Effects Loop Position

Effects Loop Position

Postby TI4-1009 » Mon Jan 10, 2011 1:51 pm

If I'm understanding things right, the usual preferred location of an effects loop is between the preamp and the power amp, but Jerry had all his effects (OBEL) pre-preamp (between the guitar tone controls and the guitar master volume, right? The preamp went directly to the power amp. Advantages and disadvantages?
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Re: Effects Loop Position

Postby waldo041 » Mon Jan 10, 2011 2:19 pm

OBEL - advantage is that ALL the effects see a full voltage signal from the pickups and the guitars volume then can tame the overall volume. as jerry noted, all the effects are voltage sensitive, so in a traditional inline effects chain, the guitars volume has an affect on each effects character depending on a where the guitar volume ( output voltage ) is . for instance a Mutron/Qtron will not quack with the guitar at half or 3/4 guitar volume. it will at full volume. so in a jerry obel, the envelope ALWAYS see the full signal and the volume becomes a master volume out to the preamp and then out the power amp and speakers. this allows for consistent effects performance, "set and forget", and also allow for an overall consistent volume with the guitars volume control.

Preamp/Amp effects loops definately do not allow for this as the voltage will swing with the same inconsistency as a traditional inline effects chain. the advantage to this effects loop is for placement such as reverbs and delays. in this position they become a part of the overall output.

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Re: Effects Loop Position

Postby TI4-1009 » Mon Jan 10, 2011 2:43 pm

Gotcha. Thanks Waldo!
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Re: Effects Loop Position

Postby TI4-1009 » Wed Jan 12, 2011 7:09 am

Follow up question- The standard place for an effects loop is after preamp, before power amp, and I know there's a good reason for it being there as opposed to before the preamp. Jerry wanted the effects to have consistent voltage as Waldo described above, but that meant that the effects still had to go through the preamp- you can't be in two places at once (that's either Firesign Theater or the Heisenberg uncertainty principal...). Did Jerry take that as the lesser of two evils, or wasn't it really a problem at all?
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Re: Effects Loop Position

Postby strumminsix » Wed Jan 12, 2011 7:17 am

TI4-1009 wrote:Follow up question- The standard place for an effects loop is after preamp, before power amp, and I know there's a good reason for it being there as opposed to before the preamp. Jerry wanted the effects to have consistent voltage as Waldo described above, but that meant that the effects still had to go through the preamp- you can't be in two places at once (that's either Firesign Theater or the Heisenberg uncertainty principal...). Did Jerry take that as the lesser of two evils, or wasn't it really a problem at all?


I think you need to try and think through it historically...

When JG first started this his main goal was for FX to see full volume plus I can't think of any amps with an FX loop at that point.

But all along the way he could have put them between his Twin pre an Mac but didn't.

I'd hypothesize it was either no problem and preference.
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Re: Effects Loop Position

Postby SarnoMusicSolutions » Mon Jan 17, 2011 1:16 am

Not sure I'm answering this correctly, but I'll take a stab.

The output signal voltage level from the Twin preamp is VERY hot, line-level. Not a place for guitar pedals as they operate at "instrument level" and would severely distort and/or be damaged by such strong line signal voltage levels. So obviously the guitar pedal effects must live before the Twin preamp.

But another question I see is that of why didn't Jerry's guitar mounted master volume control the level between the preamp and power amp instead of the way he had it before the preamp. I see a few good reasons why.

1 - The Twin's preamp is a pretty high-impedance output and really doesn't want to drive long lengths of cable as too much cable capacitance could act as a low pass filter. The shortest connection from preamp to power amp is ideal.

2 - Sending such hot, line level signals to and from the guitar may cause cross-talk with the more sensitive, instrument level signals in the guitar.

3 - And mainly, the big one, the wiring logistics just don't allow for it. If the guitar has two cords, one a normal guitar cord, and one a mic-type cable with two inner conductors and a shield for the effects pedal send & return functions, there's really no good way to use the OBEL bypass switch that handles turning on and off the pedal effects while also sending the signal thru the preamp. Effectively, you would turn off or bypass the Twin preamp when you bypassed your effects pedals. The wiring scheme simply doesn't allow for it. The OBEL loop is instrument level only, just a pedal loop. To have an on-board master volume control that was patched between the preamp and power amp would take a whole other new 3-conductor cord, and at that point things are just getting messy and unnecessary. Basically, you can't have the pedal bypass function and master volume control on the guitar AND have that master volume control controlling the volume AFTER the Twin preamp without introducing yet another send/return cable to the guitar.

I can't see any advantage of a scheme other than Jerry's setup for what he wanted to best achieve. It's a smart and perfectly functional system evolved and developed by some of the brightest folks live audio ever knew.

Like Waldo said, the line level path after the preamp is the place for rack mounted line level devices like reverbs and delays, and then directly to the powr amp. What happens before the preamp is all instrument level and is the arena for guitar pedals and bypass loops and post effects pedal volume control.


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Re: Effects Loop Position

Postby strummingturtle » Wed Jan 26, 2011 8:41 am

just got my first obel guitar was wandering if my volume pedal should be out of the effects chain and between guitar and preamp? Right now It is at the end of my effects chain and I just use it for volume control. I do not use it for the violin type effects.
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Re: Effects Loop Position

Postby Pete B. » Wed Jan 26, 2011 9:42 am

strummingturtle wrote:just got my first obel guitar was wandering if my volume pedal should be out of the effects chain and between guitar and preamp? Right now It is at the end of my effects chain and I just use it for volume control. I do not use it for the violin type effects.
Thanks,
Rob.


That how I do it.
I use a Waldo oBEL UGB pedal (o=Outboard) and run V-ped as master-volume between guit and preamp.
This allows me to combine any instrument I own with a Jerry-esque style rig.
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Re: Effects Loop Position

Postby bdhact1 » Wed Jan 26, 2011 1:53 pm

If it's onboard, than between the guitar and amp.
I have to do that because of the in ear monitor and PA setup. Our board operator has to constantly adjust if I use my volume knob because my amp is backstage and mic'ed; He has to maintain a volume balance for the house.
I end up using my volume pedal mainly for swells. I adjust the guitar volume first, than keep the pedal all the way up for regular playing and keep it completely down between numbers.
Still, everybody's situation is different.
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