Re: DL-4 hum/buzz when half-speed overdubbing?

[Kim Flint <kflint@loopers-delight.com>]

At 11:12 AM 8/16/2004, Greg House wrote:
>--- Nic Roozeboom <Nic_Roozeboom@msn.com> wrote:
>
> > This behavior (especially since both units exhibit it) could be 
> consistent with
> > a nearby noise source being sampled and aliased into the audible 
> spectrum. Have
> > you recently added something to your setup or environment that 
>radiates 
> - like
> > a monitor, something with a switched mode power supply (e.g. computer) 
>or
> > wireless link?
>
>My friend had terrible noise problems with a DL4 on his pedalboard until 
>he
>physically moved it away from his power strip (which contained a couple of
>warts).

I suspected the wall wart also when I heard this story. A couple 
possibilities:

- Wall warts normally are not well shielded and use low cost transformers 
that radiate a lot of 60Hz hum. Nearby devices that are also not well 
shielded can pick up this hum and make it part of the audio signal in 
various ways. (as the other guys noted.)

- Wall warts (and other types of power supplies) can generate "common 
mode" 
current. Normally a power supply should drive current out on the power and 
receive it back equally on the ground. Common Mode current is driven out 
on 
both, and finds some other path back to earth ground. This can happen if 
the wall wart is not designed well, or uses a cheap unbalanced 
transformer, 
or even with aging. This AC common mode current might find that path to 
earth through your audio cable grounds, in which case you get hum and 
noise.

My suggestions would be: Try moving the dl4 away from nearby wall warts or 
other power supplies as others suggested; Try replacing the wall wart (or 
using batteries to check if that is the problem.)

kim



______________________________________________________________________
Kim Flint                     | Looper's Delight
kflint@loopers-delight.com    | http://www.loopers-delight.com