Inserting PC in your guitar signal chain - do I need a DI box?

[Laimon]

Hi everyone,

lately I was trying to replace my looper (EHX 2880) with a software-based looper, namely Ableton.
My signal would roughly be as follows:

guitar -> preamp -> true bypass midi looper (send) -> audio interface in -> ableton -> audio interface out -> true bypass midi looper (return) -> power amp -> cabinet

I tried this, and it works ok. The only problem is that returning from the audio interface out introduces a constant background buzz noise.
I have experienced something similar some time ago while trying to reamp, and I thought that a DI box might solve it...but in fact, I also remembered what really solved it was the ground loop button. The problem seems to be all the more a ground loop problem, because the buzz is there even if there's a cable from my audio interface out to the true bypass looper, even if the loop itself is bypassed.

So the first question is: how do I solve this problem? What do you guys think?

Off to the second problem. I tried using my current sound card, an E-MU 1212m PCIe, which is mounted via PCIe to my computer's motherboard. However, I plan on buying an external one for simplicity of connections. Do you think that would solve the buzzing problem (if it actually is a ground loop problem)?
Thanks a lot,

Simone

PS: I was actually looking at a Native Komplete 6 audio interface, do you see any problem with that interface?

 

[mjbphotos]

Maybe the buzz is because of mismatched impedances? The return from the interface is most likely a line signal, what's the loop box made for?

 

[Laimon]

Maybe the buzz is because of mismatched impedances? The return from the interface is most likely a line signal, what's the loop box made for?

Well, as far as I can tell most true bypass looper don't have a designated impedance, they are just routing signal. It might be however that the poweramp expects a different impedance.

 

[ecc83]

Hi Simone,
Do not let anyone divert you from buying the KA6! The setup you describe needs a very low latency interface which of course a PCI or PCIe interface will generally be (except S of a Bs!) . The KA6 will give you the lowest latency you can get from an external interface unless you pay for RME kit.

The buzz I would put money on being a ground loop and the easiest solution is a 1:1 audio transformer box twixt interface out put and looper* tho' it might work in a different point in the signal chain, feed to power amp e.g.
The ART Cleanbox 2 is a well respected device but should you be UK based do investigate Orchard Electronics. You can however buy a very cheap two channel transformer unit of The Bay for under $10.00 and they are actually not at all bad. Dare I say better than electric guitar needs?

"Impedance" rarely plays much of a part in audio connection problems (some device need a specific LOAD but that is another can of worms). Nothing in audio is "matched" any longer in the old telephone/RF man's meaning of the word.. LEVEL is where the problems often lay.

You seem of an "experimental" bent Simone? If not already, I suggest you get familiar with some soldering kit. One the THE most useful "tools" the home recordist can make is a simple 10kOhm pot in a tin with a TRS jack in and out and a switch as an earth lift.

Drawings and more instructions to follow if you are interested.
*I am technologically agin "True" bypass devices, but I won't hold it against you!
Dave.

 

[Laimon]

Hi Dave,

I kind of expected you to chime in
Immediate question: do you think using the KA6 instead of the 1212m the ground loop would (likely) go away or be still there? (I have a hunch it would go away, but I know nothing of these things, really)

I'll check out audio transformers later, but feel free to send me info (in pvt maybe) on how to make the ground-loop-killer, it sound like a superuseful tool indeed ;-)

As to true bypass loopers, I actually care about them for pedals that really degrade noticeably your signal, but in my current setup it is mainly to bypass effects with midi, rather than preserving the signal.
Cheers

Simone

 

[ecc83]

Hi Dave,

I kind of expected you to chime in
Immediate question: do you think using the KA6 instead of the 1212m the ground loop would (likely) go away or be still there? (I have a hunch it would go away, but I know nothing of these things, really)

I'll check out audio transformers later, but feel free to send me info (in pvt maybe) on how to make the ground-loop-killer, it sound like a superuseful tool indeed ;-)

As to true bypass loopers, I actually care about them for pedals that really degrade noticeably your signal, but in my current setup it is mainly to bypass effects with midi, rather than preserving the signal.
Cheers

Simone

Right, I'll go and lick me pencils!
"True" bypass (or as I like to put it. "A very cheap and unprofessional way to make audio equipment"!) allows the CABLES to degrade the signal and causes "tone sucking" which is just elliptical, probably substance induced, "guitaristspeak" for treble loss! ....But I shall still be a helpful friend!

Dave.

 

[ashcat_lt]

Errr... Transformers are not cheap or easy or transparent.

The first thing to try is plugging the amp and computer into the same power strip. If that doesn't help you might try swapping out the IEC power cables involved, since you've probably got a few sitting around and it doesn't hurt. That probably wont help, though.

The next easiest fix is to cut the shield at the pedal end of the cable.

