How to supply 15V+ and 15- on a circuit?

[rizziol]

I am planning to breadboard a mic preamp that uses a tl074 and feeds it with a 15+, 15- and ground. Would a simple transformer do the job? Or could I use a regular 12-18v dc power supply and invert the voltage at some point? the schematic is here https://www.eleccircuit.com/wp-content/uploads/2014/11/01-balance-low-noise-pre-microphone-amplifier.png




Thanks!

[antonis]

[rizziol]

Thanks, Antonis! gonna make a PCB out of it and give it a shot for the preamp!

[Kevin Mitchell]

I highly suggest using an 18VAC wallwart instead of an actual transformer for that power supply design.
Looky here

[ElectricDruid]

I have a power supply on my bench that I built that uses the exact circuit Antonis posted. It's a classic. Sure, linear power supplies are bulky and heavy and old fashioned (although not so bad if you use a toroidal transformer - that would be my recommendation) but they're also quiet and reliable.

[Kevin Mitchell]

I just wouldn't encourage anyone to play with line voltages unless they're experienced or have an understanding of the dangers and are up for it. Especially when the people advising it haven't mentioned a fuse yet 

Tinker safe!

[box]

TMR 1223  that would be my recommendation.
https://www.tracopower.com/int/model/tmr-1223

[Vivek]

I guess you would need such high supply voltages if you wanted 14vP output

or the slew rates etc became much better at high voltages



Maybe if your requirements are more modest, you can try feeding the same circuit +/-6 or +/-9 to start with, and see how it goes.


Other methods can be to use Buck Convertor/Buck Invertor to create the +/- rails that you want.

[antonis]

Sure, linear power supplies are bulky and heavy and old fashioned

Sure, we love them a lot..!! 

[PRR]

...I am planning to breadboard a mic preamp....

That's not a good example. Noise may be OK for some condenser mikes but it will hiss madly when turned-up for dynamics.

This is far better.
https://www.adventures-in-audio.com/the-famous-5-preamp-everything-you-need-to-know

[bowanderror]

I use an LT1054 bipolar charge pump circuit to get ~+-15V from +9V. It's probably limited to under 100mA per supply rail, so keep that in mind.

For more power-hungry applications, I made a version of the MFOS Wallwart PSU with a 16VAC wallwart & 7815/7915 linear regulators. I haven't pushed that one, but I imagine it's good to around 300mA per rail (depending on the wallwart).

[Ben N]

That MFOS design is a nice example of an AC-wallwart half-wave rectified and well filtered to +/- regulators, adjusting the ac supply and rectifiers according to desired voltage, of course. Note that you don't need a higher voltage wallwart than your resultant +/- DC because rectification will give enough of a DC voltage boost to supply the regulators.

[Kevin Mitchell]

That MFOS design is a nice example of an AC-wallwart half-wave rectified and well filtered to +/- regulators, adjusting the ac supply and rectifiers according to desired voltage, of course. Note that you don't need a higher voltage wallwart than your resultant +/- DC because rectification will give enough of a DC voltage boost to supply the regulators.

I use it all the time. Just a few days ago I did a vero board version but with adjustable regulators instead. It was based off of my Adjust Power Supply layout, but with some modifications like trimpots, LEDs, a 10pin IDC socket (for eurorack) and more space to fold down the regulators. I'll post that layout tonight as it's actually built and verified.

[rizziol]

...I am planning to breadboard a mic preamp....

That's not a good example. Noise may be OK for some condenser mikes but it will hiss madly when turned-up for dynamics.

This is far better.
https://www.adventures-in-audio.com/the-famous-5-preamp-everything-you-need-to-know

Really nice this schematic you´ve post. But why the one i´ve posted would be noisy with dynamic mics?

[rizziol]

I highly suggest using an 18VAC wallwart instead of an actual transformer for that power supply design.
Looky here

Wonderful article!!!! Thank you!

[bluebunny]

Another +1 for Ray's circuit.  Rick (fcuk) has a board which is basically the same thing - I've got a couple and they work well.

[PRR]

............ noisy with dynamic mics?

1) The self-hiss of a TL07x is much higher than a 200Ω source (dynamic mike)

2) The self-hiss of R5 1.5kΩ is much higher than a 200Ω source (dynamic mike)

These difficulties are less if the source is a condenser mike. The self-hiss of the internal head-amp will be higher than a dynamic.

But there is no provision for Phantom Power, now almost a necessity. If you are asking how to make +/-15V, how will you make +48V?

3) There is no gain control. (The hi/lo switch is input impedance, not gain.) A generally useful mike preamp needs a wide range of gain, from room-mike on harpsichord to close-miccing a Marshall.

4) The 0.15uFd at the output will lose bass even in 22k load (-3dB @59Hz); also we like a low-low line impedance to absorb stray interference.

[rizziol]

............ noisy with dynamic mics?

But there is no provision for Phantom Power, now almost a necessity. If you are asking how to make +/-15V, how will you make +48V?

First of all, you nailed it!!! Thank you very much for the insight and the explanation!
I friend of mine asked me to build a analog-like  voice effect rack for the purpose of live performances, with an overdrive, a delay and a reverb in it.
My fisrt concern was to build a preamp for the mic before all the effects... and i have to be honest, i´ve never built a mic preamp before... so i was looking for preamps schematics in the first place to plug the dynamic mic and then i would experiment with the other stuff on the breadboard. Since mic impedances are very different from guitars, i got quite lost but i ve read a couple of stuff and  you guys are helping me so much!

the plan is to build a unity solely for dynamic mics, since is made for live vocal performances and the guy regularly uses a SM57 to sing.

P.S.: You look like Mahatma Gandi in this pic!!! lol!

[rizziol]

My last reply just to thank you all for the hints! I´ve just assembled a power rectification unity as you recommended! Added a l7809 regulator for powering other stuff in the unity i´m building and everything is working fine!!!

[Ben N]

Sorry, DP.