JLM AUDIO

Looks like my challenges with this build aren't quite done yet. I finished the fourth channel (using 2SA1804 transistors - accommodating for their different pin configuration appropriately).

Somewhere along the line testing this fourth channel, I started developing a bizarre fluctuation in the voltage supplying my PCB's. At first it would happen when I would just turn the unit on. The power light would pulse on-off... on-off... on-off... then stay steady on. After a few times of turning the unit on/off while trying to trim the fourth channel, the pulsation became unending.

Now when I turn it on, the green power LED just pulses on-off... on-off... over and over and over. When I measure the voltage at the jack or fuse, it is fluctuating up and down in concert with the LED lights. If I turn on the phantom, the phantom LEDs pulse up and down in sync with the power lights.

I have two PSU's and I tried them both with the same result. I tried detaching the new fourth PCB 48V (red) power cable but the voltage pulsations are continuing nonetheless.

I tried changing the fuse with no effect. I tried taking out the fuse altogether (to break the circuit) and measured the voltage at the adaptor jack. It measures 48V steady when there is no fuse in. As soon as I reinstall the fuse (reconnect the circuit) and turn it on, the voltage starts pulsing/spiking rhythmically again.

Any idea on earth what this is now?

mike wrote:Looks like my challenges with this build aren't quite done yet. I finished the fourth channel (using 2SA1804 transistors - accommodating for their different pin configuration appropriately).

Somewhere along the line testing this fourth channel, I started developing a bizarre fluctuation in the voltage supplying my PCB's. At first it would happen when I would just turn the unit on. The power light would pulse on-off... on-off... on-off... then stay steady on. After a few times of turning the unit on/off while trying to trim the fourth channel, the pulsation became unending.

Now when I turn it on, the green power LED just pulses on-off... on-off... over and over and over. When I measure the voltage at the jack or fuse, it is fluctuating up and down in concert with the LED lights. If I turn on the phantom, the phantom LEDs pulse up and down in sync with the power lights.

I have two PSU's and I tried them both with the same result. I tried detaching the new fourth PCB 48V (red) power cable but the voltage pulsations are continuing nonetheless.

I tried changing the fuse with no effect. I tried taking out the fuse altogether (to break the circuit) and measured the voltage at the adaptor jack. It measures 48V steady when there is no fuse in. As soon as I reinstall the fuse (reconnect the circuit) and turn it on, the voltage starts pulsing/spiking rhythmically again.

Any idea on earth what this is now?

If you read the top of this BAN thread this is fully explained. But the simplest thing to do since you have already built is just remove the 470uF 50v next to the 10R resistor at the back of each PCB. This will let the power supply start easier and leave the preamps working fine.

Yeah you're right Joe. My mistake. I had read a couple times we probably didn't need the soft start mod for the new PSU's so I didn't recognize the hickup protection for what it was.

To confirm, do you mean remove the cap I crossed off in red, or the one circled in blue? Would I need to put a jumper across where I remove it? Is there any comparative disadvantage to the expected specs by removing this capacitor vs. doing the soft start mod? I don't mind the mod. It looks like it's just:

- Add jumper wire connecting two pads
- Cut connection to one pad
- Remove jumper and install BD681
- Install 10K resistor

If that gives better performance, I'd rather do that. I've put so much into this already, and I'm due to order some parts from Mouser anyway. I can pick up 4 BD681's no problem.

Also, while I'm ordering, is there a Mouser part number for the blanking plugs you use for the DI jacks? I'd like to pick up two more.

mike wrote:Yeah you're right Joe. My mistake. I had read a couple times we probably didn't need the soft start mod for the new PSU's so I didn't recognize the hickup protection for what it was.

To confirm, do you mean remove the cap I crossed off in red, or the one circled in blue? Would I need to put a jumper across where I remove it?

First thing make sure the 4th module is working and powers up fine by itself and is not just faulty and causing this problem?
Otherwise best is just remove red cap and nothing else if you are using a 48v 25w SMPS to run 4 x BAN. If using 48v 40w SMPS nothing should need to be done.

Is there any comparative disadvantage to the expected specs by removing this capacitor vs. doing the soft start mod? I don't mind the mod. It looks like it's just:

The cap removal works best.

Also, while I'm ordering, is there a Mouser part number for the blanking plugs you use for the DI jacks? I'd like to pick up two more.

We get the blanking plugs locally so not sure about mouser. If you want some blanking plugs and BD681's we can send them for $10AUD shipping and the parts for free.

Joe Malone wrote:First thing make sure the 4th module is working and powers up fine by itself and is not just faulty and causing this problem?
Otherwise best is just remove red cap and nothing else if you are using a 48v 25w SMPS to run 4 x BAN. If using 48v 40w SMPS nothing should need to be done.

Thanks, Joe. I'll just pick up a 48v 40w PSU with my other parts then and leave it at that: http://ca.mouser.com/Search/ProductDeta ... M40B48-P1J

Also, while I'm ordering, is there a Mouser part number for the blanking plugs you use for the DI jacks? I'd like to pick up two more.

We get the blanking plugs locally so not sure about mouser. If you want some blanking plugs and BD681's we can send them for $10AUD shipping and the parts for free.[/quote]

Thanks. I'll take you up on the blanking plugs! Should I send the $10 AUD to your e-mail address by PayPal?

mike wrote:

Joe Malone wrote:First thing make sure the 4th module is working and powers up fine by itself and is not just faulty and causing this problem?
Otherwise best is just remove red cap and nothing else if you are using a 48v 25w SMPS to run 4 x BAN. If using 48v 40w SMPS nothing should need to be done.

