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PAiA 9700K MIDI2CV8, external +and- 15v supplies?
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Author:  PAiA-Scott [ Thu May 21, 2009 11:06 am ]
Post subject:  PAiA 9700K MIDI2CV8, external +and- 15v supplies?

Hello Paul.

Yes, the MIDI2CV8 can be powered by an external +and- 15v supply; however, the normal power supply to the MIDI2CV8 is a wall-mount transformer, 12vac (with a current capability ranging from about 500mA to 1000mA (1A)). The power switch on the MIDI2CV8 takes the 12vac and connects it to the circuit to apply power. A 'power supply' section takes this ac voltage and rectifies and filters it for dual-dc supplies for the analog circuits. On the schematic, these are V+ and V-. The exact voltages here are dependent upon the transformer current and whether or not other devices are connected to the MIDI2CV8 for power or not (the MIDI2CV8 is the power supply for the other modules in a P9700S), but typically, they range from about +and- 12v to +and-18v, dc. Besides going to the analog ICs for power, the V+ circuit also goes over to a 7805 voltage regulator which takes in this unregulated 12 to 18 volt supply and outputs 5v for the digital ICs.

The same points that are used for access to the dual-dc supplies on a MIDI2CV8 in a P9700S (V+, G, SG, V- (positive dc, power ground, signal ground, negative dc)) can be used as input points for an external dual-dc supply. If you just input +and-15v supplies here, the positive side will need to deliver about 145mA and the negative side about 20mA. But, if you adapt the circuit to accept external +and- dc supplies for the analog sections, and, a +5v supply for the digital section, the current flow changes to a lower +20mA and -20mA on the dual dc supplies and 125mA for the +5v supply. It isn't unusual to see multi-output power supplies having dual-dc supplies rated at 100 to 300mA and a 5v supply rated at 1 to 2 A (1000 to 2000mA). So you see, you'd be making better use of your available power if you separated the digital (+5v) section from the link to the V+ circuit it has through a 7805 voltage regulator IC. If this is done though, you'd want to change the function of the front-panel switch so it only works to reset the MIDI2CV8 and not be a power switch for the system (this will be a switch at your external power supply). Instead of switching 12vac to power the board, or not, the switch would need to send +5v dc to the capacitor/resistor circuit which works to make a pulse on the micro-controller reset pin.

It is OK to just send in dual-dc from an external source and not worry with also making changes for a separate +5v supply. You'll just need to be sure you have enough power from the supply and remember the switch must be operated so changes in the ch/mode DIP switch are acknowledged on power-up reset.

It is OK too, to just keep the MIDI2CV8 normal (using the wall-mount transformer) and just use a patch cord to link its outputs to the other modules in the system.

I have attached a pdf information sheet with more details about powering the 9700K MIDI2CV8.

Yes, the MIDI2CV8 can convert MIDI Timing Clock to pulses, but these are at the same 24 pulse-per-quarter-note rate as the MIDI Timing Clock. Some clock inputs are direct or 1 pulse per event. So, check the specs for your sequencer to see if the input for an external clock is direct or a multiple rate such as 24 ppqn. Or, patch a gate-trigger over to the input and check to see if the events advance for every gate or for many gates.

Thank you.

Sincerely, Scott Lee

Paul Conboy wrote:
> Hi
> I am interested in using your MIDI2CV8 in my modular system
> What power does it require?
> My system is running ± 15v
>
> Also, can it output a clock (ie convert MIDI clock to pulse) to drive analogue sequencers?
>
> thanks
> Paul
Attachment:
9700Kpwr.pdf [79.88 KiB]
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