Other Amps

Effects Loop Question


Are all effects loops the same? Here's why I ask. Until yesterday when my Crate Powerblock went wonky, I had what for me was a serviceable setup. The interface has stereo left and right outputs and the Crate's effects loop is labeled both send/return AND Line-In right and left. The wording in the manual basically states these inputs are dual purpose for both running an effects loop OR to run stereo cables. A lot of words but the basic question, is the Powerblock's effects loop inputs unique vs standard connections or do all effects loops basically perform the same tasks?


All effects loops are not the same. The core functionality of outputting a post-preamp signal for use by an effect, then returning the output of that effect to the input of the power amp is morless built into the terminology.

But the details of the manufacturer's intention for it, and what the circuit "expects" can differ - both in the details of the loop's placement in the amp's architecture (and the internal switching that happens when you plug something into it), and in the electrical specs.

You don't say exactly what you were using the PowerBlock's loop/line-ins for, but from the context "run stereo cables," I'm guessing you were using the "line in" option to access the power amp section without the preamp/tone stack.

I have a PowerBlock and have almost always used it that way - ie, as a stereo power amp fed by the line outs of a modeler/profiler.

If that's what you're looking for after your PowerBlock died, you'll need something stereo. While it's a reasonably safe bet that you can use the effect Return of any guitar amp with a loop as a kind of line input (see caveats to follow), most guitar amps aren't stereo.

Meaning it would take two such unstereo amps (and the closer they match in power and spec, the better) with effects loops to replace what the PowerBlock was doing. I've had good luck using the effect returns of my nearly-matching Peavey Classic 30s in that way.

The results are less happy (or at least take more fiddling) if the two amps are not virtually identical (at least in the way in which their effects loop circuits are implemented). Frinstance, I get access to the power amp of the Tech21 Trademark 60 by plugging into the effects return and enabling the loop on the footswitch - and (or but, depending on what you expect), the volume control doesn't work - that is, the power amp is wide open and is controlled from whatever I'm plugging into it.

The effect return on the Quilter Interblock 45, on der other hand, is placed elsewhere in the amp's internal circuit, and both the gain and volume controls affect its performance - which makes it not so wonderful as a pure power amp.

Those are just two examples of the way in which effect loops can be configured by the builders. The impedance each jack (send/return) "expects" of the gear plugged into them, as well as the levels at which they run (+4/-10) also varies across different products. Also...some modeling gear has mono sends and stereo returns to accommodate stereo effects; others have stereo sends as well.

All of which means you gotta be specific about what you're trying to do with the loops, maybe down to knowing the input and output impedance and level of your devices, then find the manufacturer's spec for the loop on the device you're considering. Detailed tech specs - with numbers most of us habitually glaze over when we see, and thereafter ignore - are usually available in the manual and/or online. Then you see if all your stuff is compatible.

The other approach is to plug stuff together and see what happens. Assuming you don't plug a powered speaker output into either a loop send or return, you probably can't blow anything up. Things will either work as you imagine, or it will be much quieter and/or white-noisier than you imagined (and possibly unpleasantly distorted as well)...or it will be stupid loud and again, distorted. (Distortion being symptom of level mismatches between devices.)

You could just shop for another used PowerBlock.


No....there's no standard criteria. Originally, they were for plugging studio effects into a guitar amp, so they had to send a low impedance, +4 line level signal the the device, and the return had to bring that kind of output back to whatever level the amp required at that point. Now people use them more for guitar FX or for other purposes, so there's no way to guess what the user's requirments will be. Most companies just do it the cheapest way possible.


And I thought I used a lotta words to get to my point! I'll make this short. I use Amplitube 4 software as a standalone app, run it through a Focusrite Solo 3rd Gen to the Powerblock. And picking up another Powerblock doesn't come easy in Europe.


Btw, Tim, I always value your in depth contributions even on such mundane topics as mine.


Btw, Tim, I always value your in depth contributions even on such mundane topics as mine.


