Grind Customs FX Tenebrion Reverb doesn't work with power supply

[eve-the-frog]

Hi,

I have a weird issue with this pedal.
It works perfectly when I test it with a 9V battery but when I plug it to an external 9V power supply the effect still works but I hear over the guitar a strange sound : a continuous note (like a G played on the low E) but slighltly oscillating, exactly like the sound made by an old propeller plane in a war movie...
This sound is clear and loud.

I made two other effects pedal (madbean cave dweller and TS808) using the same power supply without any issue.

The power supply is a 9V/500mA AC-DC 230V~50Hz (by he way I live in France) made by Netgear (probably taken from an ethernet switch or something like that).

Here is my board :


You can see a few strange things in the above picture :
-the 2 big electrolytic caps next to TL074 are recycle from another project thats why they are so big and one is leaning (lack of space in this area)
- the red cap and the big white one have short legs so I made "extensions"

But again : everything works fine with the 9V battery.



And the power supply used :


I try without the footswitch, I even change a pot : same sound.
Could it be a faulty 9V DC socket on the pedal ? But how that stuff could be faulty ?

Thanks for your help.

[PMowdes]

looks like a positive pin power supply.

Should be negative pin.

If it works with a battery check that the battery is wired correctly as well, remember that these pedals (unless otherwise stated) are generally +9v (negative GND).

[eve-the-frog]

Not sure I understand what you say...

What is a "positive pin power supply" ? Does it mean the center pin of the socket should be negative ?

On the picture of the power supply you can see that the positive is on the center of the socket (is it what you call "the pin" ?)

I have always considered that "9V" means "+9V" and that ground is "-9V". My two other effect are wired in this way.

I have wired the "9V" of the vero plan with the red wire of my battery holder and on the center pin (+) of my power adapter.

Tell me if I'm wrong.

I'm a newbie in guitar FX making and in DIY electronic in general. My knowkledge are very basic...

[eve-the-frog]

I found this in another thread about power supply :

I was going to suggest a 100R resistor in series with the 9v in, which I have found works wonders suppressing PSU noise on some circuits

This is the layout I used :


The 100R resistor is missing in the layout. Can I try to add one ? Is it safe ?

[PMowdes]

You need a centre negative supply (negative GND)  for a +9v layout,  your supply is centre positive (positive GND).

Your jack should be wired +9v to the sleeve and gnd to the pin.

[eve-the-frog]

I must be stupid... (and probably I am ! )
If the center pin is negative then I can choose to wire it to ground and if the center pin is positive I can choose to wire it to 9V, right ?

Anyway, I'll try to reverse what I thought was right to test it.

If you have a link to a tutorial that explain what you're trying to tell me it would be great. I feel a bit dummy...

[eve-the-frog]

Aaaaarghhh !
It doesn't work.

I also try to add a 100R resistor in series on the +9V : the sound is now on a low volume, but still there.

Is there a layout for a daughterboard that I can add to my pedal to "de-noise" that power supply ?

[eve-the-frog]

After googling a bit here is what I found.

The schematic of a 9V power supply filtering (for guitar pedal FX, found on Youtube) :


I have no 470uF capacitor at home so I tried with 220uF. The result is not perfect but I have to put the volume of my amp at 12 oclock to hear the undesired sound.
I guess it will disappear totally with 470uF caps.

What do you think about it ? Is it safe for the reverb circuit ?

[Silver Blues]

Something else to consider is, is that power supply regulated? If it reads more than 9v when nothing is connected to it, it probably isn't a great idea to use it for a pedal because it will introduce noise.

To answer your earlier question, by convention pedals are powered by supplies that are "center negative", or -9v at the tip. You are correct in assuming that the tip thus needs to be grounded, and the sleeve connected to +9v. Keep in mind that some DC power jacks have three connections on them, and one is for a switch to disconnect a battery in the event that a power supply is plugged in. Be careful you haven't soldered your +9v to this lug on the jack by mistake, because you will never get power delivered to the circuit this way.

You're not stupid! Just learning

[eve-the-frog]

Thanks for the tips !

I didn't know the "center negative" pedals convention. And I still don't understand what is the difference with a "center positive" power supply. And why all the layout on this site indicates "9V" and not "-9V"...

A lot of questions...

I've tested my 3 power supplies, all three indicates 9V 500mA. First is 13,05V second is 14,57V and third 12,45V with nothing connected to it.
Ouch !

Don't know what it means : is it poor quality stuff ? Or maybe thess values dicrease as soon as I plug the right device too it ?

Anyway, the power filter I've tried seems to work for me and that's enough for today !

[Silver Blues]

No problem! Everybody has to start somewhere, right.

That convention has been around forever in effects pedals. The difference is just the polarity of the barrel connector; the connector has a tip and a sleeve, in a "center negative" supply the tip is negative and the sleeve is positive. This is totally independent of the power applied to the circuit; connecting the sleeve of a center negative supply to the +9v input of a circuit and the tip to ground is the same as connecting the tip of a center positive supply to the +9v and the sleeve to ground, except then that power supply can only be used with one pedal, because if you hook together a pedal wired like that to one wired conventionally the whole thing gets shorted and nothing works right. Most circuits require a positive supply and negative ground, but there are some circuits that require a negative supply and positive ground: these also need to be treated specially to get them to play nice with your other conventional pedals.

Just as I suspected, your power supplies are not regulated. This will introduce a lot of noise into your signal path. I recommend you eventually get a good, high-current, regulated 9v power supply. The voltage will decrease when you connect something to it, but the output being free to fluctuate is not helping your noise issues. That's great if the filter works though, most are designed to kill noise just like this.

[eve-the-frog]

Many thanks for the explanations.

The negative tip convention only apply when I use two or more pedals together. If I use only one at a time between my guitar and amp I can do what I want (or i I only use the pedals I've built together).
This is to sum up whta I understood...

I wonder if I can build a 9V regulated power supply, and where can I get a layout for it.

[Silver Blues]

For sure!

Pretty much, but it's always good practice to build according to the convention because you never know what kind of scenario you're going to find yourself in, and that's not something you can just fix on the fly. Hypothetically yes you could keep it wired the way you have it if you only a) use that pedal or b) use only other pedals wired that way (as you say) but there's no real reason to do that when all it takes is a swap of some wires and the correct power supply (heck, you could just snip the connector off your power supply and put on a new one with the polarity reversed if you really wanted to).

You can, there are projects for pedalboard power supplies kicking around. But it's way easier to just buy a regulated, center-negative power brick.