Best Passive DI Box Schematic?

[echorec]

[quote author="Bo Hansén"]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.
[/quote]

I have some Lundahl 4602, would they make a good passive DI box?

The LL4602 is a C-core line output transformer for unbalanced (single-end) drive. Internal structure is similar to the LL5402.

LL4602 usage (turn ration 1 : 1)

Pin 1 + Pin 5 primary ground
pin 2 + pin 4 primary signal in (+)
pin 3 not used


pin 7 out +
pin 10 out -
pin 6 + pin 9 connect

 

[Bo Hansen]

echorec,

If this transformer are a 1:1 output transformer and have not any step-up ratio (step-down in this case when it shall use backwards)
it is not usable as a passive DI-box transformer, because the low impedance structure.

The best transformer for a passive DI-box are a high ratio microphone transformer with approx. 1:10 step-up ratio, that you use backwards. (guitar to the secondary and primary to the console mike input)

Look at the Lundahl LL1576, 1577, 1578 types.

--Bo

 

[echorec]

Thanks Bo!

 

[Brown Note]

Is there any reason not to assume that an Edcor WSM 10k/150 would work in this situation as well? I'd be into having a few of these boxes, and the Edcors are dirt cheap.

 

[babyhead]

Is there any reason not to assume that an Edcor WSM 10k/150 would in this situation as well?

I think the shield is the issue there...

 

[Brown Note]

I think the shield is the issue there...

...a shield between the primary and secondary or a sheild for the whole transformer?

i'm still a newb here...always confused. i had assumed that shielding was normally required because of the step-up of a mic input. why on an unbalanced hi-z/150?

 

[Bryson]

[quote author="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[/quote]

To me most piezo equiped acoustics have a sharp snap to the attack that I never like....rubberbands.
Magnetic pickups sound much smoother in an acoustic but sound more like a clean electric.
I have no experience with live acoustic DI but have gathered that the most natural sound comes with the pickup/little microphone inside the soundhole combo. I'm not sure who all makes such a rig but I imagine Baggs or Fishman might.

If the guitar has a piezo and no built in preamp, an FET DI with Hi-Z in the mega ohms would be a "proper" match.

My favorite xfrmrs for electric gtr/bass DI are the UTC A-27 (100k/600 xtal mic input) and the Jensen (200k/600).

 

[echorec]

[quote author="Bo Hansén"]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...[/quote]

I have been checking ebay and all of these pop up regularily. Do they sound the same or is any of them preffered for DI?

 

[ersatz007]

hi - does anyone have a wiring diagram for UTC A-11?