Toroidal Transformers Questions

[otherside]

Hey guys,

A couple of questions about toroidals used for chipamps.

In the UK, farnell supplies Multicomp toroidals and RS Nuvotem. Both are similar priced, any ideas which are better or even if there is any quality difference?

I live in scotland where electronics shops are quite limited so mostly i rely on internet orders, any more ideas where i could get transformers through internet/phone?

Is it worth going the extra mile for encapsulated toroidals? Is there any reduce of noise because of encapsulation?

Is it better to use one large beast (~500VA) or two small ones(~250VA)?

When using two small ones cost of course goes well up since you need double of everything, bridge, caps, regulator pcb (if used). However using two seperate rails for the two channels i guess there is a chance that will be a difference between the two channels, at your experience how exactly this effects the amp performance (having two seperate rails).

Lots of questions... :-)

Any answers greatly appreciated

Thanks again

[Craig405]

Hi,

I have used the Farnell toroid before and it has been fine, i dont know the difference between the 2 manufacturers though.

Encapsulated transformers are less mechanically and electrically noisy so they are a better option for audio, although i think they cost more. If you go for a non encapsulated then just mount it a little further from the audio wiring etc and it'l be fine.

It is better to go for 2x 250VA transformers for a stereo setup (one per channel) each with its own rectifier and seperate capacitors.. if you can afford another transformer that is.

i think the only improvement you get from feeding each channel from a seperate supply is the crosstalk between channels via the DC supply is reduced to nothing as they arent connected, apart from at ground.


Regards
Craig

[richie00boy]

Use one big transformer but separate rectifier/cap system for each amp. That gains you sufficient isolation between amps, but the better regulation, cheaper cost and smaller size and weight of the single unit.

The only real advantage of the potted ones is they look nicer.

www.rapidelectronics.co.uk are also reasonable for transformers.

[jaycee]

The Farnell Multicomp toroids are manufactured by Toroid AB as far as I can tell. They seem high enough quality

[otherside]

Thank you very much guys for your response.

[AndrewT]

Hi,
full dual mono is the best option. It guarantees no interaction between channels.

Next best is four secondaries on a double VA transformer. After the primary everything is dual channel.

Third choice is two secondaries on a double VA transformer. After the secondaries everything is dual channel.

The fourth choice is two secondaries with single, or twin bridge rectifiers feeding a dual polarity, single bank of smoothing caps and then dual amplifiers. This is a cheap option and most would not consider it for the little that it saves.

The fifth and sixth options are so far down the line that only cheap skates would use it (or fly by night manufacturers).

[richie00boy]

Some good points Andrew, but it depends on if your priority is tighter regulation or minimisation of crosstalk. I would argue that once you employ separate rectifier and cap bank that crosstalk is so vanishingly tiny that there is no need to separate transformers as well. And using two smaller transformers gives you worse regulation which could show itself more than the crosstalk.

[AndrewT]

Hi Richie,
you are confirming option three as the cost vs performance optimum.

Funny that, as most of my own built amplifiers go for option three as well. All the others are monoblock.

Four secondary transformers are too expensive.

[DJ Exprice]

It depends. 2 separate transformers might actually be better. Just use them on separate circuits - except the primaries.

Each channel (if stereo) could have its own transformer. Depends on the price too. If the single has 2 secondaries, and each secondary is the same as the VA of the smaller transformers, then that would work just as well.

[otherside]

I think, considering the cost the option 3 might be best.

a single 2x35 (for example) tranformer with the two secondaries seperated on different bridges regulation etc..