PSU noise

NickS · Post by **NickS** » Mon Jul 09, 2012 9:46 pm

Matt my son's been complaining that his pedals made a noise on AC power. Yes, there is some buzz. We had little play tonight and:
Using an old Mascot linear PSU I put some extra smoothing in - no noise.
Using the 10-way power brick thing, which uses a switching 12V 1A PSU with a 1m lead to the brick, which contains a 9V regulator - slight buzz as soon as you touch the negative to the chassis of the pedal.
Using the Johnny Shredfreak switch-mode PSU we got him for Christmas - same but worse.
So, it's not the actual smoothing of the PSU output, apparently. Has anyone else noticed this with these switch-mode thingies?

rps-10 · Post by **rps-10** » Mon Jul 09, 2012 10:18 pm

Yeah I had a same issue with my JSF PSU, sent it back and got refund. I've gone back to using the 5 output "Power Bank" brick things.

Bill Oakley · Post by **Bill Oakley** » Wed Jul 11, 2012 3:16 pm

Some people have problems with daisy chains and multi power supplies that don't have isolated outputs. That's the key. Isolated outputs. They keep any humming to a minimum. Power supplies with isolated outputs tend to be a little more expensive though.

NickS · Post by **NickS** » Wed Jul 11, 2012 4:21 pm

Yep, that I understand. However, the issue here is that a double-isolated switch-mode PSU is somehow coupling noise onto the negative of the 9v. Remember, this noise is demonstrated simply by touching the barrel of the power connector against the chassis of the pedal. On the other hand I can put a daisy-chain onto the output of my old linear Mascot 9V PSU (with extra RC smoothing incorporated) and run 3 pedals off it with no more noise than on battery.

Bill Oakley · Post by **Bill Oakley** » Wed Jul 11, 2012 4:47 pm

Is the 10-way power brick made for pedals? What brand is it?
I have a little understanding about how switched power supply works. Basically it goes into an on/off state to efficiently output a constant voltage unlike a linear power supply.
It's my understanding that switched power supplies can be a little noisy.
Usually when touching the jacks makes the noise go away it's a grounding issue which I think you already determined.
I'm not sure how to go about fixing this. Determine whether the switching PSU is making the noise or the 9v regulation?

DasBeef · Post by **DasBeef** » Wed Jul 11, 2012 6:30 pm

I've been using daisy chained boss PSA's and I've been getting quite a bit of noise. Today I got a BBE Supa charger delivered. I'm hoping this will make a bit of difference.
I still need to get some velcro, a few more George L's and mount the supply to my board. I'll report back on noise when I have finished.

Bill Oakley · Post by **Bill Oakley** » Wed Jul 11, 2012 7:03 pm

DasBeef wrote:I've been using daisy chained boss PSA's and I've been getting quite a bit of noise. Today I got a BBE Supa charger delivered. I'm hoping this will make a bit of difference.
I still need to get some velcro, a few more George L's and mount the supply to my board. I'll report back on noise when I have finished.

Should be pretty quiet. It has isolated outputs. I've been wanting to try one of these out. I have a few Dunlop Bricks which are glorified daisy chains and a PP2 and the Bricks compared to the PP2 are pretty noisy.

NickS · Post by **NickS** » Wed Jul 11, 2012 11:17 pm

The Johnny Shredfreak one is worst, and it looks as if they have stopped selling that model but it is similar to the Diago Powerstation. The other is a generic 10-outlet thing with a 9V 3-terminal regulator in the box fed by a 12V switching wall-wart, like this.

SMPSUs are popular because of their power for size. If you think about the energy you can store in a transformer magnetic core being transferred each cycle, the more frequent the cycles the quicker you can transfer that energy, and energy per unit time is power. So if you rectify the mains and use it to power an oscillator running at, say, 600 Hz, you can potentially transfer 10 times the power that you would at 60Hz for the same core size. Of course, it never works out as well as that in practice, but you get the idea. Saves a lot of iron and copper.

