BA BA2 BA4 BAD Dual99v Build Thread

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ciscan.81
Posts: 24
Joined: Sat May 26, 2012 8:33 am

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ciscan.81 »

Thanks again Joe

Turns out I did have the BD681 Transistor the wrong way. :oops:

As search of the posts revealed:
BD681 plastic face outwards is correct.
I put a new one in the right way round and all voltages now are reading as expected.

Thanks again for sorting me out.

That is the last of the preamps built and voltage tested, All A-OK.

Now just to finish off my enclosures and put it all together... :D

ciscan.81
Posts: 24
Joined: Sat May 26, 2012 8:33 am

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ciscan.81 »

Hi again Joe...yep it's me again :wink:

I've been wondering about the ratio for the EA2622 in my BA-312 style...

You recommended wiring the primaries in series with the LOW ratio jumper fitted to give 1:3.5...
...it 2 primary windings so low ratio will give 600ohm input with normal 15k load which is 1:3.5 ratio
Is the formula for working out the input impedance as follows?:

Input Z=Rload/(Transformer Ratio Squared)?

So wouldn't 15k Rload give an input impedance of around 1200ohm? What am I missing? Does this get shared across the 2 primary windings, because they are in series to give 600...? :?

Also, most of what I've read recommends running the EA2622 in parallel to give 1:7...is there a reason you recommend 1:3.5?

Is there any reason I couldn't try the EA2622 with two ratio jumpers running a HIGH 1:7? (ie could I damage anything?)

If I do, will the 100k Log pot and 15k series resistor be ok for the RLoad? Or should I up it?

IF I've got the above formula right I figure at 1:7 I would have a input Z range of 300ohm to about 2.4K which seems about right to me...

Let me know what you think...

Again many thanks for taking the time to educate me! I swear I'm nearly done!!!

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Joe Malone
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

ciscan.81 wrote:Hi again Joe...yep it's me again :wink:

I've been wondering about the ratio for the EA2622 in my BA-312 style...

You recommended wiring the primaries in series with the LOW ratio jumper fitted to give 1:3.5...
...it 2 primary windings so low ratio will give 600ohm input with normal 15k load which is 1:3.5 ratio
Is the formula for working out the input impedance as follows?:

Input Z=Rload/(Transformer Ratio Squared)?

So wouldn't 15k Rload give an input impedance of around 1200ohm? What am I missing? Does this get shared across the 2 primary windings, because they are in series to give 600...? :?

Also, most of what I've read recommends running the EA2622 in parallel to give 1:7...is there a reason you recommend 1:3.5?

Is there any reason I couldn't try the EA2622 with two ratio jumpers running a HIGH 1:7? (ie could I damage anything?)

If I do, will the 100k Log pot and 15k series resistor be ok for the RLoad? Or should I up it?

IF I've got the above formula right I figure at 1:7 I would have a input Z range of 300ohm to about 2.4K which seems about right to me...

Let me know what you think...

Again many thanks for taking the time to educate me! I swear I'm nearly done!!!
Yes while everything above is correct in a basic form. The transformer was designed as a 150/600 input so when wiring for 150 input the core will saturate earlier and when it does saturate it will lower the input impedance way down in the low frequencies even without a load on the secondary of the transformer. It will become even worse with a secondary load. Then driving that input with a 600ohm mic the saturation will roll the low end off even more at high audio input levels.

But there is no reason not to try it as it might sound great that way. I just find most input transformer work best at a 1:5 ratio or less it you still want there frequencies response to stay flat over the full audio band.
Joe :-)
JLM Audio
Capturing Audio without Injury

aevan
Posts: 9
Joined: Fri Mar 04, 2011 9:26 pm

SUmming switch on BA4

Post by aevan »

Hi, I'm building a BA4 with no output transformers, and was wondering how easy it would be to put a summing switch on channels 2,3 & 4, so that one way they all go out their direct outs, and another way they all go out the output of ch 1. Anyone tried this? Any thoughts?
For me it would be handy as I could sum multiple mics on one amp to one input on my portable when I'm out recording at places other than my studio.
Thanks

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Joe Malone
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Re: SUmming switch on BA4

Post by Joe Malone »

aevan wrote:Hi, I'm building a BA4 with no output transformers, and was wondering how easy it would be to put a summing switch on channels 2,3 & 4, so that one way they all go out their direct outs, and another way they all go out the output of ch 1. Anyone tried this? Any thoughts?
For me it would be handy as I could sum multiple mics on one amp to one input on my portable when I'm out recording at places other than my studio.
Thanks
Yes easy just take +out or pin 2 and -out or XLR pin 3 of each BA and switch them with series 1k resistors to a single sum XLR to make one +out XLR pin 2 and and one -out XLR pin 3 balanced output.

So 8 x 1k resistors and 3 x DPDT switches is all you need.
Joe :-)
JLM Audio
Capturing Audio without Injury

aevan
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by aevan »

Thanks Joe.
Cheers

ciscan.81
Posts: 24
Joined: Sat May 26, 2012 8:33 am

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by ciscan.81 »

Yes while everything above is correct in a basic form. The transformer was designed as a 150/600 input so when wiring for 150 input the core will saturate earlier and when it does saturate it will lower the input impedance way down in the low frequencies even without a load on the secondary of the transformer. It will become even worse with a secondary load. Then driving that input with a 600ohm mic the saturation will roll the low end off even more at high audio input levels.

