Compensating diode voltage drop.

[crawler486]

Hi guys.

I built the "Ultra Clean" power supplt from GGG.
http://www.generalguitargadgets.com/v2/index.php?option=displaypage&Itemid=106&op=page&SubMenu=

I placed a diode for reverse polarity protection in my enclosure which
houses 5 effects.  

Which part in the power supply will I change to increase its voltage
output to compensate for the voltage drop?

Many Thanks!!

[niftydog]

I placed a diode for reverse polarity protection

where?!

[cd]

You really don't need to add the diode, but if you want to increase the voltage, just change the values of the resitors around the regulator for higher voltage.  I don't remember the formula offhand, check the datasheet.

[crawler486]

You really don't need to add the diode, but if you want to increase the voltage, just change the values of the resitors around the regulator for higher voltage.  I don't remember the formula offhand, check the datasheet.

I dont really have to add a diode? Wont it fry something when power is accidentally feed in reverse?

Anyone else have something to say about this?

[niftydog]

do this;



then adjust the voltage using the pot to obtain the right output.

[niftydog]

about the diode.

If you are sure that all your 5 pedals work with this supply, and you intend only to use this supply for your 5 effects, then forget the diode.

[gez]

I'd agree, if your effects work with the protective diode then don't worry about raising the output of your adapter to compensate for any (small) drop.

However, if you're dead set on this then you might be able to do it as follows.  Don't know if this'll work for the LM317 but it's a trick Penfold uses with many fixed regulators. He disconnects the ground connection of the regulator and inserts a diode (ground connection to anode, cathode to ground for a +ve supply).

If you did this with a LM317 you'd have to connect the bottom of the resistor chain to the anode of the diode too but it's a bit pointless doing this as (has already been pointed out) you can just re-jig the resistor values. But if you are uncertain about how to do this then the above might just work.

[crawler486]

With a diode, the voltage drops from 9.5v to 8.9v

At 8.9 does it have an effect in terms of sound or noise
in my effects chain. I havent really tested and compared
using different voltages.

[crawler486]

hey niftydog, can I use a trimmer instead?

[R.G.]

A better way is to step sideways - use one of the improved polarity protectors from GEO. You can use either the MOSFET or the bipolar versions, your preference. Can the series diodes, use the advanced protectors.

[niftydog]

a trimmer would be fine, there's only a tiny amount of current coming out of that pin.

BTW, I made a boo boo.  You want to add the trimmer in series with R2a and R2b and the 10uF cap, but still have R1a and R1b connected directly to the Iadj terminal of the LM317.

Basically you want to increase the resistance of the R2a||R2b combination without affecting anything else.