Toroidal Transformers in B'lore

[roadkill]

Hello Bangalorean DIYers,
I posted some time ago asking where I can pick up a toroid core transformer in bangalore. Well, now I know. Miracle transformers will supply them in single-piece quantities, and even courier them to your home (for just Rs. 30!). I ordered a 225VA 25Vx2 toroid (model no M225 50) from them, it cost me Rs. 915 (MRP). Total charge including shipping was Rs. 1225.
Website: www.toroidal.com
Since then, they updated their site, they also offer encapsulated transformers, good for preamp supplies and such (small, starts at just 2VA!!!).
I've only unpacked the toroid, will check it out tomorrow (spent the day at URock ). It will end up feeding five gainclones (LM3886). Yes I know it's underpowered, but I wont be using it near full amplitude. Besides, I will be using a powered sub.
Hope this post helped!

 

[ashwin]

thanks

roadkill,

thanks for that info! I see that they also offer audio output transformers for tube amps. I didn't know that kind of thing was still being manufactured! So now I can play around with tubes for a while

Any particular reason (apart from size) you're using torroidals instead of EI?

- Ashwin

 

[tcpip]

Miracle transformers will supply them in single-piece quantities, and even courier them to your home (for just Rs. 30!).

This is fantastic news! I presume they'll ship anywhere in India. I don't even know of any toroidal tranny guys with ready-made list of models in Bombay, let alone B'lore. I keep hearing that there are guys who make toroids in Bombay, but I've yet to meet anyone who can (i) sell retail, (ii) has a range of standard specs. And the fact that these chaps have a Website is an added blessing. Bolton doesn't yet have a Website, and probably never will, for instance.

Great news! Thanks.

The price premium is interesting, though. I bought a 26-0-26V, 5A (that makes it a mite more than 250VA?) E+I transformer through Angshu's good offices from a guy called "Guru" in Delhi, and that cost me Rs.550. (I too plan to power some gainclones or P3As with it.) Your toroid is twice as expensive. But I guess I can now make my chassis slimmer.
Toroids should be ideal for low-current ratings (500mA or less?) for preamps, where I can really cram things tight and not worry about EMI. For poweramps, I'm quite often more open to E+I, specially if toroids cost this much extra.

Tarun

 

[roadkill]

ashwin, I used a toroid mostly for the size reduction. I am planning to try a cabinet design featured in Elektor, where they bolt on aluminium sheets to a pair of heatsinks. The heatsinks form the side walls, and the sheets form the top, bottom, rear and front panels. The largest heatsink extrusions I could find did not have enough height to fit an E-I of 225VA. Then there are other issues, like less EMI, simple means of mounting, etc.

tarun, the rumours must be true I've been to Lamington rd only thrice, there's this very dank-looking bridge you have to pass under if you're getting off at the local station, there was a hole-in-the-wall shop which had toroids. I didnt have enough money to buy them at the time (it was the last time I was there, on my way out... argh!) He also had C-core trannys, which apparently can be made smaller than a regular E-I, tho not as slim as a toroid. EMI is less, too, and there won't be a problem with inrush current like toroids have. Freight to mumbai would probably cost a bit more than just Rs. 30, it weighed about 3 kgs in all.

 

[ashwin]

heatsinks

The largest heatsink extrusions I could find did not have enough height to fit an E-I of 225VA. Then there are other issues, like less EMI, simple means of mounting, etc.

Hmm, I have the same problem, my 15-0-15V/5A is about 5" high. But the place where I bought the heatsink did have some tall extrusions (6-7" IIRC) which I intend to try. Where did you get your heatsinks from? I got mine from an Al shop at the entrance to SP road (from the town hall side).

- Ashwin

 

[roadkill]

heatsinks

ashwin,
I got my heatsinks from Cee Pee electronics (near Vishal). They're fairly expensive, too, so I guess I could try the place you mentioned. What's it called? Hope they're anodized ones...

 

[ashok]

Audio transformers.

Ashwin,
Where did you find the audio transformers for tubes on the Miracle web site ? I checked and seem to have missed them.

