Is the FX Loop on the Grandmeister Deluxe 40 and active or passive

Hi all,

I  am setting up various effects in the GM40's FX loop using the 4-cable method.  Up until now, I have only used the loop for a volume pedal, but I am now looking to expand beyond the effects that are in the amp.  So I need to know if the FX loop is active or passive.   If passive, I would like to add a boost so as to make it active.  But does anyone know?

Thanks for the help.

d2west

Hi D2West.  I think by the terms passive/active you most probably are getting at whether the loop is buffered or unbuffered.  If that is so then don't worry, the loop is buffered at both ends.  At least the GM36 loop is.  I should point out that, with the GM40D still being so new the schematics haven't escaped into the wild yet.  The GM36 documentation has, and that is over 90% of the way to knowing the GM40D inside.  All of the GMs are family members and share core circuitry details.

In the GM36 the loop Send is driven directly from a dedicated opamp through a 220R resistor so it is low impedance.  This very low source impedance means there is no penalty at all in using long cable runs to any of your pedals, capacitance in the cable is a non-issue.  Likewise there is no benefit in forking out for exotic solid silver cable types and the like.  The loop Return comes in to another opamp at about 33k impedance.  This should not load your pedal outputs either providing they are reasonable quality ones with no oddities in their design.

[EDIT: I should have added that the Return signal is also clipping limited (back to back zener diodes across the line) to about 7V peak for protection from spikes on the line, and maybe even over zealous pedal use. ]

And for the misdirected purists out there who rave at the inclusion of any solid state circuitry which inevitably ruins an otherwise great amp, opamps are fabulous at this sort of work and the absolute best way to achieve this sort of function.  The idea that any component that has in circuit distortion figures in the 0.01% range can "impose a quality of blandness on the signal" is the raving of a buffoon!  People who make claims like that simply do not know anything about electronics and audio.  To impose any quality on a signal at all is adding harmonic distortion to it, even taking something away is achieved by adding distortion components.  The distortion contribution of the opamps in buffering circuits like these is totally inaudible in any way when you consider you are deliberately creating distortion levels of around 20% or more as part of your tonal manipulations.  Does the contribution of a hifi setup destroy the sound that your favourite guitarist has spent many thousands of pounds creating when you listen through it?  Of course not.  And listening desks have hundreds of opamps with the signal passing through hosts of them at every stage of recording and mixing.

Anyway, hopefully that will put your mind at rest, you can simply set up your pedalboard without any worries about buffering and loading, it's all taken care of by your amp.