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Power Supply Modding
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Re: Power Supply Modding

by Nordcore on Sun Jan 28, 2018 6:34 pm

Sorry with the VCCIO... this chip (FT230X) must have it at 3.3V (or less) (as you have drawn it, so that is OK). The older ones could have it optionally at 5V.
But than the driver resistor R18 for the LED should be 560Ohms. The diode D12 is not needed.
Data sheet, page 25 http://www.ftdichip.com/Support/Documen ... FT230X.pdf shows how to connect LEDs for RX and TX.
(They don't have to be on the rear panel, just as debugging aid would be very nice. )


Resistor arrays: https://www.mouser.de/Passive-Component ... ?P=1yzu5ah

The "bussed" ones really save space, as they have one common pin for several resistors. Unfortunately we have only one application for them: the four 100k Ohms.
(I don't like to use them, if they don't belong together in the schematic or "function block". )
The 220 Ohms for the MIDI and the 1k (2k2) for the DIN-Sync are further candidates for SIL arrays with separated resistors. (Don't use too fancy types, Mouser carries a lot of them, but Reichelt, Tayda and other more DIY oriented shops, just have a few of them. )

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Re: Power Supply Modding

by antto on Wed Jan 31, 2018 5:34 pm

i had a bug, the optocoupler for the usb RX side was powered from USB5V and "GND" (of the x0xb0x)
now i changed the USB ground to a more distinct symbol

Image

for resistors and saving space, i was more thinking about moving to 1206 SMD, in places where it can actually save space versus THT resistors
also for capacitors

i added LEDs to the FTDI, and two extra LEDs on a connector, i'm also thinking about maybe adding a power LED near the barrel jack

btw, while checking out some "serial over USB" solutions, i found another one from ftdi which was in a slightly different category (it seems) - FT260
it says it doesn't need special drivers on most OSes, and is cheaper than the others (mcp2200, ft232, etc..) even cheaper than this FT232X chip
the example circuit in its datasheet also looks simpler than this one (no crystal, almost no passives..)
so i wonder, is there a catch?

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Re: Power Supply Modding

by Paradigm X on Wed Feb 14, 2018 8:05 am

Hello all

Interesting topic! Ive got my x0x open atm for adding some mods, so might give Nordcore's idea a try! ive got a dual channel scope, but not really very experienced with using it. i shall try.

if you dont mind, since this thread is active, can i ask another couple of questions?

1- If i wanted to power the x0x from a standard MOTM type +/-15v PSU, can this be done? I guess i could regulate down to 12v and inject it aat point d40/d43? would i need to remove d41 and d42?

2- i also understand there are issues with adding opamps/cmos etc as the psu is overstretched (ironically somewhat the idea of this thread!). ive read that you can 'parallel' opamps - literally solder another on top to double the current capacity. would this help in this situation? http://www.barberelectronics.com/parallelopamps.htm

apologies if spamming your thread. hope youre all well, regards
Ben
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Re: Power Supply Modding

by antto on Wed Feb 14, 2018 5:17 pm

as we've discussed already, injecting 12VDC into the x0x PSU is not so simple, since the rectifier has a voltage doubler
and you need more than 12V in order to get the opamp "regulator" produce 11.87V for the analog circuit, unless you go for a rail-to-rail opamp

stacking opamps like that basically means that you are connecting their output pins together
i wouldn't do that.. at least don't connect their outputs

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Re: Power Supply Modding

by Paradigm X on Thu Feb 15, 2018 11:51 am

oh, apologies, i though id read through thoroughly, must have missed that part.

but thinking about it then, as the motm is (regulated) 15v, that could go directly to point where d5, d43 and c5 meet (?) this should just be enough for the opamp to regulate down to 12v? could then add nordcore's lm317 mod just after that. or maybe id need a LDO version of the 317. hmm.


happy to try it but thought id run it past some people who seem to know more first! is there any risk of killing anything valuable?

cheers
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Re: Power Supply Modding

by antto on Sat Feb 17, 2018 5:51 am

D5?
i will assume you meant regulated 15V into C5/R1
so, that would (according to the discussion) provide about just enough voltage for the opamp "regulator" to produce 11.87V for the analog synth circuit

but if you do that, then what will the voltage at C3 be?
the voltage there is used to feed the 5V and 6V regulators

tbh, i don't want to play with the voltage doubler

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