DI Boxes: Jensen "JT-DB-E" equivalent?

[danjpiscina]

Hi. I need to make a few passive direct boxes. I saw this on Jensen's site:

http://www.jensen-transformers.com/as/as007.pdf

It's the right type of circuit for me, but I was wondering if anyone out there has made simple DI boxes and if so, what different types of transformers they used. These Jensen's are expensive ($70-80) and are not that great. Something less hi-fi would be great! OEP? Peerless?

Dan P.

 

[abbey road d enfer]

The design of a passive DI transformer involves a number of parameters such as: large primary inductance, low leakage inductance and capacitance, low core induction, high linearity of the magnetic core, rejection of external magnetic fields. Unfortunately, all these parameters are cost-adders. If you want cheaper transformers, which of these parameters are you ready to sacrifice?
What do you mean by "less hi-fi? A passive DI box is already a very mediocre answer to interfacing a guitar to a balanced input. Most of these transformers are rated at 50kohms input impedance, which is too low for passive guitars -they need minimum 100k, 200k is better.
For keyboards/synths, you could use cheaper transformers, because the input impedance can be significantly lower (10kohms instead of 200, less expensive shielding because the level is higher, cheaper core material because the source impedance is much lower).
You say the Jensen is not that great, but it is actually one of the less unsatisfactory transformers for that task.
You could save a lot of money if you went active-transformerless, and have much better performance.
What are your requirements? Do you need galvanic isolation?

 

[owel]

I've used Cinemag transformers for a passive DI box.

But don't discount Active DI circuits.

Here's a comparison between my Active DI kit, compared to a Radial Active DI.

http://www.fivefishstudios.com/audio/SC-1ActiveDI-vs-RadialActiveDI.mp3

You'll hear a slight tick as it swap between the two DI's.
0 - 6 seconds = SC-1 + FiveFish Active DI
6 - 12 seconds = SC-1 + Radial Active DI
12-18 seconds = SC-1 + FiveFish Active DI
18-24 seconds = SC-1 + Radial Active DI
24-30 seconds = SC-1 + FiveFish Active DI
30-38 seconds = SC-1 + Radial Active DI

 

[danjpiscina]

The design of a passive DI transformer involves a number of parameters such as: large primary inductance, low leakage inductance and capacitance, low core induction, high linearity of the magnetic core, rejection of external magnetic fields. Unfortunately, all these parameters are cost-adders. If you want cheaper transformers, which of these parameters are you ready to sacrifice?
What do you mean by "less hi-fi? A passive DI box is already a very mediocre answer to interfacing a guitar to a balanced input. Most of these transformers are rated at 50kohms input impedance, which is too low for passive guitars -they need minimum 100k, 200k is better.
For keyboards/synths, you could use cheaper transformers, because the input impedance can be significantly lower (10kohms instead of 200, less expensive shielding because the level is higher, cheaper core material because the source impedance is much lower).
You say the Jensen is not that great, but it is actually one of the less unsatisfactory transformers for that task.
You could save a lot of money if you went active-transformerless, and have much better performance.
What are your requirements? Do you need galvanic isolation?

thanks for the info! as you can probably tell, i'm not a transformer connoseur! i guess what i meant by "less hi-fi" was something a little more gritty sounding but after doing a little reading it looks like if i wanted a little distortion i'd have to make an active box. the box would be for electric bass more than anything. the most common DI boxes (Radial) have Jensens and they sound boring to me. I'm looking for something that is inexpensive and sounds different. at the end of the day, it's going to be the mic pre that has the biggest effect on the sound but i want an interesting DI box too! i'm not sure about the technical specs and that's partly why i posted this.

 

[gridcurrent]

Use a UTC A-10 or one of the LS series transformers.  They were standard issue in the great studios of the 60's and 70's.  If you insist on an active DI, build a line level box and bypass the mic pre.  The modern DI transformers are indeed SO boring; they make good paperweights.

