anybody tried this?

[anti-idiot]

hi, i wanna know if anybody have tried the Mid Scoop (prototype) found in

http://www.generalguitargadgets.com/richardo/perfboard/index.html

does it works? can work w 9v instead of 4.5 bipolar?
what is the difference between "+9v/Gnd" and "+4.5/-4.5"?

[anti-idiot]

help? please?

[GibsonGM]

9V and ground is the + and - terminals of the 9V battery...many circuits are set up this way, with only 1 polarity...they're called "unipolar".  I call them normal, lol.  You get +9V going into the circuit, and 0V at ground.

+/- 4.5 V indicates a "bipolar" supply; commonly used with op amps.  Picture trying to amplify a sine wave that goes from 0 to +3, then to 0 and -3....if this is actual voltage, the op amp can't go below zero with a standard power supply (unless it's properly biased, a different topic!).   Having + and - 4.5 volts would allow the signal to 'swing' near those values as required.   

It is obtained several ways...look up "bipolar supply" in the search forum or google.  A simple way to think of it is to connect + and - of 2 9V batts...where they join is ground, 0 volts.  The free + is +9V, and the free - is -9V.   Generally used with some caps to smooth things out, search & you'll find the idea.

Most circuits designed this way can't be simply redone using either supply; it would require modification. I haven't done the Mid project, so can't help you there (it's late, and time to crash!).

[Gladmarr]

If you check out the right hand side of that schematic, it is actually giving you + and - 4.5 volts from on 9v battery.  This is basically using a voltage divider to create a "virtual ground."  If you search that phrase, you'll learn some important stuff about single supply operation of op-amps.  Good luck!

[anti-idiot]

thanx.
now, i know using bipolar power suply will give me more headroom, but what is the proportion? 2 times? 3 times?

like, 9v will give me a headroom of 9v (0v-9v). right?
when using bipolar, will the headroom be 2 times the value? like, -4.5 to + to +4.5 (kinda 9v)?

[Ge_Whiz]

No, in your example, the 'headroom' is the same in both cases, as it is based on the difference between the highest and lowest supply voltages in a simple circuit. In a unipolar amplifier stage with a 9V supply, the input signal has to be 'raised' to an average of nearer +4.5V in order to be able to swing both sides of 'zero'. This extra 4.5V DC is filtered out by a capacitor at the end of the circuit (and sometimes between stages within the circuit).

[slacker]

In some cases whether something is bipolar or not simply depends on where you measure from. In this case if you take the midpoint of the R10 and R11 as ground like in the schematic then the top of R10 +4.5 volts and the bottom of R11 is -4.5 volts. If you take the same circuit and take the bottom of R11 as being ground then the middle of R10 and R11 is +4.5 volts and the top of R10 is +9 volts. The circuit is exactly the same in either case and will run off a 9 volt battery.
Heres a version of the schematic as a single 9 volt supply. If anyone objects to me posting this I'll happily remove it.

[anti-idiot]

thanx a lot!!