I have had a few dealings lately with them and they did not have any transformers for tubes. However they do have line level ( 70 V and 100V ) audio transformers for audio distribution purposes. I am not sure if you can use these with tubes . Their specs may not be suitable. On the other hand have you discovered that they can be used as tube OPT's ? If so that's great. Let us know.
Cheers.

 

[ashwin]

Re: Audio transformers.

ashwin,
I got my heatsinks from Cee Pee electronics (near Vishal). They're fairly expensive, too, so I guess I could try the place you mentioned. What's it called? Hope they're anodized ones...

My place was called Maruti Metals. Not an electronics shop, more an Al extrusions shop. But the Al was expensive.

Ashwin,
Where did you find the audio transformers for tubes on the Miracle web site ? I checked and seem to have missed them.

I have had a few dealings lately with them and they did not have any transformers for tubes. However they do have line level ( 70 V and 100V ) audio transformers for audio distribution purposes. I am not sure if you can use these with tubes . Their specs may not be suitable. On the other hand have you discovered that they can be used as tube OPT's ? If so that's great. Let us know.
Cheers.

Well, I'm not a tube expert, so you may be right. I assumed that they were OPTs because of the following quote on their page:

"Audio Line Matching Transformers 40


EDIT: dunno how this incomplete post happened...

 

[ashwin]

Re: Audio transformers.

ashwin,
I got my heatsinks from Cee Pee electronics (near Vishal). They're fairly expensive, too, so I guess I could try the place you mentioned. What's it called? Hope they're anodized ones...

roadkill, my place was called Maruti Metals. Not an electronics shop, more an Al extrusions shop. But the Al was expensive.

Ashwin,
Where did you find the audio transformers for tubes on the Miracle web site ? I checked and seem to have missed them.

I have had a few dealings lately with them and they did not have any transformers for tubes. However they do have line level ( 70 V and 100V ) audio transformers for audio distribution purposes. I am not sure if you can use these with tubes . Their specs may not be suitable. On the other hand have you discovered that they can be used as tube OPT's ? If so that's great. Let us know.
Cheers.

Well, I'm not a tube expert, so you may be right. I assumed that they were OPTs because of the following quote on their page:

"Audio Line Matching Transformers 40 HZ TO 20,000 HZ

The purpose of this Transformer is to match the Impedance of the loudspeaker or a number of loudspeakers to the optimum load of the tube or transistor. In other words, the transformer transforms the Impedance of the speaker, so that the impedance which it presents to the primary winding is equal to the load of the Output stage active element (tube to transistor)."

On their home page, click products -> transformers -> Audio Line Matching Transformers.

So what's the deal? Are they OPTs or not?

Why would you need a 70/100V rated transformer for audio distribution? I thought the 70/100V was for the high anode voltage of a tube stage.

- Ashwin

 

[ashok]

Why would you need a 70/100V rated transformer for audio distribution

Same reason as High Voltage power transmission. It cuts down on losses in the interconnecting wire. Higher voltage means lower current . So IxR loss drops.

70 and 100 volts distribution transformers are used universally .

I have been quite blind to the fact that if they made those transformers , I could get them to make units to our specs.
There is however a difference between OK transformers and superb transformers. We need to explore that possibility.
I did not read the blurb that followed it on the web page. I will follow up on this and let you know what transpires. If we can get some modified units I will test them out and see what we get.

Cheers.

 

[brokenbinil]

tordoil Transformers

i want to use a trodoial tranformer in my amp. it presently gives a out put of 40 + 40 Watts and then i'm using a 3amp transformer for the power supply. but i have some doubts: do i need a core with the tordoil or do i use a air core. i need one in the higher amp range ... around 8 to 10 amps. please advice where i might get them in indai and how expensive are they
Binil

 

[ashok]

Plenty of info on the Net.

Brokenbinil,
If you are trying to fit a budget , you might go broke buying toroidal transformers. For the same VA , toroids are more expensive. Toroid power transformers are not air core , they all have a iron strip core that's wound like a ring.

Why would you want a 10A transformer for a 40 watt amp? What voltage?
It might be a great idea for you to read up about toroidal transformers on the Net. You will get to know its plus and minus points. I think for normal applications there is nothing to beat the lowly EI core transformer.
You can go to www.toroidal.com for a supplier from Bangalore . There are also suppliers in Delhi who keep advertising in EFY and Elektor (India) magazines. Check it out. But first get on to the Net and read more about toroidal transformers.
Cheers.

