DI-box

[Kev]

It doesn't have to be transformered.

An output stage like the one found on the SSL or the Green is typical of what it might look like. It is likely that you will plugged into a Mic-pre that is also likely to have phantom so ...
An SSM2142 type of thing may be at risk.

I still feel that for live use a trafo can solve so many problems. See Jensen for an application note. I did a PCB and a full project for Group DIY but I don't think that will happen now. A passive trafo DI box, or two is a must for your live tool kit.

Contact Ethan M .. for my stuff on this one.

 

[Bo Hansen]

Hi Vikky,

It is ok to use a op-amp based active balanced output for a DI-box,
ther are some variant on this circuits, one is a normal op-amp coupled as a unity gain amp with a unbalanced output to pin 2 on the XLR, and from this amp output a 1:1 phase reversed op-amp to pin 3 on the XLR.
There is also a cross-coupled circuit that is very common in to days mixing consoles and other gear.
A other active output variant are the "semi balanced output" that can be find in some German pro-condenser microphones, there are only active signal drive on XLR pin-2 and the pin 3 are decoupled with a electrolytic capacitor via a resistor to ground to get equal conditions as the op-amp output, and because the capacitor to grond you can also feed phantom voltage from pin-3.

The only disadvantage with op-amps in phantom powered DI-boxes are the current consumption, if the voltage after the 6,8 kohms phantom feed resistors shall be 24 volt left to drive the op-amps, they can not draw more then 3,5 mA together, and this is same as +/- 12 volt that is ok to get good headrom and drive capacity.

There are also some nice low current consumption op-amps on the market, but if they draw to low current they also have low slewrate and this can result in a bit hard sound.
The old work horse the dual TL-072 JFET op-amp can be used in this circuit, it draw aprox 2,8 mA so this is ok, and it have a input that is usable for a lot of meg.ohms. (the TL-062 draws only 0,4 mA but is 4 times slower)

There are also some active balancsed line driver IC, as Kev wrote the SSM-2142 from ADI, (Burr & Brown and THAT have simular IC) but they draw to mush, around 5 mA and have not enough hi-Z on the input, so you must have a extra FET transistor before the input.

--Bo

 

[Vikki]

Thanks for the replies, i was trying to avoid the expense of the transformer as it will only be used for a couple of weeks. I think i will go with the tried version with a transformer. I have a ridge farms valve pre amp di but i was frightened of damaging it dragging it around the country.
Many Thanks Again
Vikki :grin:

 

[sismofyt]

Do you have a Gas Cooker, Vikki? Those rule! :green: All my Telefunken modules are in the same kinda housings (standard RS :roll: )

 

[Vikki]

Thats an RS Housing then, i'd been looking for something to match.
Vikki(uk) :grin:

 

[sismofyt]

Yeah, BUT the manufacturer changed the box! Yours is the old one, now they're with a different laquer, 'nextel' I think it's called and the cornes are not nearly as rounded... muthfukkinshitcrap :twisted: :evil: :sad: I bought like 30 of those and half was the new ones. RS couldn't do anything...

They're cheap! Like 20-30£, many sizes. I luv 'em :grin:

 

[sismofyt]

Knobs are RS too. In fact I'll bet every single part is RS.. hehe..

I'll get some pics of my boxes soon so you can see some of the possibilitis..

19" suck :green:

 

[moosapotamus]

[quote author="Bear"]I'm in the US. K&K didn't have the transformer Lundahl recomends for DI available outside of his kit. Let me know if that has changed, as I'd like to check the price.[/quote]
I'm still seeing the 1538XL posted there for $69. Probably best to just email Kevin at K&K.

~ Charlie

 

[adrianh]

Group;

Kevin Carter of KandKaudio.com emailed me as he is on vacation till
June 18th. His reply to BEAR was I quote:
"Tell him he can have all of the LL1530s he likes for his DIY DI Box."

I am at a loss why Bear stated "Kevin will not sell him transformers"
as that is what he does. He sells them all day long.
There must have been some confusion.

Remember Kevin will return June 18th.

 

[Bear]

What I said was that he doesn't have the 1530 listed seperately at the K&K site. The only place he has it listed is with his kit, and I know I can do cheaper than his kit price doing Jensen's circuit. PITA to make someone contact him to check on availability and pricing. It sends a message that he's only interested in selling it in his kit, so I become uninterested in pursuing it. We're not even talking the "call or email for price quote" nonsense, it's not on the damn list of transformers on his site. What do you think that means?

Bear

 

[BYacey]

Regarding the issue of transformer or transformerless DIs, If the DI is being used only in a studio setting, transformerless is probably just fine. However, for stage use (I use mine for both stage and studio) a transformer can save the day because often the signal is split , one feed to front of house console, and one split to a stage ampifier. This is a ground loop in the making, and a transformer can prevent many problems.

 

[BYacey]

Buttachunk, Do you have a schematic for the Hamptone circuit? I would be interested to see what it looks like.

 

[josan]

I wouldn't mind seeing a schematic either if possible

prydwen (at) telus (dot)net


thanks

 

[BYacey]

My address is byacey (at) interbaun (dot) com

Thanks!

 

[thomas911]

buttachunk: Could you e-mail it to me also? (topic starter)

My adress thomas911a (at) hotmail (dot) com

Thanks!

 

[frob]

i would like that schem too butta

frobdfas AT yahoo DOT com

 

[Consul]

I still have that article somewhere. I'll have to take a second look at it.

 

[thomas911]

If someone have that article, could you please post it here.

 

[kevinc]

[quote author="Bear"]What I said was that he doesn't have the 1530 listed seperately at the K&K site. .... It sends a message that he's only interested in selling it in his kit, so I become uninterested in pursuing it. We're not even talking the "call or email for price quote" nonsense, it's not on the damn list of transformers on his site. What do you think that means?

Bear[/quote]

Well, perhaps it does, but that isn't the intent. I just started stocking the LL1530 transformer when I developed the kit and haven't gotten around to listing it. I am happy to sell LL1530s at $52 each all day long for your own DIY DI box. My kit is offered for convenience to those who would prefer a shorter route to the finish line.

I am sorry if I unintentionally annoyed you.

 

[andre tchmil]

AHHHH: RS Boxes!!!!!!!
what's the order nr ??