ASK AMP MAN
Ins and Outs
I have a Soldano Hot Rod 50+ and on the
drive channel, while running effects in the
loop, it cuts the drive channel volume a
great deal and the clean channel a bit less.
But if I turn the effects off, then it’s just fine.
If I run the effects in line with the guitar, it’s
fine. Why would my effect loop have such a
negative effect on my overall tone? Is there
a mod or update I can do to the loop? This
is the only amp I have that my delay sounds
worse in the effect loop. Please help!
Thanks for your question. Since you say your
effects work just fine with a guitar signal,
I have to assume that they’re guitar level
effects and they’re probably functioning just
fine—which is your problem. Your effects are
guitar level effects. The signal in the effects
loop of your amp is more than likely much
greater than a guitar level signal, and the
effects are not able to process such a high-level signal. Most effects pedals are powered
by 9V DC. Those 9 volts are then generally
split into the plus and minus supplies, which
are necessary to power the ICs that are the
basis for most effects. The voltage levels of
those supplies govern the amount of signal
that the effect is capable of processing. Once
that level is reached, the effect can no longer
produce a higher signal level.
To sum it up, if the signal in the loop is higher
than the effect is capable of reproducing,
the resulting output of the effect will be substantially lower than the input, leading to a
reduction in volume. There are some effects
that are now powered by 18V DC (two 9-volt
batteries or an 18-volt supply), which would
theoretically double the amount of signal the
effect is capable of reproducing. You may
want to search these out and see if any company (mostly boutique builders) offers the
effect you require.
Another possible solution, since the effects
loop in your amp is pre-Master Volume,
would be to see if you could have the
effects loop moved to a different location
in the circuit. Since this is a circuit board
amp, it may require some trace cutting, but
if you find a technician who is experienced
enough, you could have him locate the
effects loop just prior to the phase inverter.
This would place the loop post-Master
Volume, and the signal level would be much
lower with moderate Master Volume settings. Of course, the signal level would be
dependent on the Master Volume settings,
so if you run the Master Volume at very
high settings, this may still pose a problem
for the effect—but it may be worth a try.
Now you know how the loop
affects your effects.
My issue: why is it that when I turn up
the FX mix volume on my Mesa Boogie
F- 50 to anywhere near 12 o’clock I get
feedback like crazy? My effects loop
consists of: FX Send >Cry Baby pedal
>OC3 Octave pedal >MT2 Metal Zone
With only the MT2 Metal Zone pedal on,
with the volume set at 11 o’clock on the
pedal, little to no distortion is heard. But
if you run the pedals straight through the
amp, and not through the effects loop,
they sound perfect. What’s the deal?
I have a theory regarding your effects loop
problem, which I ran past Dave Barber of
Barber Electronics. Since he actually manufactures effects pedals, I wanted to get his
take on this, and he seems to concur. I will
attempt to explain it as clearly as possible; I
hope it doesn’t become too convoluted.
The effects loop in your amp is a form of
passive parallel loop. The “mix” control is
actually blending in the wet (effected) signal
into the main (dry) signal path. The problem
is that the dry signal is always present at
the mix point, and since there is no isolation between the dry and wet signal at that
point, the dry signal can wind up appearing
back at the output of the effects. What is also
happening is that the wet signal can appear
back at the input of the effects. While this
may not be as much of an issue with time-based effects (reverb, delay, etc.), gain-based
effects may react very differently.
When a dry signal appears back at the output of an effect, the signals can, depending
on the effect, possibly be out of phase. This
could cause a substantial reduction in amplitude, which may be why your MT- 2 Metal
Zone pedal has little to no level when used in
the loop. Also, when the wet signal appears
back at the input of an effect, it may possibly
start to oscillate, giving you the feedback
symptom that you are experiencing.
There are two possible fixes for your problem. The first is to run the non-time-based
effects in the traditional manner, which is
through the guitar input of your amp. The
second would be to find a competent tech
to modify the effects loop, so that it’s a standard series loop, as opposed to its current
parallel status. That would completely isolate
the send from the return, and it should clear
up the issues you’re having.
So much for the ins and outs of your
send and return.
Co-Founder and Senior Design Engineer
email@example.com or www.budda.com
©2008 Jeff Bober