Why toroidal transformers - Page 1
Forum section: electronics / beginners

author: max.wwwang
author_rank: Frequent Contributor
timestamp: April 17, 2020, 07:30:08 am
content: It’s commonly see in audio amplifiers especially high end. I asked myself what makes them preferred over the EI ones.Here lists some reasons. But I don’t see a big deal except for the first (hum/noise). I don’t think any of size / weight / cost / arrangement etc. would be a good reason for audio amplifiershttps://www.alliedcomponents.com/blog/5-benefits-using-toroidal-transformer/

author: Gyro
author_rank: Super Contributor
timestamp: April 17, 2020, 08:46:36 am
content: Most of those reasonsareactually relevant to an audio amplifier.1. Low noise and hum field - as you say, helpful in reducing induction into adjacent parts and wiring. Mechanical noise too, you don't want the chassis audibly humming.2. Easy to mount - Debatable, but it spreads the (lower) mass of the transformer over a wider chassis area. The single bolt can dent the chassis with negative g shocks though. It also allows a slimmer case profile than the equivalent rated EI Transformer.3. Lower operating temperature. Always useful, but even more so in a device that is trying to minimise the temperature of heat dissipating semiconductors and overall cabinet temperature.4. Light weight core. Particularly important when shipping consumer items across the world in shipping containers. Better shock resistance for a given chassis thickness etc. Shipping weight is a major cost factor for manufacturers. Size / form factor are an issue too (you need to design for best fill volume in the container).5. More Economical (normally only true above a certain power rating).Allproducts are built to a price, no matter what their selling price. Consumer product dealers (and distributors) take a huge margin. The transformer is probably the highest single cost item on the BOM.So yes, they all factor in to some extent - I wouldn't be surprised if the hum/noise was one of the lower priorities on the list [EDIT: Though it looks good in the Marketing blurb!]. After all, it's well proven that it is possible to produce decent quality amplifiers with standard transformers, it's been done for decades. Toroidals also couple more high frequency supply noise, which needs to be filtered.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: April 17, 2020, 09:17:37 am
content: Quote from: Gyro on April 17, 2020, 08:46:36 amThanks. Yes, possibly these are all relevant to some degree. My point was, by referring to audio amplifiers (especially high end), for which 20kg / 30 kg or more is not a barrier, I would not say weight / cost / installation, etc.etc. is a big deal if without other (much) more important factors (I can only see hum/noise). So the question is -- acknowledging noise/hum is a factor (probably the priority) -- is it impossible (or very difficult) to eliminate (or reduce) --1) the audible hum; and2) the electromagnetic noiseof an EI shaped transformer?I have no doubt, from a purist point of view and based on instinct, a toroid transformer will give a smoother energy/waveform transmission because of its smoother (or 'purer') physical shape of core and evenly distributed windings.

author: exe
author_rank: Unknown
timestamp: April 17, 2020, 09:42:31 am
content: Hi! Toroidal trannies aficionado is here. My reasons to use toroids (or not to use) are:Pros1) smaller for the same power, ormore efficient and better regulation for the same weight. My reason to use them.2) can add additional windingsCons:1) capacitive coupling between windings, unless there is an electrostatic shield, which is very rare2) more expensive3) Slightly more complicated mounting (needs a mounting kit). That's my opinion, other people seems disagree.4) don't like DC biasNot sure about hum, I don't have much experience with EI, but all my toroidal trannies (all two or three, lol) so far quite silent, while an EI in my Keithley K2000 is audible. But, I guess, it's because it was built down to price.So, there are engineering reasons to choose one or another, but I wouldn't be worried too much it. In a properly designed device there shouldn't be much of a difference (if any).

author: max.wwwang
author_rank: Frequent Contributor
timestamp: April 17, 2020, 09:56:44 am
content: Quote from: exe on April 17, 2020, 09:42:31 amSeems to me --P1 - Not a big deal, but a good reason for purists or paranoids?P2 - This is absolutely a real win in theory and for experimenters. But practically for a built product, this sounds odd?C1 - Seems another valid point, especially for purists (or extremists)C2 - Good one. High end gear has a habit to use expensive stuff only for the reason of higher cost (and price)C3 - Could be a factor but not a thing in my opinionC4 - What does this mean?Thanks.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 17, 2020, 10:45:31 am
content: I assumed toroidal transformers became the thing years ago to reduce power amp sizes from 5, 4, and 3RU down to 2RUand or avoid having an old school transformer poking out the backAll cons aside, which style actually wins in actual working efficiency from input to circuit land, is best done in an A/B testTwo identical amps with the two styles of transformer with same HONEST (?!!) VA ratings ,and then transformers swapped out to verify the two identical amps were in fact 'identical' and not influencing the outcome/sYeah, it's work you may not need, but someone has gotta do it if they care a bit,and put any BS in the ground where it belongs

author: exe
author_rank: Unknown
timestamp: April 17, 2020, 10:49:35 am
content: I hear a lot of judgement here.In one of my projects, apart the need for additional windings, I had tight thermal budget (due to plastic enclose) and constrained space. Pancake-like shape was ideal, very easy to fit.I once repaired a rack sound amplifier of 1U height, it also used a toroidal tranny. I guess they had the same challenge -- finding a tranny that would fit (though smps, probably, would be cheaper and smaller).I don't understand why people argue about toroidal trannies. I see people talk about audiopholery, but toroidal trannies are measurably different from EI trannies. It doesn't mean these difference will make a difference for an application. I'd say they shouldn't, or the circuit doesn't have enough "error budget". But they have different properties, pick the one that suits your project the most, just don't present personal preferences and bias as objective reasons.