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DIY Stompboxes => Building your own stompbox => Topic started by: Bardkin on March 12, 2021, 09:40:30 AM

Title: question about loop lengths
Post by: Bardkin on March 12, 2021, 09:40:30 AM
So I have an external loop with some effects. Problem is the loop length is too long.- my snake is 20 ft. This means that to use the external effects I have to walk over to my amp and switch the pedals on and off by hand.

What I'd like to do is to modify them so that the on/off switches are on the pedal board. Is that too long of a loop length for the pedal to power up? What is the best way to handle this?

Thanks!
Title: Re: question about loop lengths
Post by: BJM on March 12, 2021, 10:07:07 AM
Hi,

I don't really understand the question but something like this?

http://www.geofex.com/article_folders/fxswitchr/fxswitchr.htm

Picture nr. 10, remote control for the effects loop switcher. I suppose you can keep the effects close to your amp and put the remote where you want it.
Title: Re: question about loop lengths
Post by: Bardkin on March 12, 2021, 11:00:13 AM
no.
The issue is that I can not have my external effects loop 20 ft away from my amplifier. The sound is being swallowed by capacitance. (It is barely audible at all). Remember, this is an external fx loop- the audio signal would have to travel 20 ft to the pedals, then another 20 ft back to the amp. That length is too long.

By placing these pedals closer to the amp I get a crisp clear sound. But I am not at my amp when playing. I am 20 ft away and can not get my foot that far no matter how much I stretch. and it is not at all convenient to walk back and forth all the time.

Now, say I take the push button on / off switch out of the case. I extend the 2 wires 20 ft. (The audio signal doesn't travel those wires so it is not changed.)
I wire the on off switches to work on my pedal board, NOT the actual pedal all the way back at the amplifier.

Now the pedals can be at the amplifier, and I can turn them on and off at my pedal board, at 20 ft away.

The question is weather or not the actual on / off switch is too far away for the pedals to work properly.
Title: Re: question about loop lengths
Post by: garcho on March 12, 2021, 11:11:15 AM
No offense, but I think you're coming at this all wrong. You need a buffer to drive your cables properly, and perhaps you need new cables. If "The sound is being swallowed by capacitance. It is barely audible at all", then something is seriously wrong with your rig. Yes, 40' of cable can attenuate high end frequencies, but "barely audible"? Perhaps you're exaggerating?
Title: Re: question about loop lengths
Post by: Mark Hammer on March 12, 2021, 12:01:23 PM
Jack Orman has thought deeply about this and provided an excellent solution:  http://www.muzique.com/lab/superbuff.htm

Keep in mind that cables behave more or less as lowpass filters.  There is a series resistance, and a capacitance between hot-lead and shield.  The capacitor in that configuration acts like a hall monitor, saying "Not so fast there, buddy!"  But, in the same way that being a foot taller and 50lbs heavier than the hall monitor will get you waved on through, pushing more current through the cable overcomes the cable capacitance and filtering effects thereof.

Jack parallels 4 op-amps to deliver more current to the buffer output.  Perfect for feeding long cables from the stage to the soundman at the back of the hall, or via 20ft cables to an amp behind you.
Title: Re: question about loop lengths
Post by: idy on March 12, 2021, 12:53:18 PM
To address the original (clarified) question: no, there is no problem with 20 ft of cable  and remote switching. Relays or "boss style FET momentary switching" would be fine with a long distance "remote switching" system. You would add a "control" jack to the pedals in question and then run cable(s) to a box with momentary contact foot switches.

If the boxes in question are "boss style" switching then it really can be as easy as wiring a jack in parallel to the existing switch.
Title: Re: question about loop lengths
Post by: ElectricDruid on March 12, 2021, 01:09:53 PM
Now, say I take the push button on / off switch out of the case. I extend the 2 wires 20 ft. (The audio signal doesn't travel those wires so it is not changed.)
I wire the on off switches to work on my pedal board, NOT the actual pedal all the way back at the amplifier.

Now the pedals can be at the amplifier, and I can turn them on and off at my pedal board, at 20 ft away.

The question is weather or not the actual on / off switch is too far away for the pedals to work properly.

This is a good solution. It's generally much better to ship control signals all over the place than audio. After all, they're mostly digital, so even if they got a bit degraded, you could run them through a Schmitt trigger at the far end and you'd have nice sharp on/off signals again. Not that I'm suggesting such a thing will be necessary, because I don't think it will.

