Need help finding a replacement transformer

[Organ Bender]

Hi,
another post about power supplies.

I have this Acus amplifier https://www.acus-sound.it/en/one-forstreet/24-oneforstreet-8.html which comes from Europe that I'd like to convert to work on 120V.
This should be as simple as swapping the power transformer for a 120V primary with the same rating, right?
The original is primary 230V, secondary 16VAC, 128VA
The voltage regulator is an LM2937 12V, so I suppose a 15V 120VA transformer would do.

Assuming my plan is right, the problem I am left with is finding a transformer with the right dimension to fit in. All transformers I found online where more the flat type, i.e. larger and less high. I also tried contacting Acus but they haven't replied. And the company that build these transformer cannot be found on the internet.

Dimensions are : dia 80mm, height 70mm with hardware.

Where can I find one?

[jkostb]

Have a look at toroidal transformers from Sedlbauer:
1) Model nr 825033 2x115V/2x15V/2x5A,  150VA, diameter 115mm, height 47mm
2) Model nr 826041:2x115V/2x18V/2x4,17A, 150VA, daimeter 115mm, height 47mm

https://www.sedlbauer.de/produkte/150-va-premium-polytronik-ringkerntransformator/

https://www.it-tronics.de/elektronische-bauteile/ringkerntrafos/

The LM2837 has absolute maximum input voltage 25V.  With 15Vrms this will result in 15*sqrt(2)=21V. So best to pick 15Vac transformer.

[PCB.Wiz]

Dimensions are : dia 80mm, height 70mm with hardware.

As you have found, that is a rare aspect ratio.
You could see if a more common shape can fit anywhere inside your case, and failing that, either

• get a quote on having what you have rewound, which assumes that they have machines that can manage that shape
• or buy a switching power module that can fit, ideally with low enough noise.

It looks like you have just a single output, so that simplifies things.

Maybe something along the lines of Mean Well LOP-300-18 can fit somewhere?   It gives DIMENSION 101.6*50.8* 25.4mm (L*W*H)
Or an external laptop style power unit may exist with enough watts ?

[Organ Bender]

Have a look at toroidal transformers from Sedlbauer:
1) Model nr 825033 2x115V/2x15V/2x5A,  150VA, diameter 115mm, height 47mm
2) Model nr 826041:2x115V/2x18V/2x4,17A, 150VA, daimeter 115mm, height 47mm

Unfortunately the size won't fit. But thanks

Maybe something along the lines of Mean Well LOP-300-18 can fit somewhere?   It gives DIMENSION 101.6*50.8* 25.4mm (L*W*H)
Or an external laptop style power unit may exist with enough watts ?

This one could fit, although I would have to install a plate of some kind for there would be 2 of the mounting holes in mid air on the battery side. Thanks

[Organ Bender]

I am still in the search for the solution...

• or buy a switching power module that can fit, ideally with low enough noise.

Would it be as simple removing the LM2937 and inserting the power module +/- in its place? Or are there other components I need to put out of the circuit or take into account in any way?

I am not much familiar with this kind of power circuit. I wish I had the schematic!

[Shay]

If possible on some power supplies there is an option to slightly adjust the voltage. I'd adjust the voltage to ~12.8V at least (if possible, more) and fed it into the input of the LDO. This way you can the benefit on the ripple rejection and local regulation, plus additional protections.

[PCB.Wiz]

Would it be as simple removing the LM2937 and inserting the power module +/- in its place? Or are there other components I need to put out of the circuit or take into account in any way?

Why do you need to remove the LM2937?
The power module replaces the transformer and rectifier.

The unit you linked has external battery and external Molex 6Pin? plug power in, so you could also use an external laptop type power supply, fitted with a matching connector, and simply plug in that way.

[Hydron]

Can you stack two smaller transformers to meet the aspect ratio requirement? Ideally choose voltages (e.g. 8V secondary) so that primaries can go in parallel, secondaries in series (in case there's some small variation in turns ratio that would ensure that there's no issues). Note that within each transformer you can put dual windings in parallel as they are normally designed for that.

[Organ Bender]

Last update :

I decided not to modify the amp, sell it, and buy a new one with the proper psu

So thanks a lot for your insights