But there is no reason not to try it as it might sound great that way. I just find most input transformer work best at a 1:5 ratio or less it you still want there frequencies response to stay flat over the full audio band.
Thanks again Joe,

I'm aiming for something with colour for this build so I'll try it out both ways and let you know how it turns out.

aevan
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black wire on jlm input tx?

Post by aevan »

Just wanted to check where the black wire on the 1:4 jlm tx goes on the BA PCB... is it connected to the point where a pcb mount tranny connects to 0V - between where the red and yellow wires connect, or is it not connected at all and just left floating?
Thanks

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Joe Malone
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Re: black wire on jlm input tx?

Post by Joe Malone »

aevan wrote:Just wanted to check where the black wire on the 1:4 jlm tx goes on the BA PCB... is it connected to the point where a pcb mount tranny connects to 0V - between where the red and yellow wires connect, or is it not connected at all and just left floating?
Thanks
Black wire is not connected to anything on the BA PCB just leave it floating. We just insulate it with a piece of heat shrink or electrical tape.
Joe :-)
JLM Audio
Capturing Audio without Injury

aevan
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Joined: Fri Mar 04, 2011 9:26 pm

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by aevan »

Thanks Joe, just found this answered earlier in the thread, missed it somehow.
Cheers

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Joe Malone
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

aevan wrote:HI Joe, I just finished building my BA4 and have no output from any channel.
A couple of questions -

1 - I'm using the ribbon cables with the siliconed jumper plug. So I still need to connect + and - out from the BA PCB to the XLR I/O board but not 0V on the output? I have one single end of the ribbon to the PCB, the plug with the two cables coming out of it has the jumper and the other single end is connected to the XLR I/O.
2 - Even with these connected all I get is a really low output, if I crank my monitors I can hear it really low. When I do this, the gain pot has no effect at all, but the impedance pot does.
All my voltages were fine, but when I checked them I didn't have the impedance pot connected. Is it possible this has damaged the 99V opamp in any way? I've checked them again
with z and gain pots connected and they are all correct, including the opamp sockets.

The problem is consistent across all channels , so I'm assuming it's the same problem on all of them. I'm running into pro level converters and have checked the path with a 1073 and it all is fine. I'm getting no output other than the tiny level with either a phantom powered mic or bass via a di into the mic in, but I am getting +48V at the right pins on the input xlr.
Any thoughts?

Thanks.
Yes you need to wire +/-out of the BA PCB to the XLR IO PCB to get output without a output transformer and also add a wire between pin 4 and pin 7 of the DIP8 socket.

The 99v will be fine even without the impedance wired in.

With the IDC header dummy plug fitted for when no DI is fitted do you get a short between pin 1 and 3 and also a short between 5 and 7 on any IDC header? (pin 1 is the square solder pad and odd pins continue along that front row of pins.)

Email me some large clear in focus photos of the PCBs and wiring so I can check it all over.
Joe :-)
JLM Audio
Capturing Audio without Injury

aevan
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by aevan »

Hi Joe, I deleted that post - must have been while you were replying. The fault is only in one board, the other 3 work fine (my mistake) and all opamps are good. I'm sure it is related to a mixup I had with this particular board and had to remove a ceramic cap, and in doing so may have damaged the board. I'll email you some pics and see what you think.
Thanks.

sonicwarrior
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Joined: Sun Feb 20, 2011 8:43 pm

Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by sonicwarrior »

I ordered my second BA as PCB only and now I have a problem finding a source for the three panel mounted toggle switches. Reichelt in Germany has a switch with the number MS 500FVT which looks like it will fit in the PCB but it is not panel mounted.
A Mouser part number would be nice.

Is that an ON - OFF or ON - ON switch?

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Joe Malone
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Re: BA BA2 BA4 BAD Dual99v Build Thread

Post by Joe Malone »

sonicwarrior wrote:I ordered my second BA as PCB only and now I have a problem finding a source for the three panel mounted toggle switches. Reichelt in Germany has a switch with the number MS 500FVT which looks like it will fit in the PCB but it is not panel mounted.
A Mouser part number would be nice.

Is that an ON - OFF or ON - ON switch?
DPDT ON - ON. Special low ohm contact type for audio use which we have custom made for us.

We have them available on the JLM web shop at the link below.
http://www.jlmaudio.com/shop/index.php? ... oductId=68

I looked for 30 minutes on mouser but cannot find them there. But I am sure they would would have a physical equivalent somewhere in those 25000 toggle types but there search method is useless.
Joe :-)
JLM Audio
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rpagala
Posts: 5
Joined: Thu Aug 26, 2010 8:58 am

Need more bass/bottom from my BA

Post by rpagala »

I compared my BA pre that I built vs my Maudio DMP3 and noticed that the DMP3 has more bottom, is there any way that I can get a little more bottom out of my BA?

By the way I have the JLM input tranny and the 99V, but no output tranny.

I love the tone from the BA but any help to get more bottom out would be appreciated...I dunno maybe a different value cap?

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