The Case Against True Bypass

[Rick Walker <looppool@cruzio.com>]

I found this on line while researching all the threads
about Input/Output gain and thought it would effect everyone:
It is from Pete Cornish's really great website on pedalboard design.


"Hey Pete, do you use True Bypass?"

Look out there's a lecture coming:

The "true bypass" function, which is promoted by some, can create 
dreadful problems with a system that uses many pedals. Take for instance 
a 15 ft guitar cable linked to ten pedals, each linked by a 2 ft cable, 
and then onto the amp by a 30 ft cable. If all pedals have "true 
bypass", and are off, then the total cable length hanging on the guitar 
output will be 63 ft. This will cause a huge loss of tone and signal 
level particularly if the guitar is a vintage type with low output and 
high impedance. The amp volume is then turned up and the treble control 
increased to compensate for the losses. The inherent background noise 
now increases by the amount of the gain and treble increase and is 
usually, in my experience, too bad for serious work. If one of the 
pedals is now switched on, then it's (hopefully) high input impedance 
(and usually low output impedance) will buffer all the output cables 
from the guitar and the signal level will rise due to the removal of 
some of the load on the pickups (i.e.: 17 ft instead of 63 ft of cable). 
The treble will rise and the tone and volume will not be as before. If 
that pedal was say a chorus or delay, devices which are usually unity 
gain, then your overall signal level and tone will vary each time an 
effect is added...not a very good idea.

Some pedals have an input impedance which is far from high in real 
terms; the input impedance of the vast majority of amps is 1 Megohm (one 
million ohms) and in my experience there are few effects pedals that 
have the same input impedance. A load on the guitar of less than 1 
Megohm will reduce the volume and high frequency content of the pickup 
signal thus giving rise to complaints that "this pedal looses 
tone/volume" etc. Many effects I have tested have an input impedance of 
less than 100 Kilohms (ie: only one tenth of the amp input impedance) 
and cause serious signal losses in the effects chain.

My system, which I devised in the early 70's, is to feed the guitar into 
a fixed high impedance load, which is identical to the amp input, and 
then distribute the signal to the various effects and amps by low 
impedance buffered feeds. This gives a constant signal level and tonal 
characteristics, which do not change at all when effects are added. The 
proof that this works are in the recordings of our clients: Roxy Music; 
The Police; Queen; Pink Floyd; Bryan Adams; Lou Reed; Dire Straits; Paul 
McCartney; Sting; Jimmy Page; Judas Priest; Black Sabbath....

So the answer to your question re "true bypass" is no, I do not use this 
system in my Effects Boards/Racks as it can seriously degrade your 
sound. All my current effects pedals (excluding Vintage Series) which 
are derived from our large systems have, as the main input stage, a 
fiendishly clever pre amp that has the same characteristics as the input 
of a tube amp (1 Megohm/20pF), a highly efficient filter to eliminate 
the possibility of radio breakthrough and a low output impedance so that 
any following pedals/ cables etc. will not impose a load on the guitar 
signal. This pre amp is fitted to all our large stage systems and has 
always met with huge approval; not only from the guitarist but also the 
PA operator who is so happy to have constant level and tone presented to 
his mixing board. I go further with large systems and provide several 
inputs, each with the isolating pre amp and a gain compensation pre amp 
so that many different guitars can be level matched into the system. In 
addition a 20 segment PPM type display provides visual indication of 
signal level in our Effects Boards and Rack Systems.

ŠPete Cornish 2003