[sdiy] spring reverb & hum

[phillip m gallo]

Richard,

In my experience the admonition to "just move it" is very "professional" as
part of every design cycle is to account for characteristics including those
issues as pedestrian as "hum".  You will find that the placement of
transformers, chokes, and other inductive components are "typically"
carefully and critically placed within their environment.  You can do a lot
with "orientation" and "location" that reduces or eliminates the requirement
for critical shielding.

Things such as u-metal shields are not used if they not need be.  u-metal is
pricey and to retain it high-permeability requires careful handling.  Shock
can drastically impact the resulting permeability of u-metal that's why it
is "etched" or very carefully stamped.

If you must shield, a fairly typical requirement, careful layout and
orientation (just as has been previously posted) will allow simple,
inexpensive shielding with garden variety steel shielding or even (in best
case) aluminum.

regards,
p





-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Richard Wentk
Sent: Thursday, November 14, 2002 8:05 AM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] spring reverb & hum


At 23:54 13/11/2002 +0100, you wrote:
>Hello
>
>My Doepfer A-100 Modular's spring reverb picks up a terrible amount of hum
>from the transformer. Doepfer's only suggestion was to move the unit
further
>away from the rack with the transformer in it.
>
>Any suggestions on how to make a spring reverb less hum-sensitive?

Following on from the humbucker idea - how about running the signal though
a bare wire next to the reverb, or even through the reverb tank and using
that as a hum pick up? Then subtracting that signal from the reverb output?
You'll probably need to trim it to get it right and perhaps add some
filtering. But with a bit of tweaking you should be able to get near
perfect cancellation.

Alternatively use two reverb units and subtract one from the other. Of
course you'll get some weird subtractive version of the different spring
responses - which probably won't be what you want, but will sound
interesting all the same. :)

To be honest I think the 'Just move it' reply is not very professional.
There's no reason why a spring reverb needs to hum badly if it's designed
properly. I'd also be worried that if I were getting that much hum from one
module, the transformer is radiating more strongly than it should do, with
there's a danger of getting hum within other modules too.

Richard


---
Incoming mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.419 / Virus Database: 235 - Release Date: 11/13/02

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.419 / Virus Database: 235 - Release Date: 11/13/02