I'm a bit confused as to why the return cable causes a problem and the send cable doesn't. You might find that you've got more loops to break...

The problem with true bypass comes when it leaves the guitar itself connected to a long run of cable, but there's no good point in using anything but a passive switch to do what that sort of fxloop pedal does. I always put at least one buffered pedal before mine, and of course the OP's preamp accomplishes the same thing.

 

[bouldersoundguy]

Perhaps it's a problem with interfacing balanced and unbalanced gear. Try the appropriate custom cable from this page: Sound System Interconnection

[Edit] It's going to be option 9 or 11. If the 1212 is balanced with transistors (active) use 9. If it's balanced with resistors (cross coupled) use 11, connecting ring to sleeve at the balanced output end.

 

[ecc83]

I hope my crude drawings are reasonably clear?
The top one is the schematic for an in line volume control which can be inserted in any unbalanced line level (+4 or neg 10) circuit. It is of course mono, single channel but a stereo pot could easily be substituted.

Middle is the layout drawing, point to point if you will and EEEK! I have cocked up! The view of the pot is from the rear and so the wires to the outer tags should be interchanged!
The pot value of 10,000 Ohms is about right for most jobs but you could use 22 or even 47k but keep the output lead short, under 2mtrs otherwise HF loss will occur.
The capacitor can be anything you have to hand or can get. Foil, ceramic, no matter, all it does is tie the OP jack to ground at RF when the shield is broken by the switch.

Last is a shield breaker for a balanced line (as would come out of the KA6) . I am sure the layout is pretty obvious from the above?

Transformers: Good ones are available here for about £10.00 apiece (1:1 "600 Ohm" type) VERY good ones at twice that. Yes, they CAN introduce distortion but not very much at these levels, i.e. about a volt rms, +4dBu. In any case we have all been listening to a HECK of a lot of transformers in cascade for years and years!

But then the electric guitar is hardly a "hi-fi" source and goes neither low nor high enough in frequency to bother even pretty cheap traffs. 'S,only rock n roll"!
Meant to say! The potintin can be used for "re-amping". Do have a go at that.
Dave.

 

[Laimon]

I'm a bit confused as to why the return cable causes a problem and the send cable doesn't. You might find that you've got more loops to break...

Interesting you would bring that up! In fact, it made me realize that I didn't try unplugging the two cables separately. I will do that and see what comes out.
Anyway, you did guess one thing right: PC and guitar equipment were on different power strips. I'll try them on the same strip asap!
Let's assume that's the problem: would then the problem persist also with an external sound card, usb-powered from the pc?

 

[Laimon]

I hope my crude drawings are reasonably clear?
The top one is the schematic for an in line volume control which can be inserted in any unbalanced line level (+4 or neg 10) circuit. It is of course mono, single channel but a stereo pot could easily be substituted.

Middle is the layout drawing, point to point if you will and EEEK! I have cocked up! The view of the pot is from the rear and so the wires to the outer tags should be interchanged!
The pot value of 10,000 Ohms is about right for most jobs but you could use 22 or even 47k but keep the output lead short, under 2mtrs otherwise HF loss will occur.
The capacitor can be anything you have to hand or can get. Foil, ceramic, no matter, all it does is tie the OP jack to ground at RF when the shield is broken by the switch.

Last is a shield breaker for a balanced line (as would come out of the KA6) . I am sure the layout is pretty obvious from the above?

Transformers: Good ones are available here for about £10.00 apiece (1:1 "600 Ohm" type) VERY good ones at twice that. Yes, they CAN introduce distortion but not very much at these levels, i.e. about a volt rms, +4dBu. In any case we have all been listening to a HECK of a lot of transformers in cascade for years and years!

But then the electric guitar is hardly a "hi-fi" source and goes neither low nor high enough in frequency to bother even pretty cheap traffs. 'S,only rock n roll"!
Meant to say! The potintin can be used for "re-amping". Do have a go at that.
Dave.

Thanks Dave! Yes, the drawings are perfectly legible!
I'll look up for the components and then making one myself shouldn't be too hard ;-)

 

[Laimon]

Ok, I tried plugging the guitar equipment on the same strip as the PC, and the problem seems to be more subtle than expected. Let me illustrate: it seems like the problems are "mostly" between the PC and the midi looper, so I need to give you a better explanation of how I am using the looper.
My dry signal goes in the looper input; the first loop is a compressor; from the second loop I go to my amp input, and then I come back from my amp send, hence I use the amp's preamp; then I have a bunch of post effects (delay, reverb and the like) and finally, in the last loop, I go to the PC, way and back.
Now, if I send my dry signal right to the amp's in, and from there I go back to the looper and all the effects, the connection to the PC doesn't produce any buzz. However, in the configuration described before (where I pass through the looper before the preamp) it makes a lot of hum and buzz.
Any idea how to solve this?
And whether I should expect the same problem with the KA6?

