Re: Hum from Tube Distortion Pedal into clean amp

On Aug 18, 2:29 am, Dr RaTsTaR <DrRaTs...@xxxxxxxxxxx> wrote:
On Thu, 14 Aug 2008 22:32:16 -0700 (PDT), Kerry <kbro...@xxxxxxxxx>
wrote:

cut



Found an AB/Y switch with a "ground lift" to eliminate 60 cycle hum:
Radial Tonebone BigShot. Review ratings are good, but tone changes are
mentioned at least once and no one seems to be using it for recording.

http://guitars.musiciansfriend.com/product/Radial-Tonebone-BigShot-AB...

Is all your equipment plugged into the same power strip? This might
resolve ground differences. If your computer gear is plugged into one
breaker circuit and your amp is plugged into another, there is a long
way for the grounds to come back together.

It seems that you might be better off to eliminate the cause of the
hum instead of working around it.

Quote -

"Oddly, it doesn't matter if anything is
plugged into the B cord on the other end. The level of hum is reduced
by turning the B switch OFF, but not entirely or nearly enough (e.g.
the hum is only gone when nothing is plugged into B). Also, the A
output does the same thing when I switch my connections."

It sounds like you are talking about one guitar, one passive switch,
and one amp. There is not a second piece of gear there to form a
ground loop with.

Since you experience the hum, even when the other end of the second
cord is not plugged in, and the cord is disabled at the footswitch,
the grounding issues with the second amp do not seem to be related
here. Sounds like a bum passive splitter.

There is an interesting book going around called "Electronic Projects
for Musicians", by Craig Anderton, with foreword by Joe Walsh. I have
owned this puppy since it first came out, and one of these days I am
going to build some of these projects.

Thanks to JP for pointing out this book has been posted in
alt.binaries.e-book.technical before. I recently saw it re-posted on
07-20-08.

There have been several posts lately dealing with this issue of
splitters, pan-pedals,  and two amps. The spluffer (active
splitter-buffer) project in this book seems to be an interesting take
on this subject. It uses op-amps, can be rigged to use either an A-B
switch or a pan-pedal arrangement, and can be used for either
low-level or line-level input (unity gain). It uses 7 resistors, 5
capacitors, 1 IC, 2 diodes, and a handful of hardware.

There are also some plans for a very adaptable mixer. In the basic
configuration it features eight in, one out, with 1/4" inputs and XLR
and 2 - 1/4" outputs (inverting and non-inverting), along with several
ideas for using it to blend different signals with effects.

The first project is a preamp that also has a buffered low-level
output in addition to line-level outs. This could be used to feed your
amp and sound card at the same time.

Another project that could be useful is the electronic footswitch that
uses CMOS 4016 chips to do the work. The only signals that go to the
pedalboard and back are DC control voltages. All of the music signal
stays with the amp and related gear. Electronics and signal cables are
kept off the floor and out of the way. This will only work with on-off
switching; pedals, commercial and project, must use the signal
directly, unless there is a way to control a remote pot by DC. If this
is possible, the dual-ganged pot that is used for panning could be
controlled by electronic circuitry, enabling one to leave all the
signal at the amp. In addition, a "ping-pong" effect could be made by
using two amplifiers connected to cabs at opposite ends of the stage
and continuously, by programmed rate, panning the signal between the
two.

Is there such a thing as a voltage controlled pot? Can one be built by
using two photoresistors in series?

After reading reviews on the different passive splitters and the
comments on AGA concerning using y cables, I would like to make the
following observations.

1. Some people do not hear a difference using the commercially
available passive splitters - some do. We - might - conclude this is
in part due to the number of variables involved, such as cord length
and quality, amp input impedances, guitar pickups, etc. So, what works
for one setup might not work well for another due to gear differences.

2. The same holds true for simple "Y" cords. Although they may work
ok, what might be gained by using an active splitter?

3. It would seem that guitars would all benefit from active circuitry
that would boost the signal right from the start, to help keep it
above the noise level. Since it is a low-level signal, driving
transformers and multiple inputs and passive circuitry would seem to
have a harmful loading effect. Some of the reviews claimed the passive
splitters made the sound "thin".

I am wondering how the EPFM spluffer might hold against the ToneBone,
(designed by Fonebone?) or any of the other units out there. At first
glance, the projects seem too simple, but there isn't much to the
commercial units either. According to Anderton, his units compare well
with anything on the market.

The projects all use outdated IC's. Is the NE 5534IP the right chip to
use for audio op amps in projects like these?

There are also Envelope Follower, Phase Shifter and Ring Modulator
projects, along with the usual Fuzzes and Treble Boosters.

Electric Guitar Amplifier Handbook, by J. Darr, 1973, was posted abet
on 06-12-08. It is interesting.

Dr RaTsTaR
- N00B -

"I figger the odds be fifty-fifty....",  -  FZ.

The computer is connected via a different power strip and outlet. What
you said about there not being a 2nd piece of gear to form a ground
loop with is intriguing, and as you suggest may just show that their
is a bug with the AB switch circuitry itself. I talked to a Rapco tech
(the makers of my AB switch, who said to send it in and they'll take a
look (they were very helpful), which I plan to do. He was unsure what
the problem could be but certainly didn't sound like he expected the
hum to occur. I guess since I've seen "ground lifts" on more expensive
switches, I just thought ground loop hum was an inherent issue, but in
my case where the hum is still evident even without any real loop, the
issue may be with the wiring.

Thanks again,
Kerry
.

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