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Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Fri Apr 07, 2017 6:04 am
by htm
Joe Malone wrote:
htm wrote:Hi Joe

I've been happily using my four BA's on drums and guitars for a good while, but I 've noticed that there's something going on with one of them. The gain on one is some 4 dB lower than others and it's not giving out the full 48V phantom power, only 15 or so volts comes out. I checked the wiring, but can't locate the problem there. Is there something on the board, that I should check?

Thanks, Hannu
Check 10R resistor is still 10R ?
Voltage you get on either side of the 10R measured to 0v?
Voltages at opamp pins measured to 0v?
Voltages at +/-in measurted to 0v with phantom on and no mic plugged in?
Ok, here goes

10R is 10R
47.3 on the opamp side of 10R and 47.5 on the other side

opamp pins are
+V 47.3
1/2V 23.6
0V 0
out 23.6
both ins 23.6

+/- in are 15.5/15.0

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Fri Apr 07, 2017 3:01 pm
by Joe Malone
htm wrote:
Joe Malone wrote:
htm wrote:Hi Joe

I've been happily using my four BA's on drums and guitars for a good while, but I 've noticed that there's something going on with one of them. The gain on one is some 4 dB lower than others and it's not giving out the full 48V phantom power, only 15 or so volts comes out. I checked the wiring, but can't locate the problem there. Is there something on the board, that I should check?

Thanks, Hannu
Check 10R resistor is still 10R ?
Voltage you get on either side of the 10R measured to 0v?
Voltages at opamp pins measured to 0v?
Voltages at +/-in measurted to 0v with phantom on and no mic plugged in?
Ok, here goes

10R is 10R
47.3 on the opamp side of 10R and 47.5 on the other side

opamp pins are
+V 47.3
1/2V 23.6
0V 0
out 23.6
both ins 23.6
That is perfect
+/- in are 15.5/15.0
If this is the voltage with no cables or mic plugged into the XLR in then either you have a centre tap from the primary of the input transformer wired to 0v or some short around the 48v switch and 6k8 resistors.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Sat Apr 08, 2017 10:48 pm
by htm
Joe Malone wrote:
htm wrote:
Joe Malone wrote:
Check 10R resistor is still 10R ?
Voltage you get on either side of the 10R measured to 0v?
Voltages at opamp pins measured to 0v?
Voltages at +/-in measurted to 0v with phantom on and no mic plugged in?
Ok, here goes

10R is 10R
47.3 on the opamp side of 10R and 47.5 on the other side

opamp pins are
+V 47.3
1/2V 23.6
0V 0
out 23.6
both ins 23.6
That is perfect
+/- in are 15.5/15.0
If this is the voltage with no cables or mic plugged into the XLR in then either you have a centre tap from the primary of the input transformer wired to 0v or some short around the 48v switch and 6k8 resistors.
Well it was my wiring after all. The input wire insulation had propably broken somewhere. Replacing the wire did the trick.


Thank you again Joe for the support.

Hannu

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Tue Jun 06, 2017 6:52 am
by Tim
Hi guys. Wondering if anyone can point me in the right direction.
I have a fault with my BAD dual with JLM111DC output transformer.
It was working fine, but now still passes a signal but with an extremely distorted output. Another issue,and I'm not sure if it's related, is the phantom LED is suddenly very dim and I can only measure 2.1V across the switch when on as opposed to my other channel that sits around 48v when on. So I know there is an issue but I don't know if it's related to the distorted output or where to start probing for problems. I need to get a new battery for the multimeter to test voltages further. However I need pointing in the right direction. I did recently add an output transformer but I have been over and over that and I'm pretty sure it is wired correctly. Admittedly when I first put it in,I checked it passed a healthy signal level (monitors off),which it did no prob and left it at that till I actually came to use the channel, I didn't actually listen to it at the time. Little help ? Thanks.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Tue Jun 06, 2017 8:28 am
by Tim
I should add that I am getting close enough to 48V into the problem module. OK there.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Tue Jun 06, 2017 5:48 pm
by Joe Malone
Tim wrote:I should add that I am getting close enough to 48V into the problem module. OK there.
Do you have 48v on both sides of the 10R at the back of the pcb?

If so what are the voltages at all opamp pins measured to 0v with unit on and opamp fitted?

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Wed Jun 07, 2017 5:49 pm
by Tim
Thanks Joe,

OK, I have 47V ONLY on one side of the 10R....

other side gives just a few volts, about the same I measure at the phantom switch, switched to on.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Wed Jun 07, 2017 5:54 pm
by Joe Malone
Tim wrote:Thanks Joe,

OK, I have 47V ONLY on one side of the 10R....
Then the 10R fuse is no longer 10R but open circuit. Replace with carbon 1/4W 10R resistor

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Wed Jun 07, 2017 5:57 pm
by Tim
will do , thaqnks.
Film do just to test?

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Wed Jun 07, 2017 5:58 pm
by Joe Malone
Tim wrote:will do , thaqnks.
Film do just to test?
Not sure what "Film do just to test?" means ?

You should be able to test the 10R with a ohm meter.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Thu Jun 08, 2017 8:35 am
by Tim
I meant film resistor, thats just my very lazy typing.
Found a 10 ohm carbon 1W lying around and problem is solved.
Thanks Joe.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Thu Jun 08, 2017 9:27 am
by Joe Malone
Tim wrote:I meant film resistor, thats just my very lazy typing.
Found a 10 ohm carbon 1W lying around and problem is solved.
Thanks Joe.
Ok metal film is no good for this. Needs to be 10R @ 1/4w so it protects if anything goes wrong.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Fri Sep 29, 2017 11:29 am
by Ayguid
Hi Joe. Im building a couple of BAD. And i have a couple of 600,600 ohm transformers. Similar to the JENSEN JT-MB-D,,,i was wondering what issues besides lower gain i could encounter, Higher noise floor? Mi plan is to use both stages with 5532. Maybe change the Rgain to recover the gain?
I ask, becasue here in Latin America its really hard to find audio transformers.
Thanx Guido.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Fri Sep 29, 2017 11:31 am
by Ayguid
I forgot to say INPUT transformers.

Re: BA BA2 BA4 BAD Dual99v Build Thread

Posted: Fri Sep 29, 2017 12:00 pm
by Joe Malone
Ayguid wrote:Hi Joe. Im building a couple of BAD. And i have a couple of 600,600 ohm transformers. Similar to the JENSEN JT-MB-D,,,i was wondering what issues besides lower gain i could encounter, Higher noise floor? Mi plan is to use both stages with 5532. Maybe change the Rgain to recover the gain?
I ask, becasue here in Latin America its really hard to find audio transformers.
Thanx Guido.
HI Guido
That will all work ok. If the 600:600 has a centre tap on one side you could wire to the centre tap as primary to make 1:2 ratio as that would improve you noise floor 6dB.