shared across 2 opamps.

[benranco]

Ok, thanks Joe!

One more question. If using the BAD without an output transformer do I link pins 4 and 7 of the second IC socket location (when using JLM99v or hybrid opamps), like I would with the BA? Thanks!

Ben

[Joe Malone]

Ok, thanks Joe!

One more question. If using the BAD without an output transformer do I link pins 4 and 7 of the second IC socket location (when using JLM99v or hybrid opamps), like I would with the BA? Thanks!

Ben

HI Ben
Yes link pins 4 to 7 of the second DIP8 IC socket (IC closest to 470uF caps) if using a discrete opamp in that position and no output transformer.