Powering preamp. Need help on deciding supply voltage.

[nguitar12]

Hello everyone. I am buliding a PSU for INA217 based preamp.
This chip will take supply from +-4.5v to +-18v. So far I am considering either +-12v or +-15v.
Is there any advantage of using higer voltage?
Also dose the voltage need to be precisely regulated ?

[PRR]

Key question: how hot does the OUTput need to be?

If you are driving a long wire to a remote recorder, you want a hot signal to overwhelm any humm or cross-talk that wants to sneak-leak in. Professional Audio often aims near 10 Volts on max peaks, which suggests +/-15V supply.

OTOH if you go right into a pocket recorder with a 3V battery-pack, and adjust INA gain so the recorder works wide-open, it is hard to see how you could need even 3V total supply (except the INA asks 9V just to stay awake).

The voltage does not have to be REGulated. It must never exceed the MAX rating (36V total?), should not drop so low the INA loses its focus (9V), and should not change suddenly (power-line surge/sag would thump the audio).

Since you are asking, I assume you are not experienced with wiring wall-voltage, and shouldn't mess with it. +/- DC power supplies are rare (but look on www.Jameco.com ). Find a 9V *AC* wall-wart. There is a basic 2-D 2-C rectifier which will give you +/-13V DC. C may be 470uFd. This is barely clean enough (50/60Hz ripple), so add a 220 Ohm and 470uFd in each rail. Loaded in a chip or two this will give +/-12V, low-low-low buzz, and a smoothing rate which will put wall-voltage sag/surge far below the audio band.

+/-12V regulator kits are standard parts from many suppliers.

[nguitar12]

The voltage does not have to be REGulated. It must never exceed the MAX rating (36V total?), should not drop so low the INA loses its focus (9V), and should not change suddenly (power-line surge/sag would thump the audio).

I heard someone said the power need to be regulated and as clean as possible. Do you mean that the power can be slight varied but have to be clean? I am considering using LT1054 to generate +-18v from a 9V DC adaptor. The voltage will slight varied due the the internal loss. (resulted in +-16/17v maybe?). The voltage is a bit low for me to add another 7815/7915 to get a regulated +-15v. Do you think that the regulated circuit can be omitted? Also do you think that LT1054 will be a clean supply (studio grade) for the INA217?

I assume you are not experienced with wiring wall-voltage, and shouldn't mess with it. +/- DC power supplies are rare (but look on www.Jameco.com ). Find a 9V *AC* wall-wart. There is a basic 2-D 2-C rectifier which will give you +/-13V DC. C may be 470uFd.

Yes I not a big fans on wall AC voltage though I know it is a standard for the PSU. I need my gear as portable as possible cos I need to carry them around different location. That's  why I want to unify the adapter I use ( in this case a 9v DC ). That's why I don't  even want to bring an extra 12v or other adapter.

[amptramp]

The limit will be set by the allowable input common mode range which the spec sheet says is worst case Vcc-4 volts to Vss+4 volts but typically Vcc-3 volts to Vss+3 volts.

Output swing is worst case Vcc-2 to Vss+2 volts and typical Vcc-1.8 to Vss+1.8 volts.

The device will run off ±4.5 volts but you may find your input limited to 1 Vac centred on the zero input.  Higher voltage gives you more headroom for the signal.

[PRR]

> I heard someone said.....

Listen lightly. Think deeply.

You realy need to outline your requirement.

For the one question you asked, "advantage of using higer voltage?", you need some idea of how much output level you need. For a compact job (which wasn't in your first post), this may be a critical design problem.

Now we learn you *will* use a 9V DC adapter. This limits options. And also suggests you do not need Heavy Duty audio levels.

Read Data Sheets! The INA PSRR is fantastic (better than many regulators) in the low audio band. But now you are thinking ultrasonic voltage-boosters.

With 9V clean and stable on one side, and a power voltage inverter, the *simple* path is to invert +9V to -8V and run the chip on those two. (No, the supplies do not need to be exact equal.) This can support +15dBu output, which is more than enough for any Line In.

But how bad is the INA's PSRR at the inverter's frequency? Do you need more filtering?

IMHO: K.I.S.S. Do a simple (not doubler) +9/-8V supply and try it. Do not bet that your first build will be your last build. All electronics is a progression.

[nguitar12]

you need some idea of how much output level you need. Now we learn you *will* use a 9V DC adapter. This limits options. And also suggests you do not need Heavy Duty audio levels.

I am using this preamp between shure sm58 and my Tascam record. I am recording mostly acoustic song (guitar and vocal). Usually I will record the vocal at around -10 to -6 db. I can't say how I will use the preamp later so I would like it to handle as much output as possible like a standard commercial preamp.

Read Data Sheets! The INA PSRR is fantastic (better than many regulators) in the low audio band. But now you are thinking ultrasonic voltage-boosters.

With 9V clean and stable on one side, and a power voltage inverter, the *simple* path is to invert +9V to -8V and run the chip on those two. (No, the supplies do not need to be exact equal.) This can support +15dBu output, which is more than enough for any Line In.

But how bad is the INA's PSRR at the inverter's frequency? Do you need more filtering?

As I want my preamp as close to the commercial preamp as possible for handling different task. I am hoping it to take +-15v for more headroom. I have yet suggested a bipolar supply doubler using LT1054 chip.



Do you think that LT1054 will be a clean supply (studio grade) for the INA217?

IMHO: K.I.S.S. Do a simple (not doubler) +9/-8V supply and try it. Do not bet that your first build will be your last build. All electronics is a progression.

I have build varies simple DC-DC / LED Driver / Guitar Pedal in the past and this is not my first build. I am everyone enjoy the DIY process that's why we are here. I will definitely keep my eyes on the +9/-8V supply you have mentioned. Thanks again for you warm help.