 

[corbato]

Re: thanks

roadkill,

thanks for that info! I see that they also offer audio output transformers for tube amps. I didn't know that kind of thing was still being manufactured! So now I can play around with tubes for a while

Any particular reason (apart from size) you're using torroidals instead of EI?

- Ashwin

Those are line matching transformer and not OPT's. They are used mostly in running long lengths of connector to Horns (you know...chonga’s..) spread across several zones. Well that’s the idea. I don't know how many of the local PA rental folks actually use such things.

Besides, as Ashok has rightly posted, there are several factors involved in making a good OPT. You can wind an OPT to exact load lines as per the Tube datasheet and it still may sound horrible. Winding techniques, core material, interleaving and such make a lot of difference. Most OPT's that were made in India in the past were PA quality accept some Philips SE OPT’s and some Delta "Hi-Fi" range.

I’ve tested/used most Indian OPT’s. Recently, I came across a small company in Calcutta who really impressed me with their work. They are still winding OPT’s for a small niche market of Guitar amps. You will surprised to know just how many Cal musicians still use valve combo’s. The guys had his funda very clear. I’m getting a pair of SE OPT’s for a EL34 project from them. I also bought from them, off the shelf, a spring reverb driver transformer for suitable for the 12AT7. Pending a critical tetsing of these guy's product, I thing importing a Hammond is still the best option. They are cheap, reasonable good and available in a wide spec. I can see George disapproving He has been thoroghly spoilt by his Magnequests.

Nevertheless, an interesting find that b’lore company is

 

[ashwin]

OPTs and freq response

Those are line matching transformer and not OPT's. They are used mostly in running long lengths of connector to Horns (you know...chonga’s..) spread across several zones. Well that’s the idea. I don't know how many of the local PA rental folks actually use such things.

Besides, as Ashok has rightly posted, there are several factors involved in making a good OPT. You can wind an OPT to exact load lines as per the Tube datasheet and it still may sound horrible. Winding techniques, core material, interleaving and such make a lot of difference. Most OPT's that were made in India in the past were PA quality accept some Philips SE OPT’s and some Delta "Hi-Fi" range.

I’ve tested/used most Indian OPT’s. Recently, I came across a small company in Calcutta who really impressed me with their work. They are still winding OPT’s for a small niche market of Guitar amps. You will surprised to know just how many Cal musicians still use valve combo’s. The guys had his funda very clear. I’m getting a pair of SE OPT’s for a EL34 project from them. I also bought from them, off the shelf, a spring reverb driver transformer for suitable for the 12AT7. Pending a critical tetsing of these guy's product, I thing importing a Hammond is still the best option. They are cheap, reasonable good and available in a wide spec. I can see George disapproving He has been thoroghly spoilt by his Magnequests.

Nevertheless, an interesting find that b’lore company is

Ashok, thanks for that info. I didn't realise that such an application existed (Googling gave me more info here : http://www.edcorusa.com/gadgeteer/tech_notes/tn13.htm)

Would measuring the freq response of a transformer be as simple as connecting a signal generator at one winding and sweeping it while measuring the ourput at the other winding? If that's the case, then I would be interested in measuring some transformers. The latest Elektor has an article on tube headphone amps where the author uses power supply transformers as the OPTs. It would be interesting to see their response. Perhaps you already know the frequency limits of some power transformers?

- Ashwin

 

[brokenbinil]

Re: Plenty of info on the Net.

Brokenbinil,
If you are trying to fit a budget , you might go broke buying toroidal transformers. For the same VA , toroids are more expensive. Toroid power transformers are not air core , they all have a iron strip core that's wound like a ring.

Why would you want a 10A transformer for a 40 watt amp? What voltage?
It might be a great idea for you to read up about toroidal transformers on the Net. You will get to know its plus and minus points. I think for normal applications there is nothing to beat the lowly EI core transformer.
You can go to www.toroidal.com for a supplier from Bangalore . There are also suppliers in Delhi who keep advertising in EFY and Elektor (India) magazines. Check it out. But first get on to the Net and read more about toroidal transformers.
Cheers.

hey ashok... thanks ... well the website was very infomative and it kinda of kleared my doubts.... tell me does tordoils help reduse the humming .... well any way keep in touch

 

[corbato]

Re: OPTs and freq response

Would measuring the freq response of a transformer ....

