Bo Hansen DI layout

[G-Sun]

Farnell gives me some 400 red leds.
What to shoot for?
round, 3mm, ??

 

[[silent:arts]]

the lower the current the better 

 

[G-Sun]

the lower the current the better 

Thanks!
20mcd? 120mcd? I have really no clue
(8.5mA 12V )

 

[Humner]

I know the feeling trying to find something so generic and simple like an LED from farnell and other parts suppliers.

Try this part number - HLMP4700  - I think that's as generic as you can get when it comes to a red LED.

I would even consider buying a multipack of generic LED's from a retail electronics store(one you can walk into). I did 12 years ago and I'm still going through them.

 

[G-Sun]

I know the feeling trying to find something so generic and simple like an LED from farnell and other parts suppliers.

Try this part number - HLMP4700  - I think that's as generic as you can get when it comes to a red LED.

I would even consider buying a multipack of generic LED's from a retail electronics store(one you can walk into). I did 12 years ago and I'm still going through them.

Thanks a lot!

I went with 2 leds,
- 3mm, round, 20, 12V, 8,5mA
- 3mm, round, 100mcd, 10,5mA, 14V
Hopefully one of those will be ok

DIY feels really like a nerd-hobby when looking up all those specs on data-sheets for small pennie-worth plastic objects

 

[Harpo]

I went with 2 leds,

You didn't.
You went with 2 LEDs with internally connected resistors instead.
You selected red LEDs for their lower breakthru voltage (about 1.8 - 2.0V) instead of green, yellow, amber, blue, white, whatnot, as already pointed out by Bo, but now chose a part for even worse 12V or 14V because of their internally connected current limiting series resistor (about (14V-1.8V)/0.0105A, giving 1160R). The needed current limiting resistor for the LED (if any) is already there (2 paralleled 6K81 on DI-pcb in series to 2 paralleled 6K81 inside the mixing desk/preamp).

 

[G-Sun]

You didn't.
You went with 2 LEDs with internally connected resistors instead.
You selected red LEDs for their lower breakthru voltage (about 1.8 - 2.0V) instead of green, yellow, amber, blue, white, whatnot, as already pointed out by Bo, but now chose a part for even worse 12V or 14V because of their internally connected current limiting series resistor (about (14V-1.8V)/0.0105A, giving 1160R). The needed current limiting resistor for the LED (if any) is already there (2 paralleled 6K81 on DI-pcb in series to 2 paralleled 6K81 inside the mixing desk/preamp).

Thanks for the reply, but I don't know if I understand
I plan to use one of the 2 leds above.
So, I need lower "Forward Voltage"?
Like LED, 3MM, RED, 100MCD, 643NM, 1.8V, 20mA part.nr: 2112100 ?

 

[Zygimantas Laurutis]

Hey,  please try mine. It's pretty squeezy

 

[Bo Hansen]

Regarding the red LED, this should be an ordinary inexpensive LED of the simplest type of 3 to 5 mm, and nothing else.
It shall not have any built-in resistor for current limiting, and it may also not be of the flashing type.

Note that the LEDs in this DI-box circuit is not connected in the same way as the LED is normally connected in other contexts, where it is usually connected in parallel with the voltage source and in series with a current limiting resistor.

In this DI-box circuit is the LED connected in series with the DI-box electronics supply voltage, and uses the 3.5 mA that the  DI-box electronics draws, in order to shine with a moderate brightness.

The LED should be connected with the long leg "anode" directed against the two 6.8 k resistors, with 100 uF electrolyte connected on the other side. (the short leg "cathode")
The connection can be seen on the schematic available on my webpage www.hansenaudio.se/techpage.htm

I have said it a hundred times, and will say it again.
Use only red LED, do not use yellow, green, blue, white or any other color.
The reason for this is that the red LED has a minimum voltage drop loss, and this results to the best headroom in DI-box.

--Bo

 

[G-Sun]

Thanks Bo!
And thanks for the project/design!

I'll get there with the led (order fro  China coming soon with low V red leds).

Seems like I'd done something wrong when trying the DI the other day (not working),
but I'll do the led and the missing ground to case, then I'll come back to it.

