[ReRibbon]

@pucho812

sweet.
Whopps' post didn't load all the way. I never saw it all.

@Whoops - Sorry dude. Thanks.

[EmRR]

Wolfrum's comments about the triad A series require reading between the lines.  They aren't particularly good transformers, though they may be stellar given their cost point.   Being not particularly good contributes to the favorable way they sound.  A modern Jensen/Cinemag/etc can easily measure better in all regards, and that's not what we are after.   We want 'crappy enough' for what it does here. 

[ReRibbon]

I honestly can't imagine paying $450 for this assembled circuit.

[Biasrocks]

I believe the UTC's that Bob is referring to were used in the Motown studio's DI/Gtr Amp that the guitar players would plug into as pictured below.

This would provide a direct signal to the console as well as a feed to a small amplified speaker so the players could hear themselves.

Instead of the Triad's for the passive Wolfrum DI, you could use any Line to Grid transformer in reverse ideally 60000:250 or 150 as per the Triads.

Anything close to that is going to work fine.
 
Mark

[Biasrocks]

I honestly can't imagine paying $450 for this assembled circuit.

That doesn't seem out of line considering the cost of manufacturing a long lost transformer in limited quantities.

Mark

[gridcurrent]

an UTC A20 transformer connected backwards,

looking forward to a lively discussion how that works as a DI.  Forwards, backwards, upside down ?

[lassoharp]

Also the favorable DI at Motown as per Bob Olhson source (Motown Mastering Engineer) was an UTC A20 transformer connected backwards, Bob says that in a couple of threads on the internet, he also told me about that when I met him in Nashville in 2012.
Not to say that they didnt have other DI devices at the studio, they probably had, like the Mr. Ed Wolfrum DI device.
I just pointed that out because the title says "Motown DI"

With a mic pre that has an input transformer you can plug an instrument directly into the primary and get a decent DI signal (it's not as noisy as one might think).  It makes me wonder if the A-20 was used in  a box more for basic isolation and connector conversion interfacing than providing a higher bridging impedance.  A transformerless mic pre may not fare too well with an A-20 box.  A-10/11/12 much better there.

[pucho812]

I believe the UTC's that Bob is referring to were used in the Motown studio's DI/Gtr Amp that the guitar players would plug into as pictured below.

This would provide a direct signal to the console as well as a feed to a small amplified speaker so the players could hear themselves.

Instead of the Triad's for the passive Wolfrum DI, you could use any Line to Grid transformer in reverse ideally 60000:250 or 150 as per the Triads.

Anything close to that is going to work fine.
 
Mark

  The the di's were active  fixed gain preamps with an output attenuator .  they fed the console.  I have as pdf about it it is attached below.

[EmRR]

Multiple problems.

+27 dBu, vacuum tube, and UTC A-20 don't all go together in the same sentence.  Sure, you can get that output level through one so long as you never put anything lower in frequency than guitar,  but with tubes?   Sure it can be done, but that's weird overkill design to fudge that transformer into that scenario. 

[CJ]

anything made in mass quantities can give you trouble,

you never know who built it,

UTC= You Take a Chance   

Triad= Total Ripoff-I Am Disappointed   

[ReRibbon]

Maybe the A20 added a tonal thickness  (?) and was used after the instruments' impedance had already been converted from hi to lo impedance through a DI circuit?

[CJ]

why does the A11j come in a round can?

[EmRR]

why does the A11j come in a round can?

Yeah, WTH is that about?    Is it made of little donuts? 

[ReRibbon]

Maybe it doubled as a line weight for catfishing?

[CJ]

round can = more hum rejection,

less shielding required for the cheap engineers,

probably "borrowed" from W.E.

[fredwreck]

Does anyone have any pics of their builds for this DI Box?  I just got a Triad A-12j.  The schematics are good and simple, but it always helps to have some pics as a double check.

Thanks!

[dmp]

Here you go

[fredwreck]

 

Here you go

Thank you so much!! I needed this!

But now Im confused.  In the schematic it shows that BROWN from the Triad goes to pin 2, and Red to Pin 3.  In this pic Brown is going to pin 3 and Red to pin 2.

And the Potentiometer wiring is backwards to me too.  Am I wrong?

Also Im using the Triad A-12j.  and it has a Red&Black wire.  Anyone know where this goes?

Thanks for your help everyone!

[dmp]

Red and Black are the transformer output - switching them reverses the phase. Since it is a DI, it doesn't really have a correct phase.
At this point you have more than enough info to start learning from experience. Build it and see how it works.
If the pot is wired wrong, you'll know it when you try it out when "turning it up" is actually turning it down
A DI is a great first project to learn from.
Post some pics of your build

[fredwreck]

Thanks for all your help everyone.  Finally got this thing done.  Ed Wolfrum was really nice about helping with the wiring of the A-12j.  It sounds great!