Fuzz pedals and wall warts

[hodad]

I've been playing with Fuzzface-adjacent pedal designs, & I've found that when I use a cheap 9V switching supply (like this cheap wall wart) I get a whine in my audio--and the pitch is not the same with different pedals, which may or may not be relevant. Aside from using different AC adapters, what might be a good approach for getting rid of the noise? And one more question: the adapters I have feature an annoying blue LED. I've noticed before that LEDs can add noise to a fuzz. Is it possible the LED is the problem rather than the actual power supply?

 

[CJ]

i got so tired of pwr supply noise that i hooked up 3 vape batts in series.

works good so far, that is, no house fires yet.

intuitive thought process says blue led should not make noise which means it probably does make noise, because my brain is fried from 50 lbs of weed and 10,000 gallons of Guiness just like our lead singer but we don't party like it is 1999 any more.

 

[Matador]

Aside from using different AC adapters, what might be a good approach for getting rid of the noise?

Do you know the approximate frequency of the noise?

A lot of cheap 9V switchers use a flyback topology that can switch at pretty low frequency if the current draw is too low. You might be able to shift it to a higher (filterable) frequency if you increase the load on the supply beyond that which is demanded from the pedal. Maybe for experimentation, add a 100 resistor from +9V to ground in the pedal to add (90mA of) extra load current, and see if the whine changes.

 

[hodad]

You might be able to shift it to a higher (filterable) frequency

Since the pitch changes with different pedals (different transistors, different biasing, likely slightly different current draw), it seems like a strong possibility there's not enough load. I'll throw a resistor on & see what happens.

 

[JohnRoberts]

I'd try a LxC filter...

JR

 

[Gus]

If you don't want to use an L for a L C as posted above, 47ohms with a big cap(>=470uf) can help

 

[hodad]

100R resistor helped substantially with the noise, but quickly got quite hot. Higher values changed but didn't dispose of the noise. I have some inductors somewhere--I'll see if I can dig them up & calculate a filter (digikey has what looks to be a very useful filter calculator.)

I'm thinking since this is on the DC power input, I can make the cutoff frequency as low as is practical, as long as it's well below the whine?

I might try the RC filter as well--simple enough to give it a shot.

 

[Michael Tibes]

Isn't it simpler / cheaper to buy a proper psu with a clean output?

Michael

 

[JohnRoberts]

Isn't it simpler / cheaper to buy a proper psu with a clean output?

Michael

This is a DIY forum so making stuff on hand work is part of the journey....

JR

PS: If you could get away with only 5V modern switchers with USB connectors are cheaper than dirt.

 

[hodad]

Isn't it simpler / cheaper to buy a proper psu with a clean output?

Michael

If the pedal ends up with a friend (as a few of mine have already), it'd be nice if they didn't have to think about whether their AC adapter was of adequate quality. Most musicians I know don't want to have to think about that kind of stuff.

 

[Khron]

What about adding a capacitance multiplier inside the pedal? 1-2 resistors & capacitors and whatever NPN transistor you have in your parts bin. Good enough for the likes of Neumann

 

[zzzzz]

Real over the top setup for a DIY fuzz (especially PNP) is to use a charge pump to get -9v out of a +9vdc wall wart. I like LT1054 for this purpose, but again, over the top.

My friend who collects vintage fuzz pedals just swears by those cheap cheap cheap “Golden Power” 9V batteries

 

[Clintcleveland]

This is good stuff. I wish more pedal builders/manufacturers thought about power cleanup in their designs. For my own setup, I use one of those Rockboard rechargeable NiMH batteries, but for pedal builds I usually just put a couple caps across the power input.

Now I’m inspired to come up with something more robust that I can standardize on.
The capacitance multiplier is a good thought.

 

[GeorgeToledo]

LED can definitely cause whine in a pedal like this.

 

[hodad]

I made a little box with a 27mH inductor (what I had on hand) & a 1000uF cap. Digikey's LC calculator says -3 dB point is about 30 Hz. I don't know that it's a perfect solution, but it does manage to get rid of the whine.

 

[fragletrollet]

I posted a related thread

Would love more suggestions

 

[fragletrollet]

Some interesting details over on the proaudiodesignforum

https://www.proaudiodesignforum.com...hp?t=945&sid=2faea1cff2e62de48b20b32045897fea

I got a couple of the supplies in question but not used them yet. But would be for bipolar needs, so not specifically for the typical pedal

 

[Wavelength]

Guys,
First off LED's are super quiet and would never add noise. We use them as low noise voltage references all the time.

If you have a PNP based Fuzz then your ground is positive and you would need an isolated supply. Best bet is a GigRig virtual battery:
https://shop.thegigrig.com/collections/power/products/virtual-battery

If you have a NPN based Fuzz then your problem is probably grounding. All pedals will add or subtract noise if you daisy chain the supplies together. Pedals need isolated power. With an isolated power your pedal then inherits the ground of the amp, instead of one of the other pedals or power supply.

It maybe that you pedal needs better power regulation as Fuzz pedals have crazy gain and can pick up just about anything. I use a shunt supply in my Fuzz (ToneBender 1.5 type) pedal. 9V in is isolated by a common mode choke then into the shunt. Lowers the noise by 30-40dB.

The Fuzz needs to be first in line as well as it works with the inductance of your pickups and parallel resistance (pots) of your guitar.

There are a lot of power supply options. On my small board (330ma total 8 pedals) I use 2x GigRig isolators (4 each) from a 2.1mm splitter and power with a Truetone 1 spot or off my LunchBox amp which has a 9V supply for pedals.