AC/DC & POWERSTATION KIT BUILD THREAD

[Motoloktive]

Hi everyone,
I am new to this forum, so please let me know if I overlooked a thread that already discussed this (I couldn't find any reference to the mixers I am trying to fix).
In addition, I am from Germany, so please forgive any spelling or grammar mistakes (:
As I just mentioned, I am in the process of fixing two audio mixers (a Soundcraft UREI 1605 and a 1603).
These mixers have a well-known design flaw... They cook their power supplies to death, or at least (as in my case), to a point where it introduces so much noise that the mixer is left unusable.
But let me start at the beginning... When I got these mixers (I bought both as defective), my first action was to give each and every potentiometer a thorough cleaning.
After that, both units were in a usable state. No crackling, no noise. Or so I thought...
After using the 1605 for some continuous hours, I suddenly got a very loud noise on every bus in the mixer, which would disappear when I left the mixer to "cool" off.
So I took a look at the power supply and noticed the typical discoloration of the PCB where the heat is collecting since the mixer is completely fanless and there is no active air movement in the case. (The plastic shroud around the supply only makes matters worse.)
As a next action, I ordered every cap (I ordered 105°C once whereever possible) to replace the ones on the power supply board.
So now I have one mixer, still with the original power supply, and one with a recaped one. The recaped one hasn't made any trouble since.
Now I discovered this website and found out about the AC/DC 3 Rail Power Supply Kit, which resembles exactly what I need to completely eliminate the flawed original power supply.
I looked around online but couldn't find any of the shelf supplies that output +/-16V and 8V, which are the voltages needed for these mixers.
So here I am to check with someone if my plans are somewhat realistic or if I am completely off.
I measured the current draw on the three supply rails in both the 1605 (7-channel mixer) and the 1603 (4-channel mixer):
For the 1605:
    (+V1/+16V) = 15.32V @ 696mA
    (-V1/-16V) = -15.23V @ 800mA
    (+V2/+8V) = 9.79V @ 17.12mA
For the 1603:
    (+V1/+16V) = 15.41V @ 474mA
    (-V1/-16V) = -15.44V @ 536mA
    (+V2/+8V) = 9.93V @ 19.59mA
My plan now is to replace the SMPS entirely and replace it with a combination of a 2x18V 50VA mains transformer (I found a 0050P1-2-018 from nuvotem available from a German supplier) and an AC/DC 3 Rail Power Supply Kit.
I put the bigger current values in the wattage and heatsink calculator and got ~37VA for the transformer.
Is the 50VA good enough, or should I consider a larger one (e.g., 80VA)?
I am wondering if the mixer's power consumption would increase significantly while in use...
Because the current values were measured while the mixer was turned on but unused, there was no signal at the inputs or outputs.
The calculator also returned the lowest C/W rating of ~14.84C/W for the -V1 regulator. (As far as I understood, the lowest value is the one to most care about.)
Do you think it gets enough cooling when I mount the regulators to the metal housing, or should I try to fix the 5C/W heatsink to the housing?
And as a last question:
Do you think the transformer will cause problems like coupling hum into the signal buses since it will be mounted inside the case?

Quick background info: I finished my apprenticeship as an electrician for devices and systems (translated word for word from German) last year, but I bet there is a lot more for me to learn about electronics, and that's why I would love to hear a second opinion.
So thanks a lot for any advice in advance (:
Greetings from Germany
Sebastian

[Joe Malone]

For the 1605:
    (+V1/+16V) = 15.32V @ 696mA
    (-V1/-16V) = -15.23V @ 800mA
    (+V2/+8V) = 9.79V @ 17.12mA
For the 1603:
    (+V1/+16V) = 15.41V @ 474mA
    (-V1/-16V) = -15.44V @ 536mA
    (+V2/+8V) = 9.93V @ 19.59mA
My plan now is to replace the SMPS entirely and replace it with a combination of a 2x18V 50VA mains transformer (I found a 0050P1-2-018 from nuvotem available from a German supplier) and an AC/DC 3 Rail Power Supply Kit.
I put the bigger current values in the wattage and heatsink calculator and got ~37VA for the transformer.
Is the 50VA good enough, or should I consider a larger one (e.g., 80VA)?
I am wondering if the mixer's power consumption would increase significantly while in use...
Because the current values were measured while the mixer was turned on but unused, there was no signal at the inputs or outputs.

