Bo Hansen DI layout

[Whoops]

Btw,
My own DI boxes I designed in recent years have actually fixed 10 Mohm input impedance on the input for passive instruments, and they are also JFET both on the input and output amp, with a more advanced circuit.

So I do not live as I learn 

--Bo

Nice to know that,
are you selling those DI's is it a product?

I'm into DIY but I have some coleagues that don't do DIY at all and want to buy some DI's I could recommend them your designs

thanks

 

[Gus]

Sometimes you might want less than 1 meg input resistance.
Input resistance and the high pass formed from the RC can makes things better or worse depending on what you want from the guitar or bass interaction with the DI and cable.

 

[Whoops]

Sometimes you might want less than 1 meg input resistance.
Input resistance and the high pass formed from the RC can makes things better or worse depending on what you want from the guitar or bass interaction with the DI and cable.

Definitely, and sometimes you want more than 1 meg.

I have nice passive DI's for lower input impedance.
Also any DI with attenuation at the input will lower it's input impedance when the attenuation is used.

 

[Whoops]

Yes I know, most active DI boxes on the market are around 10 Mohm.

However, the most used input impedance for most of all guitar and bass amps is 1 Mohm, which means that pickups and volume/tone controls on passive instruments have a behavior as musicians are more used to, compared with a much higher impedance.
Ok, the difference is not big but it is still there.

Hi Bo,
I don't use DI boxes for electric guitar at all, being it in the studio or live.

In live sound I use DI boxes mainly for:
- Piezo pickups without preamp (Doublebass, Violin/Cello, Acoustic Guitar, Piano)
- Acoustic Guitar with Piezo with preamp
- Samplers, Keyboards, unbalanced line level sources (low impedance)
- Bass guitar with passive (higher impedance)  or active picukps (low impedance)


80% of the time Doublebass players don't have a piezo preamp (need 10 meg)
90% of the time Violin/Cello Players don't have a piezo preamp (need 10 meg)

80% of acoustic guitars have preamps installed for the piezo (no need for 10 meg but it's fine)

line level sources (low impedance) - (no need for 10 meg but it's fine)

For Bass Guitar, in Live sound the 10 meg can be fine, but sometimes I like to use Passive DI's for Bass, depends on the bass.
I will build one of your DI's with the stock circuit (1 mega input) and the LL1538XL to use on Bass

 

[Bo Hansen]

Whoops,

Sure, I understand your need of good 10 Meg. DI-boxes, when you tell about the type of instrument you usually have on stage..

And as you say, a good passive transformer DI box can often sounds and works best on "line-level" instruments like keyboard and the like.

I like to use some types of the old big "low imp. to grid" mike input transformers as passive DI boxes, from brands as UTC, Peerless, Stancor, Triad, JS/Jørgen Schou, Telefunken/Siemens/TAB, etc.

These can provide a useful character, for example, on some Fender bases, but in such a case it is important that the balanced line to the mixing console is not too long,  because the mirror impedance in the transformer senses the cable quality and affects the connected instrument.

It's amazing how much we can talk about such a simple device as a DI box, there have been more than  900 replies and 200,000 visitors on this topic/thread since we started this project, but it's interesting and fun every time.

--Bo

 

[Whoops]

I like to use some types of the old big "low imp. to grid" mike input transformers as passive DI boxes, from brands as UTC, Peerless, Triad, JS/Jørgen Schou, Telefunken/Siemens/TAB, etc.

I would like to try that out also,
I have a few UTC, Triad and JS/Jørgen Schou transformers , what ratios and impedance would you advice for a DI?

Bob Olhsson, ex Motown Engineer told me his favorite DI and something they used at Motown was an UTC A20 wired back backwards, but seeing the A20 specs, both primary and secondary are the same so I dont think "backwards" relates in this case.
Maybe Bob confused the A20 with another UTC model, that was actually used.
Do you see any use of the A20 as a passive DI box?

thanks

 

[Bo Hansen]

Whoops,

This old "low imp. to grid" transformers have very high ratio around 1:15-1:30, and have  switchable low imp. primary from 50-600 ohms in many steps, which is good if you want to play with ratio/step down.

