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Behringer MICROHD Hum Destroyer HD400

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Behringer MICROHD Hum Destroyer HD400

Postby maskedwarrior » Tue Feb 13, 2018 4:07 pm

I'm interested in this: Behringer MICROHD Hum Destroyer HD400:

https://www.musictri.be/Categories/Behringer/Signal-Processors/DI-Boxes/HD400/p/P0387

I'm after a simple, basic way of converting an unbalanced 3.5mm jack output from a macbook pro, into two balanced XLRs running into a small PA. I have all the cables, the above will provide a simple way of connecting together. It's for a small, simple live rig, which runs from one power outlet. It was previously run through an Edirol UA-25 interface, which I think has been causing the Macbook to freeze and lock up during live shows (needing a hard reset to get QLab up and working again). So I'm trying to cut the interface out of the equation.

I was looking at a DI box, but really I wanted a low-cost solution, which doesn't needlessly drop the signal to mic-level, and this is as much about ease of connection as it is about ground loop isolation anyway.

I was going to rig up a pseudo-balanced cable, but then I saw this.

I was mostly curious about how these little boxes work, how they achieve what they claim to achieve and whether anyone's had any experience with them?
Thanks
Tony
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Re: Behringer MICROHD Hum Destroyer HD400

Postby Bob Bickerton » Tue Feb 13, 2018 5:20 pm

First up, I’ve never really had problems connecting a MacBook Pro directly to a sound system, so you could probably get away with a cable solution.

The cheaper Behringer stuff hasn’t enjoyed a good reputation and I, for one, would not use their DIs. Also that unit appears to be jack to jack, so you’re still going to need to use conversion cables to get to XLR.

A better solution would be to use an ‘AV’ DI.

The cheapest I’d recommend would be the ART DTI, https://www.sweetwater.com/store/detail/DTI which would give you the XLR option.

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Re: Behringer MICROHD Hum Destroyer HD400

Postby Hugh Robjohns » Tue Feb 13, 2018 5:26 pm

A pseudo-balanced cable would almost certainly do the job perfectly well, but an isolation box gives added peace of mind and worthwhile protection from phantom power or electrical faults in the PA system.

maskedwarrior wrote:I was mostly curious about how these little boxes work, how they achieve what they claim to achieve and whether anyone's had any experience with them?

No experience of this specific unit. It looks much like the ART Cleanbox2... but there are many others on the market at a range of prices.

Essentially, they simply contain two 1:1 ratio isolating transformers, one for each channel. Each channel's input connection is wired to the primary winding of its transformer, and the output to the secondary.

The transformers pass the signals magnetically between their primary and secondary windings, but there is no direct electrical connection so the grounds of the source and destination equipment are kept completely separate. This is what avoids creating the feared ground-loop and thus prevents ground-loop hums or buzzes.

In addition, the transformers automatically convert between balanced and unbalanced connections, which is handy.

The main differences between the various models of this kind of thing come down to connectivity options, the quality of the transformer, and the provision of EM shielding.

The last helps to prevent (or at least minimise) external magnetic fields from inducing hum into the transformers -- but you can do the same simply by locating the box well away from anything with a mains transformer in it!

The quality of the transformer affects the audio signal quality; specifically the frequency response extremes and the distortion. Better (more expensive) transformers can handle much higher levels at low frequencies with much less distortion... but whether that's critically important or not depends on the material and the application.

Connectivity requirements are also dependent on application, of course. Like Bob, my favoured box for this kind of thing is the ART DTI. It probably costs twice as much as the HD400, but it is much more than twice as versatile as it has almost every connector known to man on the thing, which also makes it really useful for signal splitting and avoids the need for adaptors in most situations!

