Effects loops: what do people use theirs for?

[Mikey R]

Hey everyone, 

I've been away for a while - far too long! I had some health issues so had to take a break from the community.

Anyway, I'm back, and I have a question: how many people find the effects loops on their amps useful, and what do they use them for?

In guitar world, the preamp gain stage comes before the loop, allowing for time based effects like reverb and phase to be added after overdrive. Guitarists often put their fuzz and distortion pedals on the input of the amp, to really push the preamp tube overdrive, and time based effects in the loop. But bass amps rarely have high gain preamps.

I'm trying to figure out if effects loops are really useful or desirable on an amp - specifically, a valve amp, where they are quite fiddly.

Cheers!

 

Edited August 23, 2018 by Mikey R

[Bill Fitzmaurice]

I use mine for effects, though the only 'effect' I have is a compressor/noise gate.

[Mikey R]

Just now, Bill Fitzmaurice said:

I use mine for effects, though the only 'effect' I have is a compressor/noise gate.

Hi Bill,

Do you notice a big difference if you put it before the input to the amp, or in the effects loop? Also, obvious question, what amp are you using? 

[Bill Fitzmaurice]

I can't put it before the input to the amp, it's line level.

[Mikey R]

42 minutes ago, Bill Fitzmaurice said:

I can't put it before the input to the amp, it's line level.

Cool, so for you it's a level and impedence thing. Gotcha!

[pete.young]

Effects loops run at line level voltage and are intended for rack and studio devices which do likewise.

Pedals mostly run at instrument level voltage and are intended to go in before the pre-amp. They may or may not work properly in an effects loop. Suck it and see.

There are exceptions: for example pre-amp pedals will usually run OK in the effects return.

The other consideration is whether you have a parallel or serial effects loop. If it's parallel, you get a blend of the clean signal and the loop signal. This might not be what you are expecting. Markbass are set up this way by default but can be changed with an internal jumper to serial. 

[Mikey R]

3 minutes ago, pete.young said:

Effects loops run at line level voltage and are intended for rack and studio devices which do likewise.

Pedals mostly run at instrument level voltage and are intended to go in before the pre-amp. They may or may not work properly in an effects loop. Suck it and see.

There are exceptions: for example pre-amp pedals will usually run OK in the effects return.

The other consideration is whether you have a parallel or serial effects loop. If it's parallel, you get a blend of the clean signal and the loop signal. This might not be what you are expecting. Markbass are set up this way by default but can be changed with an internal jumper to serial. 

Hey Pete! I forget that a lot of bass players use studio kit in their rigs. Since I've been away, are rack mounted rigs making more of a come back? I'll admit I haven't been paying attention over the last couple of years.

[Bill Fitzmaurice]

1 hour ago, Mikey R said:

Cool, so for you it's a level and impedence thing. Gotcha!

Not just that. A noise gate works best when its after the pre-amp, to gate any noise contribution from the pre-amp.

[Mikey R]

9 minutes ago, Bill Fitzmaurice said:

Not just that. A noise gate works best when its after the pre-amp, to gate any noise contribution from the pre-amp.

Hi Bill, I've been taking a look at a few schematics. The Ashdown LB30, for example, has the effects loop first thing, before the EQ stack. Granted, it's a simple amp with a passive EQ, so won't be adding much noise. However, it seems a few other amps have the loop first thing, before a more complex active EQ that will add a bit more noise.

So, a follow up thing to think about, how much noise will likely be added by a single preamp stage converting instrument level to line level? We're only talking about a gain of around 24dB.

Also, how much noise will be on a normal bass guitar signal? Sure, maybe a bit if you're running overdrive and you've been through a few other pedals too, and aren't using an isolated PSU or batteries for your pedals - if you're doing this, then your overdrive box is picking up and amplifying the noise on the ground line from all of the other boxes, particularly bad if any of them are digital. In which case, the first solution is to switch out your pedal boards PSU for one with independantly isolated outputs for each pedal, and only then if that doesn't fix it, maybe consider a noise gate / expander. (I've been putting a lot of thought into grounding recently - you can probably tell!)

There is definitely a difference between how bass players use their loop, than how guitar players do. Until I had asked this question, I didn't really appreciate that.

Thanks guys!

[Bill Fitzmaurice]

 Most of the noise is from the bass itself. A good amp won't contribute much, especially past the input stage. Whether a loop is better placed before or after EQ and tone controls is up for debate, there are valid arguments for both.

[Mikey R]

9 minutes ago, Bill Fitzmaurice said:

 Most of the noise is from the bass itself. A good amp won't contribute much, especially past the input stage. Whether a loop is better placed before or after EQ and tone controls is up for debate, there are valid arguments for both.

I do believe my old Trace had a switch to let you choose where the EQ went in the chain.

But if you did want an amp that was so configurable that it could do everything for everybody, then it would be incredibly complicated and difficult to use, as well as expensive and potentially noisy. The Fender Cyber Twin died because of this.

I keep contrasting bass amps with guitar amps here, since both bass and guitar valve amps share a common ancestor, a lot of the technology is the same. Of the common classic bass amps, only the SVT really diverges from the topology used in guitar amps. I don't remember if the original SVT allowed you to plug stuff in between the preamp chassis and the power amp chassis, though I bet plenty of people would have made this mod if they'd have needed it.
 

Edited August 23, 2018 by Mikey R

[uk_lefty]

I can't tell the difference when using the loop or not so to save on the extra cables trailing around I don't use the loop. I can't help thinking I'm doing something wrong...

[Japhet]

I've found the electrics in some venues can cause a lot of hum from my amp and on a couple of occasions running my pedal board through the effects loop has helped. As a rule I run the pedal board before the input though.

[Mikey R]

11 hours ago, Japhet said:

I've found the electrics in some venues can cause a lot of hum from my amp and on a couple of occasions running my pedal board through the effects loop has helped. As a rule I run the pedal board before the input though.

Are you using a daisy chain power supply, or one where each pedal is isolated from the rest? Do any of your pedals need a ground, or are they all ground lifted? Eliminating ground loops is something I'm reading about at the moment.

[Japhet]

9 hours ago, Mikey R said:

Are you using a daisy chain power supply, or one where each pedal is isolated from the rest? Do any of your pedals need a ground, or are they all ground lifted? Eliminating ground loops is something I'm reading about at the moment.

I use isolated supplies but some pedals share an outlet. I have one amp with a ground lift which helps, but my preferred amp has no ground lift which is a shame. It only seems to be an issue at a couple of venues though, so I generally knock off the volume on the guitar between songs. I doubt anybody else notices it anyway.