A basic test setup would be an AF generator in the primary applying a sinewave with a constant voltage to be measured by an AF meter at the other end. You will need to apply several hundred voltages to properly measure the low freq response. I had some details on how to conduct such test on a wider level somewhere. Will try to find and post here.

Philips OPT's I have tested down to 40Hz and the Delta rolls off at 55Hz. But thet are not consistent across samples.

brokenbini:
You will really be 'broken' purchasing a several hunderd VA tranny (as your application seem to suggest). I have used toriods only with low power cricuits. And they are very still expensive.

What is you actually application? What class and rating amp you are building?

 

[ashok]

Hum.

There are two kinds of 50Hz hum. One is magnetically induced and the other is electrical . You also have 100 Hz ripple from the rectified power supply . The 100Hz ripple does not sound like 50Hz "hum".

Toroidal transformers radiate less magnetic field around them and so tend to induce less 50 Hz hum in circuits sensitive to magnetic fields. Electrical hum pick is generally not due to the transformer.

The EI transformer if placed properly can also work very well. If the transformers are placed at a distance , it doesn't make a difference which type you use.

Toroids generally have less power loss and better regulation ( ac voltage drop ) . They are good especially for very compact amps. If you have more space , you can make do with an EI type. Especially for power amps - like the one you have - an EI should be good enough. Then again , you have good and bad power transformers. Make sure you use one with good regulation. Less than10% drop at full load is a minimum. Average transformers in the market are MUCH worse than that and also very cheap. So check the regulation specs carefully.
Cheers.

 

[tcpip]

Re: Hum

The EI transformer if placed properly can also work very well. If the transformers are placed at a distance , it doesn't make a difference which type you use.

I have been thinking of enclosing an E+I transformer in a metal box, ensuring full electrical conductivity through all its surfaces. Will this take care of the magnetic radiation? Randy Slone's book seems to indicate so.

Incidentally, this has in fact become a constraint on the size of the power amp chassis for me. I need to place the (largish) E+I transformer in a small metal box, and place this box inside the chassis. For instance, with the 5A 25-0-25 E+I that I have, the smallest enclosing box I found on L.Road is 4" in height, thus making 2U height chassis impossible.

Tarun

 

[corbato]

Re: Re: Hum

....enclosing an E+I transformer in a metal box...

For a majority of Power Amp I don't think that is a necessity. Just take care to orient it in such a way that the flux doesn’t interfere with the signal. At most you can think of a metal sheet partition, e.i, dividing your amp into a tranny and the signal section. But if you application is a Phono amp then enclosing and grounding the tranny would definitely help matters. It will be even better if the tranny is external. Phono amp will require a small tranny so finding a small enclosure wouldn’t be a problem.

Tube amp will off-course be an exception. You will need to consider the relative flux field of your OPT, Power T and Choke (if any) to ensure that thing don't cross into each another.

 

[gjo]

Hi Folks

Just saw this thread. I bought two toroidals(IIRC 150-200VA or therabouts) for my AKSA ss amp from Miracle Electronics. Nilesh Vad is the guy there, he is a customer service oriented guy, and I have no hesitation in recommending him. I used two trannies and used a mu-metal partition to shield the two, since mine was a dual mono design.

Ashok, Magnequest OPTs are a different kettle of fish, you know that! My latest toy-arrived this morning- is a Grounded Grid tube preamp kit from Transcendent Sound, which is to be mated to my tube power amp. Check www.transcendentsound.com for details. The customs guys gave my brother a hard time when he arrived at Bangalore on the Lufthansa flight-they first told him that the duty free allowance for him(He is a US citizen) is only Rs 4000, then when he said he would pay duty, they told him that the bank counter was closed, so it would be better to remit it into their pockets!! He was tired out after the long trip, he decided that when in India play by Indian rules..

Is ko sunne ke liye aap jaroor idhar ek trip plan karna..

Rgds

George