Look for a pair of small FRFR (Full Range Flat Response) powered speakers, which depend on whatever you're plugging in to do all the preamplification and coloration we get from guitar amps and cabls. You'll be using cab sims and/or IRs (impulse response files) from Amplitube to get there.

Or, as presumably you have speakers you've been using with the PowerBlock, any stereo power amp of the size you need will do the job.

But I find almost 30 PowerBlocks from 129.00 up Reverb right now, and at least 16 of them will ship to the UK. (I didn't know where you are in Europe, but since it's all connected, I'd think anyone shipping to the UK would ship anywhere else there.)

As for in-depth blabber, it's just that sometimes seemingly trivial things require a good bit of detail to get to the hidden complexities. In technical matters, general questions get reflexive general answers that may not get you where you want to go - or lead you astray by making too many assumptions. I do try to be responsive to the question, uncover some of the context around it (which clarifies both the question and the scope of the answer), and point out what I think I might know as well as the limits to my knowledge. That way the questioner understands if he has to do more legwork, and has some idea where to go for it.

Also, I like making words. Especially if doing so is voluntary rather than an assignment or responsibility.

Anyway...I'll be curious to know how you resolve your Cratelessness.


I have a pair of FRFRs made by M-Audio, and while they were not overly expensive, the sound they produce is light years away from any kind of "computer speakers" I've tried, cheap or expensive. And don't get me started on headphones, 99% of which seem to be specifically designed for ear-splitting, thumping, hip-hop-type bass and not much else!

Over the years, I've learned how to rough mix with a decent set of stereo-store purchased headphones (AKG at present) that promise a "flat" response, then I hook up the speakers and do what's needed to get the final adjustments done to my ears satisfaction.

But when I had a bigger "little" studio operating, I actually had a board made up that allowed me to switch from desktop stereo speakers, like some have in their bedrooms, up through three or four levels to a pair of EV 12" stereo speakers with built-in 3-way crossovers. I could thus hear the mix through multiple "projections" and although it was a lot more work, it made for better-sounding finished masters, or so I thought.

But nowadays, I rough mix to the AKGs, mix the result on the flat response speakers, tweaking the sound through them and clients seem to be okay with it.


I was going to keep this to myself but I won't because:

A. Tim put a lot of thought into this thread and....

B. I've always been the type to own up to my own stupidity!

Here's how all this started. A couple of days ago the breaker kept flipping when I turned on the power strip. Four different electronics were on that strip Through the process of elimination I determined it was the Powerblock causing the problem therefore deeming the unit muerto. But there was one teeny-tiny detail I was ignoring (and yes I did test it on another power strip). You see, I live in Spain but bought the Powerblock in the States. A plug adapter is required. It came to me while laying in bed about 1 a.m. Got up this morning, switched out the plug adapter, fired the amp up, slowly started plugging in other electronics and voila! no breaker flipping. I know there's a moral to this story but obviously I'm not bright enough to come up with one.

p.s. Thanks, Pat Quilter. Yeah, I bugged him too.


Ha! That's a great ending, doesn't bother me at all.

And it's pretty astute troubleshooting on your part. You started with the basics (ie, with the electrons feeding the device) and moved onward through the signal chain from there. That you found the problem very near the beginning of the chain is gratifying - but also fits a pattern.

When our technical systems get increasingly sophisticated and complex, we tend to think failures will be of an exotic nature. But they're often found by attending to the basics - and that's always the place to start.

In this case, all my extended traversal of effects loop topology was moot...because I failed to ask an even more basic question: what's wrong with the Powerblock. I didn't ask about conditions of its failure, symptoms, nothing. You said "went wonky" and I took that as a given, following you into a thicket of complication that ended up being totally irrelevant.

Pretty funny!

I don't know how "stupid" it is that you didn't think of the plug adapter sooner. Since I live in the US, I never have to use them, and don't know how prone they are to failure. If your experience has been that they are failure-prone...then, yeah, maybe it should have occurred to you earlier. But I wouldn't have thought right off the bat to look there. I think it was actually pretty clever of you to remember it.

Rock on.

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