Triple secondary power transformers?

There is a thread running on this list regarding the usage of DC-DC converters to obtain 48V.

I'm looking in another direction, and that is: does anyone sell a "stock" transformer with, say, 36V CT (or dual 18V secondaries) along with another winding at, say, 40-45 VAC?

Bri

Canford (UK) has a dedicated mic-pre power transformer..

The Canford transformer is always in their "clearance" section and is available for £12.50 (UKP).

It is a toroidal transformer 62mm diameter and 33mm high - with the following windings:
17.6 - 0 - 17.6 at 60mA and
0 - 44.4 at 30mA

So is only suitable for a channel or two of mic pre-amplification - and must have been specially designed for a specific project.

So I think that the answer to the question is no - there doesn't seem to be an off the shelf transformer suitable for this use.

This is possibly the reason that several mixer manufacturers have used voltage doublers to produce the required Phantom voltage from the normal windings of the transformer (certainly Soundcraft and Allen & Heath have done this).

I can provide you with any kind of custom made toroid transformers in good prices.
PM me if you are interested

fotis

The canford transformer is cool--looks like it has got a magnetic shield as well.

Samuel

Yup, it has VERY low stray field noise - designed for co-existing with an input transformer - in a little box..

Jakob E.

FWIW, I made a mental note of this circuit when it came along: http://www.blacklionaudio.com/212schem-B.pdf
from http://www.groupdiy.com/index.php?topic=12550&highlight=pro+vla
There are obviously more than a few additional components to get an 'easy' TX though.

I added 'FWIW' since I realize this is not what you're looking for. Still a nice approach imho, could be of use sometime.

That Canford iron sounds interesting, but getting Stuff from Europe is a logistics "pain" for me. Hell, just getting stuff in/out of Canada can be expensive! <g>

I had pondered a voltage doubler design, but after breadboarding a circuit using "one half" of an 18-0-18 transformer, I just barely hit 48 VDC which is too low. I would need 50-something VDC (but less than 60V) to feed into an LM-317HV regulator, and a tripler would move me waaay above 60V, thus requiring an intermediate circuit between the tripler and the regulator.

Yes, yes..I know you can "cheat" the I/O ratings of the 3-legged regulators if you NEVER allow for a short circuit at the output of the regulator. I consider that a shaky design concept and would never use that in any gear that I build.

Bri

[quote author="AudioJohn"]The Canford transformer is always in their "clearance" section and is available for £12.50 (UKP).

It is a toroidal transformer 62mm diameter and 33mm high - with the following windings:
17.6 - 0 - 17.6 at 60mA and
0 - 44.4 at 30mA

So is only suitable for a channel or two of mic pre-amplification - and must have been specially designed for a specific project.

So I think that the answer to the question is no - there doesn't seem to be an off the shelf transformer suitable for this use.

This is possibly the reason that several mixer manufacturers have used voltage doublers to produce the required Phantom voltage from the normal windings of the transformer (certainly Soundcraft and Allen & Heath have done this).[/quote]

OK, so that part would be $22.09 USD at "today's" conversion rate. Then add on the markup that VISA, etc uses for handling the money transaction, then shipping (and customs?) and it is a VERY pricey part if only a few are ordered.

I guess my only choice is to use two transformers. sigh

Bri

Brian - the TL783 seems to be readily available again - Farnell in the UK have it in stock, so perhaps you can stop using the HV version of the LM317.

During the shortage of the '783 - I developed a circuit, using an inexpensive LM317K - which does includes the addition of the "cheat" components - a zener diode and a resistor. This can provide enough Phantom current for 2 microphone channels - but can safely sustain a continuous short on the output.

If I can convert the drawing to a PDF - I can mail it on request (please PM).

JG