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Is there any point in DI'ing keyboards?

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Is there any point in DI'ing keyboards?

Postby Evie McCreevie » Sat Aug 01, 2009 10:54 pm

I've always stuck them straight into my interface / desk / whatever... Plenty of level, minimal noise (if any), no hassle.

Why use a DI box? Am I missing anything?
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Re: Is there any point in DI'ing keyboards?

Postby RegressiveRock » Sun Aug 02, 2009 12:01 am

Is it not a line level not an instrument level signal?
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Re: Is there any point in DI'ing keyboards?

Postby Evie McCreevie » Sun Aug 02, 2009 12:40 am

RegressiveRock wrote:Is it not a line level not an instrument level signal?

Exactly! But I get guys coming in with modern keys AND di boxes, thinking "this is the proper way to do it".

I ignore the DIs, stick the gear straight in, and get on with it. Never a problem. DIs are just a hangover from the Fender Rhodes days, aren't they?
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Re: Is there any point in DI'ing keyboards?

Postby narcoman » Sun Aug 02, 2009 1:10 am

sometimes nice to path them through Mic pres - keyboards sound great through 1073s....
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Re: Is there any point in DI'ing keyboards?

Postby Evie McCreevie » Sun Aug 02, 2009 2:08 am

narcoman wrote:sometimes nice to path them through Mic pres - keyboards sound great through 1073s....

Well, I don't have a 1073, let alone a pair of them... :frown:

But while it may be "nice" to DI/mic pre with keys, what you're essentially saying is there's no real technical reason for doing so. Yes?
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Re: Is there any point in DI'ing keyboards?

Postby Tomás Mulcahy » Sun Aug 02, 2009 3:00 am

Evie McCreevie wrote:
But while it may be "nice" to DI/mic pre with keys, what you're essentially saying is there's no real technical reason for doing so. Yes?
Yes! But sometimes the impedance mismatch is exactly what is needed. Boss pedals anyone?
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Re: Is there any point in DI'ing keyboards?

Postby Dave B » Sun Aug 02, 2009 7:36 am

Two issues :

1. Balancing. A lot of keyboards aren't balanced and so traditionally need something like a DI to perform this. In a studio with a wall box, this means that you can go straight in to an xlr which traditionally leads to a mic input (as Narcoman pointed out) rather than a line input. That makes senese. But for a small system with easy access to line inputs, it's fine as long as the cable runs are short.

2. Live. Again for balancing as above. Plus, having the ability to pad the signal at source can sometimes be handy - depends on the desk at the other end.

What I constantly keep an eye out for is a line driver of some kind which takes an unbalanced signal and balances it. Simple idea which can be really quite handy and let your studio run everything balanced. Etek used to have a cool, cheap box to do this but it was discontinued years ago and are like hen's teeth s/h..
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Re: Is there any point in DI'ing keyboards?

Postby ef37a » Sun Aug 02, 2009 7:48 am

"What I constantly keep an eye out for is a line driver of some kind which takes an unbalanced signal and balances it. Simple idea which can be really quite handy and let your studio run everything balanced. Etek used to have a cool, cheap box to do this but it was discontinued years ago and are like hen's teeth s/h.. "

Hi Dave, Well that is beer into water to make as a passive device, spend as much or as little as you want/need on transformers. If you want active no problem, whether transformerless but "earth" free or hybrid with iron.

OEP/Walters have some application notes and circuits and Jensen Transformers shedloads of same.

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Re: Is there any point in DI'ing keyboards?

Postby The Elf » Sun Aug 02, 2009 8:02 am

I have over 70 unbalanced keyboard signals arriving on my patchbay. The thought of buying a DI for all of them makes my blood run cold!

Nah, I always go straight into a line input - never had a problem.

Ironically, the only thing that gives me grief is a BBC-modded RMI piano that has a pair of balanced outputs - one way too hot and the other way too low.
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Re: Is there any point in DI'ing keyboards?

Postby ef37a » Sun Aug 02, 2009 8:48 am

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Re: Is there any point in DI'ing keyboards?

Postby The Elf » Sun Aug 02, 2009 8:53 am

Thanks!

Unfortunately my understanding of electronics is restricted to soldering my own leads, so this is lost on me! I'm guessing I add/replace a resistor somewhere on the balanced output?
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Re: Is there any point in DI'ing keyboards?

Postby ef37a » Sun Aug 02, 2009 10:22 am

" I add/replace a resistor somewhere on the balanced output?"

Heh! Heh! Not quite, you need to build the network.

Can you not buy line level, inline XLR attenuators these days?

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Re: Is there any point in DI'ing keyboards?

Postby The Elf » Sun Aug 02, 2009 10:48 am

ef37a wrote:Heh! Heh! Not quite, you need to build the network.

I've not the faintest idea what you mean! :crazy:

ef37a wrote:Can you not buy line level, inline XLR attenuators these days?

I just turn down the volume and use the hot output. Wonder what the original un-modded output was like...

Never looked for an attenuator, though I wouldn't know what to look for or what values I'd need. Do they quote these things in dBs? I did once try to find in-line attenuator pads for a couple of my mics, but had no luck. I think Neumann used to list some, but the price was ridiculous.

I also have an ARP Pro-Solist that has a very hot, but unbalanced output and a very low balanced output. I stick with the unbalanced, since I'm assuming the hotter signal will hold out better.

It's all guesswork, but I've never had much of a problem.
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Re: Is there any point in DI'ing keyboards?

