Mains toroids appear to be great for audio

[EC8010]

Beware that connecting a pair of back-to-back toroids to a transistor amplifier was quite a favourable connection. You would have had negligible DC offset to upset the first one (obviously none for the second) and any additional current required by the first one due to inadequate primary inductance was easily furnished by your voltage source. When used as valve output transformers, things aren't quite so good. Net DC current needs to be 2mA or less (I've also tested with 6V 50VA), and inadequate primary inductance steepens the loadline on the valves at low frequencies and increases distortion. Fortunately, this is often offset by the LF resonance of the loudspeaker, but this can't be guaranteed.

On the positive side, I've seen some remarkably 10kHz square waves through toroidal mains transformers used as output transformers. The most "bang per buck" solution would be to use a dead cheap valve amplifier purely for the treble and a cheap transistor amplifier for the bass, split by an active crossover.

 

[bigwill]

I will do some more experimentation tommorow!

 

[alexmoose]

Hello! this sounds like a great expirement.

What output transformers were you using before? (so I have a little comparison)

And, I assume you use AC 240 on the mains, making the ratio 20 to 1. So this means I should use a 120:6v tranformer (In the USA), and put the windings in Parallel?

 

[dave slagle]

The physics of it dictates that the core is only designed to handle power down to 50hz so by the time you are down to 20hz the core will be heavily into saturation. The ones I have used are at least 10 times the power rating and they cope well down to about 10hz.
Shoog

I'm not sure i agree with your logic. the majority of power transformers are designed so that the applied line voltage at line frequency is just below saturation. This design goal is generally applied independent of core size. If a 230V 50hz signal just misses saturation on a 50VA trannie, moving to a 500VA trannie designed for the same line voltage will not change much so the same signal level and frequency will saturate both equally.

One other thing, cores by themselves do no have power ratings. If the windings could be made with no resistance a typical 50VA core could easily do the work of a 500VA core.

dave

 

[TonyTecson]

Surprisingly, they let the full spectrum though seemingly with no problems at all! The bass wasn't distorted and sounded just as extended as the channel without toroids! The treble sounded equally un-harmed. There wasn't any distortion on bass notes and everything sounded "proper". The toriods probably DID colour the sound, but even if they did, they did in a very benign way. It was impressive considering the audio was going through two small MAINS transformers! If anything, I would seriously consider using them if I needed a temporary long cable run to my speakers. (Like 100v line transformers but probably better)

no surprises here, your NAD amp puts out much lower than 240volts so that even if the torroids were rated at 50hz, it does not saturate at 20 hz. even if your nad amp is capable of 200watts at 8 ohms, this is just 40volts ac! way below 240 volts........

 

[JoshK]

Can't one just sidestep the DC issue by using a series cap ala parafeed or ultrapath cap?

 

[kevinh]

Info on toroidal xformers

Plitron is a manf of toroidal trannies, they have a lot of good information on the tech issues and articles and projects (PP and SE) based on their technology.

http://www.plitron.com/audio.asp

Enjoy.

 

[Shoog]

Can't one just sidestep the DC issue by using a series cap ala parafeed or ultrapath cap?

That works well for SE designs (though parafeed presents its own issues such as where to get that big choke, or how to generate that extra 300V+ for a CCS).
With PP you need to get the DC balanced.

I think using toroids will always work best with high current low voltage applications as well.

Shoog

 

[igormak]

Re: Info on toroidal xformers

Plitron is a manf of toroidal trannies, they have a lot of good information on the tech issues and articles and projects (PP and SE) based on their technology.

Once I bought pair of that Plitron 4002. Works good from 400 Hz. Sound was awfull.
Anyway, I'm using only tors in my constructions. BigWill come to right way. With proper winding tors are very good sonically.

Some transformers here
http://public.fotki.com/igormak2/iconmak/tor2.html

 

[jrdmedford]

Readers should definitely check out those pics!

Yegor that wall mounted PP amp is about the most insanely
novel and wonderful thing I've seen in a long time. Who
would have thought that a PP DHT amp would be "too big"
for a small Moscow apartment ?!?!?

-- Jim

 

[igormak]

Readers should definitely check out those pics!

Yegor that wall mounted PP amp is about the most insanely
novel and wonderful thing I've seen in a long time. Who
would have thought that a PP DHT amp would be "too big"
for a small Moscow apartment ?!?!?

-- Jim

Jim, thanks for insane diagnosis , i'm really gratefull.
Actually, i didnt want show the amp. We are talking about toroids and i also started from mains.
Quality depends a lot from steel used.
Igor.