Bo Hansen DI layout

[Bo Hansen]

Brain,

I never used any simulation software, so I do not know how much it understands of analog design that does not always follow the theoretical rules.

But if you must try to simulate the DI-box, you should remove the two phantom resistors, and instead connect +24 volts directly over 100 uF electrolyte.

You must also connect a 1 kohm termination resistor across the XLR pins 2 and 3 to be equal to the load that the DI-box will see from all phantom resistors and input impedance of pre-amp/mixing console.

You should also measure the output signal over this 1 Kohm resistor.

I do not know if the sowtware can simulate a microphone transformer connected backwards with a ratio of 5:1, which shall then have a primary impedance of 5 Kohms when the secondary side is loaded with approx. 1 Kohms.
And also take into account how the transformer is made, the size of the core etc.

This is a very interesting experiment, and I think there are others here on the forum who understand simulation sowtware much better than me, and have comments on my claims.

Best from
Bo

 

[bds2020]

Bo,

Thanks for your comments.  I'm curious why you suggest removing the two phantom resistors (I think you're referring to the 6.8k resistors) and connecting the +24 volts directly over the 100 uF electrolyte.  I was thinking of inserting the 48v source b/t pin 2 and the first resistor.

Brian

 

[Bo Hansen]

Brian,

Sure, you can do this, because all four 6.8 kohm resistors (two in DI box and two in mike preamp) is theoretically connected in series/parallel, and then the end result is 6.8 kilohms.

But I do not know what the sowtware think about dc voltage connected unbalanced on the transformer secondary side.

Please note, the important thing about powering is that Di-box electronics internal "top voltage rail" is applied to a + 24 volt dc regulated voltage, and this voltage rail not draw more current than 3.5 mA.

And that you use a simulated transformer with right parameters, and terminate the secondary with 1 kohm.

For a simulation sowtware it is obviously very important to enter all the external circumstances that the simulated circuit will work with in the reality.

Especially as a DI box is connected between two other devices that actually affects the DI-box electronic enormously.
I.e. the guitar with the cable and the mixing console/preamplifier.

A circuit simulation that can not understand all the weird analog parameters, will probably have a very strange result, which tells you something completely different from what it is in reality.

Sorry, I'm very analog of me and very suspicious regarding simulation sowtware in analogous contexts.
But maybe I'm wrong, is there anyone else here on the forum who have experience related to this.

--Bo

 

[byoung]

I'm going to build a couple of these and was curious who has used hammond enclosures and which models work best with Lundahl or Haufe trnasformers?

 

[Bo Hansen]

byoung,

A size that is practical and has plenty of room is Hammond 1590-TBK. (see my DIY page www.hansenaudio.se/techpage.htm)

The same size is also available from other manufacturers.

--Bo

 

[bds2020]

Bo, thanks again for your comments on the CircuitLab experiment.  I asked for help on their forums, and one of the members replied with a cleaned up circuit and some good thoughts.  For those who are interested, here's the link to his re-designed circuit: https://www.circuitlab.com/circuit/5w3644/hansens-active-di-box-02/.  And here's the link to the forum thread: https://www.circuitlab.com/forums/audio-electronics/topic/s7b4up5a/bo-hansen-active-di/#comment_6233. 

I need to spend some time now trying to understand it.  It may be a fool's errand to try to simulate this device, but even if not successful, I"ll be less of a fool when done

 

[Bo Hansen]

Brian,

This is very interesting , and especially when people on CircuitLab forum are involved in your project .

I am a little confused regarding the simulated receiving transformer.
It's ok to apply +48 volts on the primary center tap, but I prefer to apply the voltage via two 6.8 k , because this is the most common way to do it .

We know neither what is the impedance and the ratio of the receiving transformer , it looks very suspicious when there is a 100 ohm resistor termination on the secondary side.

The best way is to use a similar transformer at the sending end. (same as sitting in the DI-box)

The receiving transformer has its low impedance side facing the DI box's output, which is also low impedance .

The receiving transformer secondary becomes the high impedanse side in this case , and should be terminated according to the manufacturer recommendations, which is usually 10 times the secondary impedance .

In LL1538 case , usually 33 K give the best results , and also provides a relevant mirror impedance over to primary side.

It will be verry interesting to follow your simulation project.

You should compare your results with the technical data available on my DIY page www.hansenaudio.se/techpage.htm
These measurements are made "for real" with a normal connection and peripherals.

Best of luck.
--Bo

 

[noiseattitude]

Hi Guys,
this is my first post. I write from Italy, excuse me for my english.

I have a question about this project (the first for me):
Some days ago i ordered some OEP A262A3E, but Farnell, for a mistake, sended me OEP A262A2E  .
I think is not good for this DI-BOX project. Could you confirm it please?

Thanks for all !

 

[Bo Hansen]

noiseattitude,

No, sorry,  it is not usable for this application.

It's actually just A262A3E from OEP range that fit this DI box.

--Bo

 

[noiseattitude]

Thanks a lot Bo for your kind reply !

 

[somorastik]

Thanks for the reply Bo. Is this diagram correct?

Basically use DPDT SWITCH (ON-OFF-ON) wired so:

toggle up    (SW1 CLOSED, SW2 OPEN) =    0dB
toggle mid    (SW1 OPEN, SW2 OPEN)    = -10dB
toggle down  (SW1 OPEN SW2 CLOSED) = -20dB

Have I got this correct?