Postby Tomás Mulcahy » Sun Aug 02, 2009 10:53 am

Dave B wrote:
What I constantly keep an eye out for is a line driver of some kind which takes an unbalanced signal and balances it.
Art make a couple of these. Very good problem solvers. And there's that Balun thingie, reviewed in SOS a while back.
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Re: Is there any point in DI'ing keyboards?

Postby Shreddie » Sun Aug 02, 2009 11:33 am

The Elf wrote:I have over 70 unbalanced keyboard signals arriving on my patchbay.
70?! :shock: I think I have about 20-30... I must try harder!

I've always just plugged straight into the line inputs... And other than my mic cables, there's not a single balanced cable in sight in my studio... I hum a bit but my gear doesn't!
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Re: Is there any point in DI'ing keyboards?

Postby ken long » Sun Aug 02, 2009 12:51 pm

Yeah, I DI on some older synths. To get them balanced - some do hum like bast*rds and the lift helps somewhat.

ken

PS. Yeah, 70 is obscene. But that's just envy talking... :)
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Re: Is there any point in DI'ing keyboards?

Postby Hugh Robjohns » Sun Aug 02, 2009 1:57 pm

In the majority of cases electric and electronic keyboards provide an unbalanced output at a level which is typically 10-20dB below standard line-level.

Not all line inputs are sufficiently sensitive to handle the output from keyboards effectively. But if your desk/recorder/interface has line-level inputs with sufficient gain available, then you can indeed connect your keyboard directly and get an acceptable signal.

However, given that many keyboards are not double-insulated and therefore require a chassis safety earth via the mains power supply, in some cases there may also be ground loop problems. The only safe and practical way to cure this problem is with a coupling transformer of some form. Line-level transformer isolators are available, but are far less common than DI boxes (and the good ones are generally very expensive).

Running a keyboard via a DI box has a number of useful benefits. For example, some very early electronic/electric keyboards do work better into the very high input impedances (ie well over 100k) that a DI box provides, rather than the 10k or so impedance of a standard line-level input.

A DI box inherently contains a transformer and can be used to provide galvanic isolation to prevent ground loop issues. It also provides complete protection from phantom power -- there are some preamps and interfaces that allow phantom power to appear on supposedly line-level and DI connectors! I came across a brand new one only a couple of weeks ago! Phantom power can and occasionally does destroy the output stages of keyboards and other equipment, so taking simple steps to protect against an inadvertant accident might be deemed a sensible precaution.

Most studios are well equipped with mic tie lines and mic preamps, but less well with line level tielines and line inputs -- and unbalanced runs will always be more prone to interference and ground loop problems than balanced cable runs.

Mic preamps are far more capable of adding 'sonic character' to a sound through transformer/valve/solid-state distortion artefacts which may well be deemed beneficial and appropriate than line-level input devices.

The bottom line is that unbalanced keyboards can often be connected to an interface or console directly without problems. But if there are signal/hum problems you're going to have to go the DI or line-isolating transformer route anyway. And if the keyboard is faulty you risk destroying your inteface / console because of the direct connection.

If someone had removed the mains earth from their keyboard to stop it humming, for example, connecting its output directly to your interface or console could easily result in the instant and total destruction of the line input op-amp and associated circuitry, and possibly the entire unit, because of the ground rail float to 115V AC.

Connecting a keyboard to a mic input via a DI box is inherently safe (for both keyboard (and player) and the mic input / console / interface). The transformer provides the appropriate galvanic isolation, protecting both parties from potential mains faults, as well as freedom from ground loop problems.


While I certainly have connected keyboards directly to line level inputs, it has only ever been when I've been 100% certain of their safety condition. Personally, I would never, ever connect anyone elses (untested) keyboards to a line input without a line-isolating transformer in the way, and 99.5% of the time I would use a DI box (active or passive -- depending on the situation) and go via a mic input. Mainly just to be safe, but partly because it's often more convenient and practical, and affords the option of more colour more easily.

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Re: Is there any point in DI'ing keyboards?

Postby Dave B » Sun Aug 02, 2009 5:16 pm

Just had a look at the Art website and found :

The Art T8 Isolator

Does this tick the above boxes? As far as I can see, it claims it can happily balance unbalanced signals and seems designed for line level operation. If I were to run unbalanced keys outputs into that, would it balance the signal before hitting my balanced, line-level audio interface?
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Re: Is there any point in DI'ing keyboards?

Postby The Elf » Sun Aug 02, 2009 8:36 pm

Fascinating stuff!

I have never questioned the practice of plugging a synth or keyboard straight into a line input - not once.

No wonder my RMI and ARP seem hot - I guess they are putting out a genuine line level signal (and the low RMI output giving a mic-level).

You learn something every day...

I don't find it intuitive to think that I'd want to drop the output level of a keyboard down to mic level via a DI box, to then have to find a mic input to amp it back up to line level again. That just seems 'wrong' to me - I'd always go for a line input.

So what I would actually need to go from a typical synth into a gain-less line input is a DI box with a 'not quite line level' input and a line level output? Maybe a task for my newly acquired ART Cleanbox...
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Re: Is there any point in DI'ing keyboards?

Postby ef37a » Sun Aug 02, 2009 9:21 pm

Sorry Hugh but I have to be clear about this.

You are not suggesting that a DI box (or 1:1 line transformer) can provide mains voltage isolation in the event that one side goes live?

I take the point about phantom power, did not think of that!

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