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Re: Pedal board HELL

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2/25/2000 5:14 PM

Re: Pedal board HELL

Hi, Aron. I had a similar problem with my pedalboard, except it was a bad whine. I was powering the pedals from a common 9V LM317 based regulator. The problem turned out to be my Boss CE2. I installed a 470 ohm1000uF power supply filter in the CE2, this fixed the problem.

It sounds like the Memory Man is leaking some clock or digital noise into the common supply. Filtering inside the Memory Man on the power supply line may help. Also, if the Memory Man already has PS filtering, maybe the cap is bad?

BTW, thanks a million for the great web site!

2/25/2000 5:22 PM
aron	Actually I have the whine too if you notice - after adding filtering to the adaptor. Note that none of these problems occured before using a common power supply for my pedals (except the memory man which has its own transformer/PS). Aron

2/25/2000 7:45 PM

Welcome to the world of AC power.

1) it's possible that the memory man transformer is leaking some AC to make this worse.
2) Using an AC power supply on a pedal board is going to make you vulnerable to both AC leakage/ground offset hum and to hum pickup from the fact that the ground is a continuous loop and picks up magnetic fields, just like guitar pickups do.

I would take the memory man out and get it hum free, then solve the MM problems.

You may well be able to break the ground connection to the shield of one end of the cables that connect the pedals together and kill the hum. That works sometimes, and the cables in pedalboards are fairly special purpose, so having one end ungrounded doesn't hurt much. This breaks the "loop" so the hum pickup can't occur. Try that and let us know what happens, we'll work it from there.

2/27/2000 12:16 AM
aron	I am going to break the ground connection shield between the memory man and the rest of the pedals. When the memory man is disconnected, I don't get hum. I will try this. Thanks, Aron

2/27/2000 6:05 PM

Re: Pedal board HELL-scenerio

R.G., Gus etc...,

OK, as I understand it, just the mere use of an AC adaptor makes the possibility of having hum with ground loop possible.

However, is there a scenerio where you can get hum even if you break the ground connections between each pedal via the use of disconnected shields? I mean, can the adaptor simply put hum into the signal - perhaps due to unfiltered power supply?

I guess what I am asking is could I use a good filtered/regulated power supply (ala Fulltones adaptor or the $30 radio shack one) and break every shield connection between pedals - and get a hum free pedalboard?

Thanks,

Aron

2/27/2000 9:26 PM

From what I've learned strapping DC supplies together, the only way to keep power hum out of your stuff is to bond the supply output grounds together. The bad news is that you're still going to be subject to noise pickup from radiated sources like flourescent lights, motors, and such.

It sounds like at least one of your supplies' outputs is 'floating' WRT gnd. Are any of your supplies 2-wire plugs? The 3-wire ones - is the GND on the plug grounded to the output GND?

I'm rambling, but there may be something useful in there.

Good luck

2/29/2000 2:45 AM

I solved my hum problems by substituting an 8 AA battery pack for the adaptor supplied with the SKB board. It was just a cheapo 500ma adaptor. 2 prong.

My question. If I replace it with a $30 Radio Shack regulated/filtered supply - or Fulltone's adaptor, do you think I would still get hum? I am not clear on the difference between connecting an AC adaptor vs. a battery pack with regards to ground.

The good news is I can just buy the Radio Shack adaptor and return it in 30 days if it doesn't do the job.

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