Best Schematic Design for a Passive Transformer DI that also doubles as a Reamping device?

[analogggman]

I'd prefer to keep the signal as clean as possible. So the less components the better because I want the DI to have a rich tone, not sterile "clean". I've got some vintage transformers I want to use to step down. I've noticed some of the ground lifts are attached to a capacitor/resistor combo before going back to ground. Is that worth it? What about pads vs potentiometers for adjusting volume down from the reamp side.

 

[Newmarket]

I'd prefer to keep the signal as clean as possible. So the less components the better because I want the DI to have a rich tone, not sterile "clean". I've got some vintage transformers I want to use to step down. I've noticed some of the ground lifts are attached to a capacitor/resistor combo before going back to ground. Is that worth it? What about pads vs potentiometers for adjusting volume down from the reamp side.

Have to question your terminology / meaning there.
"Clean" implies you want hi fidelity with reference to the input signal. ie same signal as input but at a lower level and impedance.
"Rich tone" implies that you want to add harmonics. "Less components" does not have any particular association with this.
What is "sterile clean" ?
Do you have any examples of DIs / Preamps that have the sonic characteristics you are looking for ?
I suggest that you are looking for something that adds a degree of second order harmonic but please clarify.

 

[user 37518]

I'd prefer to keep the signal as clean as possible. So the less components the better because I want the DI to have a rich tone, not sterile "clean". I've got some vintage transformers I want to use to step down. I've noticed some of the ground lifts are attached to a capacitor/resistor combo before going back to ground. Is that worth it? What about pads vs potentiometers for adjusting volume down from the reamp side.

You are new to this forum, but you will soon learn that the type of language you are using wont get you very far here. You are asking about something objective, like a design, but you are using subjective terms that can mean completely different things to different people. Also, your question is very generic, like when you are asking for less components. I don't know why you think less components would equal to 'rich tone' whilst more components means 'sterile clean', whatever those terms mean.

You ask about the resistor/capacitor arrangement, I am guessing you are referring to an arrangement were a cap and resistor are used to short RF frequencies to ground whilst working as an 'audio open'. This is beneficial to avoid ground loops, but stops the cable shield working as an antenna for RF frequencies.

Your question is so broad, generic and open, that is hard to give you good advice. Perhaps you could provide schematics for us to see what you actually mean (if you ask about the resistor/capacitor arrangement, provide a pic of what you are referring to). Give more information about the transformers you have and want to use, don't expect us to give you a universal template labeled 'clean but not sterile clean DI' that you can use with whatever transformers you have.

Is there a particular DI you have in mind? that would help us give you advice. Your question, as it is, is in the same line of "What is the best DI in the world?" kind of question.

Also, if you already have the transformers, that is basically the DI, the rest is just wiring and maybe passives, unless you want to make an active DI with a transformer (but that contradicts the title of the thread); again, it is difficult to guess what you want. So the sound of your DI will essentially be the sound of your transformer, if you think your transformer is 'sterile clean' that will be the sound of the DI.

To start, I suggest you take a look at the application notes and schematics at Jensen Transformers' website.

 

[analogggman]

Have to question your terminology / meaning there.
"Clean" implies you want hi fidelity with reference to the input signal. ie same signal as input but at a lower level and impedance.
"Rich tone" implies that you want to add harmonics. "Less components" does not have any particular association with this.
What is "sterile clean" ?
Do you have any examples of DIs / Preamps that have the sonic characteristics you are looking for ?
I suggest that you are looking for something that adds a degree of second order harmonic but please clarify.

Sorry for the confusion.

I'm not a fan of the Jensen DI sound. That's what I am referring to as sterile clean. Or boring.

The pic the lowest is a Motown Wolfbox. I don't see the capacitor filter network on that one, but maybe I'm missing something. The schematic for motown below shows a capacitor filtering. Did the originals have that? I guess I'm trying to come up with a Motown style DI box that doubles over as a good reamper.

So I've got two transformers. I'm thinking it only makes sense to build one with the potentiometer for reamping to adjust volume when sending back out. The other uses I wanted for this was to have something to send DI from my control room back out to the live room, without causing much drop in fidelity. Currently I have a guitar cable run, but I think it's too long and introduces high frequency roll off and volume drop.

