Best Passive DI Box Schematic?

[spamseekup]

I'm planning on making 5 high quality passive DI boxes using Jensen JT-DB-E transformers.  I have the schematic from their website, but was wondering if anyone else has played around with these circuits and know fo the best way?  Thanks, 

Ben

 

[pucho812]

Their circuit is clean in terms of sound. :thumb: I have built a di using thier trafo but for mine I didn't follow the circuit, I just connected the trafo without the resisters,caps and ground lift. I really like the sound. but thats me. works great that way.

 

[Corvus]

I guess this depends on what you want to hook-up. If it's a high impedance source like an electric guitar or Rhodes, then the classical step-down configuration is what you need. Line level active output devices have more flexibility.

I used a line output trafo from Lundahl to get a balanced output for a keyboard with a -10dBV nominal output level and 250ohm impedance. I put switches for primary and secondary windings to switch between parallel and in series configurations -> I can configure the box for 2:1, 1:1 and 1:2 winding ratios at will. I use this for getting about +/- 6 dB changes to the signal level, which has proven to be handy in band practice and jam sessions. There is no audible difference between these settings, but indeed a measurable one at higher signal levels.

I'm happy for the sound. Works well also for hooking up portable cd-players or MP3-players to active PA speakers. So far have only needed cable lengths up to 30ft - not so critical as a matter of fact. I originally needed this device for breaking ground loops that can easily occur with active speakers unless you can power the speakers from the same power outler.

just my 0.02c

martti.

 

[Bo Hansen]

Ben,

The Jensen JT-DB-E/EPC and Cinemag CM-DBX are some of the best DI-box transformer to day, but also Lundahl LL-1530, LL-1576/77/78 and Sowter 4243, 8044 are a very good alternative with high quality.

If you want a lot of nice "iron" character/transformer personality, try to get some of the great old microphone transformers (connected backwards) as UTC A-10/A-11/A-12, Triad HS-1/HS-11/HS-2/HS-4/HS-14. (I think "CJ" here on the forum, have more proposal for similar old great transformer brands)

Ok, this older types have normal more step down/loss, compare with Jensen Cinemag, Lundahl and Sowter, but they are big and have lot of headroom and a nice warm sound.


--Bo

 

[spamseekup]

Pucho,

So you just connected the input jack to the trafo then straight to the output jack? I've never made one, so sorry if thats a stupid question! Thanks for you help guys, oh, and regarding the Jensen schematics, would it be better to build the "Standard Direct Box" which only has a 6k81 resistor and the tranfo or the full of options "Direct Box Application" which includes a thru jack, 10 and 20 db pads, hi cut... and 5 resistors and 4 caps? That seems like more to interfere with the signal... am I really going to be using those pads on a the Jensen trafo? Thanks!

Ben

 

[pucho812]

It was my first diy very fist. I followed the hook up diagram in terms of color but left out all the rest. no pad, no ground lift, no resistersd, etc,etc. works great for bass and keys that way. I did it like this. take a 1/4 unbalanced and wire it to another 1/4 unbalanced this you have an amp out. then off the first 1/4 wire the yellow off the trafo to the hot(tip) then I wired the black white and orange together. Then on the XLR side wired red to pin 2 brown to pin 3 and white to pin one. No pads no nothing. I like the sound very neutral.

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

 

[jrmintz]

I've built both the standard and more fancy version of the Jensen schematic, and I use them all the time. They're both excellent sounding, and I've never used the pad or the hi-cut, so I think you'd be fine with the simple box.

 

[leigh]

[quote author="spamseekup"]...would it be better to build the "Standard Direct Box" which only has a 6k81 resistor and the tranfo or the full of options "Direct Box Application" which includes a thru jack, 10 and 20 db pads, hi cut... and 5 resistors and 4 caps? That seems like more to interfere with the signal... am I really going to be using those pads on a the Jensen trafo? Thanks![/quote]

Yeah, I wondered about this myself when I built a Jensen DI. I used their Deluxe version but pared it down quite a bit:

- two 1/4" mono input jacks in parallel (the "thru" jack)
- ground lift switch
- 20 dB pad
- XLR and 1/4" TRS output jacks in parallel

If I had built this just for bass guitar (or other passive source) I would have left the pad out. However, I wanted a dual-purpose box, a DI one way and a reamp box the other. So I put a 20 dB pad in there b/c you usually want to pad down when reamping. Also, that's the reason for including the TRS jack on the "output" side (which becomes the input side when reamping): to facilitate running a signal out from the patch bay without having to use a 1/4" TRS to XLR converter.

I've been quite happy with it in this configuration.