 

[danjpiscina]

Use a UTC A-10 or one of the LS series transformers.  They were standard issue in the great studios of the 60's and 70's.  If you insist on an active DI, build a line level box and bypass the mic pre.  The modern DI transformers are indeed SO boring; they make good paperweights.

Thanks! I was hoping there was a UTC one out there. you just made my day. We're makin' rock records here, the last thing we want is something that sounds clean! I'm sure you understand. I think I'm gonna have to go with the UTC A-10, but I have a bunch of OEP A262A2E's, do you think these could work? Maybe for a Synth DI or something?


http://www.oep.co.uk/pdf/A262A2E.pdf

 

[danjpiscina]

I've used Cinemag transformers for a passive DI box.

But don't discount Active DI circuits.

Here's a comparison between my Active DI kit, compared to a Radial Active DI.

http://www.fivefishstudios.com/audio/SC-1ActiveDI-vs-RadialActiveDI.mp3

You'll hear a slight tick as it swap between the two DI's.
0 - 6 seconds = SC-1 + FiveFish Active DI
6 - 12 seconds = SC-1 + Radial Active DI
12-18 seconds = SC-1 + FiveFish Active DI
18-24 seconds = SC-1 + Radial Active DI
24-30 seconds = SC-1 + FiveFish Active DI
30-38 seconds = SC-1 + Radial Active DI

I love the sound of your active DI compared to the Radial. Your has an interesting, thick mid-range.  It's a little difficult to get the "full picture" with an mp3 though.What was the bass used?

 

[Davo]

Agreed, the fivefish is definitely superior to the radial... by a long shot.

I built a bo hansen active di not to long ago, and it's pretty kickass... really detailed... may not be what
your looking for in terms of mojo, but it may be one to consider

http://web.telia.com/~u31617586/#active%20DI-box%20my%20work%20horse%20from%201975

cheers,
dave

 

[PRR]

> something a little more gritty sounding ... have to make an active box.

No.

A direct-box is a quick hack to bypass a crappy stage-amp and get some kinda signal into the board's existing mike inputs.

A musical instrument pickup should go into a musical instrument preamp. Take the first two stages from a Fender Bassman or Ampeg B-15. Buffer the output to drive your board line input.

For true grit, you probably need the stage-amp's power stage and speaker. This will mean cleaning-up the amp so it does not have "bad" crap (hum and hiss and crackle), only "good" crap (tube-strain, carbon-dust nonlinearity).

 

[CJ]

everybody was hot on that Bo Hansen circuit, that proved out to be the best DI of them all, and believ you me, there has been a Ton of di boxes, i think i have one floating around the back of every fender amp in the house, you can make those utc;s work as a speaker to line in thingy also, you just clip alligators right onto the spk leads, and the utc magically massages the music into 3rd harmonic submissiion.

here is the 2 second google link, you will find a ton of threads under the search engine here also.

http://www.recproaudio.com/diy_pro_audio/active_di.htm

oh, don't forget the country hick, that is also a good di, skip the weird switcher pwr supply for phantom, just use the 57.

 

[QUEEF BAG]

JT-DB-E

DB... Does that stand for David Baskind of B+B and Aphex?  I heard that at one point. 

ok, that was kinda off topic.

 

[sahib]

Few years ago I picked up a few NOS audio transformers from e-bay with 70K/700K. Reversed it and made an excellent DI.

 

[Tubemooley]

The DB in JT-DB-E stands for Direct Box. What else would it stand for? And transformer direct boxes are supposed to be boring. That's the whole point. They are for getting a clean signal version of any ultra-killer guitar or bass. They are supposed to be transparent and pass the character of an unamplified guitar or bass. You're trying to get the dry version of the pickups. All pickups sound different. Yes, I understand that this is not what you want. You want character. Well, a transformer DI box is not going to do that. I believe you want an active DI preamp as suggested. I have seen the Great River JFET DI posted somewhere recently. Or the Bo Hansen..... Many, many choices. Go to Avenson Audio and look at the Small DI. You can get all the string pluck detail and fingering sounds with a transformer DI. I don't consider that boring. We all have our own likes and dislikes. DW.

