BA BA2 BA4 BAD Dual99v Build Thread

[ajsteel]

Hi Joe,

Just wondering how I wire my EA2623 if I don't have and output trim pot? I saw another thread but the guy had an out put trim pot and the brown wire went to an xlr out via the trim pot?

Thanks
AJ

[Joe Malone]

Hi Joe,

I have LED and the power switch sorted. HOw do I wire the Hi Z pot? Do I use both 2k2 resistors or just 1? And do i solder the resistor across both pins?

Thanks
AJ

Wired as shown in the BA4 overlay in the post above. No Rload on the PCB. Instead wire 2 wires out to a resistor in series with the log pot.

JLM14 needs 2k2 resistor in series with 50k log pot (dual 100k log pot wired in parallel with front 3 legs solder to back 3 legs)
OEP/VTX needs 10k resistor in series with 100k log pot (dual 100k log pot wired only to back 3 legs)

The log pot value and series resistor parts depend on ratio and impedance of the input transformer you are using.

We sell a special centre detent 2 x 100k log pot that can be wired as 50k, 100k and 200k on the JLM Audio web shop under pots.
This Z pot is included in all BA2 and BA4 rack kits.

[ajsteel]

Hi Joe,

I have LED and the power switch sorted. HOw do I wire the Hi Z pot? Do I use both 2k2 resistors or just 1? And do i solder the resistor across both pins?

Thanks
AJ

Wired as shown in the BA4 overlay in the post above. No Rload on the PCB. Instead wire 2 wires out to a resistor in series with the log pot.

JLM14 needs 2k2 resistor in series with 50k log pot (dual 100k log pot wired in parallel with front 3 legs solder to back 3 legs)
OEP/VTX needs 10k resistor in series with 100k log pot (dual 100k log pot wired only to back 3 legs)

The log pot value and series resistor parts depend on ratio and impedance of the input transformer you are using.

We sell a special centre detent 2 x 100k log pot that can be wired as 50k, 100k and 200k on the JLM Audio web shop under pots.
This Z pot is included in all BA2 and BA4 rack kits.

So with an EA2622 Input Transformer at 1:3.5 600ohms I would wire the Log pot the same as the JLM14?

[Joe Malone]

Hi Joe,

I have LED and the power switch sorted. HOw do I wire the Hi Z pot? Do I use both 2k2 resistors or just 1? And do i solder the resistor across both pins?

Thanks
AJ

Wired as shown in the BA4 overlay in the post above. No Rload on the PCB. Instead wire 2 wires out to a resistor in series with the log pot.

JLM14 needs 2k2 resistor in series with 50k log pot (dual 100k log pot wired in parallel with front 3 legs solder to back 3 legs)
OEP/VTX needs 10k resistor in series with 100k log pot (dual 100k log pot wired only to back 3 legs)

The log pot value and series resistor parts depend on ratio and impedance of the input transformer you are using.

We sell a special centre detent 2 x 100k log pot that can be wired as 50k, 100k and 200k on the JLM Audio web shop under pots.
This Z pot is included in all BA2 and BA4 rack kits.

So with an EA2622 Input Transformer at 1:3.5 600ohms I would wire the Log pot the same as the JLM14?

Yes that will work fine.

But also in a normal API the EA2622 has no load except for the zobel. So a higher range like the OEP/VTX has can work as well as when the impedance is set to its highest setting it will be the closest to the original API.

[ajsteel]

Hi Joe,

Well I think it's working. I turned it on and nothing exploded, smoked or fried I haven't tested the voltages yet, not quite sure how to do that but I ran a bass guitar through and there was sound, no hiss, and plenty of low end. I then went Bass - SansAmp Bass Driver; Active - JLM pre and teh bass was warm and fat so I have assumed for tonight that all is well

Thanks for all your help. I'm sure I'll get the others going now. I might up teh resistor on log pot to get more like the 2520 API but I'll see. Keen to play around with it.

A.J.

[ajsteel]

Hi JOe,

Just wondering if should be using something like shielded Canare wire to connect to the XLR's or is it not going to make much of difference?

