Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
previous: Ray Ivers Win a Free Amp! -- 5/25/2000 9:34 PM view thread

Free FX Loop, Ray :)

5/26/2000 12:29 AM
Gil Ayan
Free FX Loop, Ray :)
"I also think that in some amps there exist transition points between low and hi-impedance circuit nodes where a loop could be inserted just by clipping a wire and installing two jacks. I don't really think this would affect the sound at all, do you, Gil? "
:) Interestingly enough, a great many people experience problems with their amps at that particular point... because the switch on the jack gets dirty. Ha ha, but yes, that's exactly what Mr. D does. There is nowhere else to put the "loop" though, since his amps are: stage, tone stack + volume, stage + master, into the P.I.  
" I don't know if such a place exists in the amp mentioned, so I guess I don't get the free amp, although I can supply my address if needed. >:~)"
Nice try, Ray. That hardly qualifies as a buffered FX loop though... Ha ha, I guess you will keep me honest and on my toes, buddy!  
"I personally believe that no overdrive should occur after an effects loop, but that's just me."
I agree, however, when you interface a signal interrupt "loop" like that with a buffered unit, you get a few options. The "send" from the amp comes after the master volume, so you can make that as hot as you'd like (by turning up the master). That feeds a cathode follower on the other unit, so you can clip the CF or not, up to you. From the CF, you send a signal to the FX rack, and you can make that return (provided your rack has an output signal level) as hot as you want. That feeds into a common cathode stage, so you get a chance to clip a common cathode stage (another flavor of overdrive). Finally, the output of that stage feeds into the PI... and sure, turn the thing up enough and you will be clipping the PI as well as the power tubes.  
With this arrangement, is it possible to get a different "rainbow" of tones depending upon how hard you want to hit the various point in the signal path (of course, you probably DON'T want to clip your digital FX ... ouch!). It is hard to find your favorite sweet spot, in a way, but you get that option. In amps with built in FX loops, most of the time certain signal levels are "fixed" so the designer chooses the texture of the tone for you. That may be a good or a bad thing. :)  
PS: And needless to say, the reason that "passive signal interrupt" loop doesn't work well at all is: the signal coming off the master volume pot needs lo be kept low so as to not overdrive the FX boxes. In a way that's good, because dialing the master lower will lower the output impedance of the preamp, and the outboard gear will not load the preamp so much. However, if your FX box doesn't hve enough gain to make up for that loss in signal level, then your amp may not be loud enough to be used at a gig... As per Dumble's spec sheet, the level at the "signal access" point is 2.5 VRMS... so if your FX box can bring up the line level signal to that point, you can work it.