That said, I agree with other posters that it sounds like the problems you're having currently are out of proportion to the cable length you're using. With a decent buffer to drive them and some decent cables, 20 feet isn't that far. Think about the front-of-house desk at an arena concert! Much further than 20 feet away from the stage! Nowadays, that's all digital of course, but it wasn't always.
Title: Re: question about loop lengths
Post by: BJM on March 12, 2021, 01:42:44 PM
no.
The issue is that I can not have my external effects loop 20 ft away from my amplifier.

OK, I understood the question but you're looking for another solution for the four-cable method :). Personally I wouldn't like to open up pedals to take out footswitches (if they're true bypass to begin with....) but that's because I'm not very good at this and would probably end up with some pedals no longer working...... So I would go for some remote switchin system as on the Geofex website. I suppose with a midi-cable you could wire op to five switches, which should be more than enough. Some time ago I put together a simple parallel looper, two loops with an extra pedal to ground the inputs. Only used at home with three meter cable but it  did work to turn the effects on/off remotely.
Title: Re: question about loop lengths
Post by: FiveseveN on March 12, 2021, 02:17:07 PM
with a midi-cable you could wire op to five switches
While you're at it, why not use MIDI?

Like others have mentioned, 20 ft should not be an issue, even with the 4-cable method. If it is, something is either broken or all of your effects are true bypass and/or your amp's loop is unbuffered and you're getting the worst-case scenario. Even then, a buffer or two would be a simple and cheap solution.
Setting all that aside, there are many players who have found themselves in your situation. Nowadays you can find commercial units for all needs and budgets (e.g. from GigRig (https://www.thegigrig.com/remote-loopy2) to RJM (https://musicplayers.com/2011/12/rjm-rack-gizmo-audio-loop-function-switcher/)). Or you can make one yourself.

The question is weather or not the actual on / off switch is too far away for the pedals to work properly.
But with true bypass pedals the audio signal does have to travel to the switch and back. That's why people mentioned relays. By "the 2 wires" from the pushbutton, are we to understand that the effect(s) in question use BOSS-style bypass? In that case yes, you can probably just extend it a hundred feet with no issues. But how many effects are there? Are you removing 2 wires to add a dozen more? And if they have buffered bypass, why the signal loss in the first place?!
So please check your cables first. Then tell us the details of your situation (if you only need to switch one loop, use your amp's loop bypass if it has one). Then what you're willing and able to do (if you'd rather gut your pedals and put them in an integrated box or you're looking for something off-the-shelf).
Title: Re: question about loop lengths
Post by: akmenpi on March 12, 2021, 04:41:42 PM
It's barely audible because you're 20 ft away!

All jokes aside, I think you should do a little more investigating before tearing into your pedals.

What does it sound like without FX loop?
What does the FX loop sound like with a jumper from out to in?
What does it sound like with different cables?
Does a buffer help?

Title: Re: question about loop lengths
Post by: antonis on March 12, 2021, 05:09:29 PM
The issue is that I can not have my external effects loop 20 ft away from my amplifier. The sound is being swallowed by capacitance.

That leads to outrageously high cable dielectric constant value..

(https://i.imgur.com/Daj3v15.png)
Title: Re: question about loop lengths
Post by: ElectricDruid on March 12, 2021, 06:38:05 PM
TLDR: The cable itself can't possibly be that bad. :icon_biggrin:
Title: Re: question about loop lengths
Post by: iainpunk on March 12, 2021, 06:51:11 PM
TLDR: The cable itself can't possibly be that bad. :icon_biggrin:
yes it can be, if there are fractures in the strands of wire inside, the resistance increases, and the filtering would be worse.
Title: Re: question about loop lengths
Post by: Rob Strand on March 13, 2021, 03:24:22 AM
No offense, but I think you're coming at this all wrong. You need a buffer to drive your cables properly, and perhaps you need new cables. If "The sound is being swallowed by capacitance. It is barely audible at all", then something is seriously wrong with your rig. Yes, 40' of cable can attenuate high end frequencies, but "barely audible"? Perhaps you're exaggerating?

Agreed.    Threre's a problem and it's not being fixed.  It's being stepped around with a lot of fancy boots.

What's the amp?   Find a schematic and checkout the effect loop circuit.

If it's a tube amp and the effects loop is being fed off the plate with a 100k resistor that's just asking for it.  The effect out needs a buffer.