Of course, they must be used backwards. (secondary as input and primary as output)

Useful types from UTC are, for example, A or LS 10, 12, 14, 27 or the most famous in this context is LS10X.
Other brands like Peerless, Stancor, Triad have also similar types.

--Bo

 

[Rompstomp89]

Can I still order a pcb from here?

Thanks!

Romp

 

[Bo Hansen]

Romp,

You can order PCB for my DI-box here:
https://groupdiy.com/index.php?topic=39570.0

—Bo

 

[Whoops]

Can I still order a pcb from here?

Thanks!

Romp

Really???

The first post of this thread says :

"Boards available here:
From June 2015, Volker is the new supplier of PCBs.
https://groupdiy.com/index.php?topic=39570.msg488632#msg488632"

 

[kylianvb]

Hey! First of all I'd like to wholeheartedly recommend purchasing the parts/PCB from 51xAudio/[silent:arts]/Volker/whichever name applies; Very quick service & solid, safe shipping.

I am however having some problems with my build. Quite certain it has more to do with my incompetence than anything else. I'm having some buzz/hum-issues, with no signal passing through. I just have experience in guitarpedals, where grounding tends to be pretty straightforward, so I was a bit lost on some of the techniques applied here, which is probably where I messed up.

I've got some pictures of the build here, with a video of the issue here.

The XLR-jack I ordered didn't come with any screws, and I didn't have any of the right size with fastening-bolts laying around, hence the messy gluejob on that one (& the alternate chassisground-connection) . Measuring the continuity between the chassis and pin 1 of the XLR still shows a solid connection though, and the XLR doesn't wiggle whatsoever. Also a sidenote; Because the input-jack is somewhat close to the lid, I put a piece of tape there when closing so that I'm sure there's no accidental connection to ground there.

Normally I'd try to follow the schematic (as far as I can with my limited knowledge) and poke around in the circuit with an audio-probe to see if I can find the issue, but seeing how this is working at higher voltages than I'm used to & there's levels I wouldn't want to throw into my amplifier (I believe?), I'm a little cautious.

As you can (somewhat) see/hear in the video, no guitarsignal comes through, but touching the 'guitar-end' of the cable does introduces pops to the output. Same goes for pushing/pulling the cable in and out of the input-jack. The hum is cancelled when the cable's fully removed.

Thanks in advance for reading this, and thanks in general for sharing your designs, Bo!

 

[Bo Hansen]

Hi Kylianvb,

It sounds like they have some kind of sound through the DI box, and it's quiet when you pull out the guitar cable from the DI-box input jack.

Have you checked if you have put the connections on the right side of the inut jack, it's hard to see this in the picture.

If this is done correctly, then you must start searching the error by first checking if all voltage points are correct, you will find the description of these measurements on my tech page  www.hansenaudio.se/techpage.htm

—Bo

 

[Whoops]

Normally I'd try to follow the schematic (as far as I can with my limited knowledge) and poke around in the circuit with an audio-probe to see if I can find the issue, but seeing how this is working at higher voltages than I'm used to & there's levels I wouldn't want to throw into my amplifier (I believe?), I'm a little cautious.

You should do the same for this circuit, Audio probes have normally a capacitor at the probe to block DC voltages going to the input of your amplifier.

First check the voltages like Bo suggested and then Audio probe it following the schematic, from input to the output

It's a simple circuit and easy to troubleshoot

 

[Whoops]

The XLR-jack I ordered didn't come with any screws, and I didn't have any of the right size with fastening-bolts laying around, hence the messy gluejob on that one (& the alternate chassisground-connection) .

XLR connectors don't come with screws, it's just the connector, but you can use any screws you like if they fit.

I prefer to use rivets for XLR connectors and I can see in your vieo that you also used rivets so maybe I'm missing something but I dont see any reason for the hot glue you used on the XLR connector

 

[kylianvb]

Hi Kylianvb,

It sounds like they have some kind of sound through the DI box, and it's quiet when you pull out the guitar cable from the DI-box input jack.