Image

https://www.soundonsound.com/reviews/art-dti

For completeness, I should also say that there are dedicated laptop interface boxes, too both active and passive. Several companies make them, but I'm most familiar with the Radial Engineering range such as the Radial Trim Two (passive), and JPC (active). Although these are quite expensive, they are nicely optimised for this application (I use a JPC interface quite often)

http://www.radialeng.com/trimtwo.php" target="phpbbpopup
http://www.radialeng.com/jpc.php" target="phpbbpopup

Hope that helps
H
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Re: Behringer MICROHD Hum Destroyer HD400

Postby Sam Spoons » Tue Feb 13, 2018 6:10 pm

If you can't stretch to the Art, Orchid Electronics do this one for £35 inc VAT and postage. I have a single channel TS-TRS one and a special cable that John at Orchid made for me to sum the MacBook stereo outputs to mono. That cost £27.50 in total and is useful as it only uses up one desk input/channel.
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Re: Behringer MICROHD Hum Destroyer HD400

Postby ef37a » Tue Feb 13, 2018 7:46 pm

Ten minutes ago I downloaded the manual for the Radial Catapult TX4 and RX4 isolators.

These are overkill for the OP's task as they give 4 balanced circuits over CAT 5 cable.

I have printed out the schematics (rare but VERY nice to get!) and confess I cannot as yet make a lot of sense of them. Maybe Hugh could enlighten me?

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Re: Behringer MICROHD Hum Destroyer HD400

Postby Hugh Robjohns » Tue Feb 13, 2018 8:59 pm

ef37a wrote:Ten minutes ago I downloaded the manual for the Radial Catapult TX4 and RX4 isolators. ... I have printed out the schematics (rare but VERY nice to get!) and confess I cannot as yet make a lot of sense of them. Maybe Hugh could enlighten me?

Looks pretty straightforward to me, Dave, although each schematic actually describes three different variants which doesn't help! It is quite an elegant system, though.

As far as I can see, each set (In/out or Thru) of four XLRs on the two sides of the box is wired in parallel directly with its corresponding (In/Out or thru) Ethercon RJ45 socket.

Added to that, each in/out XLR is also wired across to its correspondingly-numbered thru XLR either directly (via '0 Ohm' resistors) or via transformers (which can either be 1:1 isolating types, or step-up/down mic/line types).

And the grounds of all the XLRs can be lifted en-masse from their respective Ethercon grounds.

So what doesn't make sense?
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Re: Behringer MICROHD Hum Destroyer HD400

Postby maskedwarrior » Sat Feb 17, 2018 12:20 am

Hello! And thank you for your wonderful replies.

I am interested in the Art, however I notice it has no ground lift, unlike the Radical ones and some others with 1:1 transformers.

One thing I want to stress - my laptop/pa rig needs to be as stable as possible. Our stage show is visiting some quite posh (for us) places this year and I just can't have it hanging mid-performance! It is super stressing me out.

I have tested the rig, without the PA attached, for about 12 hours with no hangs. I will continue to test, but I'm starting to think it may be a ground-loop/surge which occurs when the PA is attached, hitting the USB interface and locking up the mac. It seems less unlikely the more I think about it and I wonder if I've been silly not using a DI until now!

I like using my interface, so may I ask, how effectively will the Art insulate/isolate my mac from the PA etc, and protect it from this (completely theoretical) interference? Is it going to totally isolate the ground, or is this why ground switches are present on the Radical boxes etc?

However, pending feedback, I may do away with the USB interface altogether and opt for a small mixer and connect via the laptop 3.5mm jack, as it seems like less of a vulnerable way to connect the mac than a usb straight into the motherboard. (It does, however, risk a rogue laptop system sound sneaking into our show score, if I haven't been thorough enough at silencing everything!)

I'm also interested in the isolators I've linked below: they get slightly better feedback on studio spares than the Art, they seem like a professional box, albeit a bit more paired down - but perfect to pair with a small mixer (I have a very slim wallet on this production so I'm after bang for buck, without compromise in terms of hardware safety):

IMG Stageline FGA-202 2-Channel Line Transformer
https://www.gear4music.com/Recording-and-Computers/IMG-Stageline-FGA-202-2-Channel-Line-Transformer/25YP#full-des

AND Stageline FGA-102 Stereo Line Transformer
https://www.studiospares.com/Microphones/Mic-Transformers/Stageline-FGA-102-Stereo-Line-Transformer_255290.htm

I know it's horses for courses but your feedback would be great! As stated, this needs to be an ultra-reliable setup and resulting stress has already shortened my life too much.
Thanks so much,
Anthony
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Re: Behringer MICROHD Hum Destroyer HD400

Postby Bob Bickerton » Sat Feb 17, 2018 1:32 am

The Art DTI provides permanent isolation, so no ground lift switch required.