If you have 100pF/m (30pF/ft)  cable and the entire run is 40'  then that's 40'*30pF/ft = 1.2nF.  A 100k plate resistor is 38k output impedance (https://www.aikenamps.com/index.php/designing-common-cathode-triode-amplifiers).   The HF cut-off is 1/(2*pi*38k*1.2n) = 3.5kHz  which is noticeable.   If the cable has a lot of capacitance then you could find that's a lot worse.
Title: Re: question about loop lengths
Post by: anotherjim on March 13, 2021, 04:41:00 AM
Some amp FX returns are not high Z instrument inputs at 1M, they may be medium Z like 100k. The FX send may not be a low source impedance either. The send could be tapped off a class A amp stage which could be quite high impedance and definitely will be dulled by the capacitance of a long cable.

Really need to know the amp model.

Some FX cannot drive low Z inputs - you need a buffer or a buffered bypass pedal such as a Boss driving the cable back to the amp.
At the amp, I would suggest another buffer at the FX send if it turns out that the amp output doesn't have a buffer/driver to that jack.

For testing purposes, any buffered pedal can be used to act as the buffer with its effect bypassed.

If the 20' cables work ok for normal guitar to amp playing and don't crackle when handled, they are probably good.
Title: Re: question about loop lengths
Post by: Bardkin on March 14, 2021, 01:01:45 PM
Thanks for all the input, I appreciate it. So to answer a couple questions-

Amp- Is an old digitech GSP2101 (circa mid '90s. It has a send and two returns (L&R)  I do have the schems and am looking at them now.

When the pedals are hooked up close to the rig, they work just fine.  When they are on the pedal board I can hardly hear them at all.

The pedals are boss style with true bypass. Two delay/reverb and a stereo analog chorus.

I had asked some people about using a buffer but wasn't all that enthusiastic about the answers I was getting. They are kind of expensive just to test with an that's why I thought about moving the switches in the first place.

Replies:
As for sound man /concert hall settings- Your foot pedals really shouldn't have any connection what so ever with the mixer itself. You want to mike amplifiers, even if you can line out to the board. But either way your pedal board goes to your amp, not the mixing board.  Big name acts have the loops at the amplifiers and there is usually a tech that will switch them for you. Alas, I haven't ever been big enough to have a guitar tech that could do that for me.

My cables are fine, I have tried other cables with the same results and have tested line voltage and resistance on them, so it isn't the cables.

My thoughts have been geared more towards possibly removing the guts of the pedals, and getting them all inside an old rack mount line mixer with line in and 2 outs for the stereo output. Ive always hated having to stoop down to change rates and times. be nice to have them at eye level on a rack mount unit.

(And before anyone starts going off about that please note that I have 2 15 watt tube power amps that I built myself to provide a left and right output. (6v6 setup from the old 1960's Gibson GA 30 stereo amp. Plenty of sound for practice and can be miked for any size stage. The digitech is my pre-amp, and I can model just about any type of amp sound as I have control over both tubes and there is a 7 band EQ in the analog section of the pre-amp.


Anyhow, Thanks again for all the help


Title: Re: question about loop lengths
Post by: FiveseveN on March 14, 2021, 03:38:21 PM
The pedals are boss style with true bypass.

No. "BOSS-style" means buffered bypass with JFET switching, that is not true bypass.
Why is the identity of these pedals such a secret?  :icon_biggrin:

Quote
[buffers] are kind of expensive just to test with
For commercial units sky's (https://www.effectrode.com/products/effects-pedals/glass-a-triode-buffer/) the (https://www.andertons.co.uk/guitar-dept/guitar-pedals/buffer-pedals/29-pedals-euna-elite-unity-amplifier-pedal) limit (http://redironamps.com/buffer/), but for DIY they're some of the simplest and cheapest things you can make: http://www.muzique.com/lab/buffers.htm
Title: Re: question about loop lengths
Post by: PRR on March 14, 2021, 04:55:13 PM
The Return(s) from pedalboard to Digitech: what pedals drive it/them?
Title: Re: question about loop lengths
Post by: Phend on March 14, 2021, 05:44:06 PM
Not knowing,  how about wireless.
Title: Re: question about loop lengths
Post by: Phend on March 14, 2021, 05:48:15 PM
Know nothing about these, do they work  ?
(https://i.postimg.cc/JsJSqDLR/61-KYDTSLXr-L-AC-SX679.jpg) (https://postimg.cc/JsJSqDLR)
Title: Re: question about loop lengths
Post by: iainpunk on March 14, 2021, 07:40:22 PM
Know nothing about these, do they work  ?
(https://i.postimg.cc/JsJSqDLR/61-KYDTSLXr-L-AC-SX679.jpg) (https://postimg.cc/JsJSqDLR)
i find the signals are prone to entanglement, and they stop working if someone steps on the signal... ow, wait, that's wires.
those cheap wireless are great if you don't use low input impedance fuzzes.

cheers
Title: Re: question about loop lengths
Post by: Bardkin on March 15, 2021, 02:21:59 PM
FiveseveN:
My Loop:
Send goes to patch bay and it is split into two signal paths. Each path can have up to 3 outputs. On left side I have a single output delay and a stereo chorus pedal. On  the right side, a single output delay (same model) pedal and a stereo flanger pedal.