Thanks, Joe. I'll just pick up a 48v 40w PSU with my other parts then and leave it at that: http://ca.mouser.com/Search/ProductDeta ... M40B48-P1J

Also, while I'm ordering, is there a Mouser part number for the blanking plugs you use for the DI jacks? I'd like to pick up two more.
We get the blanking plugs locally so not sure about mouser. If you want some blanking plugs and BD681's we can send them for $10AUD shipping and the parts for free.

Thanks. I'll take you up on the blanking plugs! Should I send the $10 AUD to your e-mail address by PayPal?

40w smps looks correct. Just email your address so I can cut and paste it to the shipping system. And we will send the blanking plugs for free.

EDIT : Found your address 4 blanking plugs sent today

Found your address 4 blanking plugs sent today

I got the 48v 40w SMPS power supply but it did not help at all. The unit has been going into protection mode (cycling green power LED) with any more than 2 PCB's attached. It doesn't matter which PCB combination I used, with 3 or 4 attached it would go into protection mode. This is true with the 40w and 25w PSU's.

I therefore went ahead and removed the suggested capacitors (1 from each PCB). This has helped a bit, and with the 40w PSU I can now get 3 channels working simultaneously. Adding the fourth puts it into protection mode again. It does not matter which 3 PCB's I use, so I know it's not a faulty channel. All channels have been tested and pass audio correctly so seem to be well assembled.

What is my next step? Should I remove yet another capacitor (what are these caps doing exactly)? Or should I put the caps back and do the whole soft start mod listed in the OP?

mike wrote:I got the 48v 40w SMPS power supply but it did not help at all. The unit has been going into protection mode (cycling green power LED) with any more than 2 PCB's attached. It doesn't matter which PCB combination I used, with 3 or 4 attached it would go into protection mode. This is true with the 40w and 25w PSU's.

I therefore went ahead and removed the suggested capacitors (1 from each PCB). This has helped a bit, and with the 40w PSU I can now get 3 channels working simultaneously. Adding the fourth puts it into protection mode again. It does not matter which 3 PCB's I use, so I know it's not a faulty channel. All channels have been tested and pass audio correctly so seem to be well assembled.

What is my next step? Should I remove yet another capacitor (what are these caps doing exactly)? Or should I put the caps back and do the whole soft start mod listed in the OP?

Measure the voltage drop across each 10R on each BAN PCB and let me know the voltages you get. As something is very wrong as we run 8 x BAN on 40w with ease.

Let me know the exact model number of the supplies you are using so I can check they are same types as we use.

I can get any combination of 3 boards working with the GS25A48-P1J 25W PSU as well as the GSM40B48-P1J 40W PSU. Whenever I add a fourth board (any board, I've tried different combination) it goes into protection mode. Voltages across the 10R are 0.350, 0.361, 0.284, and 0.285. All boards have been audio tested and are producing good results.

Hello. I have a BAN related question, and I wonder if anyone here can help. I am thinking of building a fully balanced passive summing mixer (32x4x2) which has 4 group busses feeding one main mix bus. So 32 inputs in total, which are divided into 4 sets of 8 inputs feeding one stereo sub group bus each which are then feeding the main mix bus. For the sub groups (8x2) I am thinking of using BAN pres for the make up gain. Would NE5532As be good? I am looking for good noise properties as make up gain noise would build up, no transformers.
My main question being: since the BAN has a very high input impedance, would it be beneficial to design the 8x2 passive summing with higher than the normal 150-200Ohms output impedance? Could the shunt resistor be set at a high value? How would that change things?

Thank you!

mohausler wrote: ↑

Mon Nov 28, 2022 7:38 pm

Hello. I have a BAN related question, and I wonder if anyone here can help. I am thinking of building a fully balanced passive summing mixer (32x4x2) which has 4 group busses feeding one main mix bus. So 32 inputs in total, which are divided into 4 sets of 8 inputs feeding one stereo sub group bus each which are then feeding the main mix bus. For the sub groups (8x2) I am thinking of using BAN pres for the make up gain. Would NE5532As be good? I am looking for good noise properties as make up gain noise would build up, no transformers.
My main question being: since the BAN has a very high input impedance, would it be beneficial to design the 8x2 passive summing with higher than the normal 150-200Ohms output impedance? Could the shunt resistor be set at a high value? How would that change things?

Thank you!

The BAN noise is mainly set by the input transistors used in its front end. Can you draw up a rough circuit of the mixer you are thinking of building so I can work out the best way this could be done.

Attached is a basic signal flow image for the mixer I am planning and a couple circuits for the subgroups I am thinking of pairing with BAN mic amps. Two different versions (with and without mono inputs). Resistor values are actually 7.15kOhm not 7.2kOhm. The impedance calculations are done for a mic amp with an impedance of about 1.2kOhm. So my question is: would it make sense to adjust for BANs? What would be the benefits or disadvantages for the passive summing network to have a higher output impedance / higher value shunt resistors? Would BANs be quiet enough (since we have multiple stages of passive summing)? And are there any concerns regarding headroom? Thanks!