Cgs synth

A couple of answers -

>I had a few questions, with the two 10n decoupling capacitors do i
>just solder them onto the two sets of pads on the back adjacent to
>the power connections? and also can someone explain exactly what
>they do...well i know its for ps decoupling but what exactly does
>this do or acheive? sorry im still learning, its happening fast but
>some of this si still a mystery.

Baically it is a "local power supply" for the circuit in question. When the
circuit demands extra power for a split second, it is delivered by these
capacitors. These peak power demands cannot be delivered by the power supply
itself, due to the resistance of the wires. Note that the resistances are
tiny, as are the peak power demands, but without these decoupling
capacitors, the power lines are dragged around by these peak demands,
resulting in noise on the power lines.

Yes, just solder them on the pads on the back of the PCB.

>Where I am lost is i kind of assummed that if the icon for the
>transistor on the PCB shows an arrow pointing out of the device that
>that indicated the emmitter and if it had an arrow pointing into the
>devide that indicated the collector but i've done some web browsing
>and have found sites suggesting that a PNP is shown with an arrow
>pointing into the device for the emmitor and that an NPN uses an
>outward pointing arrow for the emmitter???? guess im trying to get
>this right.

Correct. It essentially represents the diode that is the base-emitter junction.

>Ken kindly taught me how to test transistors with my multi meter (ok
>im very new at this) so with that i was able to determine that one
>of the transistors was a NPN and the other a PNP and what was the
>emitter etc but now im not sure which way they should have gone into
>the board......with my thinking i put the 2n3904 with the emitter
>connected to the pad with the arrow pointing out of the device and
>with the 2n3906 i soldered the connector to the pad with the arrow
>pointing into the device. I think this may be where i went wrong as
>from my research the icons are reversed depending on if its a PNP or
>NPN so i think i ahve one in the wrong way :(

Emmitters fo the the arrow symbols, yes. The little half-circle that is
drawn around the transistor symbol on the PCB actually indicates in which
way the package should be installed.

Ken
_______________________________________________________________________
Ken Stone sasami@... or sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
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