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Art dPDB passive/active question

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Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 3:55 pm

I'm looking to get the Art dPDB so that I can plug in my electric guitar straight into the sound desk to record a dry signal. Ideally it'd have an extra output so I can route it to my guitar amp so I can hear the tone from the amp, but the signal recorded stays dry.

I found the Art dPDB but I'm not sure about a number of things. One is it is passive... What is the benefit of an active DI?

Secondly, according to the specs, the input is only 50k Ohms. I was told on the forum that High-Z needs 500k Ohms to 1 MOhms. But all the material I can find say the pDPB will work for a passive guitar pickup. So I'm naturally very confused!

Any help would be appreciated thanks.
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Re: Art dPDB passive/active question

Postby Hugh Robjohns » Mon Dec 04, 2017 4:36 pm

Passive DIs are fine for devices with electronically buffered or amplified outputs, like keyboards, drum machines, DJ mixers, active basses etc but, as you rightly say, the input impedance is generally far too low to work nicely with electric guitars. The ART passive Di has a nominal input impedance of 50k Ohms, but you really need something in excess of 500k Ohms, and the only practical way to achieve that is with an active DI box.

In terms of the basic design, a passive DI box is just a step-down transformer. The input side is wired to accept an unbalanced instrument-level source, and the output is balanced at mic level. An active DI precedes the transformer with a very high-impedance buffer amplifier, usually giving something like a 1M Ohm input impedance. Of course, that buffer amp will need power, which can come either from a battery, or from phantom power from the mixing console.

There are countless active DIs to choose from, but (with one exception*) don't buy cheap; it's a false economy. A good DI box will outlive you, so the cost per year of use is trivial even if it costs £150 in the first place. A cheap DI will never sound as good, and you'll end up replacing it, probably more than once. People have different preferences, but I like the Radial J48, the Klark Teknik DN100, the BSS AR133 and the (now discontinued) Canford Active box.

*However, these days I mostly use one of the Orchid Electronics active DI boxes, and the reason is that they are incredibly good value for money, extremely well built, and sound better than anything else I've tried, ever. The Micro DI doesn't have a loop-thru socket, so it's no good if you want to split the guitar to an amp as well, but for recording direct into the desk, it's just the job. The classic DI is the one most likely to meet your needs, and the Muting DI is great for performing if you want to mute the signal while tuning up.

Image

The only potential downside is that these units don't have transformers at all, so there is no electrical isolation. That's party of what makes them cheap and so good-sounding, and if you are confident that what you're plugging into is electrically safe, that's no problem.

But, when performing on stage and plugging into an unknown PA company's gear, or an unknown musician is plugging into my recording equipment, I like to know there's an isolation transformer between them and me for safety -- and that's when I reach for the traditional BSS or Canford boxes! ;-) (Note, there's no audio isolation transformer in the J48 either.)

https://www.soundonsound.com/reviews/or ... s-di-boxes

http://www.orchid-electronics.co.uk/products.htm
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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 4:44 pm

I know you say don't buy cheap, and I understand that. But while I'm looking at multiple options, what about this: http://amzn.eu/i5N6mKc ?

It's rated at 470kOhms
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Re: Art dPDB passive/active question

Postby Hugh Robjohns » Mon Dec 04, 2017 4:52 pm

I've not used it, and I don't recall anyone I know using one, so I can't comment on its quality. However, the ART stuff is designed in the US and built in China, which is how they keep the price down, and everything I've tried from ART so far has surpassed expectations.

But having said that, if you're in the UK (I think you are), and this is for use at home, I'd question your sanity if you didn't buy the Orchid Electronics Classic DI... ;-)

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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 4:56 pm

My apologies Hugh!

I just checked out the Classic DI... £36!!!! And it looks perfect.

Am I right in thinking I can use both outputs at once... The unbalanced into my guitar amp and the balanced into my desk? The problem I have is the unbalanced is a low impedance signal so am I right in assuming I couldn't put it into my guitar amp?
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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 4:57 pm

Additional: My amp is a Peavey Transtube Envoy 110
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Re: Art dPDB passive/active question

Postby Hugh Robjohns » Mon Dec 04, 2017 5:07 pm

garrettendi wrote:I just checked out the Classic DI... £36!!!! And it looks perfect.

:-)

Am I right in thinking I can use both outputs at once... The unbalanced into my guitar amp and the balanced into my desk?

Yes of course -- that's the intended application. The DI box connects between guitar and amp -- guitar plugs into the 'normal' input, and the 'amp' output plugs into the guitar amp (you'll need a second instrument cable, obviously). The 'mixer' output plugs into your mixer with an XLR cable.

The -20dB 'line' input is for the outputs of keyboards or other line-level devices. Don't use both the standard and -20dB inputs at the same time -- it's one or the other!

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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 5:51 pm

How dangerous is it not to have the isolation transformer? This will be home use only but one can never be sure without getting things tested!
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Re: Art dPDB passive/active question

Postby Hugh Robjohns » Mon Dec 04, 2017 6:06 pm

For home use, where your equipment is looked after properly and you won't be mad enough to start disconnecting earths from mains plugs, its perfectly safe. And I use Orchid DIs all the time quite happily.

