direct boxes

general questions, comments and ideas about recording, audio, music, etc.
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loudmusic
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direct boxes

Post by loudmusic » Sun Oct 12, 2003 7:09 am

Hi. I know we have all talked about this before, but let's do it again.

My specific question:

I plan to purchase a reamp. I want to get the best signal to tape that I can before I go back out to an amp. My board is a ALlen and Heath... would it be a waste of money to get a super nice direct box if I am going to be re-recording it back through the console pre's? I don't really want to spend much on the direct box...say $250 TOPS!! But would save pennies and wait longer if it was worth it to hold out for a avalon or summit or ???
Are the $50-75 boxes a waste of time? What should be my plan of attack??!!!!

Thanks in advance,
Martin

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Meriphew
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Re: direct boxes

Post by Meriphew » Sun Oct 12, 2003 9:01 am

Check out the Groove Tubes Ditto. I think it goes for around $350.

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rhythm ranch
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Re: direct boxes

Post by rhythm ranch » Sun Oct 12, 2003 10:25 am

The Ditto is available at Musician's Friend for $319.99:
Ditto

For $29.99, I've been tempted to try the Behringer box. It may not sound like a $500.00 box, but for $30 it's probably useful for something and is definitely worth a look. Who knows,it might be cool.
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Re: direct boxes

Post by chris harris » Sun Oct 12, 2003 10:44 am

for $250, you can get a di AND a re-amp in one box.

http://www.littlelabs.com/redeye.html

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NewYorkDave
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Re: direct boxes

Post by NewYorkDave » Sun Oct 12, 2003 11:07 am

If you have a good-sounding preamp with plenty of clean gain available, a high-quality, high-ratio mic input transformer run "backwards" makes a good direct box. The typical passive guitar pickup doesn't work well into loads under 100kOhms, so you need a turns ratio of 1:10 or more. (Typical mic preamp input impedance is 1.5kOhms, so a 1:10 transformer would IDEALLY* reflect 150k to the guitar pickup since the impedance ratio is the square of the turns ratio). High frequency response suffers with higher turns ratio, but you don't need ruler-flat response up to 20kHz for guitar, anyway. The better high-ratio input transformers are pretty flat up to 15kHz or so.

The reason you need a fair amount of clean gain at the other end is that the transformer steps down your signal voltage by the turns ratio; so if your guitar signal is 100mVRMS on average, you have 10mV going into your preamp. The gain required to amplify that to, let's say, 0dBU is 77.5 times, or 38dB of gain. For a +4dBU average output level from the preamp, you need a gain of 123, or 42dB. Vintage pawnshop specials with very low-output single-coil pickups may require even more gain.

* The real impedance that the transformer can reflect to the pickup, across the audio bandwidth, is limited by the winding inductance and capacitance. You need to know the actual output impedance of your pickup (not the DC resistance) to be able to calculate the minimum inductance required, and the maximum capacitance allowable. In practice, any high-quality transformer specified to be flat down to 20 or 30Hz and up to 15kHz or more should work fine with most pickups.

Jensens are the best, but very costly. Good quality transformers at lower cost are available from OEP, Beyer, Cinemag and Lundahl.

The advantage of the transformer over a dedicated active DI is size, simplicity, reliability, and the option of using any number of your favorite sweet-sounding mic pres as DI boxes. Conversely, the advantage of an active DI is the the input impedance can be as high as you want and optimized to your pickup.

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loudmusic
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Re: direct boxes

Post by loudmusic » Sun Oct 12, 2003 3:33 pm

Thank you thank you thank you.

You guys are thee best.

Martin

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soundguy
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Re: direct boxes

Post by soundguy » Sun Oct 12, 2003 4:44 pm

hey martin-

dave's idea is cool if you are diy. If you are buying a box, the little labs stuff has I believe a custom transformer design, and its the best DI I have ever heard on guitars. Something about that thing just makes everything sound good. And it will reamp as well. At this point there are a few to chose from. John mentioned at AES that there is plans for a mic pre coming up but in his words "needed to make it special". Im looking forward to it.

For a totally differet flavor, Id also reccomend the aguilar tube DI. they arent cheap, and they arent complicated, its basically a 12ax7 driving a jensen, minimal circuitry, but they have incredible air and very little weight, if that makes sense. I dont like it on much, it makes stuff sound too big for me, but its the perfect thing to record an electric piano, I havent recorded a rhodes with an amp since I got it. I record a lot of rhodes too.

One other thing you can do, which may not mathematically work out too well, but I use api 325's as DI's quite often. It doesnt quite have the right impedance for a guitar (or at least none of mine) but for just about anything else, its pretty badass. I use those for echoplex returns all the time and for whatever reason, like it better than any of the other di's around here.

dave

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