 

[analogggman]

You are new to this forum, but you will soon learn that the type of language you are using wont get you very far here. You are asking about something objective, like a design, but you are using subjective terms that can mean completely different things to different people. Also, your question is very generic, like when you are asking for less components. I don't know why you think less components would equal to 'rich tone' whilst more components means 'sterile clean', whatever those terms mean.

You ask about the resistor/capacitor arrangement, I am guessing you are referring to an arrangement were a cap and resistor are used to short RF frequencies to ground whilst working as an 'audio open'. This is beneficial to avoid ground loops, but stops the cable shield working as an antenna for RF frequencies.

Your question is so broad, generic and open, that is hard to give you good advice. Perhaps you could provide schematics for us to see what you actually mean (if you ask about the resistor/capacitor arrangement, provide a pic of what you are referring to). Give more information about the transformers you have and want to use, don't expect us to give you a universal template labeled 'clean but not sterile clean DI' that you can use with whatever transformers you have.

Is there a particular DI you have in mind? that would help us give you advice. Your question, as it is, is in the same line of "What is the best DI in the world?" kind of question.

Also, if you already have the transformers, that is basically the DI, the rest is just wiring and maybe passives, unless you want to make an active DI with a transformer (but that contradicts the title of the thread); again, it is difficult to guess what you want. So the sound of your DI will essentially be the sound of your transformer, if you think your transformer is 'sterile clean' that will be the sound of the DI.

To start, I suggest you take a look at the application notes and schematics at Jensen Transformers' website.

I apologize for being vague. I will try to be as specific as possible with future posts. If you look at the post I just made, the idea is to do a motown style box that can double as a reamper. I'll be using vintage transformers to make it. I have two transformers. I was thinking one wired up just as a simple DI, and the other with some more controls for the reamp side.

I definitely don't want to make an active DI.

 

[ccaudle]

the idea is to do a motown style box that can double as a reamper

(shows picture of active DI circuit with no transformer)

I definitely don't want to make an active DI.

[EDIT] Did you (or someone else) use a dual triode symbol in a circuit that is supposed to indicate a transformer? Very confusing.

 

[analogggman]

(shows picture of active DI circuit with no transformer)





[EDIT] Did you (or someone else) use a dual triode symbol in a circuit that is supposed to indicate a transformer? Very confusing.

I'm thinking maybe they used the dual triode symbol instead of transformer symbol. That was not my circuit.

 

[dmp]

Try searching, there's previous posts on the wolfbox and passive DIs.

For passive DIs I've compared quite a few. Jensen DB, UTC LS-10, Triad. The Wolfbox used a Triad 10/11/12-J. Those transformers have a really noticeable and distinct sound. The sound is in the transformer, not the components around it. In fact I throw out all the filtering, impedance pot, level pot, etc... not needed.
But the Triad's are hard to find. And with the materials and winding methods probably a modern reproduction is impossible.
The LS10 is the "Bruce Swedian" DI. Also sounds great, but not nearly as noticeable as the Triad. I personally think the Triad sounds great but it's heavily 'affected' so I wouldn't use it all the time. The Jensen DB is not that special, but I have a pair and they come in really handy for synths etc... whenever I need a DI. I almost always chose a tube DI over any of the passive DIs, for a guitar or bass.

For reamps I've used the UTC O-10, which was used in the original. It's always reproduced the sound right, so I haven't experimented as much. You can even use a 1:1 transformer, just bring the send level down. In fact, a lot of people skip the transformer altogether. The transformer in a DI is interacting with the pickup in the guitar. For a reamp, it's being driven by the interface or console, and the transformer is less important. I want to be able to get the same sound with DI->preamp-> DAW -> reamp -> amp as I get with the DI thru going into the amp, and with the O-10 I get that.
But I usually use a tube DI versus the passive DI.

 

[analogggman]

Try searching, there's previous posts on the wolfbox and passive DIs.

