I'd like to add a bit on various points;
I used to build a lot of stompboxes, and I often used op-amps. I mainly used to use the TL062/064 since it has a lower current draw than the TL072/074, which extends the useful battery life. LF444 was another low current op-amp I remember using successfully. I never had any problems with headroom. Whilst a few volts either way might not sound like a lot to synth people used to +/-10V levels, for guitarists who have instruments with outputs measured in the 100s of mV, it's perfectly ok.
It's true that some op-amps cope better than others with being run at low voltage - but this is on the datasheet. Just check the minimum supply voltage spec. If it says +/-3V or so, you'll be fine. +/-4V is a 9V battery after a bit of use, so that's not so good. Again, like the current draw, it's a question of useful battery life - the lower the op-amp goes, the longer the life you'll get before it dies.
Given that many modern op-amps are designed to work on the 5V and 3.3V supplies found in digital gear, I'd have thought there are far more decent options available now than when I was looking years ago - assuming they go as high as 9V!
Good luck with it,
Tom
I used to build a lot of stompboxes, and I often used op-amps. I mainly used to use the TL062/064 since it has a lower current draw than the TL072/074, which extends the useful battery life. LF444 was another low current op-amp I remember using successfully. I never had any problems with headroom. Whilst a few volts either way might not sound like a lot to synth people used to +/-10V levels, for guitarists who have instruments with outputs measured in the 100s of mV, it's perfectly ok.
It's true that some op-amps cope better than others with being run at low voltage - but this is on the datasheet. Just check the minimum supply voltage spec. If it says +/-3V or so, you'll be fine. +/-4V is a 9V battery after a bit of use, so that's not so good. Again, like the current draw, it's a question of useful battery life - the lower the op-amp goes, the longer the life you'll get before it dies.
Given that many modern op-amps are designed to work on the 5V and 3.3V supplies found in digital gear, I'd have thought there are far more decent options available now than when I was looking years ago - assuming they go as high as 9V!
Good luck with it,
Tom
On 15 Nov 2010, at 17:40, nn3nn3 wrote:
> The problem with dividing the supply voltage is the opamp headroom. Whether you use a LM1458 or TL072, the output voltage swing can be as bad as 3V less than the supply (but usually it's only 1-1.5V less). So with +/-4.5V supply you could be down to +/-1.5V headroom on the output.
>
> Worse than that, FET opamps can flip the phase under certain conditions especially when going negative and will "create unwanted results".
>
> Using a resistor divider will waste some battery life but you can live with that. But opamps like to be kept up in their sweet area and the divider will puts this right on the edge even with a fresh battery.
>
> I'd suggest either finding a rail-to-rail opamp, using two batteries or using a voltage converter (eg: LTC1144 http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1039,C1014,P1377) to maintain a full range.
>
> Best of Luck,
> Brian Dunn
>
> --- In cgs_synth@yahoogroups.com, Dave Kendall <davekendall@...> wrote:
> > I
> > guess I could use a resistor divider with a 9V battery to, generate
> > ±4.5V, with the centre tap to GND on the PCB, and something like a 47uF
> > cap between the centre tap and 0V on the battery (which is now -4.5V on
>
>