Ken Fox
From:
Nashville GA USA
|
Posted 28 May 2011 11:06 am |
|
Here is something I posted a while back:
Often amps are designed with effects loops that actually do not work well with standard pedals. The problem can seen in this example of the N-400 loops (not so unlike many amps out there). Using a pre amp out to drive an effects unit is a bad idea, as it is a line level signal!
This was an earlier reply I made on the N-400 amp itself:
After 30 years of experience and training with the design of audio systems I know a bit about overloading devices.
Let's take a Boss RV-5 pedal for example:
nominal input level rated for -20dbu (0.21 volts)
Nominal level is the normal operating signal that allows 10db of headroom in live music or 20db of headroom in recording application to allow for volume dynamics associated with playing or recording music. That from my old Yamaha manuals of years ago!!!
The preamp output of the N-400 is 1 volt nominal and can go as high as 8 volts! That is 5 times the nominal voltage the Boss RV-5 want to see for it normal operating range and best signal to noise ratio.
The RV-5's nominal output is also -20dbu, 5 times to weak to properly drive the power amp of the N-400 amp.
The pre EQ patch output of the N-400 is amazingly a nominal of 0.2 volts, same as the effects pedal requires!
The patch EQ input of the Nashville 400 is 0.2 volts, the same as the nominal output of the effects pedal.
There is no supporting argument for using the preamp to drive a common effects pedal. Those pedal are designed for unity gain and a guitar level signal at their input.
So in layman's terms. using the pre-amp out to feed a common effect pedal is like trying to shove 5 lbs of stuff in a 1 lbs bag.
Your choice, do it either way. I just believe in the things I learned while I studied and trained in the Pro Audio field to preserve proper signal to noise ratio and prevent gain overlap (that leads to distortion)
I could go on further into gain overlap, impedance matching and a ream of other subject matter but I do not think it necessary for this application!!
A bit more from the net about operating levels:
Nominal level is the operating level at which an electronic signal processing device is designed to operate. The electronic circuits that make up such equipment are limited in the maximum signal they can output and the low-level internally-generated electronic noise they add to the signal. The difference between the internal noise and the maximum output level is the device's dynamic range. When a signal is chained improperly through many devices, the dynamic range of the signal is reduced. The nominal level is the level that these devices were designed to operate at, for best dynamic range.
In audio, a related measurement, signal-to-noise ratio, is usually defined as the difference between the nominal level and the noise floor, leaving the headroom as the difference between nominal and maximum output.[1][2] It is important to realize that the measured level is a time average, meaning that the peaks of audio signals regularly exceed the measured average level. The headroom measurement defines how far the peak levels can stray from the nominal measured level before clipping. The difference between the peaks and the average for a given signal is the crest factor.
There is some confusion over the use of the term "nominal", which is often used incorrectly to mean "average or typical". The relevant definition in this case is "as per design"; gain is applied to make the average signal level correspond to the designed, or nominal, level.[/quote] |
|
