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Author Topic: direct box or Shure line matching transformer  (Read 14431 times)

Chris Harwood

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direct box or Shure line matching transformer
« on: February 13, 2011, 03:44:48 pm »

I have a variety of mid level DI boxes and a bunch of these Shure line matching transfomers (A95UF).  I honestly don't hear much of a difference.  Is this because they are all cheap, or my hearing aint up to snuff?
I just bought a Rapco DBR400 direct box (4 channel - very inexpensive used, but $275 retail), which I haven't used yet.  Will it be more of the same?

I guess I am asking what is best for hooking keys, guitar stompers, etc...directly into the PA from the stage, where I need to convert them to a lo-z input?

Also, not looking to spend $400/direct box, as I need 6 channels for my live rig. Continue using what I've got, or will the extra $$$ make a huge difference with my Roland synths and Line6 floor stuff?

Thanks.
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Tom Young

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Re: direct box or Shure line matching transformer
« Reply #1 on: February 13, 2011, 04:23:02 pm »

It depends on two things:

1) the level you feed into the DI or in-line (aka:barrel) transformer. Cheaper (smaller) transformers will distort when fed a "hefty" line level sigal as can be provided by a electronic keyboard or electric guitar or bass with active electronics. This distortion is more likely to occur at lower frequencies and during peaks in amplitude, as well.

2) the acoustics and system. In a very live space the subtle benefits of better designed DI's and transformers may not be evident. Likewise, if your system is not well designed and optimized and it introduces distortons of its own (combfiltering and other phase anomalies, distortion, etc) this will mask the improved sound from a better quality DI or transformer.

Actually, there are other factors that go into finding and using the "right" interface and/or the effects of the wrong devices. Impedance is one.

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Tom Young, Church Sound section moderator
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Chris Harwood

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Re: direct box or Shure line matching transformer
« Reply #2 on: February 13, 2011, 07:47:25 pm »

Thanks Tom.
This will be in "non"-optimal situations... untreated churches and the best would probably be outside events.
So as I understand, watching the levels on my synths and floor stompers (going in direct) is the main issue.  I can deal with small "subtle" deficiancies, as in the "mix" it isn't going to matter much....or at least compensate at the source.
Use the little Shure barrel transformers and/or the $75 DI boxes and save the good stuff for the studio??
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Dick Rees

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Re: direct box or Shure line matching transformer
« Reply #3 on: February 13, 2011, 09:35:37 pm »

The quality of the input devices in the signal chain is arguably the most important part of the overall sound system.  Compensating downstream  for poor input quality is never easy or completely effective.  If you've spent good money for quality gear on which to play, then it just makes good sense to get what it takes to give as good a quality input into the sound board.  

Good mics and DI's are indispensable.
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Chris Harwood

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Re: direct box or Shure line matching transformer
« Reply #4 on: February 13, 2011, 11:42:28 pm »

Dick Rees wrote on Mon, 14 February 2011 02:35

The quality of the input devices in the signal chain is arguably the most important part of the overall sound system.  Compensating downstream  for poor input quality is never easy or completely effective.  If you've spent good money for quality gear on which to play, then it just makes good sense to get what it takes to give as good a quality input into the sound board.  

Good mics and DI's are indispensable.


I'm thinking I might have been mistaken with my "compensating" word. I meant to compensate AT the source.  IOW, if the synth sounded lacking in bass because of an inexpensive line transformer, I'd add bass with the synth patch, AT the source.

Additionally, I didn't want to spend 6 x $400 ($2400) for
Countryman quality direct boxes if I was only losing 2% (as a guess).  Since I already have DI and line transformers that do work, my $2400 might be better spent somewhere else.  But I do understand the "weak link" theory.  Thanks for the reply.
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Dick Rees

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Re: direct box or Shure line matching transformer
« Reply #5 on: February 14, 2011, 10:19:30 am »

Chris Harwood wrote on Sun, 13 February 2011 23:42

Dick Rees wrote on Mon, 14 February 2011 02:35

The quality of the input devices in the signal chain is arguably the most important part of the overall sound system.  Compensating downstream  for poor input quality is never easy or completely effective.  If you've spent good money for quality gear on which to play, then it just makes good sense to get what it takes to give as good a quality input into the sound board.  