Here’s Hugh’s review: https://www.soundonsound.com/reviews/art-dti

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Re: Behringer MICROHD Hum Destroyer HD400

Postby ef37a » Sat Feb 17, 2018 7:30 am

Anthony, I would go for the Art for two reasons.
1) It has a much more versatile compliment of connectors.
2) It has been under Hugh's 'ruler' and use! In any case, the spec of those linked devices is poor.."Frequency RANGE"??

The reason some 'DI' boxes have ground lift switches is because they are often used to feed a second device, almost always a guitar amplifier and that device may or may not be earthed. This is becoming increasingly so with the rise of solid state 'modelling' amps that use Class ll, earth free insulation. Then, in any given situation the hum level might be better or worse if the ground is lifted.

Your situation is rather different. You need to isolate the feed from just ONE device to another, you are not going to hook in other stuff and in any case what is needed is a 1:1 transformer isolator, not a 10:1 guitar DI box.
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Re: Behringer MICROHD Hum Destroyer HD400

Postby Hugh Robjohns » Sat Feb 17, 2018 9:27 am

maskedwarrior wrote:I am interested in the Art, however I notice it has no ground lift, unlike the Radical ones and some others with 1:1 transformers.

I'm not entirely convinced you're comparing like with like here... DI boxes are generally used with an instrument that needs to be grounded, but that ground may need to come from the PA or from the guitar amp... so the ground continuity situation is more complex, making the gnd-lift switch an important facility.

But that's not the case in a situation where you want to galvanically isolate the source from a single destination. In such cases there should be no ground connection between the two, and providing a switch on the box -- especially a box which only has balanced inputs and outputs -- is to completely miss the point of using the box at all! :headbang:

The reason the DTI has no ground lift switch is because the input and output grounds are separated permanently. There is no direct connection between the input grounds and the output grounds... Which is kinda the whole point of the thing!

may I ask, how effectively will the Art insulate/isolate my mac from the PA etc

Totally. That's what it is designed to do. There will be no electrical connection whatsoever between the equipment connected to each side of the transformer box. It is the perfect definition of 'galvanically isolated'!

...and protect it from this (completely theoretical) interference?

It depends how you define 'interference' -- its a word that means different things to different people. The DTI (and boxes like it) is useful in removing ground-loops when used appropriately, and ground-loops can cause hums and buzzes. Its also ideal for balancing unbalanced sources for connection over long cables to something with balanced inputs.

Like all these devices, the DTi Is a tool that is used for a specific job. It can resolve specific problems... But it is important to identify the relevant problems accuractely and use the right tools and techniques to resolve them.

Is it going to totally isolate the ground

Yes.

I did say there are many other makes of line isolation transformer box, but I can't offer much of an opinion on those specific boxes as I've not tested or used them. What I can say is that their published specs appear rather limited and the provision of a ground lift switch on one model makes me wonder if the designer really knew what they were doing.

However, I have tested the DTI, I use it almost everyday, and I've recommended it widely to many people who use it to solve ground-loop (and other) problems everyday and all are very happy with it. The product is also fully specified -- including the distortion at different line levels -- and the handbook includes the schematic.... All of which is very confidence inspiring.

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Re: Behringer MICROHD Hum Destroyer HD400

Postby maskedwarrior » Sat Feb 17, 2018 2:16 pm

That's great feedback thanks. I get the impression the Art is the weapon of choice here

And please don't think I'm second guessing this, I totally respect everyone's opinions, particularly when you've actually used the device in question. However since you said, Hugh,
The quality of the transformer affects the audio signal quality; specifically the frequency response
I was interested in exploring either a more paired-down, better quality option or perhaps just getting something in the next bracket up.

It's just that, glancing at various retail sites, there isn't a consensus on the audio quality of the Art. I don't know myself, I haven't used it. I know you like it, Hugh, and I respect your opinion but clearly you linked to the Radicals for a reason, as they represent the full professional scale.

