Author Topic: question about loop lengths  (Read 1065 times)

iainpunk

Re: question about loop lengths
« Reply #20 on: March 14, 2021, 07:40:22 PM »
Know nothing about these, do they work  ?

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.

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Bardkin

Re: question about loop lengths
« Reply #21 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!

FiveseveN

Re: question about loop lengths
« Reply #22 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.
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idy

Re: question about loop lengths
« Reply #23 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.

idy

Re: question about loop lengths
« Reply #24 on: March 15, 2021, 04:50:29 PM »
And good grief, no one has said

Welcome to the Forum!

PRR

Re: question about loop lengths
« Reply #25 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.
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idy

Re: question about loop lengths
« Reply #26 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.


anotherjim

Re: question about loop lengths
« Reply #27 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.


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Ben N

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Re: question about loop lengths
« Reply #28 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.

anotherjim

Re: question about loop lengths
« Reply #29 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.
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Rob Strand

Re: question about loop lengths
« Reply #30 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.
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PRR

Re: question about loop lengths
« Reply #31 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.)
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Rob Strand

Re: question about loop lengths
« Reply #32 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.
« Last Edit: March 17, 2021, 06:21:37 AM by Rob Strand »
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anotherjim

Re: question about loop lengths
« Reply #33 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?
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Rob Strand

Re: question about loop lengths
« Reply #34 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.)
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