How to build a transformer and find core

AI Thread Summary
The discussion centers on building a transformer to use an OEM amplifier with dual-voice coil subs for a single voice coil sub of higher impedance. The user seeks to hand-wind a transformer with a 2:1 turns ratio, aiming for around 20-30W RMS, while grappling with the challenges of low-frequency performance and transformer size. They express interest in finding affordable cores and wire, and mention resources like Amveco for custom cores and articles by Bill Whitlock on audio transformer requirements. The user is motivated by curiosity and the challenge, despite feeling discouraged by the complexities of transformer design and performance limitations. Ultimately, they are looking for basic winding calculation formulas and effective search terms to aid their project.
Cliff_J
Science Advisor
Messages
789
Reaction score
7
In my car the OEM amplifier runs dual-voice coil subs. Its a SMT PCB with all ICs on even the outputs, no SMPS so its just 12V for the rails and the outputs are already bridged. Easy to see why many junk it and use an aftermarket amplifier come upgrade time. But I want to try to use it as is on a single voice coil sub of higher impedance and don't know the formulas to build a transformer (and would like to do it cheap by hand winding).

So I need two primaries to feed a single secondary with a 2:1 turns ratio. I'm figuring 20W RMS (maybe 30W) but have been told the low frequencies of a sub make the transformer large (and I thought it was more a function of VA capacity/saturation level than freq).

I'd like to think I could ballpark this thing and buy a cheap torrid doughnut and some 22ga enameled wire and wrap a couple hundred turns to start testing and then scope it to see how bad it performs. So can anyone give me a idea where to find a cheap doughnut (or U-shaped laminate core) and an idea what gauge/turns to start with?

I'm guessing that if we start with say 60Hz like mains power will the performance suffer greatly at 30Hz, and if we start with 30Hz then the inductance would need to be managed to keep the performance in-check at 60Hz? Ahh, I have a ton of questions but will try to keep this short so any help is appreciated.
 
Engineering news on Phys.org
I don't know where you could buy a core alone, but if you go to this company
http://www.amveco.com/
they will make you one for a reasonable cost (probably ~$100.) Also, they
may tell you how to get a core or sell you one.
 
Last edited by a moderator:
Antiphon - thanks, that was a little more than I wanted to spend but I always did appreciate the beauty of a nice torroid.

Ok found a couple sources of cores through the Thomas Registry - well a couple that sell single units anyways.

Also found a resource that helps with some of the requirements for an audio transformer in an article written by Bill Whitlock of the Jensen Transformer company (who makes $300 signal transformers with excellent performance). Its focused on low-signal performance and gives no formulas for determining windings though.

In the article he details that the lower frequency performance is a product of inductance but to keep phasing correct the -3db point should be kept very far beyond the intended range, so far below he referenced primary windings of 1000 henries! And that high frequency performance is a product of capacitance in the windings.

Little discouraged thus far, and when he mentioned how poorly regular silicon steel is with hysteresis distortion I was more discouraged, but I'll explain why I'd like to continue exploring. At this rate, the idea is dwindling but curiosity is persistent and the challenge of making it work keeps a neat goal. Especially in a day when car audio amplifiers with peak wattage ratings that are outrageous can be found at just about any retail store.

Our hearing is poor at low frequencies for both amplitude (Fletcher-Munson) and distorition with even 10% THD representing the threshold for audibility. Frequency response below even 40Hz is difficult even in a car with the advantages it offers in terms of bass reproduction. So within the envelope of frequency response of 40-60Hz with 10% THD this narrow bandwidth and high distortion I'd hope (really like to know but still hope it works) I could make it work.

In short, this is more a hobby experiment than a precision exercise. Can anyone even give me a basic transformer windings calculation formula like would be used for a regular old mains transformer? Or what would be good search terms on google. Thanks in advance.
 
Nevermind, I finally found some good sites after the internet search terms were sorted out. Seems the inclusion of the word "tube" helps tremendously and was much easier than trying to find an old article on winding a eletrostatic transformer.

Ok, now off to try to find surplus suplpies for cheap...
 
Hi all I have some confusion about piezoelectrical sensors combination. If i have three acoustic piezoelectrical sensors (with same receive sensitivity in dB ref V/1uPa) placed at specific distance, these sensors receive acoustic signal from a sound source placed at far field distance (Plane Wave) and from broadside. I receive output of these sensors through individual preamplifiers, add them through hardware like summer circuit adder or in software after digitization and in this way got an...
I have recently moved into a new (rather ancient) house and had a few trips of my Residual Current breaker. I dug out my old Socket tester which tell me the three pins are correct. But then the Red warning light tells me my socket(s) fail the loop test. I never had this before but my last house had an overhead supply with no Earth from the company. The tester said "get this checked" and the man said the (high but not ridiculous) earth resistance was acceptable. I stuck a new copper earth...
I am not an electrical engineering student, but a lowly apprentice electrician. I learn both on the job and also take classes for my apprenticeship. I recently wired my first transformer and I understand that the neutral and ground are bonded together in the transformer or in the service. What I don't understand is, if the neutral is a current carrying conductor, which is then bonded to the ground conductor, why does current only flow back to its source and not on the ground path...

Similar threads

Back
Top