Leigh

 

[SonsOfThunder]

I'll hopefully clarify something a little bit more...

If you are only using gtrs or bass, you don't need pad or ground lift.

If you are plugging in keys or loop machine or other thing that plugs into the wall outlet, you *might* need the ground lift.

If you are using the DI for line level sources, you probably need the pad.

The highpass is probably redundant if you have highpass on your mixer or mic pre.

Hope that helps!
Charlie

 

[CJ]

I think the Pro Co DI uses a Jensen transformer. If you just want a transformer in a box, it might be less hassle to by one. Probably 50 or 60 bucks, but if you add up your mechanical time etc,...

only drawback is the cheap-ass hardware that they use.

 

[mrc]

CJ,
I've got a proco, but haven't cracked it open, but I don't think much of it. It knocks a lot of high end off my '59 0018 with the Martin transducer, as well as the same thing with my '72 Les Paul Signature off the amp jack, not to mention how it kills the 74 Jag bass. Never tried it on the Strat. I used the proco live on the Martin in my last band for signal, but backed it with an AT pro 37r at the sound hole, both to the mixer, with enough of the proco to keep a level if I went a bit off mic.
mrc
ps, I dug it out of the closet, DB-1....looks like I'd have to chisel it open, that or gas wrench. Too late for that tonight.

 

[CJ]

Thats the one I had, i think. Pop rivets? Easy to drill. It might be easy to go in there and rip out some resistors to get more high end. Plus, i think there is a cap in there. I ripped out the tranny and jacks and mounted it next to the country hick, so i have a passive and active side by side in a 1U rack.
If anything, the passive is just in case the batteries go dead on the hick side of the rack.

Pro Co is listed on the Jensen site, so that small core transformer is probably a Jensen.

 

[mrc]

CJ,
Cool, thanks, yeah drill, chisel, gas wrench :thumb: I have a JD-10 that's an active direct or amp emulator, that sounds real good as a clean DI and gives a split (it says output to tuner, but works great going to my vibrolux) without loading the pickups. Works pretty good as an amp emulator, too. Don't think they make these anymore. It's got phillips, to bad I don't have one of those new fangled digital picture makers.
mrc

 

[spamseekup]

Also, I had a question about mounting... Do I go for the DB-E which is cased and has leads coming out of it, the uncased version (like they use in microphones) or the cased version with PC mounts? Right now I'm thinking of using just the jensen trafo and the 6k81 resistor on the input side, like the stripped down DI schem they show on the website. I'm thinking of using the ground lift and making a switch to to the pad (I'm using it for bass, electric guitars, and keys). I'm going to put it in a aluminum guitar pedal case, unless you guys have a better suggestion.

Also, the AS007 schem has a thing for AC Coupling. If I'm using it on keys, do I need this option? Also, since it will be in the studio, the cable out of it will travel more than the 10-15 feet and they suggest to permentantly use the pad to prevent the capacitance of the cable loading into the trafo. Should I just permanently wire both the AC Couping mod and the Pad mod into the unit?

Thanks,
Ben

 

[pucho812]

I did the version with the leads comming off which is shielded and canned/ made not having to breadboard anything plus has a mouting bracket type thing.

 

[Mike Keith]

I use the RE-DB from Bauer Comm, same trans as the Jensen. I also do not use the caps, go straight in, works and sound great. Use the ground lift, comes in handy when your splitting the signal.

 

[jrmintz]

Mike,

How do you get in touch with Bauer? I thought they had gone out of the transformer business several years ago, but obviously not.

Thanks

 

[Mike Keith]

800-627-7277, I think their about $56.00, not sure, have several on the way right now...

 

[spamseekup]

Well I've decided to do without AC Coupling and the pad from AS007 as a switch. So I'll have in total a 1/4" in, 1/4" thru, 6.81K ohm resistor, DB-E, ground lift, pad switch, and male XLR out all in a guitar pedal box. Thanks for your help!

Ben

 

[hejsan]

Hidillyho there, I want to make a DI box to connect my passive acoustic guitar pickup to a PA.

Everybody seems to mention electric guitars and passive DI in the same sentence, so I'm wondering if I'm going to be able to make a sweet sweet clean DI using the passive method? Or should I go for an active?

This thread also made me wonder, since I understand that guitar amps usually have something like 1M input Z, how can a 160k transformer primary be enough ? Am I confusing things?

Third thing I'm wondering about is, well, you know how acoustic guitars with pickups sometimes sound all plastic in the highs?.. My guitar actually sounds very rich and sweet unplugged, but when plugged into my electric-guitar amp it gets like that, so I'm wondering if a good DI into the PA is less likely to behave that way?

thanks,
hejsan