Bo Hansen DI layout

[Mondy]

Hi Bo

I have modified the schematic for the Pin 1 connection, I hope this is OK

Of course you may use it on your tech pages, it would be an honour!! Just let me know if you need anything further on the schematic and I will sort it out for you.

Thanks for a great DI!

Ray

 

[5cienti5t]

Hello!

Bo, would it be correct to call your DI's transistor configuration a Darlington pair?  I understand that the first NPN's purpose is to provide high input Z, and has a low out Z.  The second, as you say on your site is to provide the necessary current to drive the transformer.  I would love as thorough of an explanation as you can muster - I'm presenting your project to my University's electronics class.  For example, one question I had was why there had to be two transistors - would the second be unnecessary if there were no output transformer?  Also, just curious as to why you have the less commonly used PNP instead of using two NPNs.

Also, I'm unsure of how the ground loop suppressor works.  You had said that you would like to post an explanation of this on your site - is there any news on that front?

Thanks so much, I can't wait to hear how mine sound!

This site is so cool and I love all of you for expanding my mind...

 

[Bo Hansen]

5cienti5t,

No, this is not a circuit with two transistors in the "Darlington" configuration, this is just two emitter followers dc-connected in a row.

The first transistor work at low current so that the base input allow the high-resistance bias resistors, which in turn permits the DI-box input impedance at 1 Mohm.

The second transistor works with almost 3.5 mA, which will guarantee for a good drive to the transformer, which reflects the load connected to the DI-box balanced output.

Why I used a NPN followed by a PNP is more a way I was thinking during the 1970's.
There have been some theoretical aspects concerning tempratur stability and linearity when one of each polarity is used, but in this application it would work equally well with two NPN.

The ground loop supression circuit works so that the 100 ohm resistor prevents it from going too high mains safety earth/ground current through the DI-box grounding system.
The 0.1 uF capacitor suppresses buzz and RF / HF frequencies and the two diodes are there to ensure that not the 100 ohm resistor is burning up in case of short circuit in an external device, and provide an opportunity for a fuse to blow up.

Btw, there is also a good circuit discription for this DI-box on www.hansenaudio.se/techpage.htm

--Bo

 

[band_master]

hey guys,
so i finished up one of my DI boxes last night and all is well so far. haven't tried connecting through to an amp yet though. quick question about strapping the grounds on the input...i am not sure how to do that with the jacks i got from mouser. they don't seem to have extra 'solder tabs' like the ones in Bo's pictures.

http://www.mouser.com/Search/ProductDetail.aspx?R=NJ2FD-Vvirtualkey56810000virtualkey568-NJ2FD-V

 

[Bo Hansen]

Band_master,

No, this jack does not have a switch function, you should instead choose Neutrik NMJ4HFS or a other good choise are Cliff CL1160A/S2BNB or Rean NYS2122.

--Bo

 

[band_master]

thanks, Bo!

 

[band_master]

hey Bo,
i have a question on the pad mod wiring. sorry i am not very good at reading chris' schematic. attached is a diagram of the wiring I have setup with a DPDT on-off-on switch. i am able to get the -10db pad setting to work, but the -20db setting is still -10db? can you tell me what i am doing wrong?

thanks,
BD

 

[Bo Hansen]

Band_master,

I changed your sketch, do this instead:

--Bo

 

[band_master]

awesome! thanks for doing that.

 

[Bo Hansen]

This is amazing, it has now been over 50,000 views in this thread.

I'm very happy for your great interest in my Active DI-Box 1975.

Best from
Bo

 

[scheppart]

Hello everybody!

i want to build the DI box and i am about to order all the parts from one website. there is only one problem. the site has only 12V 1W zenerdiodes, no 500mw.
can i use the 1W or will this "destroy" the DI-box?

greetings!!!
scheppart

 

[Bo Hansen]

Scheppart,

You can use 1 watt Zener diodes, (or more) makes no difference in function, just make sure that they fit on the PC card.

--Bo

 

[scheppart]

thx for the answer =).

i wil not use the PCB Board. so there is no problem =)

greetz!

 

[dirtyhanfri]

Hi, I got a Behringer DI-1000 wich case will be for one of my 1975 DI's, and I found that the pcbs has 2 transformers, one blue, labeled OT-1 and the other one, smaller, black and unlabeled, the blue in the input and black in the output, could I use one of them for this design? if so, do I need to change any resistor values in the circuit?

Sorry for the generic question, but couldn't find any info on these...

 

[Bo Hansen]

Dirtyhanfri,

I have no knowledge of the Behringer DI-1000, also that it has two transformers seem strange, but if you can give me more information, so maybe I can give you any advice.

--Bo

 

[dirtyhanfri]

Sorry, but couldn't find any info about that, gonna look harder this afternoon, and if I got something interesting I'll post it here...

Thanks

 

[Classicaudio77]

Has anyone tried using the Neutrik NTE4 or NTM4 transformers in this build?

These are 1:4 mic transformers that are rather easy to obtain here in the U.S.
I built 4 DI's. Two with the OEP, one with a Jensen, and one with a Neutrik NTE4.
The NTE4 is a small transformer with wire leads and only cost about $10.00
The NTM4 is labeled as "studio transformer", is PC mpunt, and is about $45 in a mu metal can
They had the NTE4 stock and I am waiting for the NTM4 to arrive (1-2 week lead time).

I was rather surprised with the sound of the NTE4. To my ears it sounded very close to the Jensen.
I like both the Jensen and Neutrik better than the OEP. The OEP sounds more rounded with less detail.
Will try the more expensive Neutrik NTM4 next week.

So far I have only tested these DI's on Bass.

 

[Bo Hansen]

Classicaudio77,

These Neutrik transformers are very small and can be compared in quality with the old German 1:5 ratio transformers such as Beyer TR/BV-3.51.0.05.0300 or TR145/BV-35799 or MB/KeMo-4481.

Transformers of this size usually works very well in high-frequency end and goes high up with a good square wave response, but unfortunately the small-core gives poor headrom and quality in the low frequency end.

NTE4/NTM4 with ratio 1:4 may be slightly too low ratio in case the DI-box is loaded with too low impedance.

But as always, do you think it sounds good and is good enough for your purposes, then just carry on.

--Bo

 

[scheppart]

Hello,

i finished the di box today. and it does not work =(

i followed bo final test measuring.

my phantom power is 47,3v

where i should get 24V i get 45,5V.... (at the 6.8 resitors.)

has someone an idea where to start checking first? and what kind of problem this could be?

i have not used a PCB.

 

[scheppart]

update:

found a missing connection.

now i have 19.5 where it should be 24.
and 9.7 where it should be 12...

signal is coming through but with much background noise

i keep on searching....