I'm also aware I didn't explain my circumstances very well, and perhaps I gave the wrong impression about what I want to achieve and had a misguided impression of price points.

I am using this device to deliver a stage play sound design and backing tracks to my LD Maui PA, and (potentially) provide aux outs to various theatre systems of varying quality throughout the UK to add some subtle reinforcement. The setup in question is a macbook pro running Qlab 4, with an Art-net-DMX ethernet device connected from the mac to an LED lantern. The whole PA is built into a stained glass window set-piece and I operate the QLab audio/LX remotely while acting onstage, using a USB clicker. The audio is a UA-25 interface, running on generic sound device mode (without drivers).

It is a fiddly setup. The audio interface needs updating, and perhaps I had an unrealistic impression of price-points for isolators to begin with, and underrepresented the factors involved. However, audio consistency does matter to me and I'm like... if I can't get something more dedicated but a bit cheaper, I may as well fork out the extra money for a really widely appraised model... like this one:

http://www.radialeng.com/stagebugsb6.php" target="phpbbpopup" target="phpbbpopup

Incidentally this isolator has a ground lift. So, why? Is this just a hangover that manufacturers include because it's what customers expect to see?
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Re: Behringer MICROHD Hum Destroyer HD400

Postby ef37a » Sat Feb 17, 2018 2:53 pm

"Incidentally this isolator has a ground lift. So, why? Is this just a hangover that manufacturers include because it's what customers expect to see?"

Quite possibly! Like standby switches on valve guitar amps*.

There is no doubt that the Radial devices are of excellent quality but I seem to recall that the much cheaper Orchid boxes measured almost or even AS well? Do not forget as well that for all their bandying of superb figures, the performance of a transformer, its response, distortion and losses are very dependant upon drive and load impedance. All transformers have to obey the laws of physics (though active boxes can do magical things with a bit of feedback!) .

I am sure that if the Art DTI is good enough for Hugh it will be good enough for you! Why pay for facilities you don't need? Then there is the safety isolation matter to mention?

The Art is about as safe as you can get. The transformers are likely proofed to at least 250V AC and possibly 2kV. The absence of a gnd lift switch means there is nothing else that could breakdown in the VERY rare event of a chassis becoming live. A dinky 'audio' switch might not save you at peak mains V?

*I have a theory. Valve manufacturers, SB switches destroy rectifier valves!

BTW, you are looking to replace the interface? Do consider the NI KA6, as reliable, hard and software as a wood burning stove.
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Re: Behringer MICROHD Hum Destroyer HD400

Postby Hugh Robjohns » Sat Feb 17, 2018 3:42 pm

maskedwarrior wrote:That's great feedback thanks. I get the impression the Art is the weapon of choice here

Its a useful tool because it caters for a lot of different connection formats, is pretty affordable, and the technical performance is quite acceptable in most applications. I've not found anything better for the price.

But, in ultra-demanding situations, I use a canford audio line isolator instead, which has Lundahl transformers. One of the high-end Radial boxes fitted with original Jensen transformers would be as good.... but there aren't many applications where the quality improvement would be audible -- including (I suspect) your application! And I'm talking here about boxes costing close to £150 instead of £50.

It's just that, glancing at various retail sites, there isn't a consensus on the audio quality of the Art.

Consensus on any audio product is a pretty rare thing... but everyone has an opinion whether they know what they're talking about or not! ;-)

I may as well fork out the extra money for a really widely appraised model... like this one: http://www.radialeng.com/stagebugsb6.php

Incidentally this isolator has a ground lift. So, why? Is this just a hangover that manufacturers include because it's what customers expect to see?

No. Its because the box is also intended to serve as an unbalanced-to-balanced converter, and in that role it may be appropriate to link source and destination grounds.

Radial products are always well-built and reliable, and I'm sure this one will work as expected.... However, will you really hear the difference between 0.01%THD and 0.05%THD (from a +18dBu input level) over your PA system hidden in the scenery? Because that, and reduced connection flexibility, is all that doubling the price gets you! Personally, I doubt you'd hear any difference between that and the DTI at all... ;-)
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