# Whats up with a 9.6 volt power adaptor for pedals.



## GTmaker (Apr 24, 2006)

HI Folks
I needed another power adapter for my second little pedal board and just got this cheapo Kijiji 
Boss PSA-120T adapter...
I tried it out and it seems to work just fine.. Actually much quieter then the other cheapo adapter I have
( my ONE SPOT not included).

I did notice that the boss adopter has a 9.6 volt output while all my other adapters are 9.0 volts.

Is this common ?
Does the 9.6 Volts cause a problem with some pedals?

just wondering...
G.


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## greco (Jul 15, 2007)

I think you should be fine. Some adapters have a voltage regulator which only "permits" 9 volts max. Others are not regulated and the output voltage with no load on it can vary...9.6 volts would not be unusual and (AFAIK) will not harm/cause problems with your pedals. 

The main thing is that it is well filtered and, as a result, your pedals get a DC supply that is less "noisy".

If mhammer and/or other electronics enthusiasts see this thread, I'm hopeful someone else will comment.


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## mhammer (Nov 30, 2007)

Many fresh "9 volt" batteries put out 9.6V. You should be fine.

The voltage one reads is also a function of the load the adaptor is seeing. If the only thing a supply is feeding is the meter, the meter can sometimes read a few volts above its nominal rating; a 9v supply can read over 11V. But feed the supply to a pedal, and when you read the supply voltage on any chips, the reading might be 8.8v.


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## GTmaker (Apr 24, 2006)

Just to be clear, although I do have a meter, I have not taken any readings on anything...
The voltages I referred to was from whats written on the box and on the power adapter itself.

_Many fresh "9 volt" batteries put out 9.6V. You should be fine._

I find the above statement very interesting. Is the 9.6V number a coincident? I think not.

G.


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## greco (Jul 15, 2007)

I think mhammer is indicating that fresh 9V batteries can put out more than 9V ...and chose 9.6 V as an example. It could be 9.3V, 9.5 V, etc.

The manufacturer of the power supplies is likely putting 9.6 V on the box as the typical/nominal output voltage read with no load on the supply. You should put your meter on it and see...I'll bet it won't be 9.6 volts. Very few that I have measured have ever read the exact number sated on the supply.


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## GTmaker (Apr 24, 2006)

greco said:


> I think mhammer is indicating that fresh 9V batteries can put out more than 9V ...and chose 9.6 V as an example. It could be 9.3V, 9.5 V, etc.
> The manufacturer of the power supplies is likely putting 9.6 V on the box as the typical/nominal output voltage read with no load on the supply. You should put your meter on it and see...I'll bet it won't be 9.6 volts. Very few that I have measured have ever read the exact number sated on the supply.


Sometimes, your a pain in the butt Dave....
So I got all my power supplies on my work bench...plugged each one in and measured the output voltage.

Boss ( this is the only one that stated a 9.6 output voltage. ) actual reading 9.53 Volts
all the rest state a 9 volt output on the box.
actual readings:
One Spot = 9.32 volts
Korg = 12.86 volts
Zoom = 13.11 volts
unknown maker = 11.63 volts

I don't know what to make of these numbers. They are what they are but I am now wondering why most of my power adapters are noisy.

the moral of this story is that I'm going to measure each and every adapter before I start to use it.

G.


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## mhammer (Nov 30, 2007)

Define "noisy". Do you mean lots of hum, or do you mean higher-frequency hash?

Again, the voltages you read from the supplies when they have no load other than your meter is not what they provide to the pedal.


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## GTmaker (Apr 24, 2006)

mhammer said:


> Define "noisy". Do you mean lots of hum, or do you mean higher-frequency hash?
> Again, the voltages you read from the supplies when they have no load other than your meter is not what they provide to the pedal.


the best way I can describe it is the effect that the power supply has on my pedals.
My Boss overdrive for example, when turned on is much noisier with one power supply then it is with another.
Its not a hum but more of what I think you call "hash".
My MXR flanger also reacts to the power supply.

that's the best way to explain it.

G.


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## greco (Jul 15, 2007)

GTmaker said:


> Sometimes, your a pain in the butt Dave....
> So I got all my power supplies on my work bench...plugged each one in and measured the output voltage.
> 
> Boss ( this is the only one that stated a 9.6 output voltage. ) actual reading 9.53 Volts
> ...