Happy Easter

 

[Bo Hansen]

You should not keep you up at the LED, it's only a "phantom power on" indication. and is not important for the DI-box itself.

DI box works best without LED, ie that the two connection holes shall  be bridged with a wire instead.

Why order a special LED from China? As I said earlier, it is the simplest, most common, cheapest red LED that can be purchased at any hobby electronics stores around the world, no marvels at all.

If the DI-box is not working, always check two voltage checkpoints in the first place.
Over the 100 uF capacitor it should be 24 volts plus/minus some volts, and between ground and the emitter on the last BC560 transistor it should be 12 volts, plus/minus some volts.

Are these two voltages at these locations ok, the electronics should work right.
If there is sound out from the unbalanced tele-jack, and not from the balanced XLR, maybe the transformer is  wrong connected or defect.

--Bo

 

[Lee_M]

Bit of a newbie question...

I'm planning on building this DI box, But don't have any actual 5:1 transformers on hand.

I do however have a pair of Lundahl LL1521B's here, Which have a 1+1:2.28+2.28 turn ratio. Aside from that they are like the LL1540.

Will these be suitable if I wire the secondaries in series and use it backwards?
My maths makes that 4.56:1, Would that work ok?

Edit- I'm going to be doing this on perfboard so the number of pins on the LL1521B isn't an issue.

 

[Bo Hansen]

Lee_M,

The LL1521B is a high impedance line- input transforme, so it will not match a microphone input impedance/load.

The best transformer types for my Di-box circuit is microphone input transformer with a ratio between 1:5 to 1:7 used backwards.

--Bo

 

[Lee_M]

Thanks Bo!

I've also got a Lundahl LL6804 (Same as LL7902 according to Lundahl, But with one less primary winding) that is currently doing nothing. They can be wired as 1:4 for microphone/line input, Would that be suitable for the DI?

 

[Lee_M]

I've just finished testing out my freshly wired DI and it is sounding sweet!  ;D

I've got it hooked up to a BBC LL/101SA at the moment, Using the centre tap on the primary for about 1:6 ratio and it's sounding very nice.
I also have a Lundahl LL4901 on the way so will test that out when it arrives.
The BBC xfmr is going to be tricky to electrically isolate from the chassis, Due to it's size, weight and mounting style...So the Lundahl may win out when I get to putting this in an enclosure.

I used tag board, The layout is far from perfect but I can draw it up and post here if anyone wants it.

A big thank you to Mr Hansen!

 

[G-Sun]

Ok, got it together now, Checking
Just noise from XLR.

Led is lighting up.

Over the 100 uF capacitor it should be 24 volts plus/minus some volts,

21,3V

and between ground and the emitter on the last BC560 transistor it should be 12 volts, plus/minus some volts.

10,2V

Are these two voltages at these locations ok, the electronics should work right.
If there is sound out from the unbalanced tele-jack, and not from the balanced XLR, maybe the transformer is  wrong connected or defect.

So, seems like voltages are ok?

Then transformer, Haufe ST8456:
I've mounted it with text facing edge, facing away from the transistors. Can anyone confirm direction?

Edit: Seems like the transformer is fool-proof for direction. 3+4 legs.

So, Bo, your guess is bad transformer then?

 

[Lee_M]

your guess is bad transformer then?

I'm not Bo, But you should check the DCR on each of the windings using a multimeter. If any of them are reading "open circuit" then you likely have a damaged winding...Which would suck, But it does [very rarely] happen.

 

[G-Sun]

I'm not Bo, But you should check the DCR on each of the windings using a multimeter. If any of them are reading "open circuit" then you likely have a damaged winding...Which would suck, But it does [very rarely] happen.

Thanks! I'll do that.

 

[G-Sun]

Then transformer, Haufe ST8456

Man, that's a hard thing to desolder.. 

 

[G-Sun]

Haufe ST8456

Reading
Pin 3-4: 55,2ohm
Pin 1-2: 54,2ohm
Pin 5-6: 65,7ohm

Seems ok, doesn't it?