Have you checked if you have put the connections on the right side of the inut jack, it's hard to see this in the picture.

Thanks for the response! I used the example-pictures on your website to figure out the wiring of the jack. However, looking at this again I already may have found an issue.
I ordered a switched insulated jack with 6 lugs, whereas the one in the example has 4. This could change the way I should wire this up.
Here's a crude clarification-image (also added to the original album) of how it's currently wired compared to the example on the right.

If this is done correctly, then you must start searching the error by first checking if all voltage points are correct, you will find the description of these measurements on my tech page  www.hansenaudio.se/techpage.htm

—Bo

With the negative cord on the input jack ground (which is not really supposed to be ground, as I found out later in this post, heh), I measured 12.3v on the anode of the LED, and nothing on the junction mentioned on the page. However, with the negative cord on the chassis these points gave me 25.1v and 11.7v respectively.

You should do the same for this circuit, Audio probes have normally a capacitor at the probe to block DC voltages going to the input of your amplifier.

Thanks! I threw this probe together myself, and it certainly has a cap in there. Just starting out probing without power, it already confirms that my input is messed up beyond belief. Using the labels from the diagram/image up above, lug 1 & 6 carry guitarsignal (instead of ground as I imagined), as well as 5. Seems like probing further in the circuit's going to have little use right now.

XLR connectors don't come with screws, it's just the connector, but you can use any screws you like if they fit.

I prefer to use rivets for XLR connectors and I can see in your vieo that you also used rivets so maybe I'm missing something but I dont see any reason for the hot glue you used on the XLR connector

Fair enough! I actually just used pointed screws, like the ones you'd drill into a plank. It's not a beautiful solution, but I figured I'd atleast fill up the holes from the outside perspective. I probably could've found a more elegant solution had I searched around a little more, to be real. But y'know, reckless 'let's get it dooone!' project-excitement ...

So the input jack's definitely a mess. How should I wire this? In a normal situation I'd know how to DMM-check what (tip/sleeve) connects to what lug, but with the added switching I lose sight of what's going on quick (I know, basic stuff  :-[). I also currently don't have any replacement switched jacks, so I'd rather not experiment with the soldering too much. I assume the low-impedance output has similar issues (seeing as I also used the 6-lug jack for that one), but fixing that one should be as simple as I described above with the DMM and should basically function the same as any jack I've used in the past, right?

 

[RogerB]

Hi

I want to build 4 DI's in a 1U enclosure with it's own power source. I understand from the following:

"you can run the DI box electronics with a stabilized +24 V voltage that is connected to the point where the two 6.8 k resistors are connected together.
-/ground 24 volts should of course also be connected to the ground rail on electronics.
(remove the two 6.8 k resistors if not using phantom powering)"

Q1. Does that mean If I change the schematic like in the drawing it will work?
Q2. Also can I add diodes to XLR 2 and 3 to prevent Phantom power from entering the xlr?

I understand that the PSU needed is dual rail +24 -G -24V. So will the G not be connected to the DI?

 

[[silent:arts]]

Q1 No. You leave the 6K8 out, you don't bridge them!
Q2 No.
Q3 You only need a single +24V and ground.
Corrected drawing attached.

 

[RogerB]

Thank you for correcting the drawing. 
What happens when someone switches the phantom power on from a console while it is being powered form an internal PSU?
also thank you for clarifying that It needs +24V and G.

Q1 No. You leave the 6K8 out, you don't bridge them!
Q2 No.
Q3 You only need a single +24V and ground.
Corrected drawing attached.

 

[[silent:arts]]

Without the 6K8 transformers phantom power won't get into your DI Box circuit, and the transformer doesn't care if phantom power is present or not.

 

[RogerB]

thank you for clearing it all up!

Without the 6K8 transformers phantom power won't get into your DI Box circuit, and the transformer doesn't care if phantom power is present or not.