For passive DIs I've compared quite a few. Jensen DB, UTC LS-10, Triad. The Wolfbox used a Triad 10/11/12-J. Those transformers have a really noticeable and distinct sound. The sound is in the transformer, not the components around it. In fact I throw out all the filtering, impedance pot, level pot, etc... not needed.
But the Triad's are hard to find. And with the materials and winding methods probably a modern reproduction is impossible.
The LS10 is the "Bruce Swedian" DI. Also sounds great, but not nearly as noticeable as the Triad. I personally think the Triad sounds great but it's heavily 'affected' so I wouldn't use it all the time. The Jensen DB is not that special, but I have a pair and they come in really handy for synths etc... whenever I need a DI. I almost always chose a tube DI over any of the passive DIs, for a guitar or bass.

For reamps I've used the UTC O-10, which was used in the original. It's always reproduced the sound right, so I haven't experimented as much. You can even use a 1:1 transformer, just bring the send level down. In fact, a lot of people skip the transformer altogether. The transformer in a DI is interacting with the pickup in the guitar. For a reamp, it's being driven by the interface or console, and the transformer is less important. I want to be able to get the same sound with DI->preamp-> DAW -> reamp -> amp as I get with the DI thru going into the amp, and with the O-10 I get that.
But I usually use a tube DI versus the passive DI.

I feel you on the tube DI. I absolutely love it for bass, and usually now is my go to for synths. I was thinking it would be cool to use the DI vintage transformer into the line level of the tube box for a mix of colors.

How exactly do you mean using a 1:1 to bring the send level down? Like send it out to a 1:1 transformer box with a trim and trim it back down before it hits the amp?

I picked up what look to be some no name vintage step up transformers from Phoenix Trans. Co. They look pretty hefty and I'm hoping will do a good job.

Regarding your UTC O-10 box... is it just wired up like a simple DI? No pots or pads? I suppose you can just adjust it with the fader in the DAW. Maybe I will just keep mine simple and only include a ground lift and thru jack.

 

[TriadMagnetics-Bill]

www.OnlineComponents.com is stocking the A-10/11/12J. Unfortunately, they are expensive to manufacture. We're building them in our California facility (USA) using the original paper-layered winding method, nickel lamination and deep-drawn mu-metal shield cans. We've upgraded the lead-wires to higher temp Teflon insulation vs. the original PVC making them easier to solder. In any case, the A-11J was $19.20 each in 1960, adjusted for inflation that would be $199.65 in 2023, so the price has actually decreased: www.onlinecomponents.com/en/triad-magnetics/a11j-12695159.html

 

[sodderboy]

(shows picture of active DI circuit with no transformer)





[EDIT] Did you (or someone else) use a dual triode symbol in a circuit that is supposed to indicate a transformer? Very confusing.

Thats a secret P48 powered tube DI!
Dang that reminds me of my first electronics phone call to the "ham store" to get parts for a code oscillator. I had the ARRL Morse book and thats about all. Highlights:
Him: "How can I help you ma'am?"
Me: "Do you have 10 squiggle-squiggle F, um, capacitors?"
I soldered that sucker on a terminal strip with a woodburning tool and plumbing solder but it got me to my novice class license.
There are two DI schools- transparent and coloring. I am in the transparent school and folks can color it how they want in the box. You can't always have your "secret DI" with you. . .
I would build ANYTHING first and then judge how it sounds, working on build quality.
Mike

 

[Philbo King]

Some interesting insights on using a transformer for reamping:
https://gearspace.com/board/geekzone/1396016-diyre-reamp-transformer-upgrade.html

 

[MisterCMRR]

That "Motown DI Box" schematic has got to be an April fool joke? It couldn't possibly work as drawn!

 

[Dylan W]

I believe the transformer in that schematic is a Bogen TM200, which plugs in into a noval tube socket.

 

[MisterCMRR]

I see. So it's OK to put any symbol I like on a schematic as long as I reference what it really is with a part number? It's a separate reality I suppose ... sigh.

 

[Whoops]

the idea is to do a motown style box that can double as a reamper.

By reading your posts I'm not really sure if you know the difference between Mic Level and Line Level.
Maybe you know, but I can't be sure

A DI box transforms Hi-Z unbalanced instrument level to Low-Z Balanced MIC LEVEL

A Reamp Box transforms Low-Z Balanced LINE LEVEL to Hi-Z unbalanced instrument level

Those are 2 different devices and 2 different implementations,
I'm not seeing any good way of trying to get both from the same box. You should build 2 separate devices.

By the way, contrary to many wrong assumptions, a Passive DI box used backwards is NOT a Reamp Box