Bill Oakley · Post by **Bill Oakley** » Wed Jul 11, 2012 11:31 pm

Do any of the pedals you are powering with it draw more than 100mA? I'm not sure if that could cause the problem though.
The PSU you linked to shows 100mA per output max.
Sorry I'm not much help with this. PSU's are not my specialty.

NickS · Post by **NickS** » Thu Jul 12, 2012 8:15 am

Bill Oakley wrote:Do any of the pedals you are powering with it draw more than 100mA? I'm not sure if that could cause the problem though.
The PSU you linked to shows 100mA per output max.

That's only because it's a 1A PSU with 10 outlets.

As you can see, there's a single 3-terminal regulator.

Both these PSUs introduce noise even when they are not actually plugged in to the pedal and providing power. Scenario: Guitar plugged into true bypass pedal in bypass mode, pedal to high-gain amp. The only noise is white(ish) noise. Touch the barrel of the PSU plug to the metal of the jack socket and this introduces the same buzz as you get when you power the pedal from the PSU. This does not hapen with the Mascot linear PSU.

NickS · Post by **NickS** » Tue Jul 17, 2012 8:01 am

DasBeef wrote:I've been using daisy chained boss PSA's and I've been getting quite a bit of noise. Today I got a BBE Supa charger delivered. I'm hoping this will make a bit of difference.
I still need to get some velcro, a few more George L's and mount the supply to my board. I'll report back on noise when I have finished.

Any news?

I haven't opened the JSF one, as it may be possible to sell it (to someone who doesn't use high gain/doesn't care too much) but I notice my switch-mode lump has a small cap across the opto-isolator that provides feedback from the low volt side to the high-volt side. That may be coupling some noise, so I may try disconnecting that.

DasBeef · Post by **DasBeef** » Sat Jul 21, 2012 6:23 pm

Finally cabled up. Done very quickly today, and I still have a few cheap cables in there. Need to buy some more George L's. 'spensive.
Anyway, a good bit quieter. I am still getting noise from somewhere, but definitely a positive step.

Thomas · Post by **Thomas** » Sat Jul 21, 2012 6:57 pm

Jeeez, you'd have to be a tap dancer to keep on top of that setup!

DasBeef · Post by **DasBeef** » Sat Jul 21, 2012 8:01 pm

I feel the years I was forced to do Scottish Country Dancing has finally paid off........

Nick · Post by **Nick** » Sat Jul 21, 2012 8:27 pm

Thomas wrote:Jeeez, you'd have to be a tap dancer to keep on top of that setup!

I'm fairly sure that the pedal on the bottom right is a loop switcher, probably to switch several at a time.

Still, way too many effects for me to handle.

NickS · Post by **NickS** » Mon Aug 27, 2012 10:54 pm

Friday night, just before going to a gig, I modified my multi-output PSU above to replace the switch-mode wall wart with a 12V 1A linear PSU from an old Netgear switch. Hum was huge so I swapped them back and put up with the whine for the night.

This morning I investigated again. With nothing powered by the PSU, everything running on battery, there was still noise. It disappeared when I unplugged the PSU; so this noise was being created on the mains and picked up by the Marshall JTM60 through the mains! This is different from the Johnny Shredfreak PSU, where the noise seems to be generated on the output.

I checked the output of the Netgear PSU with an oscilloscope and found there was practically no smoothing, so I wired it up again in place of the switch-mode PSU with an added 2200uF smoothing cap. Marvellous. No whine, no hum.

Unlike my multi-out's old PSU, plugging the Yamaha keyboard SMPSU into the mains caused no noise on the Marshall.

Matt is using the Shredfreak daisychain with a modfied Mascot linear PSU to power three pedals (Fender tuner, Joyo fuzz, Boss NR) but it's only 300mA output and generated significant hum when I tried it on my full pedalboard (A/B switch, Dunlop wah/volume, Boss TU-2, silicon fuzz face, Boss CH-1).