All 6 outputs go to a line mixer and get combined back into a Left (mono) and a right (stereo) signal path back to the returns on the pre-amp. This is done by placing the left outs from the two modulation pedals into the right bank of the mixer. the other 4 outs, which are mono, get plugged into the left side.

This configuration allows me to have two independent delay states in addition to the ones available on the 2101 giving me more flexibility on my sound.  It also doesn't mess with either of the modulation pedals.

Now, Why do you think its some kind of secret? It really doesn't matter what the pedals are, the results are the same.

So, if I can turn those puppies on and off at the pedal board rather than have to walk to the amp and take a chance on tripping over cables and falling into the drummer or keyboardist....


Sorry, couldn't remember who brought it up- I have several wireless units (Sennheiser Half racks)  and I did in fact try to do a wireless from guitar to pedal board, then pedal board to rack unit and the results were not all that pleasant. If you have minimal things going on such as just a distortion box or just a wha pedal then it is ok. But as you add more stuff it gets a a little funky. I found just running guitar to pedal board was the easiest, but then got tired of batteries and went back to cords.

As for the pictured wireless units, I have a few sets of some that are similar, but look more like a thumb drive with a swivel TRS jack. They actually work pretty well, I use them on all my acoustic guitars since they dont plug into the pedal board any way. And they are USB chargeable!
Title: Re: question about loop lengths
Post by: FiveseveN on March 15, 2021, 04:19:59 PM
It really doesn't matter what the pedals are, the results are the same.
It matters whether they are buffered or not, because your initial question was "Is that too long of a loop length for the pedal to power up?", right?
The ability of a pedal to drive long cables is entirely dependent on its output impedance. Additionally, some pedals are easier to modify for remote bypass control.
But now we find out that the pedals couldn't be to blame anyway because the loop return is actually driven by "a line mixer"...
These are the kind of details that matter.
I'll settle for a blurry picture, it would at least make the guesswork more fun :D

So getting back to Is that too long of a loop length for the pedal to power up?, what one could say with the information at hand is that the GSP2101 should be able to drive the 20' or 40' just fine. If the cables are good then the issue must be between (and including) the patch bay and the anonymous line mixer.
Title: Re: question about loop lengths
Post by: idy on March 15, 2021, 04:49:12 PM
There seems to be some "talking past" one another. Often a new participant shows up with a lifetime of knowledge....about guitar, music, bandcraft, using their gear....  But not so clear on the meaning of words that have specific meanings to Electrical Engineers and the people who try to understand them.

So the question "is this too long.. for the pedal to power up..." is a little confusing. Did you mean "is the cable impedance something which the pedal is incapable of driving" ("powering"), or "can I add a forty foot control cable to remote switch the pedal ("powering it up")?

Since the poster is willing to consider putting all the guts of their delay/modulation setup in a rack, the mod of just adding a remote foot switch for these pedals could be very easy and practical. So that is one reason everyone keeps asking what exact pedals, what exact models are you talking about. 

The early mention of "boss/true bypass" made all the regulars jump up and down...these are "opposites." Like saying your new pet is "typical cat/%^&*atoo." Or my new vehicle is a "standard pickup truck/sedan." Or my new axe is a "regular Strat/Les Paul."

And then there is the counter point to the original question which has to do with..troubleshooting...every....step....of what is in.... that loop. Cables, mixers(!), individual pedals....It looks like we're getting there!

And amps/preamps have their own individual needs for their effect loops. It is not uncommon to have to drop the level coming out (from some kind of "line level" to "instrument level") and then boost it back up again (to "line") before reinserting.
Title: Re: question about loop lengths
Post by: idy on March 15, 2021, 04:50:29 PM
And good grief, no one has said

Welcome to the Forum!
Title: Re: question about loop lengths
Post by: PRR on March 15, 2021, 09:22:58 PM
> Since the poster is willing to consider putting all the guts of their delay/modulation setup in a rack, the mod of just adding a remote foot switch for these pedals could be very easy and practical.

"Foot switch" usually switches audio directly. So we have not saved any length.

Yes, we could replace with a 3P2T *relay* and a remote switch. And if that was the actual situation, it might be a good plan.

