Nashville 400 effects loop question

George Kimery · From: Limestone, TN, USA

Am I understanding the owners manual correctly that the rear panel pre-amp in and power amp out can be used as the effects loop for stomp boxes?

Erv Niehaus · From: Litchfield, MN, USA

George,
There could be an effects loop but I doubt it would work the way you describe it.
Erv

Mike Auman · From: North Texas, USA

George: yes and no. The "Pre EQ Patch" out and in jacks on the front are for typical guitar stomp boxes that run a signal level around 0.2 volts (instrument level.) The "Preamp Out/Power Amp In" jacks on the back are for effects that can handle around 1 volt (line level.) Some stomp boxes can handle that level without distorting, others can't. No harm in trying them in the back, and moving to the front if they don't sound good.

Front jacks are after the input preamp, before the EQ. Rear jacks are after EQ and reverb, before the power amp.
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ajm · From: Los Angeles

Erv: I don't understand your answer.
Please explain.

Erv Niehaus · From: Litchfield, MN, USA

I think Mike explained what I was thinking. Very Happy

Erv

Bob Sykes · From: North Carolina

What Mike said with the added caution; Stomp boxes that go "pop" when switched on or off can behave very badly if used between pre-out and power-in.
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Ken Fox · From: Nashville GA USA

This is from an old post I did some years ago. Hope this helps

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.

Steven Paris · From: Los Angeles

Ken's reply is right on the money except for one small error. In terms of rms levels, 0.21 volts [210mV] equals ~-13.5 dbV or -11.4 dbm; -20 dbu equals 0.0775 volts (77.5mV). The actual designed levels quoted in the PV NV400 manual for the pre-EQ patch point is -14dbV/0.2 volts (200mV) rms. The RV-5 is indeed spec'd at -20 dbu; so it expects a bit less level (8 db)than the NV 400 puts out, but not enough difference that can't be compensated by the NV400's pre gain control.
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Ken Fox · From: Nashville GA USA

Thanks for that correction. Been years since I wrote that info. I’m glad you caught that error Smile

K Maul · From: Hadley, NY/Hobe Sound, FL

I’ve never had great luck with effects loops. Tried plugging volume pedals in that way, too. Didn’t care for that. Now I put all effects except fuzz after the volume pedal( unless they are noisy- I get rid of those), plug into the amp input and go to town.
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Richard Sinkler · From: aka: Rusty Strings -- Missoula, Montana

since the reverb died in my NV400, I have been using a pedal to get my reverb, and run it the front pre-eq loop. Works great. I did run a pedal in the rear loop for a short while. It worked OK, but when turning the amp on and off, you get a scary and obnoxiously loud crash, similar to kicking the side of a spring reverb amp.
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