[sdiy] +/- 9v synth circuits

[Jay Schwichtenberg]

Ryan,

If you are going to use voltage regs and want things to run off 9 volt
batteries then you're going to have to do some thinking.

Standard voltage regs (LM317/LM337, 78XX/79XX) need about 3 volts above the
regulated voltage. So to run things at +/-9 you'll need to use 12V
batteries. That will become marginal as the batteries loose their charge
since there isn't much headroom. When voltages drop below the 3V headroom
weird things can happen. I think it depends on the manufacture and what they
are driving as far as load and caps. I've seen them just shut off, erratic
random behavior and oscillations.

There are what they call LDO (Low Drop Out) regulators which require only
0.1V to 0.6V over the regulated supply. Depends on which one you pick.
You'll find a large number of positive LDO regs but a fairly small number of
negative ones.

If there is going to be AC then a wall wart, connector, a couple of diodes
and a few caps are all you need to get DC good enough for regulators to
work. You could go with either +/-12V or +/-15V. That might be less of a
headache then doing a +/- 9V thing.

Jay

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Ryan Guilfoyle
> Sent: Tuesday, December 02, 2003 10:56 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] +/- 9v synth circuits
>
>
>  Wondering if anyone can give me some insight on a
> project I'm working on. I'm trying to make a small 9v
> battery powered synth, for open mic nights/use at
> college. It does not need to be very complex or
> expensive, only portable and stable tuning wise. I've
> already got an LFO/AR and some cv processing circuits
> working on +/-9v, the main problem I see is making a
> making a multimode SVF, and a VCO. The synth does not
> need to have more then a 3-4 octave range on the vco's
> ect.. My planned config is 2 pulse/tri vco/2 lfo/ 2
> env/ 3way mixer/MM vcf/lag and S&H/noise and 2 vca's.
> I have a bunch of EFM boards I thought I lost in my
> last move, and it would be very nice if i could get
> them to run on +/-9v.I will be following the bat's
> with voltage reg's. Any pointers tips ect.. would be
> greatly appreciated.
>
>
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