But now we have a many-input multiple output mixer, somewhere.
Title: Re: question about loop lengths
Post by: idy on March 15, 2021, 10:38:59 PM
Remote single pole momentary switches to trigger "boss style" FET switching. 4 conductors plus ground, or maybe a "snake" of four instrument cables or some lighter zipcord or something. No signal on the snake, just a path to ground for the flip flops.

But yes the mixer is still a mystery.

Title: Re: question about loop lengths
Post by: anotherjim on March 16, 2021, 05:19:56 AM
I found the Digitech manuals at Electrotanya.
https://elektrotanya.com/digitech_gsp2101.zip/download.html#dl
It's a .zip so I can't directly show an image.
The specifications in the user manual don't list the FX send & return. Guitar input impedance is given as 470k and the main outputs are 50ohm drivers.
Looking at the schematics, the FX returns have 100k input impedance.
The FX sends are 50ohm like the main outputs.


Title: Re: question about loop lengths
Post by: Ben N on March 16, 2021, 07:23:29 AM
I didn't quite understand the recitation of the signal chain, but if the patch bay & splitter at the input to the fx board are passive & unbuffered, and the (2? 4?) paralleled fx don't have a very high Z-in, that might be a problem spot, too. Say four boss-style fx with input impedances of 500k each in parallel -- that leaves you with 125k total Z-in.
Title: Re: question about loop lengths
Post by: anotherjim on March 16, 2021, 11:29:49 AM
By the way, most, if not all Behringer pedals are buffered bypass like the Boss types. I mention that just in case someone is ashamed of the "B" word.


Low Z loading can mean less bass and volume.
Dull sound on the other hand is as said, cable capacitance on a source with too high an output impedance.

Another common issue with FX loops is caused by phase cancellation. Anything in an FX send-return loop can't have any dry sound or invert signal polarity. So the wet/dry mix in the loop FX should be set to 100% wet. If the FX doesn't give an option to cut the dry sound, you can't use it in a send/return loop without special consideration.
Not only that, but you should not bypass a loop effect either, since it then outputs 100% dry.
The problem is that the device already has a dry signal path from input to output, the FX loop path is in parallel to the dry path.
But if it works ok with short cables, it ain't phase cancellation.
Title: Re: question about loop lengths
Post by: Rob Strand on March 16, 2021, 06:54:59 PM
Quote
Looking at the schematics, the FX returns have 100k input impedance.
The FX sends are 50ohm like the main outputs.
Perhaps the output buffers are damaged/faulty.
Title: Re: question about loop lengths
Post by: PRR on March 17, 2021, 01:10:43 AM
> Perhaps the output buffers are damaged/faulty.

But it works on short cables?? (The out buffers are not complicated enough for a fussy part-failure.)
Title: Re: question about loop lengths
Post by: Rob Strand on March 17, 2021, 01:57:39 AM
Quote
But it works on short cables?? (The out buffers are not complicated enough for a fussy part-failure.)
Maybe the output stage is partially fried and looks high impedance.    With ESD or people plugging speaker cables into the jack who knows what will happen.

The point is we don't know the buffer is working and assuming the buffer is working is asking for trouble.   Clearly something is wrong.  If the buffer was working we wouldn't expect to see the behaviour in the first place.    If it was mine I would wire a short cable from effect-out to effect-in and see what type of load I could shunt to ground before I lose signal.  It's an easy test and if you got down to 1k you would have some confidence the output buffer is working find and then move onto something else.

Placing a buffer pedal at the effects out is a way of replacing the buffer in the unit.     That's already been suggested.

Has the OP tried different cables?

A more remote possibility is the output buffers are oscillating with the capacitive load of the cable.   It's fair enough making the output buffers low impedance but it's not much good if the output resistors are so low the buffers oscillate with a capacitive load.    Using a Boss pedal to at the effect out should answer than.  I have NOT seen a Boss pedal buffer oscillate.

Some basic debugging will certainly help narrow down the problem.
Title: Re: question about loop lengths
Post by: anotherjim on March 17, 2021, 04:45:52 AM
Digitech FX send is from an LF353 with 50pf neg feedback. TRS jack impedance balanced with 51R. Is this good enough to guarantee stability with the long cable?
Title: Re: question about loop lengths
Post by: Rob Strand on March 17, 2021, 06:26:53 AM
Quote
Digitech FX send is from an LF353 with 50pf neg feedback. TRS jack impedance balanced with 51R. Is this good enough to guarantee stability with the long cable?
Funnily enough that depends on the LF353 output impedance.  Without modelling it on spice it looks like the phase margin of the LF353 should handle it.  (That's assuming the LF353 output stage is good.)