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Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 14:20
by Super Locrian
Hi all,

I have a T-Rex Fuel Tank Classic power supply that delivers 3 x 500 mA from three sections, 9V DC, 12V DC and 12V AC. I have exhausted the capacity of the 9V outlets (I only buy 9V pedals as a matter of principle), and so I wonder if there is a simple voltage reducing circuit that I can either put inside, or piggy-back on top of the Fuel Tank. I imagine T-Rex would just ignore me if I sent such a request to their customer support (or at best they would recommend purchasing another T-Rex product). My electronics knowledge is not exactly impressive, but I figure it should be a fairly simple deal to reduce the voltage. Is it just a matter or adding a resistor or two? I just need a simple schematic and parts list. Can anyone help? PS. I know a lot of 9V pedals can handle 12V too, but I don't want to risk anything, so I'd prefer to get the voltage down.

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 14:42
by alexradium
Super Locrian wrote:Hi all,

I have a T-Rex Fuel Tank Classic power supply that delivers 3 x 500 mA from three sections, 9V DC, 12V DC and 12V AC. I have exhausted the capacity of the 9V outlets (I only buy 9V pedals as a matter of principle), and so I wonder if there is a simple voltage reducing circuit that I can either put inside, or piggy-back on top of the Fuel Tank. I imagine T-Rex would just ignore me if I sent such a request to their customer support (or at best they would recommend purchasing another T-Rex product). My electronics knowledge is not exactly impressive, but I figure it should be a fairly simple deal to reduce the voltage. Is it just a matter or adding a resistor or two? I just need a simple schematic and parts list. Can anyone help? PS. I know a lot of 9V pedals can handle 12V too, but I don't want to risk anything, so I'd prefer to get the voltage down.
many pedals work just as well with 12Vdc,mostly dynamics,you have to check out the specs in manuals to find out any problem with higher voltages.
Anyway,you can get 9Vdc easily with a 7809 voltage regulator and 4 caps from the 12Vdc output.
You can do the same with the 12Vac,just inserting a 4 diode bridge rectifier between the output and the aforementioned circuit.(more dissipated energy so you need a heatsink.)
Its everywhere,check out any site like Geofex or General guitar gadgets or Tonepad for complete projects

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 19:18
by tip142
alexradium wrote:
Super Locrian wrote:Hi all,

I have a T-Rex Fuel Tank Classic power supply that delivers 3 x 500 mA from three sections, 9V DC, 12V DC and 12V AC. I have exhausted the capacity of the 9V outlets (I only buy 9V pedals as a matter of principle), and so I wonder if there is a simple voltage reducing circuit that I can either put inside, or piggy-back on top of the Fuel Tank. I imagine T-Rex would just ignore me if I sent such a request to their customer support (or at best they would recommend purchasing another T-Rex product). My electronics knowledge is not exactly impressive, but I figure it should be a fairly simple deal to reduce the voltage. Is it just a matter or adding a resistor or two? I just need a simple schematic and parts list. Can anyone help? PS. I know a lot of 9V pedals can handle 12V too, but I don't want to risk anything, so I'd prefer to get the voltage down.
many pedals work just as well with 12Vdc,mostly dynamics,you have to check out the specs in manuals to find out any problem with higher voltages.
Anyway,you can get 9Vdc easily with a 7809 voltage regulator and 4 caps from the 12Vdc output.
You can do the same with the 12Vac,just inserting a 4 diode bridge rectifier between the output and the aforementioned circuit.(more dissipated energy so you need a heatsink.)
Its everywhere,check out any site like Geofex or General guitar gadgets or Tonepad for complete projects


If you haven't lying around the 7809,simply put for 1n4.... in series and you drop from 12v to 9,2 v quite happily and satisfactory.
:thumbsup

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 19:35
by deltafred
tip142 wrote:If you haven't lying around the 7809,simply put for 1n4.... in series and you drop from 12v to 9,2 v quite happily and satisfactory.
:thumbsup

The forward voltage drop of a 1N400x is somewhere around 0.7v so you would need 4 or 5 in series to drop around 3v.

New 9v batteries are usually a bit higher, around 9.6v so 4 should be ok but it depends how accurate your 12v supply is. If you are worried then start off with 5 and measure the pedal voltage. Take one out if it is below 9v, add another if it is over 9.6V. I would add a 100uF 16v electrolytic in parallel with 0.1 disc ceramic decoupling capacitors across the 9v output.

Not the most elegant of solutions but it will work.

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 22:38
by bcalla44
Can't you do it with a 9.1 v zener diode with a resistor in series?

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 22:47
by DrNomis
I've actually seen some 9V batteries measure something like about 10V when measured by a multimeter.... :thumbsup

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 18 Sep 2013, 22:54
by deltafred
bcalla44 wrote:Can't you do it with a 9.1 v zener diode with a resistor in series?

You can but you waste more power because you need a certain current through the zener for it to operate properly (and 9v batteries don't have a lot to waste).

With the 1N400x you only draw the current the pedal draws, a zener needs a few milliamps extra.

Re: Reducing voltage from 12V to 9V on power supply

PostPosted: 19 Sep 2013, 00:21
by mictester
bcalla44 wrote:Can't you do it with a 9.1 v zener diode with a resistor in series?


You can, but the resistor will just be wasting energy as heat! Also, zener diodes tend to be a bit noisy.