Thanks for all your input, best wishes

Chris
« Last Edit: February 25, 2010, 12:22:54 PM by chrispbass »

Can someone help me make a schematic out of this? This is the only thing I could come up with:

Toggle Up PAD1 PAD2 connected - 0dB
Toggle Mid PAD2 only- -10dB
Toggle Down PAD2 PAD3 connected - -20dB

I probably havent got it right....

 

[Bo Hansen]

somorastik,

No, your drawing is not correct.

I will describe it in the text instead of doing a sketch.

Use a simple toggle switch, 1 pole 3-position, on-off-on.

You have 3 pieces connecting pins on a line.

The one outer pin is connected to tip on the input jack, and on the same outer pins connect a resistor of 2.2 mohm in paralell with a capasitor at 18 pF over to the middle pin, also from the middle pin a connection to "+ input" ie 10k resistor on the PC card.

Finally, a resistor of 330 k connected from the other outer pin to ground (same ground as the input jack)

Now you have a PAD switch to 0 dB in one outer mode and -10 dB in the middle position and -20 dB in the other outer position.

--Bo

 

[somorastik]

Thank you so much Bo.

Now I think i got it!

 

[Kir_For_Pleasure]

Kir_For_Pleasure,

Tack, hoppas du får mycket glädje av din DI-box.

--Bo

bygger just nu på 3 till ;-)

 

[Kir_For_Pleasure]

Built the Di with oep transformer, after some reading i got interested to try LL1538XL
Got the LL today and mounted it very excited over how the result would be
Got very disappointed when i liked the oep better, more open and natural
1-0 to oep in my search for the perfect bass sound.
still got the recording if someone are interested to hear the diffrence ?

 

[Bo Hansen]

Thomas,

If an audio transformer sounds good or bad in this case where the bass or guitars are involved, is of course a personal taste and preference.

The OEP A262A3E transformer have more "iron-character" compared with Lundahl LL1538 which is very neutral.

LL1538 without XL, has slightly higher bandwidth, but XL tolerate somewhat more level in the low end.

Lundahl's transformers are extremely neutral and clean, with no ringing or overshoot. (may sometimes be too good to be a transformer)

--Bo

 

[jasonallenh]

Hopefully I can get some wonderful expert help on this 

My DI has what appears to be ground hum- When I use the DI with my guitar, I hear a hum that goes away when I stop touching the strings. The same hum goes away If I touch the XLR pin 1. I measured my voltages per Bo's instructions and I got this-


BC560 Emitter voltage - 11.24V (Good!)

+ of 100uF capacitor - 24.24V (Good!)

Pin 2 to pin 1, and pin 3 to pin 1.... 36V (Higher than good??)

I am using the Jensen JT-13K6-C Transformer in reverse, and Bo confirmed with me in a previous post on this thread that I have connected it correctly. I am fairly certain I did something wrong in regard to the chassis ground scheme, but I want to make sure that my noise couldn't some way be related to my higher than expected voltage on my output XLR.

OTHER THINGS

Is the switched 1/4" connector for the INPUT or the amp OUTPUT?

Is it ok that I used a PLASTIC Neutrik XLR?

Thanks

=jh=

 

[Bo Hansen]

Jasonallenh,

The voltage between XLR pin 1 to pin 2, and pin 1 to pin 3 should be around 36 volts, so this is quite ok.

You say "ground hum" and that it disappears when you touch in the strings or when touching the XLR pin 1.

I think you mean "buzz", which is also common for a guitar / bass to pick up from various electrical disturbances on the stage or the room you are in.

How do you use the DI-box?
Guitar to DI box input and XLR out to a pre-amp, or do you have anything else connected to the DI-box, as an amplifier or mains connected effect pedal.


Have you installed a DI-box electronics in a metal box?

Please show a picture of how your DI box is built.

--Bo

 

[jasonallenh]

BO! Thanks for responding.

I am using the DI with the XLR output connected to a recording interface with a guitar plugged into the Input. The guitar is an Epiphone Wildkat. The 1/4" output is not connected to anything.

I connected my Jensen transformer properly (double and triple checked per your instructions) and I have both XLR pin 1 and the chassis connected to the correct point (the 100 Ohm Resistor)

As my transformer does not fit the bboard, I have isolated it from the chassis by using PLASTIC cable mounts and Zip-ties. I don't currently have a picture, but I know for sure that there is about 1/8 inch of plastic separating the transformer from the chassis. The only point at which I have strayed from the grounding scheme is that I have used a plastic XLR connector. I'm using the plastic 1/4" connectors (the Rean models you've specified).

I don't currently have a picture to upload, but I am going to try and bring in a friend with a decent keyboard that I can test it with, because like you said, I may just be hearing normal guitar noise.

 

[somorastik]

Hi Bo!

I am using an old transformer from TESLA (socialist electronic company) it is 1:4 but the problem is probably that the primary is about 40 Ohm (measured with digital multi meter) and secondary is 10 Ohm. As oposed to Lundhall which is 880 Ohm to 44 Ohm.

For now it works good, but on 24V it eats more than 10 mA, at 9 V it is about 3,78 mA.

What should I modify to adjust the current? What would you recommend?

The transformers I used are high quality, so I want to keep them in the layout.