 

[ecc83]

Is this the looper?...EHX.com | 2880 - Stereo Multi-Track Looper - DISCONTINUED | Electro-Harmonix

If so I see it is powered from a 9volt 500mA mains adapter and it is very likely that said adapter caries the mains earth thru' to the unit, i.e. the looper is grounded. Nothing you can do about that but as someone else suggested you could use an audio lead with the shield disconnected one end. Often this fixes ground loops but sometimes it throws up other issues such as RF Intreference hence the better solution of a ground lift box or transformers.

Would the KA6 still exhibit this problem? In truth probably yes, the problem is not of any one component's making it is one of "assembly". Ground (we calls 'em "earth" loops) have bedevilled the audio industry since time immoral. Fully balanced operation is a very effective defense but even that is not foolproof! Each situation has to be sorted on its own terms.

BTW. Do NOT I implore you waste any money on so called "hum destroyers" that you plug into the mains. At best they don't work and at worst I think they might be dangerous. Also do not fall for the "Filtered and Surge protected" mains strips. Some of them can actually make ground noise worse by shunting crap into the earth line!

Forgot!..And! Regardless of what you read or anyone tells you DO NOT under any circumstances remove mains earth connections from equipment.

Dave.

 

[Laimon]

Hi Dave,

so, that's the looper I own, in the sense of phrase sampler, yeah. However, I am now talking of a *true bypass* looper (namely, this one: Picolooper3 - ARESAUDIO electronics & audio engineering) that I use to route my signal.
To try breaking out the earth loop, I inserted a DI box (behringer Ultra-g) between the looper and the amp input (only because it has a ground loop switch), and actually the switch helps greatly! However, the signal does seem to lose a bit of gain...nothing dramatical, but again I would avoid that.
Do you have any opinion about these findings?

Thanks also for the heads up about hum destroyers and earth connections, I wasn't gonna remove any anyway ;-)

 

[ecc83]

Hi Dave,

so, that's the looper I own, in the sense of phrase sampler, yeah. However, I am now talking of a *true bypass* looper (namely, this one: Picolooper3 - ARESAUDIO electronics & audio engineering) that I use to route my signal.
To try breaking out the earth loop, I inserted a DI box (behringer Ultra-g) between the looper and the amp input (only because it has a ground loop switch), and actually the switch helps greatly! However, the signal does seem to lose a bit of gain...nothing dramatical, but again I would avoid that.
Do you have any opinion about these findings?

Thanks also for the heads up about hum destroyers and earth connections, I wasn't gonna remove any anyway ;-)

How is that looper powered? Again I suspect it uses a wall rat which tie is to ground. The Behringer DI will lose you quite a bit of signal since it is designed to take a guitar level signal down to mic level. This is why you need one to one, i.e. same voltage in and out, transformer isolators.

Dave.

 

[Laimon]

How is that looper powered? Again I suspect it uses a wall rat which tie is to ground. The Behringer DI will lose you quite a bit of signal since it is designed to take a guitar level signal down to mic level. This is why you need one to one, i.e. same voltage in and out, transformer isolators.

Dave.

I am not sure what "rat" and "tie" mean in this context, but I would guess "plug" and "earth" respectively, right? Well, I am using a selectable voltage power supply (set at 12v), and that has no ground unfortunately (somehow it's uncommon for this power supplies to have it).
The DI box I mentioned has buttons for attenuating 20 and 40 db, but if none is pressed, the signal should be theoretically only be converted to balanced (as far as I understand DI boxes )

In any case, I think I found a solution. All the routing experimentation lead me to reconsider my setup a bit: I noticed that going to the looper before and after the preamp was introducing extra noise and hum per se (actually, I have always known; only I didn't know that going before the amp was mainly responsible for the noise), and I realized that I keep the compressor pretty much always on (it's quite transparent and I like it everywhere!), so I decided to go to the looper only after the preamp...well, now it's dead quiet

Ah, I and I pulled the trigger (it was an online auction) on the KA6, wish me luck

 

[ecc83]

"I am not sure what "rat" and "tie" mean in this context,"

Sorry, sloppy of me. "Rat" because many of the supplies are about that size and plug into a "wall" with the cable "tail" hanging down (except the stupid, stupid, STOOOOPID ones that have the cable coming out of the top at the earth pin. N.B. We cannot have two pin plugs here, won't go in) .

"Tie" means "connected to". The mains side of a supply often has an earth pin and that is carried through inside to connect to the sleeve of the low voltage DC plug which is usually negative except for most guitar pedals when it is, for some bizzar reason I have never fathomed, positive.

This earthed DC power is very commonly the case with laptop chargers and is a prime cause of ground loops and digital hash. There is no reason why a laptop should be earthed in this way and you can often find alternative supplies that are earth free.

But glad you are silent and sorted!

Dave.