@mhammer...by "noisy", I was referring to hum. Does the word "hummy" exist? LOL

I definitely am a "pain in the but" because I want you to delve deeper into the wonderful, fascinating and exciting world of physics, applied electronics theory, etc.

mhammer will be able to explain the details much more clearly and succinctly. I have to drive to Cambridge soon, but here it is in brief. The output of many power supplies is poorly filtered (with capacitors) and the DC voltage produced is not all that "pure" and translates into "hum". 

Don't worry about the numbers.

As I was mentioning in my recent email to you, I have wanted to build a filter (simple capacitance) interface to reduce the hum from these power supplies. 

Here is a video of what I mean. I think mhammer has a tutorial video of his version of the same thing,but I couldn't find it.


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## greco (Jul 15, 2007)

"hash"...."hashy"


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## mhammer (Nov 30, 2007)

1) All a supply requires to be called DC is to go from ground to some positive voltage, with nothng zipping below 0V. Many devices don't actually require more than a single diode to block the unwanted negative voltage fluctuations. There may be 60hz ripple up the wazoo, but as long as that 60hz is not positive AND negative voltage, it "counts" as DC.

Now, the difference between what a battery provides, and what an ideal regulated supply provides, involves a lot more circuitry than that. In some instances, the smoothing out of that "DC" to more closely resemble smooth battery power is a matter of component values. So, a 220uf smoothingcap will remove more ripple than 10uf, 470uf more than 220uf, and 1000uf more than 470uf. Trouble is, more capacitance generally requires more space. So a wallwart aiming to be compact may forego 1000uf and content itself with 330uf or less. There will be _some_ smoothing and ripple rejection, but not as much as there could be. Supplies vary in how effectively they reject ripple and smooth out the DC. Same thing goes for pedal, too. Some will assume that the pedal is powered ONLY by a battery, and others will include additional power smoothing on-board. Assuming there is space, one can always add more smoothing capability inside the pedal, or in line with the adaptor so that multiple pedals benefit.

2) Switching power supplies are a more recent type (although at least 15 years old) and use internal high-frequency clocks to turn things on and off in a manner that transforms 60hz AC into a version of DC. Their strength lies in being able to convert large amounts of wall current in a tiny space and light package. The supplies that come with laptops are switching supplies, and for the amount of current they provide would have weighed more than the laptop itself 20 years ago. Now they are trivially light.

What they often don't do is keep the clock spikes from showing up on the DC voltage. If you are old enough, you may remember the hash that would occur on the TV or radio if the refrigerator compressor motor came on or your mom/sister started using the sewing machine or your dad was vacuuming somewhere in the house. The spikes on the wall current from those motors would be "shared" with every appliance in the house. In the case of switching supplies feeding pedals, those spikes are similarly shared. They are generally high-frequency enough that we can't hear them. However, if the individual pedal happens to use a HF clock of some kind - and this can include delays, chorus, flangers in addition to digital pedals - the spikes on the power can interact with those clocks in a manner similar to a ring modulator, producing sums and differences of the clocks. You won't hear the sums, but the differences are often audible.

Many folks will be perplexed when they purchase a digital pedal, or have a digitl pedal and get a new switching supply, and all of a sudden things that used to be dead quiet now sound like a hornet's nest. Nothing is wrong with the supply OR the pedal, but they interact.

3) Feeding a pedal a higher than suggested supply voltage can have several potential outcomes. In many instances, assuming the increase is not too big, there is no audible effect. In other instances, there _may_ be a small increase in headroom. In all instances, the supply-voltage should not exceed the voltage rating of the capacitors. And good practice suggests it probably should not exceed 3/4 of the rating. So powered at 9v a 16vdc cap should be absolutely fine. If the supply voltage is 12vdc or higher, the chip may be good for it, but the cap may go out of spec and provide less smoothing of supply voltage than one needs.

This caveat would pertain only to caps used in the power path and not to caps in the audio path. So, if the output cap on the last chip before the volume pot is rated at 16vdc, changes to the power supply should have no bearing on its functioning since you won't likely see more than 3V or so going through it.


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## Jamdog (Mar 9, 2016)

Another way is to use large battery packs.


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