Cgs synth

>Hi all.
>
>Mad idea I know, but it's a request from a guitarist mate.
>
>As noise levels are not critical for his intended use, for power, 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
>the PCB)
>
>I 'll need to attenuate the level after the effect, which will have
>quite a lot of gain, in order to approach unity gain. Question is,
>keeping a 1K output impedance, how could I alter values in the circuit
>to achieve this? I don't understand the circuit , and I guess I could
>always do the obvious, and use a voltage divider at the output using
>the 1K final output resistor as one half, and a pot or fixed resistor
>to GND as the other half of the voltage divider, but I suspect that
>might have a big effect on the output impedance - I don't know if
>that's a real problem or not. The output will directly drive a guitar
>combo input.
>
>Would such a voltage divider make potential problems for a guitarist?
>
>Any thoughts welcome
>
>
>cheers,
>Dave
>
>
>
>------------------------------------
>
>The CGS Modular Synth home page: http://www.cgs.synth.net/
>Yahoo! Groups Links
>
>
>

On Nov 13, 2010, at 20:57, Jason Proctor wrote:

> could just use the CGS stompbox adapter :-)
>
> http://www.cgs.synth.net/modules/cgs46_sba.html
>
> >Hi all.
> >
> >Mad idea I know, but it's a request from a guitarist mate.
> >
> >As noise levels are not critical for his intended use, for power, 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
> >the PCB)
> >
> >I 'll need to attenuate the level after the effect, which will have
> >quite a lot of gain, in order to approach unity gain. Question is,
> >keeping a 1K output impedance, how could I alter values in the
> circuit
> >to achieve this? I don't understand the circuit , and I guess I could
> >always do the obvious, and use a voltage divider at the output using
> >the 1K final output resistor as one half, and a pot or fixed resistor
> >to GND as the other half of the voltage divider, but I suspect that
> >might have a big effect on the output impedance - I don't know if
> >that's a real problem or not. The output will directly drive a guitar
> >combo input.
> >
> >Would such a voltage divider make potential problems for a guitarist?
> >
> >Any thoughts welcome
> >
> >
> >cheers,
> >Dave
> >
> >
> >
> >------------------------------------
> >
> >The CGS Modular Synth home page: http://www.cgs.synth.net/
> >Yahoo! Groups Links
> >
> >
> >
>
>

On Nov 13, 2010, at 21:23, sasami@... wrote:

>
> >As noise levels are not critical for his intended use, for power, 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
> >the PCB)
>
> You would need two capacitors, one across each leg of the voltage
> divider.
> It would not be particularly kind of batteries though.
>
> >I 'll need to attenuate the level after the effect, which will have
> >quite a lot of gain, in order to approach unity gain. Question is,
> >keeping a 1K output impedance, how could I alter values in the
> circuit
> >to achieve this? I don't understand the circuit , and I guess I could
> >always do the obvious, and use a voltage divider at the output using
> >the 1K final output resistor as one half, and a pot or fixed resistor
> >to GND as the other half of the voltage divider, but I suspect that
> >might have a big effect on the output impedance - I don't know if
> >that's a real problem or not. The output will directly drive a guitar
> >combo input.
>
> You will find that with a reduced input, the output of the filter
> will not
> be that high either, so chances are you will not need any output
> divider at all.
>
> Ken
> __________________________________________________________
> Ken Stone sasami@... otherunicorn@...
> Modular Synth PCBs for sale <http://www.cgs.synth.net/>
> Australian Miniature Horses & Ponies
> <http://www.blaze.net.au/~sasami/>
>
>
>

--- 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

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
>
>