Thanks
AJ

[Joe Malone]

Hi JOe,

Just wondering if should be using something like shielded Canare wire to connect to the XLR's or is it not going to make much of difference?

Thanks
AJ

No ribbon with twists and output wires twisted together is all that is needed and works best.

[tazwolf]

Hi
How many BA's can I run from one of your older SMPS external Power supply, the 380ma one?

regards
/TAz

[Joe Malone]

Hi
How many BA's can I run from one of your older SMPS external Power supply, the 380ma one?

regards
/TAz

I have seen the old 380mA run 8 x BA depending on opamps used. But really 4 to 6 BA should be the limit.

[ajsteel]

Hi Joe, I just wired my second BA Mic pre and it seems to be getting no power, the transformer and the opamp remains cold compared to the first BA Pre where the opamp and transformer seem to heat reasonably fast. I tested the pre with a mic and got a small level coming in, -24Dbfs on Didgidesign 192 I/O. I have wired the gain pot and the Hi z pot to the PCB. The first BA pre I wired works fine. Any ideas?

I've checked the phantom power from the the first to the second pre and it seems to be ok. The 48V LED comes on when I flick the switch, it's wired from +V in the first pre to +IN on the second pre. I also have the 0V on the first pre going to 0V on the second pre. I'm using a GAR 2520 and Ed Anderson Input and Output Transformers.

I have wired the transformer leads as per my first mic pre pre and this thread http://www.jlmaudio.com/forum/viewtopic.php?f=2&t=206

I have also soldered the Transformer pins as per the directions on the EA, GAR 2520 PCB picture on pg 1 of this thread. Hopefully it's not too major.




Thanks
A.J.

[ajsteel]

HI Joe,

My Phantom power light is now on but I'm getting no signal output?

Thanks.

A.J.

[ciscan.81]

Hi Joe

...I have recently upgraded to an UA Apollo 16 interface and will be needing to expand my pre collection...

I've just ordered the parts for a couple of budget 312 builds for now to bring me up to 8 JLM channels, but I'll definitely be considering the 1290 x 4 later when my bank account has been released from intensive care!

My last pair of builds were BA 312-style with JLM25HVFET op amps and EA 2622/2503 transformers, input set to low ratio...I included variable Z (15k + 100k log pot)...I'm considering bringing the input ratio jumpers out to a DP4T switch so I can switch between low and high ratio...(I did another BA312 build a while ago which I set to high ratio and I like the aggressiveness of it, but want to experiment with the new builds)

My question is:

Is the variable Z values I have implemented useable for both low and high ratio? If not what would you recommend?) Will the above proposed setup work ok? Any issues you can foresee? (bare in mind I sometimes use the pres with ribbon mics)

Thanks as always for your time and help.

Regards

Wayne

[ajsteel]

Hi Joe,

Pictures of PCB below. I'm only getting 10V on the Secondary of the EA2622? I'm using a 39V Zener. I've got signal. I missed the R Gain resistor. My GAR 2520 +N is getting 24 volts in. Is this too high? I thought it was 18 Volts Max?

Thanks A.J.

IMG_1414.jpg

IMG_1415.jpg

[Joe Malone]

Hi Joe,

Pictures of PCB below. I'm only getting 10V on the Secondary of the EA2622? I'm using a 39V Zener. I've got signal. I missed the R Gain resistor. My GAR 2520 +N is getting 24 volts in. Is this too high? I thought it was 18 Volts Max?

Thanks A.J.

Ok 39v zener with BD681 will give you roughly 36 to 37v at +V opamp pin on the BA as the BA run on one rail like most vintage gear not split rails.

The GAR2520 want +/-18v split rail = 36v single rail.

The voltage at the secondary and +in should be roughly half of that voltage so 18v with no opamp plugged in.

With the opamp plugged in you should also have 18v at -in and out of the opamp.

[Joe Malone]

Hi Joe,

IMG_1415.jpg

You have C & E under the BD681 pins solder together so it is bypassing the BD681. You only solder these pins together if NO BD681 is fitted. This may or may not have destroyed the 39v zener.

Remove the solder short and see if you get 36 to 38v at +V or not?

Also check you get 39v volts across the zener or not?