Good mics and DI's are indispensable.


I'm thinking I might have been mistaken with my "compensating" word. I meant to compensate AT the source.  IOW, if the synth sounded lacking in bass because of an inexpensive line transformer, I'd add bass with the synth patch, AT the source.

Additionally, I didn't want to spend 6 x $400 ($2400) for
Countryman quality direct boxes if I was only losing 2% (as a guess).  Since I already have DI and line transformers that do work, my $2400 might be better spent somewhere else.  But I do understand the "weak link" theory.  Thanks for the reply.


If the device in question will not handle a particular frequency range, increasing the amount will do nothing to help.  In fact, it may well overload the circuitry making the problem worse.  

Secondly, there are several very good DI's for much less than the amount you're quoting.  The BSS 133 sells new for around $160/channel, used for a bit less.  Gather some more information and spend some time shopping for a deal.

One other possibility is using a small, good quality sub-mixer on stage to handle the multiple signals and then route them to the house mixer over a balanced stereo feed.

There are a lot of things you can do here with a little time and study.  
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Chris Harwood

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Re: direct box or Shure line matching transformer
« Reply #6 on: February 14, 2011, 07:15:13 pm »

thanks Dick,

I hope you are not implying that I have not done any research or time spent studying.  As far as the submixer... I realize all that, and am surprised you might offer that as a suggestion, as that only takes away of the flexibility the FOH mixer has.  Merging signals only to go thru a marginally better DI doesn't make much sense to me.
As far as the DI not passing thru a true signal, I was hoping to be clear that should the DI have a hi-pass, inherent quality, I could compensate and hopefully we are all on the same level that we wouldn't be clipping with improper gain staging, by cramming a pile of 20hz freqs thru it and wondering why those frequencies aren't making it to the mains.
I appreciate your suggestions, but think they are a tad off course of my original questions which were asking as to the amount of quality gain over the ubiquitous line transformers by Shure to something "better".

Thanks again,
Chris
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Lee Buckalew

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Re: direct box or Shure line matching transformer
« Reply #7 on: February 16, 2011, 03:01:06 pm »

Chris,
You are missing or misinterpreting one of the comments that Tom made.  A lower quality transformer may be saturated by low frequency energy much more easily than a higher quality one.  This does not mean that it does not pass bass, it means that the entire transformer is now suffering from magnetic saturation and the THD of the lower frequencies signals is very large.  decreasing your signal level, but boosting bass in an attempt to compensate for this would be the wrong approach.  You would need to keep your linear frequency response but reduce the level at the source then apply makeup gain at the console input.  You are having to avoid hitting the inexpensive transformer too hard.

Also, the Countryman DI's do not sound nearly as good as the BSS 133, although they do cost much more.

His,
Lee Buckalew
Pro Sound Advice, Inc.
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Chris Harwood

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Re: direct box or Shure line matching transformer
« Reply #8 on: February 16, 2011, 04:38:41 pm »

thanks Lee,
I totolly understand now.
The only downside to the BSS is that they are active, but I suppose I could grab the phantom power.  I'll need to see if they offer multi channels, as it'd be nice not to have a bunch of them lying around versus a rack, etc.  Since they really aren't that expensive, I ought to pick one up on the recommendations here and try one and see what I think.
Then get more if I like them.
Thanks again all.
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Jonathan Johnson

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Re: direct box or Shure line matching transformer
« Reply #9 on: February 19, 2011, 10:28:06 pm »

As a rule of thumb, consider an active direct box (requires a power source) for a passive source (guitar pickup), and a passive direct box for an active source (keyboard).

Of course, that's just a rule of thumb and there are always exceptions to the rule and ways of making a less than ideal tool work when that's all you have.
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