Bo Hansen DI layout

[Bo Hansen]

Amaziad,

When you build it in a metall box, you not need the mumetal case for the OEP transformer.

--Bo

 

[neodyms]

Hi bo,

I just finished Two of your Active Di's with Lundahl LL1538 mount and i'm starting some tests.

for the input impedance no problem with a big input load it work very good very clear(tested with an active Bass).

but the problem is more around the output level witch is quite low .

to compare, i have a 6dB less than a basic BSS AR133 DI Box.

is it possible to boost this output ?

 

[Bo Hansen]

Neodyms,
(and other that wonder about output level and input impedance)

About your low output problem.

Here are a copy from one of my early postings. (19 December 2009)

If everything is ok, and you have connected the transformer fore 5:1 configuration you shall have around 15 dB loss from instrument input to XLR balanced out. (no loss, 1:1 from instrument input to monitor amp out)

Because you use a microphone transformer backwards you get "loss" negative gain, and a 1:5 ratio transformer have approx. 15 dB step-up gain, or loss used backwards.

You want loss in a DI-box, because the level from a guitar or bass, (after a 1:1 impedance converting) are to high to match a console microphone input.

I will guess that mostly of active DI-boxes on the market have approx. 5-15 dB loss, and passive have approx. 20-30 dB loss.

If you after all need more gain, use the 2,5:1 configuaration instead for the 5:1 configuraton on the Lundahl LL-1538 transformer and you get only 10 dB loss instead for 15 dB, and have 5 dB more gain out from the DI-box.
(but the best transformer match in this circuit are the 5:1 configuration)

I will add to the posting above.
There are some active transformator-less DI-boxes on the market, some of them have high output, because the electronic have unity gain 1:1 from in to output, (some have +6dB gain) and they have only a pad with a small amount of dB.
This can sometime be to much output level for a microphone input on a preamp or mixing console.

About the input impedance.

I megohm is not a low impedance for passive instruments as electric guitars and bass guitars.
I megohm are the most usually impedance for instrument amplifiers around the years, and I think the guitar manufactures have this in mind when they design pickups and guitar electronics.

Many JFET DI-boxes on the market have 10 megohm input impedance and this can be very nice for some instruments, because it will "suck out" everything from a passive guitar, and it also change the sound character and volume/tone knobs behavior.

10 megohms impedance can also be nice when you use acoustic guitars with Piezo pickups direct to a DI-box.

My old DI-box design from 1975, have not a JFET transistor as front end transistor, it is a bipolar silicon type, and it can not handle higher impedance then some megohms.
I will not change this design to JFET, because it is "the part of the sound" and it is also easy to find bipolar transitors and it work without any adjustments.

If you use an active bass, you have internal electronics with a output driven from a op-amp or transistor amp, so in this case, 1 mohm is very high and nice impedance for instruments with internal active electronics.

--Bo

 

[mac]

apologies if I missed this in the thread somewhere, but what is the significance of the 1% for the 6k8 resistors?


Mac

 

[neodyms]

hi bo thank you for your reply.

i didn't yet test that mod but i have an other question ?

have can you do to make a variable input impedance on this schematic? and witch values ? (in the wish to get polyvalent DI)

cordially

 

[AMaziad]

Amaziad,

When you build it in a metall box, you not need the mumetal case for the OEP transformer.

--Bo

Thanks for the quick response Bo - if only my reply was as quick.  Also, thanks for this great design, I can't wait to get started on the build.

- Ali

 

[Bo Hansen]

Mac,

This two 6,8 kohm resistors are the receive phantom feed resistors in the DI-box end, so to not distrub the balanced line, (common mode reaction) the resistors must be in 1% tolerans.

--Bo

 

[mac]

Hey Bo,
First up thanks for this project - awesome. I made one last night (self etch) and used a XSM Edcor 600/10k for testing. I have some other transformers on the way to trial (OEP, a cheaper Chinese one).

Yeah, now you say it, the 1% make sense for the phantom.

Last night I tried a few transistor pairs pulled from old gear I have lying around and there wasnt a huge difference in sound.

20 year old BC548 and BC558
brand new BC550 and BC558
20 year old BC109 and BC178

It is anticipated that different transistor pairs would make a big impact on the nature of the sound? Obviously the different transformers will make a huge difference.

Mac

 

[Bo Hansen]

Neodymsn

There are no need to change input impedance on this DI-box because it have a good compromise impedance of 1 megohm usable for the mostley of all passive electric guitars and bases.

There are som bass guitars that can be coloured in a nice way when you use a passive transformer DI-box that have lower impedanse as 100 kohms or less.
(UTC LS10X or similar old great "low-Z mike or line to grids" types)

So if you want lower impedance on my DI-box, you can try to connect for a example a 100 kohm resistor direct on the guitar cable plugg or on the DI-box input jack between tip and ground.
But I think a input on a DI-box transformer can have a other sound behavior on passive guitars compare with a resistor.

Mac

When you try "new" transistors, be sure that you use types from good manufactures as Philips/PH, Motorola/Onsemi, SGS/Ates, Fairchild, National, because this other "no name" MBR types can bee very awful in small signal parameters, and this can infect the sound quality even in this simple "dual emiterfollower circuit.

