Hello everyone.
Here is a circuit I am considering using to supply +/- 12V to a couple of op-amps - these as part of an active notch filter for my subwoofer. This will be at preamp level before the subwoofer power amp.
This is the circuit I am considering.
My question is the specification of the transformer - should this be say +/- 15V or something so that the regulators see over 12V?
Can I also make any assumptions on the current draw, my transformer supplier made a calc that for 3 filters (one Op-amp / filter) as 2.88 va, not sure how he did this?!?!
Thanks,
Here is a circuit I am considering using to supply +/- 12V to a couple of op-amps - these as part of an active notch filter for my subwoofer. This will be at preamp level before the subwoofer power amp.
This is the circuit I am considering.
My question is the specification of the transformer - should this be say +/- 15V or something so that the regulators see over 12V?
Can I also make any assumptions on the current draw, my transformer supplier made a calc that for 3 filters (one Op-amp / filter) as 2.88 va, not sure how he did this?!?!
Thanks,
It would be good if you could give more details about the circuit you want to power or at best, tell us how much current you will need from each rail.
I´m not sure I would want to buy a transformer, rectifier, smoothing caps for just a couple of mA of current.
I would consider a 5V USB supply, then feed the 5V into a Traco TEN 3-0522N and you´re done.
If you´re worried about some ripple voltage remaining you could use a TEN 3-0523N instead and follow that with your 7812/7912.
The Traco SMPS given above assume that you need no more than 3W.
If it´s just 2 opamps for a line-level-filter you might get by with smaller SMPS.
I´m not sure I would want to buy a transformer, rectifier, smoothing caps for just a couple of mA of current.
I would consider a 5V USB supply, then feed the 5V into a Traco TEN 3-0522N and you´re done.
If you´re worried about some ripple voltage remaining you could use a TEN 3-0523N instead and follow that with your 7812/7912.
The Traco SMPS given above assume that you need no more than 3W.
If it´s just 2 opamps for a line-level-filter you might get by with smaller SMPS.
Ok - great, I have a quote for a small +12/0/-12 AC transformer so I can use this then if building a small power supply is the most sensible approach
If it´s only two opamps even a 1W SMPS would be plenty.
The TRACO Power TBA 1-0522E (or alt. TBA 1-0523E if you still want to use your regulators) costs 3€ and most people have an additional USB charger at home. Just saying this could be an alternate solution which is cheaper, smaller and also less dangerous for the beginner.
Yes.
To say same with other words:
1) transformer voltage is shown on schematic, it´s a 12VAC + 12VAC transformer, some may label it 24V CT (center tapped) , same thing.
2) power is very low, if your supplier offers a 2.88 VA unit, fine.
Common values are 12+12VAC 100 mA units so 2.4VA (24*0.1) or 12+12VAC 250mA so 6VA , any of them is way more than enough, your Op Amps need less than 10mA , go figure.
3) video shows 11 + 11VAC , I´m certain it´s a 12 + 12 VAC (simply because it´s a VERY common rating) BUT either very poor quality or wall voltage is low, not surprised at either because Video is made in a quite poor/improvised setting.
Not dissing the video maker, he´s doing it the best he can, just under somewhat primitive conditions.
4)
Why make it easy when you can complicate it?
To say same with other words:
1) transformer voltage is shown on schematic, it´s a 12VAC + 12VAC transformer, some may label it 24V CT (center tapped) , same thing.
2) power is very low, if your supplier offers a 2.88 VA unit, fine.
Common values are 12+12VAC 100 mA units so 2.4VA (24*0.1) or 12+12VAC 250mA so 6VA , any of them is way more than enough, your Op Amps need less than 10mA , go figure.
3) video shows 11 + 11VAC , I´m certain it´s a 12 + 12 VAC (simply because it´s a VERY common rating) BUT either very poor quality or wall voltage is low, not surprised at either because Video is made in a quite poor/improvised setting.
Not dissing the video maker, he´s doing it the best he can, just under somewhat primitive conditions.
4)
Oh! .... Germans!!!!!
Why make it easy when you can complicate it?
Not saying, we aren´t complicating things sometimes
but in this case and in MY view I find it easier to buy a 3€ SMPS than buying a tiny transformer+ x +x and working with 220VAC (you will need a proper case, proper cabling to safety-standards, fuses etcpp.)And this whole effort to have +-12V at 5mA or so?
SMPS can have pretty stellar performance nowadays.
(We use them in our own test equipment and never had a failure.)
But as I said, this is my view and it pretty much boils down to what tonescout might have in his drawers and what he´s comfortable to do himself and spend.
Just giving another option.
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Not saying, we aren´t complicating things sometimes
And this whole effort to have +-12V at 5mA or so?
SMPS can have pretty stellar performance nowadays.
(We use them in our own test equipment and never had a failure.)
But as I said, this is my view and it pretty much boils down to what tonescout might have in his drawers and what he´s comfortable to do himself and spend.
Just giving another option.
It's a fair point, I am just aware as an audio snob that SMPS are a dirty word for SQ, but it maybe the way to trial the reality of the notch filter as a solution and then at my leisure I can 'upgrade' and realise what a waste of time that was...maybe
I've used things like a RAC20-12DK/277 for things like this. Digi has the Recom for $14, so may be less expensive than a transformer. They are switchers though. I usually keep 5 and +/-15 around just so I don't have to wait for ordering. Sometimes I will go traditional linear with transformer/rectifier/cap/regulator as you are doing. Just depends. The other super nice thing about the little modular ones is they are tiny, and usually are 120/240 compliant. They seem to be quite rugged as I have used them outside and in the attic and they are still running after at least 6 years of service now.
That´s another cool option. I myself prefer to use 5V USB-chargers because that´s the one thing that I have at least 3 (read = too many) of and thus don´t have to deal with 220VAC etc.
If you are snobby enough to pay 80$ for a solution here´s a SMPS that might persuade you of their "SQ":
Linear Audio Silent Switcher V3 – diyAudio Store
Well this is an interesting option, I could put this in the board that will sit in between the Preamp and Power amp of the subwoofer (there's about 100mm of space) and borrow some 240v from the mains input and run a small shielded cable into the board.
In my ignorance I assume this is SM unit effectively?
Thanks!
This is also interesting I have a 15V DC supply inside the Sub amp, it currently powers the preamp, from the PS and Power amp board. So if I am not overloading it I can borrow this and supply one of these for the +/- 12V board maybe? TEN 3-1222N
Ah, the problem with the vast number of options with electronics today! Too many choices. The Recom's and that type are almost always SM. Your idea of tapping the existing +15 may be the best, but not sure how you can validate load capability of the existing +15 unless you have schematics. Less 240 floating around is good. Also curious why you went +/-12 instead of +/-15. With +/-15 you could get away with just synthesizing -15 from +15 and use the +15 direct.
Just been and checked again - I have + and - 15V coming in from PS into preamp and a near 0V 3 wires. boom, just use these into the opamp and active filter board.
BUT what's the load on the supply capable of....hmmm.
How much additional current would 2 x OPA134PA take, spec sheet seems to imply 40 mA on each amp and +/- rail? so maybe 100 mA, I wonder how much the existing circuit takes, and how much the supply is limited to. Maybe a call to the supplier?
Just looked at spec sheet, 40 sounded way high. Quiescent current is 4-5ma. 40ma is the max short circuit current of the output drivers, which would of course consume 40ma of supply current. I suspect you will draw very near 5ma as the load is probably around 5K and swing will be a volt or 2. So basically nothing. I'd think the P/S could afford an extra 10ma load on it. (2X OPA134PA)