Need help finding a replacement transformer - Page 1
Forum section: electronics / projects

author: Organ Bender
author_rank: Contributor
timestamp: September 15, 2025, 08:31:29 pm
content: Hi,another post about power supplies.I have this Acus amplifierhttps://www.acus-sound.it/en/one-forstreet/24-oneforstreet-8.htmlwhich 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, 128VAThe 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?

author: jkostb
author_rank: Regular Contributor
timestamp: September 17, 2025, 04:43:51 pm
content: Have a look at toroidal transformers from Sedlbauer:1) Model nr 825033 2x115V/2x15V/2x5A, 150VA, diameter 115mm, height 47mm2) Model nr 826041:2x115V/2x18V/2x4,17A, 150VA, daimeter 115mm, height 47mmhttps://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.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 17, 2025, 11:24:32 pm
content: Quote from: Organ Bender on September 15, 2025, 08:31:29 pmAs 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, eitherget a quote on having what you have rewound, which assumes that they have machines that can manage that shapeor 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 ?

author: Organ Bender
author_rank: Contributor
timestamp: September 19, 2025, 07:35:37 pm
content: Quote from: jkostb on September 17, 2025, 04:43:51 pmUnfortunately the size won't fit. But thanksQuote from: PCB.Wiz on September 17, 2025, 11:24:32 pmThis 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

author: Organ Bender
author_rank: Contributor
timestamp: September 30, 2025, 07:54:52 pm
content: I am still in the search for the solution...Quote from: PCB.Wiz on September 17, 2025, 11:24:32 pmWould 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!

author: Shay
author_rank: Regular Contributor
timestamp: September 30, 2025, 10:41:01 pm
content: 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.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 30, 2025, 11:12:01 pm
content: Quote from: Organ Bender on September 30, 2025, 07:54:52 pmWhy 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.

author: Hydron
author_rank: Super Contributor
timestamp: September 30, 2025, 11:21:27 pm
content: 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.

author: Organ Bender
author_rank: Contributor
timestamp: October 02, 2025, 01:30:40 pm
content: Last update :I decided not to modify the amp, sell it, and buy a new one with the proper psuSo thanks a lot for your insights