FX pedal DIY power supply problems

[norburybrook]

Hi Guys,

Wonder if any of you talented people could help here.

Been trying to build a power supply and have started with the Weber transformer that has 8 13v secondary taps.

So I have separate taps each going to a separate (per tap)little bridge rectifier chip which gives me about 14v DC then I have a 1000uf electrolytic going to the voltage regulator ;a positive 9v 1 amp then a 10uf electrolytic before going to the output socket.

When measured I'm getting 9.0-9.1 v DC at the jacks but when I attach a hungry pedal like the TC HOF the regulator gets so hot it starts to melt the perf board they're all mounted on!!!

Also I get a terrible noise when I plug more than 1 of the pedals in to my amp.


Any thoughts?


Marcus

[JazzGuitarGimp]

The HOF requires only 0.1A of current. Even if you have as much as 16V at the regulator input, that's only (16-9) x 0.1 = 0.7 Watts of power the regulator needs to dissipate. Are you using the 7805's in the TO-92 case, or the TO-220 case? I would suggest the TO-220 case, and I'd leave enough room on the board for a small heat sink for each regulator. But I would also suggest that if you're melting the perf board, then you might have a wiring error. Have you measured the DC Voltage at the regulator's input and output pins?

[Stevem]

What regulators are you using and how much current are they rated for, and how much current does that pedal call for?

[norburybrook]

thanks guys.

OK ,

here's the schematic I've used but I've upped the first capacitor to 1000uF

the regulator is rated at 1 amp.

voltages;

I've got 13v AC going to about 14v DC after the rectifier which drops to around 9v DC after the regulator.

I've got 6 pedals plugged in which all light up, but I started getting smoke after a couple of minutes. I thought it was a cap going but I realised it was the regulator getting so hot on one of the channels that it was starting to melt the perf board.

Also when plugged in there was a terrible noise through the amp too, I'm not sure the two things are related.


Marcus

[ToneMerc]

thanks guys.

OK ,

here's the schematic I've used but I've upped the first capacitor to 1000uF

the regulator is rated at 1 amp.

voltages;

I've got 13v AC going to about 14v DC after the rectifier which drops to around 9v DC after the regulator.

I've got 6 pedals plugged in which all light up, but I started getting smoke after a couple of minutes. I thought it was a cap going but I realised it was the regulator getting so hot on one of the channels that it was starting to melt the perf board.

Also when plugged in there was a terrible noise through the amp too, I'm not sure the two things are related.


Marcus

The devil is in the details; you say that you using a 1A regulator, but posted a diagram of a scheme that uses 100mA regulators. If you using the 78L09 regulator as depicted in that diagram the current output is only around 100mA, not 1A.

I'm with Lou, use the LM780x(TO-220 case) 1A (1A if using a heatsink) linear regulators. If you keep the input voltage only 3-5 volts above the listed target output voltage, you can load these to around 300-325mA without using a heatsink.

However, any input voltage greater than 5 volts above the target output is wasted and will be dissipated as heat, so if you feed let's say 34 volts into a LM7809, that extra 21 volts will create heat. Thus, eventhough its rated at 1A and loaded at only 200mA, you might need to have a heatsink installed to keep it out of thermal overload.


Also, verify the regulator pinout, not all positive regulators have the same pinout scheme.

TM

[norburybrook]

Sorry ,well spotted.

I'm actually using these

L7809CV Voltage Regulator

•Voltage regulator type: Positive Fixed
•Voltage, output: +9V
•Current, output max: 1A
•Voltage, input max: 35V
•Pins, number of: 3
•Case style: TO-220
•Temperature, operating min: 0°C
•Temperature, operating max: 150°C
•Base number: 7809



Marcus

P.s. the regulators are the wrong way round in the board that's on the desk I realised after the photo was taken and reversed them.

[ToneMerc]

Sorry ,well spotted.

I'm actually using these

L7809CV Voltage Regulator

•Voltage regulator type: Positive Fixed
•Voltage, output: +9V
•Current, output max: 1A
•Voltage, input max: 35V
•Pins, number of: 3
•Case style: TO-220
•Temperature, operating min: 0°C
•Temperature, operating max: 150°C
•Base number: 7809



Marcus

P.s. the regulators are the wrong way round in the board that's on the desk I realised after the photo was taken and reversed them.

Ok, that clears up which regulator you using, these things are robust. I was going to ask if they were installed backwards. Where's the regulators ground reference?

TM

[JazzGuitarGimp]

With 13VAC, you should have more than 14VDC at the regulator input. Here's the math: 13 VAC minus two diode drops of 0.7V each equals 11.6VAC times 1.414 (to get the peak voltage, which is what the 1000uF cap will charge to) equals 16.4VDC.

(13 - 1.4) x 1.414 = 16.4

If you're only seeing 14VDC, it's likely something is miswired.

[norburybrook]

Ah... You might have hit on something....


I don't have any ground , the plugs are plastic so nothing there . I was wondering about this but the schematic showed no grounds.


Am I been an idiot here?

Marcus

[norburybrook]

OK some actual numbers here.


The transformer is giving me 12.1v AC

Rectified I'm getting 15.1v DC

After the regulator. 9.05v DC


Still doesn't explain the tremendous heat.

Could someone explain the grounding needed on a pedal power supply?


Marcus

[sluckey]

The transformer is giving me 12.1v AC

Rectified I'm getting 15.1v DC

After the regulator. 9.05v DC

Those numbers are fine.

Still doesn't explain the tremendous heat.

You need a proper heatsink. If you can rotate the chips 90° then you could use a single long heatsink to mount all chips.

Could someone explain the grounding needed on a pedal power supply?

There is no grounding involved. All outputs are isolated from each other just as individual 9 volt batteries inside each pedal would be isolated from each other. Any necessary signal ground will be provided by the instrument cables at the individual pedals. But your power supply does not need a 'ground' reference. All it needs to do is supply correct polarity 9 volts via two wires to each pedal.

If you used a three conductor AC power cord then connect the green wire to the metal case of the power supply chassis.

[norburybrook]

Thanks, that's what I thought.

Would the heat explain the terrible noise issue though when I plug into the amp?

I was hoping building this way would give me nice clean power but there's something amiss at the moment.

Marcus

[Structo]

I messed around with DIY power supplies for a couple years.

I decided I didn't need to re-invent it so I bought a Voodoo Pedal Power® 2 Plus.

I know, a bit spendy, but I don't have to worry under powering or isolation with it.

[norburybrook]

Ha that's so funny ....I'm on tour at the moment and have just got a deal with the voodoo importers so have a voodoo power supply exactly the same as yours delivered to my hotel last night.

Now that's good service.



Marcus

[Structo]

Well done!

Cheers!