I'd be more concerned about a fault occurring with your guitar amp than with the mixer or computer interface -- and the DI box transformer can't do anything to protect you from that!

The risk of which I spoke earlier is theoretically possible if the recording equipment or PA (to which you connect the balanced DI output) has a catastrophic fault -- such as a missing safety earth connection AND the line connection somehow meets with the earth, making all the exposed metalwork live.

It sounds an unlikely combination of faults, and it is, but I've actually seen it happen for real right in front of me when a pillock disconnected the mains safety earth from a mains plug to prevent a ground loop hum, and then another pillock managed to put a metal chair leg down on the mains cable, cutting through the sheathing and shorting the line and earth wires together. :o Fortunately no one was hurt, but some of the connected equipment wasn't so lucky!

In that kind of (extreme) situation, having an isolation transformer between the dodgy equipment and the guitar hanging around your neck is a very comforting thing! it'll probably never happen... but if it does the transformer will probably save your life!

So, as I said earlier, it's not something I worry about with my own gear, or the gear of those I trust to maintain and use it properly. But I would take the precaution of using a DI box with a transformer when connecting anything I'm not 100% certain about... just in case. For me, the boxes are available anyway so I'd be daft not to use them in that situation.

The rest of the time, I use Orchid boxes and enjoy their cost-effectiveness and effortless clean sound.

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Re: Art dPDB passive/active question

Postby The Elf » Mon Dec 04, 2017 6:23 pm

I haven't used the Orchid device, but I can vouch for the quality of their other boxes, and I can also vouch for the benefits of the transformerless design of the Radial J48.

While you're at it, consider Orchid's re-amping box. If you're recording DI then you'll likely want to spit that DI out to an amp or some pedals at some point.
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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 7:33 pm

Funny you mention that Hugh, as my multitrack doesn’t have a metal earth pin... so how is that grounded? It has a wall wart
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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 7:54 pm

It’s a Tascam DP-24SD btw
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Re: Art dPDB passive/active question

Postby Hugh Robjohns » Mon Dec 04, 2017 8:20 pm

garrettendi wrote:Funny you mention that Hugh, as my multitrack doesn’t have a metal earth pin... so how is that grounded? It has a wall wart

It's a class-2 device, also known as double-insulated. You'll probably find the 'box within a box' logo on the bale of the wall-wart.

The tascam doesn't need a safety earth connection because it is designed in such a way that the live side of the mains can not, under any circumstances, come into contact with any exposed metalwork.

So it doesn't need grounding for safety reasons. It might, though, need grounding for interference screening reasons, and that would be achieved via the cable screen of connected audio devices, like powered speakers etc.

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Re: Art dPDB passive/active question

Postby garrettendi » Mon Dec 04, 2017 9:09 pm

Thanks Hugh! I think I’ll get the Classic DI :thumbup:
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Re: Art dPDB passive/active question

Postby Martin Walker » Mon Dec 04, 2017 9:51 pm

garrettendi wrote:Thanks Hugh! I think I’ll get the Classic DI :thumbup:

Bravo - that's the correct decision garrettendi ;)

Enjoy!


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Re: Art dPDB passive/active question

Postby garrettendi » Tue Dec 05, 2017 8:31 am

Hi Hugh

The output impedance of the unbalanced output is 1k Ohm. Isn’t that too low for a guitar amp? Mine is a Peavey Transtube Envoy 110.
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Re: Art dPDB passive/active question

Postby Sam Spoons » Tue Dec 05, 2017 9:50 am

It will be fine. Modern Boss pedals, for example, (and many buffered, non-'true bypass' pedals) have an output impedance of 1k.
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Re: Art dPDB passive/active question

Postby garrettendi » Tue Dec 05, 2017 9:53 am

Thanks Sam!
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Re: Art dPDB passive/active question

Postby Wonks » Tue Dec 05, 2017 9:53 am

Don't confuse output impedances with input impedances. The high input impedance of a guitar amp won't take much current from the output, but that's fine as it's looking at voltage, not current. You'll be fine.
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Re: Art dPDB passive/active question

Postby Hugh Robjohns » Tue Dec 05, 2017 9:54 am

garrettendi wrote:The output impedance of the unbalanced output is 1k Ohm. Isn’t that too low for a guitar amp?

Nope. The only rule you need to worry about in this kind of interfacing situation is that the input impedance of the destination is at least ten times higher than the output impedance of the source. And in the case of the guitar, because there are complex interactions between the resistance, inductance and capacitance of the pickup, cable, and amp input, a much higher factor is actually preferable.

So, a typical guitar pickup might have an output impedance of 5k Ohms or so, and the typical amp's input impedance will be 500k or more. So a lot more than 10 times higher, and closer to 100 times, in fact. Tick. That will work nicely.

The Classic DI's output impedance is 1k, so still a lot more than ten times, and it will work perfectly.

...and I wouldn't recommend anything to you that would't work brilliantly! ;-)

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