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new member, passive DI build help
Old 6th August 2020
  #1
Here for the gear
 

new member, passive DI build help

Hello, everyone, I haven’t been on a forum since the Metro Amp, Harmony Central days long past. Been a lurker here for a while, time to jump on board.
I want to build a couple Di boxes for multi purpose use.
I have the actives covered.
J48
BSS AR-116
Countryman Type 85
SCV DI2 MKII (3)
Rodam (cant remember the model) haha

passives:
Whirlwind imp-2 (missing at the moment)
Rapco DB-100

I want to build two passives to use for my interface I just bought (Focusrite 18i20) which has TRS outputs. I was running trs to xlr cables to the board and thought, if someone hits the phantom power switch is my Interface toast?

That got me thinking, I need two passive Di’s as a safety net.

I don’t want to degrade the Signal so I need a couple quality transformers.
I can order Jensen, Cinemag, Souter etc., but thought I’d check locally to see if there’s anything available.

I found a local hi-fi shop that has some NOS
UTC 1148 and F-7101
Chicago Standard Transformer Corporation 13
Tesco No.322
Hammond 850L
Plus a big pile of Hammond 800 series, and a couple 585j and 585F
*I’m in Canada hence the pile of Hammonds*

I’m not familiar with any of these and after some digging I saw a post where a guy said he built some boxes with the Hammond 850L which were very comparable to the Jensen JT-DB-E.

I’m not not a tech and not very knowledgeable with specs, I’m learning as I go and have beginner level fundamentals.

If anyone has any advice on the transformers I listed and can chime in, I’m all ears (well eyes I guess).

My other options are to just buy a couple used Cable Factory Di-Pro passives which have the Lundahl 1530 (I think), they’re going for 160.00 each.

Holy long winded first post.

Last edited by Stumpy the Rook; 6th August 2020 at 04:43 PM.. Reason: Mistake
Old 6th August 2020
  #2
Lives for gear
 

passive DI box

get that Hammond 585f quick !
makes a 850L sound broken.
Old 6th August 2020
  #3
Here for the gear
 

Quote:
Originally Posted by cathode View Post
get that Hammond 585f quick !
makes a 850L sound broken.
Really, this is what I want to hear. You have experience with the 585f?
I appreciate your input, thanks.
Old 7th August 2020
  #4
Lives for gear
 

Can you run XLR to TRS cables to line inputs on the board? The line inputs don't have phantom power (well, on any mixer I've come across). I'm of the opinion that "no transformer" will cause less signal degradation/coloring than even a really good transformer.
Old 7th August 2020
  #5
www.jensen-transformers.com
sells the DB transformer. They also have schematics to build your own, very complete.
Old 7th August 2020
  #6
Here for the gear
 

Quote:
Originally Posted by DrewE View Post
Can you run XLR to TRS cables to line inputs on the board? The line inputs don't have phantom power (well, on any mixer I've come across). I'm of the opinion that "no transformer" will cause less signal degradation/coloring than even a really good transformer.
I want two boxes to act asa pair of Di boxes, reamp, and isolation boxes for a stereo signal, multi purpose. The interface has TRS outputs so I ran a TRS>XLR cable to the XLR inputs on my mixer set for line level. I like the idea of having balanced cables to the board, just worried about the phantom power getting accidentally pushed. I’m asking a lot from these two boxes haha.
Old 7th August 2020
  #7
Here for the gear
 

Quote:
Originally Posted by Jim Williams View Post
www.jensen-transformers.com
sells the DB transformer. They also have schematics to build your own, very complete.
I originally wanted to use the Jensens or the Hammond, Cinemag, Souter etc. equivalent but I’d have to order, them, pay taxes shipping currency exchange yada yada. That’s why if these vintage Hammond’s would work it would be great, I can get them for less than any of the others and they might have some mojo (guessing, no idea).
Old 7th August 2020
  #8
Here for the gear
 

