Okay to run TL072 with TWO 9v Batteries?

Kindly Killer · May 25, 2011, 01:47:27 PM

I am making a chintzy little onboard buffer for a Jazz bass to run into an EMG preamp that for some reason needs "active" input. Anyway, the pre runs on 18v so I'm wondering what will happen when I take my little 9V buffer and run it at about 20v from 2 fresh 9v batteries. The data sheet says "absolute maximum" voltage is 18v, so I'm wondering whether it will really melt down at 18.5v or above? How will its audio performance compare at 18v vs 9v? What would happen if I ran my buffer off just one battery (tapped the negative side of the first battery in the clip)?

ayayay! · May 25, 2011, 02:02:16 PM

Most 9V bats fresh out of the package are typically 10.1 ~ 10.3! I wouldn't try it myself. However you could try a voltage drop resistor.

familyortiz · May 25, 2011, 02:10:06 PM

The datasheet gives +/- 18V as absolute max, i.e., V+ can be up to 18V and V- can be down to -18V. If you're running it single ended or suppling the V+ with the 2 batteries and V- to ground, I wouldn't do it.
You might check both buffer and preamp schematics to see how they are handling the supplies, since you may have to capacitively couple the signal from buffer to preamp. Another thing... the grounds have to be common to both buffer and preamp. If things work out, the effect on your performance is increased output voltage swing, better singal to noise, etc. from your buffer. If you could post the schematics, you'd get some more feedback on this as well as your question of running on one battery.

Galego · May 25, 2011, 03:32:47 PM

Quote from: familyortiz on May 25, 2011, 02:10:06 PM
The datasheet gives +/- 18V as absolute max, i.e., V+ can be up to 18V and V- can be down to -18V. If you're running it single ended or suppling the V+ with the 2 batteries and V- to ground, I wouldn't do it.
You might check both buffer and preamp schematics to see how they are handling the supplies, since you may have to capacitively couple the signal from buffer to preamp. Another thing... the grounds have to be common to both buffer and preamp. If things work out, the effect on your performance is increased output voltage swing, better singal to noise, etc. from your buffer. If you could post the schematics, you'd get some more feedback on this as well as your question of running on one battery.

Are you sure? What's the difference between using +9v and -9v with vref at 0v(gnd) and using +18v and 0v(gnd) with vref at V+/2? If the chip can handle a difference of 36V between V+ and V-, i don't see why 18V would be a problem, but please correct me if i'm wrong.

Kindly Killer · May 25, 2011, 04:01:59 PM

as you can see i'm not, how you say, very literate. i already breadboarded it, moved it to a proto style PCB and tried it at 9v. works fine. i'm basically wondering whether it's going to go up in smoke if i try 18v

BTW most of the info in my original post was wrong - the preamp does not require low Z input and it can run at 9v, so the obvious solution would be to just use one battery. however, in my "nice" basses i have noticed that changing to 18v adds a little air to the sound. not that you can hear it at the crap casuals i'm playing nowadays....

anyway...

Kindly Killer · May 25, 2011, 04:05:50 PM

BTW again:

the point of this circuit at this point is that it gives me an actual blend knob. most basses - even blinged out boutique basses with lane poor's and LOOK AT ME!!! hardwoods - have the double ganged, custom tapered blend pots that don't work, except as a crappy 3 way switch. doing it this way actually blends between the pickups.

plus this cures friends laughing at me for having a les paul toggle switch on my peavey cirrus LOL

merlinb · May 25, 2011, 04:47:02 PM

You can use 18V no problem, it will work fine.

Gurner · May 25, 2011, 04:49:56 PM

You can take the TL072 right up to 35.99999V....I find that 35V just doesn't cut it.

familyortiz · May 26, 2011, 11:49:26 AM

As stated, 18v on the V+ input is not a problem, because that is the absolute maximum rating, but I would not exceeed any absolute max.

merlinb · May 26, 2011, 12:05:27 PM

Quote from: familyortiz on May 26, 2011, 11:49:26 AM
As stated, 18v on the V+ input is not a problem, because that is the absolute maximum rating, but I would not exceeed any absolute max.

Kildly Killer's circuit is a conventional single-rail design, so using an 18V supply is exactly equivalent to using +/-9V. It won't be operating anywhere near absolute max. The opamp only cares about the differential supply voltage (the difference between Vcc and Vee), which is 36V for most opamps.

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Okay to run TL072 with TWO 9v Batteries?