Amplifire Power Supply (wall wart) Things to be aware of

MJ Slaughter

Silver Supporting Member
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2,021
I am not an electronics engineer or even very knowledgeable but I've been forced to learn a couple of things I never knew about power supplies. In particular, power supplies for the Amplifire. The Amplifire PS is a switching PS vs linear and the positive is the center tip, inside the barrel where most of the PS I've used have the positive on the outside of the barrel and seem to be linear. So far all switching PS I've looked at have the positive center. Maybe someone could confirm whether or not this is always the case.

My desire was to daisy chain 9 volt DC power between my midi controller, tuner, Amplifire and another device if I decided to put something in the Amplifire's FX loop later. Since the Amplifire's PS has a positive center I used an adapter to switch the polarity. This setup worked but caused noise around 258-260 Hz and the only thing I can do to fix it is to keep the Amplifire on it's own power supply. Oddly enough, with either just the controller and Amplifire or tuner and Amplifire sharing a PS the noise wasn't a problem. Go figure.

If anyone is successfully powering their Amplifire on a daisy chain with other 9 volt DC devices and not having noise issues please let me know what you're using.
 

mac jones

Member
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1,133
The manual states that it's either positive OR negative tip (internal switching I guess )

Manual:

"9 or 12 volt power supply (DC or AC, either polarity), 1A minimum . Accepts a standard 2.1mm coaxial plug (either polarity) ."



Also, I daisied with a Zoom (which is a digital noise maker) without any noise at all.
 
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JoeB63

Silver Supporting Member
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13,969
Ya -- I tried the Amplifire using a One-Spot with some other effects in the chain, and it worked fine. I did not change polarity. As Mac Jones said above, either polarity works.
 

GuitaRasmus

Member
Messages
232
Yep - It's quite an ingenious little circuit (although not Atomics original idea), and I would love for all pedals to do this.


Negative current can only run against the arrows, and positive current can only follow the arrows (the arrows are diodes) - try imagining a positive or negative current in either place where the wave is, and follow the path - It will always end up the right place. Very clever.
 

Jay Mitchell

Member
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5,299
Yep - It's quite an ingenious little circuit (although not Atomics original idea),
Hardly. It's a full-wave bridge rectifier, and it's been used in almost every electronic device that connects to AC mains since ca. the 1950s. It can be implemented with tube diodes as well as with SS ones.
 

GuitaRasmus

Member
Messages
232
Hardly. It's a full-wave bridge rectifier, and it's been used in almost every electronic device that connects to AC mains since ca. the 1950s. It can be implemented with tube diodes as well as with SS ones.
Absolutely - I was just trying to convey that it wasn't Atomics original circuit - I apologize if my english doesn't come across clearly enough, it's my second language (I'm from Denmark).

I'm just wondering why more pedal/gear makers don't implement the idea.
 

MJ Slaughter

Silver Supporting Member
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2,021
Thanks for the feedback. Now I'm more baffled why I have noise and no one else does. I even tried a different midi controller but had the same results.
 

Greatdane

Member
Messages
451
Just found this tread.

I´m having terrible ground loop problems with my brand new Amplifire.

The original wall wart died on me after less than 2 minutes. I´ve since tried using 4 different ones and plugged it in various places around my house - listening through my headphones.

The ground loop noise is really loud and reduces when I actually touch the Amplifire.
Have nothing else connected and have tried various cables between guitar/Amplifire.

Anyone experienced this or have any recommendations to what I could do about this ?
 

Chris Hayden

Member
Messages
1,428
I tried using a One Spot and had a lot of noise as well so I went to using individual wall warts for the pedals on my board that I use the AmpliFire with. I'm using the Atomic supplied wall wart for the AmpliFire.
 

StudioDevil

Member
Messages
117
Tips for using power supplies with pedal boards:

1. The power adapter included with AmpliFire will work to power AmpliFire, but do not use it in a chain with other pedals. The polarity of the supply included with AmpliFire is not center negative, and could damage other pedals if used with them.

2. You MAY use a different adapter with AmpliFire, including center negative plugs compatible with other pedals, as long as it is 9-12VDC any polarity (or 9 VAC) and can deliver at least 700mA.

3. You really should use separate, isolated, supplies for pedals on your boards because ground loops can cause noise and hum. This is because digital gear, including AmpliFire, loopers, MIDI switchers, digital delays, etc, all take relatively larger currents and can have large transients in current demand. This causes noise to appear on most power supplies, and more so on the less expensive ones, due to less than perfect load regulation found on these power adapters. To make matters worse, analog pedals usually have poor filtering on their supplies and poor power supply rejection, which means you will often hear any noise on the supplies on the analog outputs of analog pedals. This combination of things usually means the following rule of thumb: keep analog pedals running on a different supply from digital pedals. To really play safe, power everything on its own separate isolated output. Many companies make these now and they work well.

The best and quietest setups we have built here used the included supply running AmpliFire alone, with a multi-output isolated pedal power supply running all the other pedals individually. We have also used a multiple output pedal power supply to run each pedal individually, including AmpliFire on its own 9VDC, 800mA output. Not many isolated pedal power bricks have a high output that high, but you can find some.

Hope this helps.
 

patriot7

Member
Messages
127
Does anyone know if Atomic sells the included power supply as a standalone item in case you want a spare?
 

weshunter

Silver Supporting Member
Messages
6,281
FWIW, it works great with a Voodoo 4x4 and current doubling cable to put two of the 400mA outlets together. Leaves plenty of other isolated power for other pedals.
 

Greatdane

Member
Messages
451
Thanks for all the input.
Have been in great contact with Tom too.
Will take it to band rehearsal one day next week and see if it acts differently there.
 

aleclee

TGP Tech Wrangler
Staff member
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13,417
I used to use a 1-Spot but moved to a VL 4x4 when I added a tuner and got ground loop issues.
 

southpaw68

Member
Messages
189
2. You MAY use a different adapter with AmpliFire, including center negative plugs compatible with other pedals, as long as it is 9-12VDC any polarity (or 9 VAC) and can deliver at least 700mA.
....

The best and quietest setups we have built here used the included supply running AmpliFire alone, with a multi-output isolated pedal power supply running all the other pedals individually. We have also used a multiple output pedal power supply to run each pedal individually, including AmpliFire on its own 9VDC, 800mA output. Not many isolated pedal power bricks have a high output that high, but you can find some.
Just to be sure...this one would work, right?
Then, why the 1A minimum in the manual?
Could you clarify please?
Thank you.
 

StudioDevil

Member
Messages
117
Just to be sure...this one would work, right?
Then, why the 1A minimum in the manual?
Could you clarify please?
Thank you.
The 9VAC @ 800mA should work fine. We specified 1A because that the most common power adapter size that covers the current draw of the pedal. Also, it's not the best idea to run a supply near it's maximum all the time. But you are probably OK with an 800mA output. I don't have experience with this unit so I can't say for sure. Best thing to do is try it and hope it holds up. It should if it can deliver 800mA continuously, which I would expect it to...
 






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