Another thing I just thought of, I don’t think the TRS outputs from my interface (Focusrite 18i20) will be accepted by the unbalanced input of a Di. Can the inputs of a Di be balanced? Are the primary and secondary both capable of having balanced connections?
Old 7th August 2020
  #9
Lives for gear
 

vibey DI box transformer

Quote:
Originally Posted by Stumpy the Rook View Post
Can the inputs of a Di be balanced? Are the primary and secondary both capable of having balanced connections?
absolutely.
simply use /TRS jack(s) for the input connections and wire appropriately.

as to your earlier comment if the Hammonds have "mojo": definitely !
all the older Hammond designs including the 850 series have good tone.
the hard to find 585 series even more so, plus designed in noise rejection:
mu-metal case, hum bucking construction, and internal electrostatic shield.

the 585f is special due to the very high turns ratio, read that as extremely low input loading.
modern, trendy di box transformers not only sound vanilla, but present more load to a source,
nearly all the current crop use 12:1 ratios.
Attached Thumbnails
new member, passive DI build help-585_.jpg  
Old 7th August 2020
  #10
Here for the gear
 

Quote:
Originally Posted by cathode View Post
absolutely.
simply use /TRS jack(s) for the input connections and wire appropriately.

as to your earlier comment if the Hammonds have "mojo": definitely !
all the older Hammond designs including the 850 series have good tone.
the hard to find 585 series even more so, plus designed in noise rejection:
mu-metal case, hum bucking construction, and internal electrostatic shield.

the 585f is special due to the very high turns ratio, read that as extremely low input loading.
modern, trendy di box transformers not only sound vanilla, but present more load to a source,
nearly all the current crop use 12:1 ratios.
So they’d be good for a passive P bass? That’s my main instrument. Like I’ve stated I’m hoping to get multiple usage out them, line level from keys, interface etc.

The guy I’m buying them from said they’re mic SUT but the chart says line to grid, as long as they work I think I’ll go ahead and buy them. They’re not cheap but not crazy either, cost me about the same as ordering Jensen/Cinemag plus shipping taxes etc.

Thanks a lot for you’re input, it’s why I joined this forum, I knew somebody here would have the knowledge.

Thanks again!!
Old 8th August 2020
  #11
Lives for gear
 

Quote:
Originally Posted by Stumpy the Rook View Post
So they’d be good for a passive P bass? That’s my main instrument. Like I’ve stated I’m hoping to get multiple usage out them, line level from keys, interface etc.
passive P bass ? maybe and maybe not.
despite high turns ratio and reflected impedance of the 585f, you well might prefer an active DI.
allow me to plug the Countryman; it has stood the test of time for 50 years.

passive DI's were certainly popular with passive instruments in the 60's.
Columbia had boxes made up with UTC A series transformers wired for maximum turns ratio.
RCA had boxes made up with UTC LS types.

keyboards, active bass: passive DI well suited.
Old 8th August 2020
  #12
Here for the gear
 

Quote:
Originally Posted by cathode View Post
passive P bass ? maybe and maybe not.
despite high turns ratio and reflected impedance of the 585f, you well might prefer an active DI.
allow me to plug the Countryman; it has stood the test of time for 50 years.

passive DI's were certainly popular with passive instruments in the 60's.
Columbia had boxes made up with UTC A series transformers wired for maximum turns ratio.
RCA had boxes made up with UTC LS types.

keyboards, active bass: passive DI well suited.
I’d love to find a suitable Triad or UTC but I’m wanting two boxes to do the stereo thing, buying one of those is a lot more than I’m hoping to spend. I’m kind of caught in the middle because I want to have a poormans Motown Di aaaand a versatile stereo pair.

If the Hammonds won’t do the vibey extended low end, warm mids vibe, I might as well go with a cheaper modern stereo Di if it’s just for utilitarian use.

Would I be better off just paying (a lot) more for a single transformer like an LS10x specifically for the passive P bass, and forget about the Hammonds in this case?

Sorry for all the questions, I’m so on the fence, haha
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