Isolated DC/DC converters for P48?

[Alex1238]

I'm working on adapting an old obscure mic pre design that runs on 24v and lacks P48. Seeing as 24v/2x12V trafos are cheap and easy to get while 24v+48v ones really aren't, so i'm thinking of having a 24V to 2x24V isolated converter (like the IA2424S from XP Power) on the actual preamp board instead, that runs on the existing 24V rail. On paper this seems pretty foolproof as it really just creates a clean 48V voltage at a reasonable current that can pretty easily be piped into the pre input, but i haven't heard of this ever being done in practice. Is there some sort of caveat i'm missing?

 

[gyraf]

..as some of those converters are noisy, you may need to add a noise filter (cap multiplier, C-R-C, or C-L-C).

Try it and see, it should work.

The 21mA rated current is enough for at least two channels of P48

/Jakob E.

 

[Alex1238]

..as some of those converters are noisy, you may need to add a noise filter (cap multiplier, C-R-C, or C-L-C).

Try it and see, it should work.

The 21mA rated current is enough for at least two channels of P48

/Jakob E.

Specsheet says 75 mV noise, so about -20dBu, which feels like a lot now that i'm looking at it, that said i have no idea how that affects P48, what would you say?

 

[My3gger]

Try it and find it will probably need additional filtering as proposed by Gyraf. 48V transformers with ct aren't uncommon if you want to make simple linear supply with TL783, LM317HV, etc.

 

[Alex1238]

Try it and find it will probably need additional filtering as proposed by Gyraf. 48V transformers with ct aren't uncommon if you want to make simple linear supply with TL783, LM317HV, etc.

That's absolutely my plan B although ideally I'd really like to only have the one transformer since I'll be slightly cramped for space and as i said 24v+48v isn't a common combo, maybe i could look for a a 4x24v one but I'm doubtful that's anymore common. Of course if the noise is insurmountable i won't have a choice

 

[My3gger]

Not long ago we had discussion about using 2x24V transformer for 24V and 48V. I'm not sure who said they made hundreds of supplies like this, maybe Dan Kennedy? Ian Bell (Ruffrecords) probably remembers it better than i do.

 

[Alex1238]

Not long ago we had discussion about using 2x24V transformer for 24V and 48V. I'm not sure who said they made hundreds of supplies like this, maybe Dan Kennedy? Ian Bell (Ruffrecords) probably remembers it better than i do.

I pondered the idea but i figured that if i did like a CT full bridge rectifier that would mean the two windings are asymmetrically loaded which in my head is trouble, the only way would be if the windings could be both in parallel and in series at once but i don't really think that's possible lol, that said i know relatively little above bare minimum about PS design so who knows. I'll look up Ian

 

[My3gger]

Found it here:
https://groupdiy.com/threads/carnhill-vtt2326-transformer.88245/
IA2424S looks simpler, probably also cheaper and more reliable.

 

[Alex1238]

Found it here:
https://groupdiy.com/threads/carnhill-vtt2326-transformer.88245/
IA2424S looks simpler, probably also cheaper and more reliable.

Damn that's not a cheap transformer lol, i guess that's some motivation to make the IA2424S work out, should really be pretty ideal with some filtering, either way noise can't be a huge deal for P48 no?

 

[My3gger]

Check the last post with schematic.

 

[thor.zmt]

I'm working on adapting an old obscure mic pre design that runs on 24v and lacks P48. Seeing as 24v/2x12V trafos are cheap and easy to get while 24v+48v ones really aren't, so i'm thinking of having a 24V to 2x24V isolated converter (like the IA2424S from XP Power) on the actual preamp board instead, that runs on the existing 24V rail.

Why not put a voltage doubler that runs from the existing transformer. Schematics in various pro gear over the years.

It there a need to use noisy switchers when there is already 24V AC present?

To hang with all the kook kids?

On paper this seems pretty foolproof as it really just creates a clean 48V voltage at a reasonable current that can pretty easily be piped into the pre input, but i haven't heard of this ever being done in practice. Is there some sort of caveat i'm missing?

Switchers create noise. Just at different frequencies than normal AC supplies. The one you pinged switches at 80kHz "variable".

Thor

 

[tinn]

I built exactly that in 2005 .
works fine, drives P48 for 4 Preamps.


The converter is a isolated 24/24 1 watt Module (HN, Murata , Recom . . .)
You don't need the greyed out filter on the left in the schematic.
I needed that, cause the preamps are supplied by a 24V switchmode power supply.
the following RC Filter for the little P48 converter is fine.

 

[emrr]

Meanwell 709-RS25-48 works well. $11.15.

 

[mjrippe]

Meanwell PD-2515 works well.

That one is AC to +/- 15v. The RS-15-48 is AC to +48v and I use them all the time for phantom with a simple R-C filter.

The XP Power IA2424S is +/-24v out, may work OK.

As @thor.zmt mentioned, a voltage doubler is quick and easy. You can fit the whole deal on a 1.75" x 1.75" piece of perfboard.

 

[emrr]

corrected

 

[Alex1238]

I'll be building a power supply from scratch, funnily enough i didn't consider a voltage doubler at all, i'll play around with both options and see what works out easiest. Honestly i never considered diode/cap voltage doublers as a stable/clean solution but that's probably more prejudice and inexperience than anything.