--Bo

 

[chrispbass]

Hey Bo,
First up thanks for this project - awesome. I made one last night (self etch) and used a XSM Edcor 600/10k for testing. I have some other transformers on the way to trial (OEP, a cheaper Chinese one).

Yeah, now you say it, the 1% make sense for the phantom.

Last night I tried a few transistor pairs pulled from old gear I have lying around and there wasnt a huge difference in sound.

20 year old BC548 and BC558
brand new BC550 and BC558
20 year old BC109 and BC178

It is anticipated that different transistor pairs would make a big impact on the nature of the sound? Obviously the different transformers will make a huge difference.

Mac

Hi Mac, can you let us know how you found the edcor in your testing please?
Cheers
Chris

 

[neodyms]

Hi bo

about 1Mohm i'm sure it's a good input impedance to. (for basses to piezzo)

But i was thinking about a variable imput impendance from 1MOhm to 10 MOhm.

Do you think it's a interesting idea ?

 

[Bo Hansen]

Neodyms,

Yes, 1 megohm is very ok for guitar and bases, but not for piezo pickups that need about 10 megohm.

Have you read what I wrote to you here ??
http://www.groupdiy.com/index.php?topic=36569.msg491675#msg491675

You can not go up to 10 megohm on this DI-box design that have a bipolar transistor as front end.

If you want 10 megohm you shall build one with JFET-transistor as "countryhick" that you also can find on this forum as a DIY project.

Omong some other things, the 1 megohm and a bipolar front end transistor are "the part of the sound" for my "DI-box 1975"

Instead you shall build three different DI-boxes, one as mine with 1 megohm input, one with lower impedance as a passive transformer box, and one with higher impedance with JFET-transistor (or JFET op-amp) as front end to get 10 megohm.
This is nice because they will sound in three different way, and it is very usable to try on different instruments.

--Bo

 

[mac]

Hi Mac, can you let us know how you found the edcor in your testing please?
Cheers Chris

Hey Chris, I hate grappling for adjectives to describe sound (very subjective) - but to my ears I was surprised that the Edcor actually sounded a little bigger and clearer than the little OEP.

at the risk of sounding quite rediculous - the OEP sounds more APIish .... (i will now go and inflict punishment upon myself)...

Of course the edcor is physically much bigger and would need mounting off board so you would need a much larger enclosure (particularly if you are building a stereo unit for keyboards like I am)....

Mac

 

[chrispbass]

Hi Mac, can you let us know how you found the edcor in your testing please?
Cheers Chris

Hey Chris, I hate grappling for adjectives to describe sound (very subjective) - but to my ears I was surprised that the Edcor actually sounded a little bigger and clearer than the little OEP.

at the risk of sounding quite rediculous - the OEP sounds more APIish .... (i will now go and inflict punishment upon myself)...

Of course the edcor is physically much bigger and would need mounting off board so you would need a much larger enclosure (particularly if you are building a stereo unit for keyboards like I am)....

Mac

Thanks for the reply Mac, now go and shut your computer down and promise not to return to Prodigy Pro for at least 24 hours as your punishment  ;D
Interesting regarding the edcor, I'll get some extra ones to try when I place my order with them for DAOC trannys. They're cheap enough I suppose. Flavours, flavours, flavours...
Cheers
Chris

 

[mac]

<<<<RED CARD >>>>> 24HR break inserted>>>>

Yes, actually it makes me wonder about switchable transformers or maybe some simple filters. A friend of mine wants me to try and solve a problem for hi buy building one with different flavours in the box. He has a couple of different acoustic guitars that all present slightly different tone challenges and at the moment he runs a DI, a BBE sonic maximiser and an EQ to solve these issues on stage (banjo too bright, Maton too muddy, etc etc).

One box - DI with different flavour transformers and some simple two channel parametric tone control in one box might solve all these problems for him.

Mac

 

[Bo Hansen]

Note,

Under this summer I done changes on my web site, so some pages is not in function just now. (as the old link for DI-box schematic)

My DIY/Tech Pages have now a new address, and have access from my main page: www.hansenaudio.se
the direct link is: www.hansenaudio.se/techpage.htm

Sören,
please, can you change the schematic link in your first posting.

--Bo

 

[Soeren_DK]

Note,

Under this summer I done changes on my web site, so some pages is not in function just now. (as the old link for DI-box schematic)

My DIY/Tech Pages have now a new address, and have access from my main page: www.hansenaudio.se
the direct link is: www.hansenaudio.se/techpage

Soeren, please, can you change the schematic link in your first posting.

--Bo

Hi Bo.
I have corrected the first page links.
I like your new structure of your tech site. Easy reading and understanding ;D

God Sommer

Cheers
Søren

 

[mac]

Hi All,
finally got around to dropping my first one in a box last night (only using recycled junk I have around here). Note the transistor sockets...

I listened to about thirty pairs last night until I swear I was hearing things!!
Next one will be in a proper box with enough space for edcors!

 

[AMaziad]

I really like the case.  If you don't mind me ask, what type is it?

 

[mac]

Hey Amaziad,

It is just a recycled enclosure (an old blown 12v -240v inverter). I had to cover the existing holes with some creative thinking (hence the alloy badge!!).


Mac