 

[Tubemooley]

The Lundahl LL1538 shown in the Bo schematic is at least $70. So is that Sowter. If you're going to match impedances from the output of your active DI to a mic input, well, there's your 70 dollar transformer.

 

[Rossi]

Here's a bit I posted a while ago:

A lot of people seem to believe that passive is always better than active. But when it comes to DI, passive boxes are merely a compromise.

A typical mic input is about 1.5k impedance. A typical passive DI has a 10:1 step down transformer, so the guitar sees an imput impedance of about 150k. That's much lower than is desired (500k-5M) - the guitar pick up will be loaded down and lose part of its presence peak. Of course 150k is still better than a 10k line in but nowhere as good as a "real" instrument input. A guitar amp input is typically 1M, active DI boxes are about the same. The passive DI concept is merely a compromise between impedance increase and level loss. An active DI will give you higher impedance and higher level at the same time. A passive device can't do that. A passive DI will also load down your guitar input, if both are connected in parallel, so your amp tone will suffer to some degree.

 

[CJ]

there was also a great box for bass, i forget, roger nichols talked about it at the aes lecture, it is made in the uk, i think it had a blue case, dang, need to lay off the weed.

 

[danjpiscina]

And transformer direct boxes are supposed to be boring. That's the whole point. They are for getting a clean signal version of any ultra-killer guitar or bass.

Not sure I agree with that. Considering they are dropped to mic level and then put into a mic pre. You're going to get a lot of grit from the mic pre anyway. My hope was to double that. "gridcurrent" pointed out that the UTC A-10's were used in the 60s and 70s (a great time for musicality). These transformers were anything but clean, and they go for $150-$200 on ebay. They have character and they do something to the lo-end that is beautiful and full. I want that. I want a "killer bass" to sound better than it already sounds. larger than life.

Remember, distortion is our friend.

Rock on!

P.S. that Avenson DI sounds interesting.

Dan P.

 

[Tubemooley]

I like distortion as much as everyone else. But I don't reach for a DI box when I want distortion. I have Summit TD-100's and ADL-200's and an ADL-300 plus several others for direct. When I want clean, I go direct. When I want distorted, crank up the tube amp and mic it. Crank up the 5W tube amp so the neighbors don't bitch. Crank up my rackmount Marshall preamp clone and run it without any speaker at all. Crank up my Ampeg SVT II tube preamp which has a balanced line-level output. A passive transformer DI box is my last resort. Go back to the Jensen website and look at more of their DI schematics. At least one of them wires into the speaker circuit with the transformer. Then yer gonna' get the balls and grit of the amp AND the speaker. There are many, many ways to skin this fish. DW.

 

[gridcurrent]

"I like distortion as much as everyone else. But I don't reach for a DI box when I want distortion."

A UTC A-10 configured as a DI exhibits less than .001% total harmonic distortion over most of the audio range.  Musicality does not imply distortion.

 

[pstamler]

A Triad A-11J transformer, hooked up backwards, makes an excellent DI with a little bit of mojo in the low frequencies. Unfortunately, these days it costs as much as, or more than, a Jensen.

I second the recommendation of building a tubed preamp stage. An alternative to buffering and sending at line level might be to connect the preamp output to the input of a DI transformer. Okay, yes, you're now spending even more money. But you'll get a really good-sounding DI. Try the tone stack from a Fender Deluxe AB63 -- it does wonders on a bass guitar.

Another possibility: grab a Groove Tubes Brick. It's an okay but not great mic preamp, but it's one of the best DIs I've ever heard. Maybe the best.

Peace,
Paul