Idle current is all you need to know so that is fine

The calculator also returned the lowest C/W rating of ~14.84C/W for the -V1 regulator. (As far as I understood, the lowest value is the one to most care about.)

The total c/w is what you need to know which is lowest C/W number

Do you think it gets enough cooling when I mount the regulators to the metal housing, or should I try to fix the 5C/W heatsink to the housing?
And as a last question:

If you use a 2 x 15vac 30VA or 50VA transformer the heat on the +/-15v will be minimal. The 9v rail uses minimum current so will be fine as well. So either bolt regs to case or use pcb heastink.

Do you think the transformer will cause problems like coupling hum into the signal buses since it will be mounted inside the case?

Yes it could especially if any audio input transformers but depends on the transformer type. You could run an external transformer and keep the AC/DC pcb mounted inside the rack.

[Motoloktive]

Thanks for your input.
Just ordered two v4 PCBs so I can try to make it work.
If it turns out to not work with the transformer inside the case I will put it in an external (Powerbrick like) box.
PS: If anyone is interessted I will come back with my findings once I finished the powersupply exchange.

[Joe Malone]

Thanks for your input.
Just ordered two v4 PCBs so I can try to make it work.
If it turns out to not work with the transformer inside the case I will put it in an external (Powerbrick like) box.
PS: If anyone is interessted I will come back with my findings once I finished the powersupply exchange.

Ok v4 will work but you will need the pcbs to sit level with the bottom. The newer EM version can have the regs under the pcb so can clamp them to the side of the case in silicon tubes which might work better as it is lower profile out into the case. But it depends on the height of the side of the case. How wide was the original SMPS pcb?

[Motoloktive]

Thanks for your input.
Just ordered two v4 PCBs so I can try to make it work.
If it turns out to not work with the transformer inside the case I will put it in an external (Powerbrick like) box.
PS: If anyone is interessted I will come back with my findings once I finished the powersupply exchange.

Ok v4 will work but you will need the pcbs to sit level with the bottom. The newer EM version can have the regs under the pcb so can clamp them to the side of the case in silicon tubes which might work better as it is lower profile out into the case. But it depends on the height of the side of the case. How wide was the original SMPS pcb?

The original supply is 50mm x 175mm. I have around 75mm to 80mm height on the side of the case to play with (the height of the assembly into the case doesn't really matter to me since there is enough space left around where the original supply is mounted). My plan now is to mount the regulators to the case and bend the legs upwards at a 90°angle. The pcb will be mounted with standoffs over the regulators and soldered in afterwards, so the distance matches exactly. I know it won't be exactly user friednly to dissassemble, but with this mod I hope to not have to do that very often in the future anyways.

[Joe Malone]

Thanks for your input.
Just ordered two v4 PCBs so I can try to make it work.
If it turns out to not work with the transformer inside the case I will put it in an external (Powerbrick like) box.
PS: If anyone is interessted I will come back with my findings once I finished the powersupply exchange.

Ok v4 will work but you will need the pcbs to sit level with the bottom. The newer EM version can have the regs under the pcb so can clamp them to the side of the case in silicon tubes which might work better as it is lower profile out into the case. But it depends on the height of the side of the case. How wide was the original SMPS pcb?

The original supply is 50mm x 175mm. I have around 75mm to 80mm height on the side of the case to play with (the height of the assembly into the case doesn't really matter to me since there is enough space left around where the original supply is mounted). My plan now is to mount the regulators to the case and bend the legs upwards at a 90°angle. The pcb will be mounted with standoffs over the regulators and soldered in afterwards, so the distance matches exactly. I know it won't be exactly user friednly to dissassemble, but with this mod I hope to not have to do that very often in the future anyways.

Ok that will work.