DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

I just finished putting together the PSU 1848 kit. I'm getting identical voltage across the +, -, and phantom terminals and adjusting the voltage regulators does nothing to change this. The voltage remains whether or not the power switch is on.
Also, only LED2 is lighting up even though I accidentally put it in upside down - noticing this, I flipped the orientation so that it was in correctly (longer leg down as it says in the manual) and then it did not light up. LED1 is in correctly and is not lighting up.
I'm wondering if I wired the transformer wrong because on the transformer it says that the red and yellow wires carry 18V and black and orange carry 0V, but your diagram above says differently. Or maybe my assumption that AC1 and AC2 on the PSU are where the 18V wires go is wrong. At any rate, I tried it both ways and got the same result both times. Any ideas on what the problem is?

I have a feeling you have something wired wrong. If the power switch is OFF, you should not have any voltage. PERIOD.

Please review your wiring as per the Assembly guide and the diagram above.



There is no need to "wonder."
Please follow the assembly guide.
Do not assume anything.
The diagram above works and the assembly guide is correct.

There is no need to "wonder." As I said in my instructions....
connect RED and ORANGE wires together, connect to "CT" pad of PSU
connect BLACK to "AC1" pad of PSU
connect YELLOW to "AC2" pad of PSU


There is no need for you to ASSUME anything.
DO NOT ASSUME ANYTHING.
Everything is spelled out in the assembly guide and the pictorial wiring guide above on how to do it.
JUST FOLLOW THE INSTRUCTIONS.
Do not experiment and try different ways.
There is no need for you to "try both ways" or try different things. There is a correct way to wire this and all you need to do is follow it.

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ok, so my psu is wired EXACTLY as your diagram says, and I'm still having the same problem. I have gone over every nano-inch of the pcb and there is no cold solder anywhere, no shorts anywhere. One thing I did notice is that all three of the voltage trimmers that came in the kit are 5K instead of one 5K and two 2K. Would that be the issue?
And speaking of voltage trimmers...the component layout guide in the manual for the SC-1 preamp shows the voltage trimmers are installed in opposing directions, but all the pictures show them oriented in the same direction. Which is correct?

Can you take photos of the unit. In the photo,
a) Show the wiring.
b) Show the top side of the PCB.
c) Show the bottom side of the PCB (solder side).



You probably ordered the PSU-2448. It's not an issue. You'd just have the capability to adjust the PSU to the higher 24V-25Volts.



It's not an issue. The trimmers (which are just resistors) can be mounted either direction. The clockwise/counterclockwise adjustment will just be the opposite. But it doesn't affect how the PSU works.


Tell me
a) What voltage reading are you getting across AC1 and AC2 (in volts AC).

b) What voltage reading are you getting across V+ and GND.

c) across V- and GND

d) across +48V and GND

Does varying the trimmers change the voltage for your answers on b, c, d above?

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My fault, I thought I had the 1848 psu. I thought that's what came with the 4-channel everything kit. That would explain why i had three 220R instead of one 220 and two 120, and also three 5K trimmers.

Voltage across AC1 and AC2 is 44V. Across AC1 and CT is 22V, and similar for AC2 and CT.

Here's what's weird: Voltage for GRND and 48 is 0V, for + and GRND is 0V, and - and GRND is 0V. Changing the trimmers does nothing. The weird thing is that when I only touch one of the multimeter probes to a terminal I get voltage that varies between 9V and 12V but as soon as the second probe touches the other terminal it goes to 0V.

This makes absolutely no sense to me. I don't think it's the multimeter because it works fine to check AC1 and AC2 voltages and also the incoming 120V. Although, I'm only getting 120V between the ground terminal and the terminal wired to the transformer. Voltage between ground and the terminal going to the fuse is 0V. Is this how it should be? I checked the fuse and it's not blown.

Also, thanks for the great customer service. I really do appreciate it. If I can get this thing working, I'll definately be buying more units in the future.

Here are the pics. In the photo of the underside of the PCB it looks like there is cold solder in a couple spots, but I thouroughly examined the PCB and it's only solder flux that has caught the light. Also, I've got both LED's working. The pics are with power off because I was getting glare from the LED's.









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Also, I forgot to mention...you can't see it in the pics, but the psu is not sitting on the chassis, I have a 1/4" thick rubber mat that it is sitting on as a temporary spacer while I'm working on it before I mount it with screw-in spacers. At no time during my testing did any part of the psu touch the chassis.

This may be a silly suggestion... but i've done it before. When you're measuring the voltages from the PSU, make sure your multimeter is measuring DC voltage... not AC (which is what you're using for AC1/AC2/120v).

That's good. No problems there.



As guitarguy said.... did you switch the meter to "DC" ??? Maybe your meter is still set to measure "AC" volts?

Are the LEDs on the PSU board "lighting up" ??

Were they inserted in the right orientation? I think Long Leg at the bottom of the board (towards the big capacitors).

Is the LED Panel lights working? What if you switch the wires (in case the LEDs are wired incorrectly.)


Don't worry, we'll get your PSU up and working.

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Man, do I feel like an idiot!!! I knew it was something stupid like that because I had both LED's lighting up and nothing burning or exploding.
Switched my multimeter to DC and it works fine! I was able to adjust the voltages perfectly.

Thank you so much for the help, even though it was a bonehead mistake on my part. I don't know the last time I bought something and had the person I bought it from help me out to this extent. Much appreciated!!!!

The next session I've got booked in my studio is just after Christmas, and I'll definately be using the SC-1. I'd love to post some audio once it's mixed.

Hurray! It works!

Don't feel too bad. We've all done it at one point in the past.... Like troubleshooting something that is not working because it's unplugged

Would love to hear recordings you make out of it!

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